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M.Sc. (Final) BOTANY
SELF INSTRUCTIONAL MATERIAL
Paper VI - Plant Ecology
Unit I
Unit II
Block - I
Madhya Pradesh Bhoj (Open) University
Bhopal
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F - 06
Block - I
PLANT ECOLOGY
Unit I
-
Climate Soil & Vegetation pattern of
the world.
Unit II
-
Ecosystem organization
Editor -
Dr. Renu Mishra
HOD - Botany & Microbiology
Sri Satya Sai College for Women, Bhopal
Writer -
Dr. Smt. Chitra Jain
(M.Sc. PhD Botany, B.Ed.)
93/6, 1250 Tulsi Nagar
Bhopal (M.P.)
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------------------------------------------------------------------------------------------------
UNIT - 1
Climate Soil & Vegetation patterns of
the World, Vegetation organization and
Vegetation development
-----------------------------------------------------------------------------------------------1.0
Introduction
1.1
Objectives
1.2
Life Zones, Major Biomes and Major Vegetation
1.3
Soil types of the World
1.4
Concepts of Community and Continuum,
Ordination, Coefficient, Analysis of Communities
1.5
Community coefficients
1.6
Interspecific associations
1.7
Concept of Ecological Niche
1.8
Temporal changes
1.9
Mechanism of Ecological Succession
1.10
Changes in Ecosystem properties during succession
1.11
Let Us Sum Up
1.12
Check Your Progress : The Key
1.13
Assignment / Activity
1.14
Reference
___________________________________________________________________
1.0 INTRODUCTION :
Ecology is a broad discipline comprising many sub-disciplines. A common, broad
classification, moving from lowest to highest complexity, where complexity is defined
as the number of entities and processes in the system under study, is:

Ecophysiology examines how the physiological functions of organisms
influence the way they interact with the environment, both biotic and abiotic.

Behavioral ecology examines the roles of behavior in enabling an animal to
adapt to its environment.

Population ecology studies the dynamics of populations of a single species.

Community ecology (or synecology) focuses on the interactions between
species within an ecological community.

Ecosystem ecology studies the flows of energy and matter through the biotic
and abiotic components of ecosystems.
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
Systems ecology is an interdisciplinary field focusing on the study,
development, and organization of ecological systems from a holistic
perspective.

Landscape ecology examines processes and relationship in a spatially explicit
manner, often across multiple ecosystems or very large geographic areas.

Evolutionary ecology studies ecology in a way that explicitly considers the
evolutionary histories of species and their interactions.
Ecology can also be sub-divided according to the species of interest into fields such
as animal ecology, plant ecology, insect ecology, Marine Ecology, and so on.
Another frequent method of subdivision is by biome studied, e.g., Arctic ecology (or
polar ecology), tropical ecology, desert ecology, The primary technique used for
investigation is often used to subdivide the discipline into groups such as chemical
ecology, genetic ecology, field ecology, statistical ecology, theoretical ecology, etc.
World Climate
Climate is the characteristic condition of the atmosphere near the earth's surface at a
certain place on earth. It is the long-term weather of that area (at least 30 years).
This includes the region's general pattern of weather conditions, seasons and
weather extremes like hurricanes, droughts, or rainy periods. Two of the most
important factors determining an area's climate are air temperature and precipitation.
World biomes are controlled by climate. The climate of a region will determine what
plants will grow there, and what animals will inhabit it. All three components, climate,
plants and animals are interwoven to create the fabric of a biome.
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1.1 OBJECTIVES
1.
Description about various Life Zones, Major Vegetation and Soil Patterns.
2.
Determination of Analytical and Synthetic characters of Communities by
various methods.
3.
Studies of various Dynamic changes which take place due to the occurrence
of succession and effect of various factors on succession.
4.
During the Vegetational Development due to various climatic changes can be
studied by different factors and Cyclic and Non-Cyclic replacement.
5.
Study and classification of various communities (Synecology) provided
structural features, physical habitats, ecological niche and functional
behaviour of communities.
1.2 LIFE ZONES, MAJOR BIOMES &
MAJOR VEGETATION
The relationship between mean annual temperature and the distribution of flora and
fauna recognized that similar zones or belts of vegetation occurred with both
increasing latitude and increasing elevation, these belts are called as Life Zones.
Biomes are the major regional groupings of plants and animals discernible at a
global scale. Their distribution patterns are strongly correlated with regional climate
patterns and identified according to the climax vegetation type. However, a biome is
composed not only of the climax vegetation, but also of associated successional
communities, persistent subclimax communities, fauna, and soils.
The world
contains many biomes
Arctic Tundra
The Arctic tundra is a cold, vast, treeless area of low, swampy plains in the far north
around the Arctic Ocean. It includes the northern lands of Europe (Lapland and
Scandinavia), Asia (Siberia), and North America (Alaska and Canada), as well as
most of Greenland. Another type of tundra is the alpine tundra, which is a biome that
exists at the tops of high mountains. This is the earth's coldest biome.
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Coniferous Forest
The coniferous forest biome is south of the Arctic tundra. It stretches from Alaska
straight across North America to the Atlantic Ocean and across Eurasia. The largest
stretch of coniferous forest in the world, circling the earth in the Northern
Hemisphere, is called the “taiga.” It supplies the bulk of the world's commercial
softwood timber, which is used to make paper. These forests consist mainly of conebearing trees such as spruce, hemlock, and fir, which are well suited to the cold
climate
Deciduous Forest
This biome is in the mild temperate zone of the Northern Hemisphere. Major regions
are found in eastern North America, Europe, and eastern Asia. Deciduous trees lose
their leaves in fall. The natural decaying of the fallen leaves enriches the soil and
supports all kinds of plant and animal life
Desert
A desert is an area where little or no life exists because of a lack of water. Scientists
estimate that about one-fifth of the earth's land surface is desert. Deserts can be
found on every continent except Europe. There are two different kinds: hot and dry
(such as the Arabian and Sahara deserts) and cold and dry (such as Antarctica and
the Gobi desert). The lack of water and intense heat or cold make this biome
inhospitable to most life forms. Most of the plants in the desert are species of cactus.
Grasslands
Grasslands are places with hot, dry climates that are perfect for growing food. They
are known throughout the world by different names such as prairies, veld, savannas,
steppes, pampas etc.
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Mountains
Mountains exist on all the continents of the earth. Many of the world's mountains lie
in two great belts. The Circum-Pacific chain, often called the Ring of Fire. The other
major belt, called the Alpine-Himalayan, or Tethyan, system. Mountains are usually
found in groups called chains or ranges, although some stand alone. A mountain
biome is very cold and windy. The higher the mountain, the colder and windier the
environment. There is also less oxygen at high elevations
Rainforests
Tropical rainforests are found in Asia, Africa, South America, Central America, and
on many of the Pacific islands. There are other types of rainforests around the world,
too. Tropical rainforests receive at least 70 inches of rain each year and have more
species of plants and animals than any other biome. Many of the plants used in
medicine can only be found in tropical rainforests. The combination of heat and
moisture makes this biome the perfect environment for more than 15 million plants
and animals. The thick vegetation absorbs moisture, which then evaporates and
completes the cycle by falling again as rain. A rainforest grows in three levels. The
canopy, or tallest level, has trees between 100 and 200 feet tall. They block most of
the sunlight from the levels below. The second level, or understory, contains a mix of
small trees, vines, and palms as well as shrubs and ferns. The third and lowest level
is the forest floor, where herbs, mosses, and fungi grow.
1.3 SOIL TYPES OF THE WORLD :
Soil is an essential part of growing own food. There are four main soil types: clay,
loam, sand, and peat, with loam being a mixture of sand and clay.
Clay soil
structure is sticky when wet, and hard as a brick when dry. In Sandy soil the
nutrients are quickly washed away. Also sandy soil suffers in drought conditions as it
drains so much faster than a heavy soil. Loam is the intermediate between clay soil
and sandy soil. It drains well, but also holds nutrients well. With the addition of a little
humus, and sometimes a little lime, a loam is often the best soil for most growing.
Peat soil is very rare which is a pity because it contains so many nutrients. Peat
forms when vegetable matter dies and settles at the bottom of a swamp. Climate,
vegetation and soil are intimately related and soil formation is affected by vegetation
and climate.
In the world Dokucharyev gave first classification of soil. He divided the soil into 3
groups which are :
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(i)
Zonal Soil :
ZONE
(ii)
SOIL TYPE
1.
Boreal
Tundra (dark brown soil)
2.
Taiga
Light grey podsol soil
3.
Forest steppe
Grey and dark grey soil
4.
Desert steppe
Chestnut brown or white soil
5.
Steppe
Chernozem soil
6.
Desert
Aerial yellow soil
7.
Sub tropical and tropical forest
Laterite and red soil
Transitional Soil
(iii)
1.
Dry land moor soil
2.
Carbonate containing soil
3.
Secondary alkaline soil
Abnormal Soil
1.
Moor soil
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Cold region soil
2.
Alluvial soil
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Transported through water
3.
Aeolian soil -
Tranported through wind
The most recent classification of soil type is proposed by soil survey staff of USDA
(1960), which is following:
1.
Entisols
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Azonal soil
2.
Vertisol
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Grumu soil
3.
Inceptisol
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Brown forest soil
4.
Aridisol
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Desert redish desert soil
5.
Mollisol
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Chernozem, chestnut, brunizem
6.
Spodosol
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Podsol, brown podsolic soil
7.
Uttisol
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Red yellow podsolic, laterite soil
8.
Oxysol
-
Laterite soil, latosols
9.
Histosol
-
Bog soil
10.
Alfisol
-
Grey brown podsol soil
Check Your Progress - 1
Notes: i) Write your answer in the space given below.
ii) Compare your answer with those given at the end of the unit.
Identify and write the current trends in each of the following media.
1.
Explain the various terms of Ecology.
a) Ecophysiology…………………
b) Landscape ecology ………….
c) Arctic Tundra ……………. …..
d) Forest steppe soil ……………...
e) Moor soil ………………………..
f) Biomes …………………………..
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1.4
CONCEPT OF COMMUNITY AND CONTINUUM, ORDINATION,
COEFFICIENT, ANALYSIS OF COMMUNITIES
The group of similar type of plant growing in similar climate and edaphic zone. It is
called as community and the study of community is known as synecology. Basically,
the name of the community is provided and classified on the basis of following
feature:
1)
Major structural features like: dominate species, life forms or indicates.
2)
Physical habitat of the community.
3)
Functional behavior of the community.
Actually, community maintains the continuity, because the edge effect and ecotone
zone is the common area in between two communities. This concept of continuity is
called as continuum concept, which is determined by the gradient analysis based on
so many coefficient, which are known as community coefficient.
When the
communities and species are arranged according to their gradients, then this is
known as ordination and the ordered arrangement of species and community is
known as continuum.
Continuum and Ordination of Community
Community is the complex structure of vegetation, the main basis of its classification
and name of classification and community is structure of community, because its,
composed of organisms.
So according to some ecologist, the name of the
community should be given on the basis of dominant, then known as pine
community. But it is suitable when only one or two species are changing, then these
criteria cannot be used. It is also proposed that the name of community should be
given on the basis of eco system. It should be meaningful and indicate the structure
of community. So, generally the stable characters of community are used. Like for
aquatic communities, stream rapids community, mud flat community and pelagic
community or sand beach community.
It is well known that communities show
successive changes. So it is the interesting problem that where is the boundary of
one community and from which place, second community gets started, and in the
majority of cases, the communities and the species are delimited from one another
and the continuity is maintained from one community to another community.
According to Clements and Daubenmire, communities are discrete units with definite
boundaries. But according to Gleason, Curtis, Whittaker and Goodball, population
indicates the response, which is independent of environmental gradient.
In this
case, communities overlap with each other, and it is named as continuum. Whittaker
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analysed the great smoky mountain national park and obtained the altitudinal
gradient view from floor to top. Five zones are studied which are following :
i)
Multihued cove forest
ii)
Dark green Hemlock forest
iii)
Dark red oak forest
iv)
Reddish brown oak heath vegetation
v)
Light green pine forest
We can consider the 5 zones as discrete communities, or 5 zones can be considered
as single continuum. In these communities, the response of individual species is
changing according to environmental conditions.
Whittaker studied about 15
species, which are dominant trees and observed the overlapping along gradient.
To find out the continuum in the continuity, population species and community is
arranged in ordered form, for which different techniques are used.
These techniques are called as ordination techniques and ordering the species,
population and community is called as ordination. So, the ecologists who are using
the geographical approach observe the continuity in the communities, while ecologist
working in the topographic or steep gradient uses the term zonal concept.
Continuum concept is based on the continuity of community. Beals compared the
vegetation change in a steep and gentle attitudinal gradient and clearly indicated that
in the gentle gradient, the discontinuity is very less, while in the steep gradient, the
discontinuity is much more. It is studied with the help of dissimilarity indices.
Beals concluded that in steep gradient, vegetation could impose disjunctions.
Although the environment gradient is continues while in a gentle gradient indicates
reverse condition. So the three important processes are responsible for creating
differentiation in community.
1.5
a.
Competitive exclusion
b.
Symbiosis between groups of species
c.
Co-evolution of the groups of species.
COMMUNITY COEFFICIENTS
Community is a group of different population component. It is vast group of species,
and as the number of species increased, the complexity of community is also
increased. So, for the determination of the complexity in community, some indices
are used. These indices are based upon some coefficients, which are known as
community coefficients.
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For determining the continuum and discontinuity, similarity or dissimilarity in the
community is studied as well as the degree of association is also important. On the
basis of degree of similarity, species are places in same community or different
communities. For finding the similarities in the community, coefficient of similarity is
calculated. It is the main criteria for community classification. It shows that greater
the number of species is common in the communities, then greater affinity in the
community is seen. Some important coefficients are following which indicate the
species structure in the community.
Index of Dominance (C)0
C = ∑(n/N)2
Where n, is the importance value for each species (number of individual, biomass,
production, and so forth).
N is the total of importance values.
Index of similarity (S) between two Samples
S = 2 C / (A+B)
Where
A is the number of species in sample A
B is the number of species in sample B
C is the number of species common to both the samples.
Note: Index of dissimilarity = 1-S
Indices of Species Diversity
1.
3 species richness or variety indices d
d1 = S-1/log N
d2 = S / /n
d3 = S per 1000 individuals
Where S is the number of species,
N is the number of individuals, etc.
2.
Evenness index e:__
e = H/log S
Where,
__
H is the Shannon index
S is the number of species
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3.
Shannon index of general diversity H
__
H = - ∑ (n/N) log (n1/N)
= ∑ Pi log Pi
Where (--) n, is the importance values for each species
N is the total of importance values
P1 is the importance probability for each species (n1 / N)
1.6
INTERSPECIFIC ASSOCIATION
The association of two or more than two species is known as interspecific
association or species association. In the association species must grow together,
like in many areas Stipa cornata and Bouteloua gracilis grow together in Great
Plains. In British Colombia Agropyron and Poa grow together. In the Malwa zone
Dicanthium and Indigofera grow together. This association is actually occurring due
to same ecological amplitude of two or more species.
It may be similar in
geographic range, climatic factors and life forms. Many times the different life forms
exclude the competition ad increase the dependence of species on one another.
This increasing dependence is indicated by association index. This association may
be due to shed, food and protection etc.
When the environmental conditions
change, then the association may be changed. When any species is growing as
dominant species in one stand then it may be sub-dominant in another stand. Like in
North Dacota Agropyron is associated with Muhenbergia, Carex, Eurotia, but in
British Colombia Agropyron is dominant but other genera are absent. This presence
and absence indicates the favourable or unfavorable environment.
The interspecific association can be calculated by different formulae. The simplest
method is to find out the presence of 'A' species with 'B' species and following
formula can be used for association index.
Association index = Number of samples where 'A' occurred with 'B'
Number of samples for species 'A'
If species 'A' is present in 40 sample area and in 30 sampling area 'A' and 'B' are
present together, then association index of species 'A' will be :
Association index = 30/40 = 0.75
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So the maximum association index may be 1 or 100% generally this index is less
than one. This result shows that 3/4th area is indicating association of 'A' and 'B'.
The association index can be calculated by following formula Ψ2 =
(a+d)2 - (b+c)2
(a+b) (b+c) (c+d) (a+d)
Where,
A =
number of samples where species a and b both are present.
B =
the number of samples in which species a is present and b is absent.
C =
the number of samples in which species a is absent and b is present.
D =
the number of samples in which both the species are absent.
1.7 CONCEPT OF ECOLOGICAL NICHE
Griennel proposes ecological niche term. He proposed the term for reducing the
competition in the ecosystem. Actually, each organism has limited range of space
and diet selection and this range is determined by so many factors. So, the limited
favorable area where species can enjoy the different factors is known as Ecological
Niche. Basically, niche is related with Micro-habitat. According to Griennel, species
is the distributional unit in which it is held by structural and instinctive limitations and
no any two species can occupy the same space. The meaning of niche is a place,
employment or best-fit activity of organism.
So, the nicheis differentiated from
habitat. It is based on the physical and functional role of the organism. So on the
basis of habitat and trophic level niche can be differentiated.
Types of Niche
Habitat Niche
It is also known as Spatial Niche. When any organism is showing the fixed territory
or living space, then it is known as Habitat or Spatial Niche.
It shows the
differentiation in microhabitat. It means the habitat of many species may be similar,
but the micro-habitat of organisms differs, which reduces the competition in the
organisms. It is supported by so many examples. O'Neill reports one interesting
case.
He studied the seven species growing at the same habitat and all species having the
same trophic level.
But it is observed that all seven species show different
microhabitats, and it produces many gradients in the decomposition stage. These
species and microhabitats are following :
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1.
2.
3.
4.
5.
6.
7.
Euryurus erythropygus: Dominants in heartwood of logs.
Pseudopalydesmus serratus: Superficial wood of log.
Narcueus amerelcanus: Outer surface of logs but below the bark.
Seutotus aranulatus: Under log but on log surface.
Fontaria Virginians: Under log but on ground surface.
Cleidognia species: Within litter leaves.
Abacion: Below litter on ground surface.
log
Litter
(Microhabitat of Mellepede O'Neill)
Similar examples were studied by Sharma and Dwivedi.
They studied that the
microhabitat of fungal species indicate the same habitat, but the microhabitat differs
like Myrothecium roridum present at upper inflorescence axis, while Myrothecium
stratisporum the middle internodes, and Stagnospora Graminella present at lower
internodes.
Trophic Niche
The niche, which is based on the functional behaviour of the organisms in the
ecosystem, is known as Trophic position of the organism in the ecosystem. Many
examples are given in the favor of Trophic niche. The Galapagos is land of the
South America, the nature of three bird species is studied. These birds indicate
similar habitat and microhabitat. But the food trophic position is different.
a.
Geospiza: It searches the food from ground surface.
b.
Camarhynchus: It searches the food from upper surface of tree.
c.
Certhidia:
It is insect eaten.
Similarly, in another example it is
indicated that two birds are living in the same nest, it means the
microhabitat is similar, but these indicate major differences in the
trophic level, like ploceous melanoephalur is the insect eater bird, it
means it is carnivorus while ploceus collasis is seedeater bird.
It
means it is herbivores in nature. One interesting point is studied in
aquatic ecosystem, where two aquatic bugs is living together in the
same habitat. These are Notonacta and Corixa. But, Notonacta is
predator, while Corixa is detritivore.
- 14 -
Multifactor Niche
If the organisms is affected by two or more than two factors at a time, then it is
known as Multifactor Niche. Hutchinnson gives this idea. According to him, at a
time, many pressures are applied on organism, which determine the various range of
organism's movement. Generally, the space of organism movement is limited in the
ecosystem, which is known as Niche space. If any organism is controlled by two
factors at a time, then it is known as area Niche. If Area Niche of two organisms is
independent, then it shows the organisms is independent, and then it shows the
Non-competitive environment. Similarly, if organism is controlled by three factors,
then this niche is known as 3-D Niche or Hyper-volume niche. Hutchison proposes
this term. If the niche of two organisms is completely separated, then it will be Noncompetitive niche. But, if any part of Niche overlap with each other, then it is known
as Overlapping Niche. It shows increasing competition in the environment. If we
take the 4th factors, then it is known as fundamental niche. With the help or study of
fundamental Niche, we can find out the degree of competition in the ecosystem. As
the overlapping increases, the competition parallel increases.
The complete
overlapping of organism is going on, then the species fight with each other, and in
this competition, one species is destroyed and only one species survive. It favours
the "Survival of the fittest" concept proposed by Darwin.
Check Your Progress - 2
Notes: i) Write your answer in the space given below.
ii) Compare your answer with those given at the end of the unit.
a)
The features of community is provided and classified.
b)
Species are having microhabitats
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
1.8
TEMPORAL CHANGES
In any ecosystem, dynamic changes take place, these changes may be fast or slow.
Due to these changes, vegetation pattern in the ecosystem goes on changing, or we
can say that another community is replacing one community. But a stage comes,
- 15 -
which shows stability, which is called as climax stage. Hence, those natural serial
stages, through which serial changes occur in the community and vegetation pattern
is also changed, is called as succession. Succession goes on by different pathways
and is affected by different factors, Succession depend mainly on the following
factors.
1.
It is a sequence of environmental and vegetation changes.
2.
It is based on the Disturbances of area.
3.
In succession, different steps occur in a serial.
During the succession, continuous vegetation changes occur and one type of plant
community is replaced by another type of plant community. That is why, succession
is the most dynamic stage. Following are the type of changes that occurs in the
vegetation.
Replacement changes
When in any community one type of vegetation stand destroyed due to any cause
like forest fire, change in climate and change in edaphic factor, then new vegetation
appears at this place which is known as replacement change. This replacement
change may be two types, which is Non-cyclic Type and Cyclic Type.
Non-cyclic Replacement
It is considered as normal change. When an individual of any species die away,
then another member of the community occupies this area. But it may be same
species or it may be other species like after the death of chestnut tree; area is
covered by Chestnut Oak, Red oak and Red maple. Such changes are taking place
at species level. It is not based on one species replaced by other species. So, it
takes a long time for the development. When a large dominant tree died away, then
at its place seedlings of different species appear.
But out of these so many
seedlings, signal the significant change in the community. But if slowly this process
is continued then the floristic composition of the community will be completed
changed. So, such changes are created inside the community.
Cyclic Changes
When a series of vegetation and habitat changes with time then these are known as
cyclic changes with time, and then these are known as cyclic changes. When Watt
studied the seven different types of communities, then in each community, different
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type of patches was observed and all the patches were selected with each other.
These changes were in the definite order, which may beupgrade series or
downgrade series, like in the cairngorms community, colliona vulgaris is found at the
peak level, which becomes dominant after the death of cladiona silvakita. When
cladiona disintegrates and base soil is exposed, then calliona stems starts the
growth. Another species Arctostaphyllos also initiate the growth in the bare soil and
slowly it becomes dominant. With these changes, the environmental gradient is
associated in grassland in Daccota of North-West, where where wheats, small
shrubs and grasses occur.
In normal conditions, Botelua, Stipa, Corax and
Agropyron occur. In the downward series, development of saline takes place. Then
due to leaching of soluble salts, alkaline soil develops. It is having less ion exchange
capacity, so the vegetation is destroyed. In this case Botelua becomes dominate but
in the saline soil it is replaced by Agropyron, Digitalis and Puccinalla, while in the
upgrade series, calcification and sodium ion concentration reduces it to low shrub
stage the first grass stage the second stage and final stage can be seen and these
changes takes place in a cyclic manner. Polygonum, Lepidium, Atriplex, Plantago
indicates shrub stage. The first grass stage is indicated by Agropyron. Puccinalla
and Disticlis and second grass stage is indicated by Buchloe grass is dominant and
in the first stage Boutelua, Stipa, Corax, and Agropyron are dominant. So, the cyclic
changes are intracommunity changes, while directional changes are intercommunity
changes. The upgrade series of cyclic changes may be confused with succession
(so, the replacement changes may be simple to complex changes).
Non-cyclic
changes are simple, while cyclic changes are complex changes. These changes are
within the climax and within the direction and the cyclic series is the internal
dynamics of community.
1.9 MECHANISM OF ECOLOGICAL SUCCESSION
Nudation
Beginning of vegetation growth in the bare area is called as Nudation, which
depends on following factors;
1.
Topographic:
Topography of any region is important for vegetation and
according to this topography growth begins. Eg. growth and attachment of
lichens on rocks, growth of phytolanktons in lakes or bryophytes in cold
desert.
- 17 -
2.
Climatic factor: The rate of plant growth depends on climatic factor of the
region as light, temperature and rainfall. If factor is favorable, then rate of
succession will be more.
3.
Biotic factors: When vegetation startes growing then struggle starts among
different species. This struggle may be positive or negative.
Invasion
When species invade any new area, then it shows following processes :
Migration
Temporary transference of species from any other area to newly developed area is
called as migration. Due to migration, species increases its dispersal area.
Ecesis
Process of establishment of a species in the new area is called as ecesis. During
species development it shows positive or negative relationship with other species. If
positive relationship is there then species can be better established.
Aggregation
When slowly many species aggregate in the area then struggle takes place among
them and the species, which get well established during this struggle, is sown in the
form of effective species. This species are found in a group.
Competition and Co-action
When many species aggregate at the same place, then among them either a
struggle takes place for shade and nutrients, it is called as competiton or species
positively associate with each other to benefit each other, it is called as reaction.
Reaction
When plants grow in the bare area then it affects soil and climate, it is called as
reaction.
Stabilization
When continuous changes are taking place in the community, then a stage comes,
when the community becomes stable, it is called as climax and the process is called
stabilization.
- 18 -
Disturbance
Migration
Ecesis
Biotic reactions
Biotic reaction
Biotic reaction favors new migrants
Competition
Biotic reactions favor
already established dominance
Climax
Current Concepts of Succession
Succession pattern is a serial process, which takes place in definite steps. Following
steps are important for primary succession :
Table 1.3: Life history
Xerarc
Mesarch
Hydrarch
Crustose lichen
Grassland
Phytoplankton
Foliose lichen
--
Submerged
Moss stage
--
Free floating
--
--
Reed swamps
--
--
Marsh meadow
Herb stage
Herb stage
Herb stage
Shrub stage
Shrub stage
Shrub stage
Climax stage
Climax stage
Climax stage
Two models have been given for primary succession of plants.
1.
Relay floristic model: In it, when next community develops then this area is
formed.
The first community disappears, while in the second model all
community adds new community and develops together.
2.
Initial floristic model: A model has also showed Autogenic mechanism for
succession, which are mainly based on three processes;
- 19 -
a.
Facilitation: This process indicates adopted species in the distributed
area.
b.
Tolerance: This process indicates that by changing environment, there
is no effect of it on the species or, if there is, then very small because
species can tolerate this environment.
c.
Inhibition: When environment is modified by early species, then it is
not suitable for early species and this species inhabits growth and due
to which, growth of another species get increased.
1. Crop
2. Weeds
3. Grassland
4. Herbs
5. Shrub
Specie
abundance
6. Trees (Forests)
(Ist Model)
Time
- 20 -
1.10 CHANGES IN ECOSYSTEM PROPERTIES
DURING SUCCESSION
In the ecosystem, changes occur during the successional stages. These changes
may be progressive or retrogressive but successional changes are always
progressive during the succession.
Here are the following type of changes that
occur.
Fluctuation changes
When the random changes are taking place in the ecosystem then they are known
as fluctuation changes. These changes occur due to the response of climate and is
also known as adaptability. These changes may be regular and cyclic type as well
as the changes may be irregular. Fluctuation occurs at large level, local level or at a
smaller area.
Generally, ecosystem is the complex system so if one factor is
changed then it causes the sequential changes and the changes in the environment
cannot be easily predicted, while the fluctuation changes within the community can
be expected. So, if one species is affected then it shows a log series of changes.
These changes may be in kinds of species, dominance penology and in growth rate.
Directional changes
These are the real successional changes. Although these are known as non-cyclic
changes, but the changes are taking place in an ordered sequence and due to
directional changes, the community becomes more complex, which is known as
progression and changes from more to less complex community is known as
retrogression. If the succession occurs due to changing the factors plant then they
are known as antigenic changes but if the changes are created by any outside (or
external) factor, then they are known as allogentic changes. Generally succession is
a progressive development, which takes place from simple to complex community.
During succession many factors change like diversity, stability, productivity, selfmaintenance and soil maturity.
These are positive directional changes like in
hydrosere succession the sequential step are
i.
Phytoplankton stage
v.
Marsh meadow stage
ii.
Free floating stage
vi.
Herb stage
iii.
Submerged stage
vii.
Shrub stage
iv.
Reed swamp stage
viii.
Climax stage
In this stage, climax stage is the most stable stage and these changes are
continuous changes.
If any stage is interpreted, then nature of all community
- 21 -
changes. Some directional changes may be deflected like formation of savanna
from tropical rain forest through forest and shrub stage. Some ecologist considered
the retrogressive changes as successional changes, which is induced by changes in
climate, grazing, browsing, trampling, soil erosion, repeated flooding etc.
Rate of Change
In the different communities, rate of changes is differing. It is dependent on the
factors causing the succession like the xerosere lichen stage can be seen hundreds
of year. In the areas like arctic and alpine zone, the rate of change is very less,
because climate is complex there. So there community shows stability in the primary
stage. But if the rate of disturbances is higher, then rate of change in community will
also be higher. During the development stages the trends of changes are as follows:
Table 1.1: Community Energetic
Ecosystem attributes
i. Gross production/community
Developmental stages
Mature stages
Greater or less than 1
Approaches 1
High
Low
Low
High
iv. Net community production
High
Low
v. Food chain
Linear, predominantly
Web like
Respiration (P/R ratio)
ii. Gross production/standing
crop biomass (P/B ratio)
iii. Biomass supported/Unit
energy flow (B/E ratio)
grazing
predominantly
detritous
Table 1.2: Community Structure
vi. Total organic matter
Small
Large
vii. Inorganic nutrients
Extra biotic
Intra biotic
viii. Species diversity -
Low
High
Low
High
x. Biochemical diversity
Low
High
xi. Stratification and spatial
Poorly organized
Well developed &
variety component
ix. Species diversity
equability component
heterogeneity
organized
- 22 -
Table 1.3: Life history
xii. Niche specialization
Broad
Narrow
xiii. Size of organism
Small
Large
xiv. Life cycles
Short, simple
Large, complex
Table 1.4: Nutrient Cycling
xv. Mineral cycles
Open
Closed
xvi. Nutrient exchange rate between
Rapid
Slow
Unimportant
Important
organism and Environment
xvii. Role of detritus in
nutrient regeneration
Table 1.5: Selection Pressure
xviii. Growth form
xix. Production
For rapid growth
For feedback
(r-selection)
control (k-selection)
Quantity
Quality
Table 1.6: Overall Homeostasis
xx. Internal symbiosis
Undeveloped
Developed
xxi. Nutrient conservation
Poor
Good
xxii. Stability
Poor
Good
xxiii. Entropy
High
Low
xxiv. Information
Low
High
Check Your Progress - 3
Notes: i) Write your answer in the space given below.
ii) Compare your answer with those given at the end of the unit.
Identify and write the current trends in each of the following media.
a)
The formula of Interspecific Associaton……………………………………………
b)
Directional changes during succession …………………………………………..
- 23 -
1.11 LET US SUM UP
Ecology is a vast branch of Biology. The various subdivisions of the subject i.e.
animal ecology, plant ecology, marine ecology, synecology, genetic ecology, field
ecology, statistical ecology, political ecology, landscape ecology are giving us a
broad knowledge of BioGeo system of Climate which are interrelated to all
components (living and non-living) and determine interaction between atmosphere
and communities.
Types of soil and life zones and concept of vegetational
organization describe and determinate on the basis of analytical and synthetic
methods.
___________________________________________________________________
1.12 CHECK YOUR PROGRESS - THE KEY
___________________________________________________________________
1.
a) Determine physiological functions of organisms interact with environment.
b) Examine process and relationship in a specially explicit manner.
c) A cold vast, treeless area of low, swampy plains in the far north around
the Arctic Ocean.
d) Grey and dark grey soil.
e) Cold region soil.
f) The major regional groupings of plants and animals discernible at a global
scale
2.
a)  Major structural features like: dominate species, life forms or indicates.
 Physical habitat of the community.
 Functional behavior of the community.
b)
 Euryurus erythropygus: Dominants in heartwood of logs.
 Pseudopalydesmus serratus: Superficial wood of log.
 Narcueus amerelcanus: Outer surface of logs but below the bark.
 Seutotus aranulatus: Under log but on log surface.
 Fontaria Virginians: Under log but on ground surface.
 Cleidognia species: Within litter leaves.
 Abacion: Below litter on ground surface.
- 24 -
3.
a)
Association index = Number of samples where 'A' occurred with 'B'
Number of samples for species 'A'
b)
i.
Phytoplankton stage
ii.
Free floating stage
iii.
Submerged stage
iv.
Reed swamp stage
v.
Marsh meadow stage
vi.
Herb stage
vii.
Shrub stage
viii.
Climax stage.
1.13 ASSIGNMENT / ACTIVITY
1.
Study the various types of Physical and Chemical characteristics of soil
samples.
2.
Study the various water sample of various water system of Bhopal and their
Chemical analysis.
3.
What do you know about Continum and Coordination of Communities.
Describe it at least in 250 words.
4.
Describe Ecological niche with their types.
1.14 REFERENCES :
1.
Plant Ecology by S.K. Singh
2.
Plant Ecology by Peter George
3.
Plant Ecology by Ambust
- 25 -
--------------------------------------------------------------------------------------------
UNIT 2 -
ECOSYSTEM ORGANIZATION
-----------------------------------------------------------------------------------------------2.0
Introduction
2.1
Objectives
2.2
Structure and Function,
2.3
Primary Production (Methods of measurement, global pattern,
controlling factors)
2.4
Energy Dynamics (Trophic organization, energy flow
pathway, ecological efficiencies)
2.5
Litter fall and decomposition (mechanism, substrate quality
and climatic factors)
2.6
Global biogeochemical cycles of C, N, P and S,
mineral cycles (pathways, processes, budgets) in
terrestrial and aquatic ecosystems
2.7
Impact of additional photon on photosynthetic efficiency and
ecosystem
2.8
Let Us Sum Up
2.9
Check Your Progress : The Key
2.10
Assignment / Activity
2.10
Reference
___________________________________________________________________
2.0 INTRODUCTION
The ecosystem concept :
An ecosystem is a natural unit consisting of all plants, animals and microorganisms(biotic factors) in an area functioning together with all of the non-living
physical (abiotic) factors of the environment
The term ecosystem was coined in 1930 by Roy Clapham to denote the combined
physical and biological components of an environment. British ecologist Arthur
- 26 -
Tansley later refined the term, describing it as "The whole system,… including not
only the organism-complex, but also the whole complex of physical factors forming
what we call the environment". Tansley regarded ecosystems not simply as natural
units, but as "mental isolates". Tansley later defined the spatial extent of ecosystems
using the term "ecotope".
Central to the ecosystem concept is the idea that living organisms interact with every
other element in their local environment. Eugene Odum, a founder of ecology,
stated: "Any unit that includes all of the organisms (ie: the "community") in a given
area interacting with the physical environment so that a flow of energy leads to
clearly defined trophic structure, biotic diversity, and material cycles (ie: exchange of
materials between living and nonliving parts) within the system is an ecosystem."
The human ecosystem concept is then grounded in the deconstruction of the
human/nature dichotomy and the premise that all species are ecologically integrated
with each other, as well as with the abiotic constituents of their biotope.
A central principle of ecology is that each living organism has an ongoing and
continual relationship with every other element that makes up its environment. The
sum total of interacting living organisms (the biocoenosis) and their non-living
environment (the biotope) in an area is termed an ecosystem. Studies of ecosystems
usually focus on the movement of energy and matter through the system.
2.1 OBJECTIVES
1.
The systematic classification of Ecosystems maintained a well developed
Flora and Funna, with interrelationship of Biotic and Non-Biotic components.
2.
The Biotic and Non-Biotic components represent complex relationship in the
Ecosystem.
3.
Ecological Restoration can be controlled brought and economic problem.
4.
Living organism requires 40 necessary minerals that deposited in the organic
form in the body and later on after death microbes decompose them that
phenomenon determinate by various minerals cycle which are helping BioGeo
study and relationship of atmosphere.
- 27 -
2.2 STRUCTURE AND FUNCTION
Almost all ecosystems run on energy captured from the sun by primary producers via
photosynthesis. This energy then flows through the food chains to primary
consumers (herbivores who eat and digest the plants), and on to secondary and
tertiary consumers (either carnivores or omnivores). Energy is lost to living
organisms when it is used by the organisms to do work, or is lost as waste heat.
Photosynthetic plants fix carbon from carbon dioxide and nitrogen from atmospheric
nitrogen or nitrates present in the soil to produce amino acids. Much of the carbon
and nitrogen contained in ecosystems is created by such plants, and is then
consumed by secondary and tertiary consumers and incorporated into themselves.
Nutrients are usually returned to the ecosystem via decomposition. The entire
movement of chemicals in an ecosystem is termed a biogeochemical cycle, and
includes the carbon and nitrogen cycle.
Ecosystems of any size can be studied; for example, a rock and the plant life
growing on it might be considered an ecosystem. This rock might be within a plain,
with many such rocks, small grass, and grazing animals -- also an ecosystem. This
plain might be in the tundra, which is also an ecosystem (although once they are of
this size, they are generally termed ecozones or biomes). In fact, the entire terrestrial
surface of the earth, all the matter which composes it, the air that is directly above it,
and all the living organisms living within it can be considered as one, large
ecosystem.
- 28 -
Ecosystems can be roughly divided into terrestrial ecosystems (including forest
ecosystems, steppes, savannas, and so on), freshwater ecosystems (lakes, ponds
and rivers), and marine ecosystems, depending on the dominant biotope.
Examples of ecosystems

Aquatic ecosystem

Chaparral

Human
ecosystem

Large marine
ecosystem

Savanna

Subsurface
Lithoautotrophic Microbial
Ecosystem

Coral reef

Desert

Littoral zone


Taiga
Greater

Marine
ecosystem

Tundra

Urban ecosystem
Yellowstone
Ecosystem

Rainforest
Check Your Progress - 1
Notes: i) Write your answer in the space given below.
ii) Compare your answer with those given at the end of the unit.
(a) Write any 10 examples of Ecosystem ………………………………………….
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
2.3 PRIMARY PRODUCTION
Primary production is the production of organic compounds from atmospheric or
aquatic carbon dioxide, principally through the process of photosynthesis, with
chemosynthesis being much less important. All life on earth is directly or indirectly
reliant on primary production. The organisms responsible for primary production are
known as primary producers or autotrophs, and form the base of the food chain. In
terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae are
primarily responsible. Primary production is distinguished as either net or gross, the
former accounting for losses to processes such as cellular respiration, the latter not.
- 29 -
Overview
The Calvin cycle of photosynthesis
Primary production is the production of chemical energy in organic compounds by
living organisms. The main source of this energy is sunlight but a minute fraction of
primary production is driven by lithotrophic organisms using the chemical energy of
inorganic molecules.
Regardless of its source, this energy is used to synthesize complex organic
molecules from simpler inorganic compounds such as carbon dioxide (CO2) and
water (H2O). The following two equations are simplified representations of
photosynthesis (top) and (one form of) chemosynthesis (bottom) :
light
CO2 + H2O
CH2O + O2
CO2 + O2 + 4 H2S
CH2O + 4 S + 3 H2O
In both cases, the end point is reduced carbohydrate (CH2O), typically molecules
such as glucose or other sugars. These relatively simple molecules may be then
used to synthesise further more complicated molecules, including proteins, complex
carbohydrates, lipids, and nucleic acids, or be respired to perform work.
Consumption of primary producers by heterotrophic organisms, such as animals,
then transfers these organic molecules (and the energy stored within them) up the
food web, fueling all of the Earth's living systems.
GPP and NPP
Gross Primary Production (GPP) is the rate at which an ecosystem's producers
capture and store a given amount of chemical energy as biomass in a given length of
time. Some fraction of this fixed energy is used by primary producers for cellular
respiration and maintenance of existing tissues. The remaining fixed energy is
referred to as Net Primary Production (NPP).
NPP = GPP - respiration
Net primary production is the rate at which all the plants in an ecosystem produce
net useful chemical energy; equal to the difference between the rate at which the
plants in an ecosystem produce useful chemical energy (GPP) and the rate at which
they use some of that energy through cellular respiration. Some net primary
production will go towards growth and reproduction of primary producers, while some
will be consumed by herbivores.
- 30 -
Both gross and net primary production are in units of mass / area / time. In terrestrial
ecosystems, mass of carbon per unit area per year is most often used as the unit of
measurement.
Terrestrial production
An oak tree; a typical modern, terrestrial autotroph
On the land, almost all primary production is now performed by vascular plants,
although a small fraction comes from algae and non-vascular plants such as mosses
and liverworts. However, before the evolution of vascular plants, non-vascular plants
played a more significant role. Primary production on land is a function of many
factors, but principally local hydrology and temperature (the latter covaries to an
extent with light, the source of energy for photosynthesis). While plants cover much
of the Earth's surface, they are strongly curtailed wherever temperatures are too
extreme or where necessary plant resources (principally water and light) are limiting,
such as deserts or polar regions.
Water is "consumed" in plants by the processes of photosynthesis (see above) and
transpiration. The latter process (which is responsible for about 90% of water use) is
driven by the evaporation of water from the leaves of plants. It allows plants to
transport water and mineral nutrients from the soil to growth regions, and also cools
a plant down. It can be regulated by structures known as stomata, but these also
regulate the supply of carbon dioxide from the atmosphere, so that decreasing water
loss also decreases carbon dioxide gain. Crassulacean acid metabolism (CAM) and
C4 plants use physiological and anatomical workarounds to increase their water-use
efficiency and allow increased primary production to take place under conditions that
would limit "normal" C3 plants (the majority of plant species).
Oceanic production
Marine diatoms; an example of planktonic microalgae
- 31 -
In a reversal of the pattern on land, in the oceans, almost all primary production is
performed by algae, with a small fraction contributed by vascular plants and other
groups. Algae encompass a diverse range of organisms, ranging from single floating
cells to attached seaweeds. They include photoautotrophs from a variety of groups:
prokaryotic bacteria (both eubacteria and archaea); and three eukaryote categories
the green, brown and red algae. Vascular plants are represented in the ocean by
groups such as the seagrasses.
In another departure from the situation on land, the majority of primary production in
the ocean is performed by microscopic organisms, the phytoplankton. Larger
autotrophs, such as the seagrasses and macroalgal seaweeds are generally
confined to the littoral zone and adjacent shallow waters, where they can attach to
the underlying substrate but still be within the photic zone. There are exceptions,
such as Sargassum, but the vast majority of free-floating production takes place
within microscopic organisms.
Factors for Primary Production
The factors limiting primary production in the ocean are also very different from those
on land. The availability of water, obviously, is not an issue (though its salinity can
be). Similarly, temperature, while affecting metabolic rates, ranges less widely in the
ocean than on land because the heat capacity of seawater buffers temperature
changes, and the formation of sea ice insulates it at lower temperatures. However,
the availability of light, the source of energy for photosynthesis, and mineral
nutrients, the building blocks for new growth, play crucial roles in regulating primary
production in the ocean.
Light
The sunlit zone of the ocean is called the photic zone (or euphotic zone). This is a
relatively thin layer (10-100 m) near the ocean's surface where there is sufficient light
for photosynthesis to occur. For practical purposes, the thickness of the photic zone
is typically defined by the depth at which light reaches 1% of its surface value. Light
is attenuated down the water column by its absorption or scattering by the water
itself, and by dissolved or particulate material within it (including phytoplankton).
Net photosynthesis in the water column is determined by the interaction between the
photic zone and the mixed layer. Turbulent mixing by wind energy at the ocean's
surface homogenises the water column vertically until the turbulence dissipates
(creating the aforementioned mixed layer). The deeper the mixed layer, the lower the
average amount of light intercepted by phytoplankton within it. The mixed layer can
- 32 -
vary from being shallower than the photic zone, to being much deeper than the
photic zone. When it is much deeper than the photic zone, this results in
phytoplankton spending too much time in the dark for net growth to occur. The
maximum depth of the mixed layer in which net growth can occur is called the critical
depth. As long as there are adequate nutrients available, net primary production
occurs whenever the mixed layer is shallower than the critical depth.
Both the magnitude of wind mixing and the availability of light at the ocean's surface
are affected across a range of space- and time-scales. The most characteristic of
these is the seasonal cycle (caused by the consequences of the Earth's axial tilt),
although
wind
magnitudes
additionally
have
strong
spatial
components.
Consequently, primary production in temperate regions such as the North Atlantic is
highly seasonal, varying with both incident light at the water's surface (reduced in
winter) and the degree of mixing (increased in winter). In tropical regions, such as
the gyres in the middle of the major basins, light may only vary slightly across the
year, and mixing may only occur episodically, such as during large storms or
hurricanes.
Nutrients
Mixing also plays an important role in the limitation of primary production by
nutrients. Inorganic nutrients, such as nitrate, phosphate and silicic acid are
necessary for phytoplankton to synthesise their cells and cellular machinery.
Because of gravitational sinking of particulate material (such as plankton, dead or
faecal material), nutrients are constantly lost from the photic zone, and are only
replenished by mixing or upwelling of deeper water. This is exacerbated where
summertime solar heating and reduced winds increases vertical stratification and
leads to a strong thermocline, since this makes it more difficult for wind mixing to
entrain deeper water. Consequently, between mixing events, primary production
(and the resulting processes that leads to sinking particulate material) constantly
acts to consume nutrients in the mixed layer, and in many regions this leads to
nutrient exhaustion and decreased mixed layer production in the summer (even in
the presence of abundant light). However, as long as the photic zone is deep
enough, primary production may continue below the mixed layer where light-limited
growth rates mean that nutrients are often more abundant.
Iron
Another factor relatively recently discovered to play a significant role in oceanic
primary production is the micronutrient iron.[1] This is used as a cofactor in enzymes
- 33 -
involved in processes such as nitrate reduction and nitrogen fixation. A major source
of iron to the oceans is dust from the Earth's deserts, picked up and delivered by the
wind as eolian dust.
In regions of the ocean that are distant from deserts or that are not reached by dustcarrying winds (for example, the Southern and North Pacific oceans), the lack of iron
can severely limit the amount of primary production that can occur. These areas are
sometimes known as HNLC (High-Nutrient, Low-Chlorophyll) regions, because the
scarcity of iron both limits phytoplankton growth and leaves a surplus of other
nutrients. Some scientists have suggested introducing iron to these areas as a
means of increasing primary productivity and sequestering carbon dioxide from the
atmosphere.[2]
Measurement of Primary Production
The methods for measurement of primary production vary depending on whether
gross vs net production is the desired measure, and whether terrestrial or aquatic
systems are the focus. Gross production is almost always harder to measure than
net, because of respiration, which is a continuous and ongoing process that
consumes some of the products of primary production (i.e. sugars) before they can
be accurately measured. Also, terrestrial ecosystems are generally more difficult
because a substantial proportion of total productivity is shunted to below-ground
organs and tissues, where it is logistically difficult to measure. Shallow water aquatic
systems can also face this problem.
Scale also greatly affects measurement techniques. While biochemically-based
techniques are appropriate for plant tissues, organs, whole plants, or plankton
samples, they are decidedly inappropriate for large scale terrestrial field situations.
There, net primary production is almost always the desired variable, and estimation
techniques involve various methods of estimating dry-weight biomass changes over
time. Biomass estimates are often converted to an energy measure, such as
kilocalories, by an empirically determined conversion factor.
Terrestrial
In terrestrial ecosystems, researchers generally measure net primary production.
Although its definition is straightforward, field measurements used to estimate
productivity vary according to investigator and biome. Field estimates rarely account
for below ground productivity, herbivory, decomposition, turnover, litterfall, volatile
organic compounds, root exudates, and allocation to symbiotic microorganisms.
Biomass based NPP estimates result in underestimation of NPP due to incomplete
- 34 -
accounting of these components[3][4]. However, many field measurements correlate
well to NPP. There are a number of comprehensive reviews of the field methods
used to estimate NPP[3][4][5].
The major unaccounted for pool is belowground productivity, especially production
and turnover of roots. Belowground components of NPP are difficult to measure.
BNPP is often estimated based on a ratio of ANPP:BNPP rather than direct
measurements.
Grasslands
The Konza tallgrass prairie in the Flint Hills of
northeastern Kansas
Most frequently, peak standing biomass is assumed to measure NPP. In systems
with persistent standing litter, live biomass is commonly reported. Measures of peak
biomass are more reliable in if the system is predominantly annuals. However,
perennial measurements can be reliable if there was a synchronous phenology
driven by a strong seasonal climate. These methods may underestimate ANPP in
grasslands by as much as 2 (temperate) to 4 (tropical) fold[4]. Repeated measures
of standing live and dead biomass provide more accurate estimates of all
grasslands, particularly those with large turnover, rapid decomposition, and
interspecific variation in timing of peak biomass. Wetland productivity (marshes and
fens) is similarly measured. In Europe, annual mowing makes the annual biomass
increment of wetlands evident.
Forests
Methods used to measure forest productivity are more diverse than those of
grasslands. Biomass increment based on stand specific allometry plus litterfall is
considered a suitable although incomplete accounting of above-ground net primary
production (ANPP)[3]. Field measurements used as a proxy for ANPP include annual
litterfall, diameter or basal area increment (DBH or BAI), and volume increment.
Aquatic
In aquatic systems, primary production is typically measured using one of three main
techniques:
1. variations in oxygen concentration within a sealed bottle (developed by
Gaarder and Gran in 1927)
- 35 -
2. incorporation of inorganic carbon-14 (14C in the form of sodium bicarbonate)
into organic matter
3. fluorescence kinetics (technique still a research topic)
The technique developed by Gaarder and Gran uses variations in the concentration
of oxygen under different experimental conditions to infer gross primary production.
Typically, three identical transparent vessels are filled with sample water and
stoppered. The first is analysed immediately and used to determine the initial oxygen
concentration; usually this is done by performing a Winkler titration. The other two
vessels are incubated, one each in under light and darkened. After a fixed period of
time, the experiment ends, and the oxygen concentration in both vessels is
measured. As photosynthesis has not taken place in the dark vessel, it provides a
measure of respiration. The light vessel permits both photosynthesis and respiration,
so provides a measure of net photosynthesis (i.e. oxygen production via
photosynthesis subtract oxygen consumption by respiration). Gross primary
production is then obtained by subtracting oxygen consumption in the dark vessel
from net oxygen production in the light vessel.
The technique of using 14C incorporation (added as labelled Na 2CO3) to infer
primary production is most commonly used today because it is sensitive, and can be
used in all ocean environments. As 14C is radioactive (via beta decay), it is relatively
straightforward to measure its incorporation in organic material using devices such
as scintillation counters.
Depending upon the incubation time chosen, net or gross primary production can be
estimated. Gross primary production is best estimated using relatively short
incubation times (1 hour or less), since the loss of incorporated 14C (by respiration
and organic material excretion / exudation) will be more limited. Net primary
production is the fraction of gross production remaining after these loss processes
have consumed some of the fixed carbon.
Loss processes can range between 10-60% of incorporated 14C according to the
incubation period, ambient environmental conditions (especially temperature) and
the experimental species used. Aside from those caused by the physiology of the
experimental subject itself, potential losses due to the activity of consumers also
need to be considered. This is particularly true in experiments making use of natural
assemblages of microscopic autotrophs, where it is not possible to isolate them from
their consumers.
- 36 -
Global
As primary production in the biosphere is an important part of the carbon cycle,
estimating it at the global scale is important in Earth system science. However,
quantifying primary production at this scale is difficult because of the range of
habitats on Earth, and because of the impact of weather events (availability of
sunlight, water) on its variability.
Using satellite-derived estimates of the Normalized Difference Vegetation Index
(NDVI) for terrestrial habitats and sea-surface chlorophyll for the oceans, it is
estimated that total (photoautotrophic) primary production for the Earth was 104.9 Gt
C yr-1.[9] Of this, 56.4 Gt C yr-1 (53.8%), was the product of terrestrial organisms,
while the remaining 48.5 Gt C yr-1, was accounted for by oceanic production.
In areal terms, it was estimated that land production was approximately 426 g C m-2
yr-1 (excluding areas with permanent ice cover), while that for the oceans was 140 g
C m-2 yr-1.[9] Another significant difference between the land and the oceans lies in
their standing stocks - while accounting for almost half of total production, oceanic
autotrophs only account for about 0.2% of the total biomass.
In the ecosystem mainly two components are proposed - Biotic factors and Abiotic
factors. Biotic factors have the efficiency to accumulate the food. So, the amount of
food that is either produced or taken from other factors is known as productivity. The
important component that can synthesize food itself, ae known as producers. All the
green plants are producers. Basically, the food synthesized through the green plants
is known as primary production and this primary productivity are of following types :
Gross Primary Productivity
The total amount of food synthesized by plants per unit time per unit area is known
as gross primary productivity.
It is also known as total photosynthesis or total
assimilation.
Net Primary Productivity
After synthesis of food, its some part is used in the metabolic processes, so the
amount of food retained after metabolism, is known as net primary productivity. It
can be calculated by following formula :
NPP = GPP - R
Where
NPP - Net primary productivity
GPP - Gross primary productivity
R
- Respiration rate
- 37 -
Net Community Productivity
In the plants, large amount of food is accumulated. But, it is used by herbivores.
SO, after taking of the food by herbivores from plants, the remaining food is known
as Net community productivity.
NCP = NPP - GSP
Where
NCP - Net community productivity
GSP - Gross secondary productivity
Methods for Determination of Primary Productivity
The best method to determine the primary productivity is to determine the rate of
energy flow, but it is too difficult. So, in the different conditions, different methods
can be used to determine primary productivity. Some important methods are as
follows :
1.
Harvest method : In this process, small plot is selected, the standing crop is
cut down and particular time is given for the regeneration of crop which may
be 7 to 15 days. After this time period, standing crop is again cut down. It is
dried away at 600C in oven. Then, its dry weight is determined or with the
help of calorimeter, its value is determined in calorie.
With the help of
following formula, NPP is determined :
NPP = Dry weight of plants x Area
Time in days
The unit of productivity will be gms/ day/ unit area.
But, with the help of this method, we can find out only NPP, not GPP.
2.
Oxygen measurement (D.O. method or Light and dark bottle method) :
This method is suitable for determination of NPP and GPP in the aquatic
ecosystem. It is based on the oxygen measurement. Its basic principle is to
evolve oxygen during photosynthesis. It is clear that its rate of photosynthesis
is higher, and then the rate of oxygen evolution will be high. In this method,
three bottles are taken and the pond water is filled in these bottles. Then, the
D.O. of first bottle is determined. THen, one bottle is covered with black
paper or black cloth, which is known as dark bottle.
In this bottle,
photosynthesis cannot occur but respiration will take place. The third bottle is
known as light bottle where photosynthesis as well as respiration will occur.
These bottles are hanged in the pond . After 6-8 hours, bottles are taken out
and D.O. is determined in both the bottles, and following observatiosn are
taken :
- 38 -
a.
b.
c.
D.O. of bottle A (initial D.O.) = A ppm
D.O. of dark bottle = B ppm
D.O. of light bottle = C ppm
Now, the NPP and GPP are calculated by the following formula :
a.
b.
c.
Respiration rate = (B-A) ppm
NPP = (C-A) ppm
GPP = NPP + R
It is useful only for aquatic ecosystem but not for terrestrial ecosystem.
3.
Carbon assimilation method :
This method is based on use of carbon
dioxide during photosynthesis. In this process, 3 plants having similar shape
and size are selected. These plants are covered with bell jars. Each bell jar
is having inlet for air and outlet is connected with calcium hydroxide. Now, the
first set is control set, second set is covered with black paper or black cloth,
which will indicate only respiration and the third, will indicate photosynthesis
as well as respiration. This set up is kept in the sunlight and after 6-8 hours,
the quantity of calcium hydroxide is determined in the limewater. Actually,
CO2 reacts with limewater to form calcium carbonate. This calcium carbonate
is taken out, dried away and its weight is determined, and with the help of
molecular weights, the weight of carbon dioxide is calculated.
Its basic
principle is :
100 gm CaCo3 Eq. = 44 gm of CO2
The main observations are following :
a. Amount of CO2 in Ist set = A gms
b. Amount of CO2 in IInd set = B gms
c. Amount of CO2 in IIIrd set = C gms
With the help of these observations, productivity can be calculated as follows:
a. Respiration rate = (B-A) gms
b. NPP = (A-C) gms
c. GPP = NPP + R
4.
pH method : This is suitable for aquatic ecosystem. In aquatic ecosystem,
CO2 is present as soluble gas and presence of CO2 will indicate lowering of
pH. So, as the CO2 is used in the photosynthesis, pH parallels increase. This
increase in pH will be directly proportional to rate of photosynthesis.
5.
Disappearance of raw material : Any synthetic process needs the nutrients
so, the calculated amount of nutrient is transferred into the soil and the initial
analysis of soil sample is carried out. After 24 hours, again the analysis of soil
sample is carried out and the loss of nutrients during 24 hours is calculated.
The rate of photosynthesis is directly proportional to loss of nutrients. In the
- 39 -
ecosystem, CO2 is present as soluble gas and presence of CO2 will indicate
lowering of pH. So, as the CO2 is used up in the photosynthesis, pH parallels
increase.
This increase in pH will be directly proportional to rate of
photosynthesis.
6.
Radio isotopic method : It is the standard and exact method to determine
the productivity. In this process,
14CO
2
is provided to the plant and after 2
hours, radioactivity is measured in the plants. It is directly proportional to the
rate of photosynthesis.
7.
Chlorophyll method : It is indirect method. It is clear that photosynthesis is
based on the amount of chlorophyll. So, if the plants have higher amount of
chlorophyll, then the rate of photosynthesis will be higher. In this method
chlorophyll is extracted from the leaves and its concentration is determined
through spectrophotometer. Generally, this method is used for comparison of
productivity of different communities.
8.
Herbage cover method : It is indirect method because in it the plants or in
community, amount of green canopy is higher, then the rate of photosynthesis
will be higher. So, it is used for the comparison of productivity of different
communities.
9.
Global pattern of primary productivity : "Annual average rate of net plant
production. The number after the bar is K cal/M2/year; the number within the
parentheses is area in 106 Km2.
Factors controlling Primary Productivity
Primary productivity is controlled through all these factors that control the rate of
photosynthesis some important factors are the following :
1.
Size of community : If the community is large, then the productivity of the
community will be high.
2.
Herbage cover : The green canopy of the plant is known as herbage cover,
and this is the plant part where photosynthesis occurs. So, larger the canopy
more the productivity.
3.
Availability of nutrients in soil:
It is proved that the rate of absorption of
nutrients is directly proportional to productivity. If the soil is nutrient rich, then
the productivity will be high.
- 40 -
4.
Concentration of CO2 : CO2 is the raw material for photosynthesis and as the
CO2 concentration increases, the rate of photosynthesis will increase up.
5.
Types of plants :
It is clear that tropical plants have the higher rate of
photosynthesis, because in the tropical plants, photorespiration is absent. So,
efficiency of synthesis will rise up.
6.
Density of vegetation : If community is large, but vegetation is small, then
productivity will be less. But if community is smaller and vegetation is desnse,
then productivity will be high.
7.
Rainfall: The water is the raw material for plant photosynthesis so; higher
rainfall will indicate higher productivity. It is the reason that tropical rain forest
will indicate highest productivity.
8.
Solar radiations: Light is another important limiting factor for photosynthesis.
So, as the amount of solar radiations increase, the rate of photosynthesis is
also increased.
Generally, solar radiations are not barrier in terrestrial
ecosystems. But it is barrier for aquatic ecosystem.
9.
Disturbances in community :
If community is disturbed by anthropogenic
factors, and then its productivity will be low.
10.
Type of community: The productivity is based on type of community, like
desert community, tundra biome, alpine community, indicates low productivity.
Whereas rain forests indicate higher productivity.
Check Your Progress - 2
Notes: i) Write your answer in the space given below.
ii) Compare your answer with those given at the end of the unit.
Describe the terms :
(a) GPP………………………. ………………………………………………….
(b) NPP……………………………………………………………………………
(c) CO2 + O2 + 4 H2S
……………………………………………
(d) GSP . …………………………………………………………………………
- 41 -
2.4 ENERGY DYNAMICS (Trophic organization, energy
flow pathway, ecological efficiencies)
Amount of radiant energy (short wave) available to drive biosphere–atmosphere
exchange of CO2, H2O, CH4 and for transfer into other energy forms were
determined for a tropical mangrove forest at the land ocean boundary of north-east
(NE) coast of Bay of Bengal from January to December 2006. The mean annual
incoming short wave radiation (435±32.8 W m−2) was partitioned into 29% sensible
heat, 35% latent heat, 4% ground heat, 7% physical storage energy and 10%
photosynthetic
storage
energy.
The
mean
budget
closing
energy
flux
(68.96±24.6 W m−2) or, budget error was 15.8% of incoming short wave radiation. In
Varimax factor analysis, budget closing energy flux showed high loading in
association with leaf chlorophyll of different mangrove species, indicating its major
role for reflectivity of the surface for short wave. There was significant seasonality in
CO2 exchange with net primary productivity of 14.1 μmol m−2 s−1. The mean
methane emission was found higher (7.29 μg m−2 s−1) during the daytime than that
of night time (1.37 μg m−2 s−1) with maximum methane emission rates of 36.1 and
21.1 μg m−2 s−1 in December and January, respectively. Stepwise multiple
regression analysis between storage energy [ΔHs(P)] and fluxes of CO 2, CH4, H
(sensible heat), HL (latent heat of evaporation), ΔR (budget closer energy) showed
that the combined explained variability for CO2 flux, evapotranspiration and budget
closer energy (39%) was less than that of CH4 and sensible heat flux (46%). The
extent of warming effect by CH4 and sensible heat flux was predominant over the
resultant
cooling
effect
due
to
the
processes
such
as
photosynthesis,
evapotranspiration and albedo. The mangrove forest with two trademarks of low
albedo and high surface roughness was poorly coupled to the environment
- 42 -
Ecological efficiency
Ecological efficiency is defined as the energy supply available to trophic level N +
1, divided by the energy consumed by trophic level N.
Thinking about ecological efficiency brings the transfer of energy through trophic
levels and up the food chain. In general, only about 10% of the energy consumed by
one level is available to the next. For example, If hares consumed 1000 kcal of plant
energy, they might only be able to form 100 kcal of new hare tissue. For the hare
population to be in steady state (neither increasing nor decreasing), each year's
consumption of hares by foxes should roughly equal each year's production of new
hare biomass. So the foxes consume about 100 kcal of hare biomass, and convert
perhaps 10 kcal into new fox biomass. In fact, this ecological efficiency is quite
variable, with homeotherms averaging 1- 5% and poikilotherms averaging 5-15%.
The overall loss of energy from lower to higher trophic levels is important in setting
the absolute number of trophic levels that any ecosystem can contain.
From this understanding, it should be obvious that the mass of foxes should be less
than the mass of hares, and the mass of hares less than the mass of plants.
Generally this is true, and we can represent this concept visually by constructing a
pyramid of biomass for any ecosystem.
A pyramid of biomass showing producers and consumers.
2.5 LITTER FALL AND DECOMPOSITION
Litterfall and litter decomposition represent a major contribution to the nutrient and
carbon inputs in forest ecosystem. We measured litterfall quantity and nutrient
dynamics in decomposing litter for two years at the Kwangnung Long-Term
Ecological Research (LTER) site in Korea. Litterfall was collected in circular
littertraps (collecting area : 0.25m2) and mass loss rates and nutrient release in
decomposing litter were estimated using the litterbag technique employing 30cm
- 43 -
nylon bags with 1.5mm mesh size. Total annual litterfall was 5,627kg/ha/yr and leaf
litter account for 61% of the litterfall. The leaf litter quantity was highest in Quercus
serrata, followed by Carpinus laxiflora and C. cordata, etc., which are dominant tree
species in the site. Mass loss rates from decomposing litter were more rapid in C.
laxiflora and C. cordata than in Q. serrata litter. About 77% and 84% of C. laxiflora
and C. cordata litter disappeared, while about 48% in the Q. serrata litter lost for two
year. Lower mass loss rates of Q. serrata litter may be attributed to the difference of
substrate quality such as lower nutrient concentrations compared with the other litter
types. Nutrient concentrations (N, P, Mg) of three litter types except for potassium
(K) increased compared with initial nutrient concentrations of litter over the study
period. The results suggest that litter mass loss and nutrient dynamic processes
among tree species vary considerably on same site condition.
Introduction
Litterfall inputs and litter decomposition represent a large and dynamic portion of the
nutrient cycling in forest ecosystem. In addition, the turnover of litter is a major
pathway of the nutrient and carbon inputs to forest soils. Significant amounts of
organic matter and nutrients in the soils can be transferred during litter
decomposition processes.
Natural hardwood stands in the temperate forest zone of Korea are mixed with
various kinds of deciduous tree species. Although several studies have reported
litterfall inputs and litter decomposition in hardwood forest ecosystem in Korea, little
is known about the direction and rates of change associated with mixed-hardwood
forest ecosystem. The objectives of this study were to measure litterfall and nutrient
quantity; 2) to examine decomposition rates in Quercus serrata, Carpinus laxiflora
and C. cordata litter; 3) to determine patterns of nutrient release from decomposing
litters at the LTER site of Kwangnung, a mixed-hardwood forest ecosystem in Korea.
Check Your Progress - 3
Notes: i) Write your answer in the space given below.
ii) Compare your answer with those given at the end of the unit.
Write the definition of :
a) Ecological efficiency ………………………………………………………….
…………………………………………………………………………………..
…………………………………………………………………………………..
b) Photosynthetic efficiency….………………………………………………….
…………………………………………………………………………………..
…………………………………………………………………………………..
…………………………………………………………………………………..
- 44 -
2.6 GLOBAL BIOGEOCHEMICAL CYCLES of C, N, P
and S, MINERAL CYCLES (PATHWAYS, PROCESSES
BUDGETS) IN TERRESTRIAL AND AQUATIC
ECOSYSTEMS
The earth system involves interactions amongst the physical climate, chemical
cycles and living organisms. In any ecosystem there is relationship between two
major components. These are abiotic and biotic components. Biotic components
represent all the living organisms, which are plants, animals and microbes, while
abiotic components represent non-living and living components. These components
consist of lithosphere, hydrosphere and atmosphere. Hence recycling of matters
takes place in all these environments.
Actually living organisms require 40
necessary minerals, which get deposited in the organic form in the body and later on,
after death, microorganisms decompose them. These type of cycles, which depend
on living organism and non living matter, are called as "Biogeochemical cycle".
Actually this word consists of Bio + Geo, where Bio word is represent living
organisms, and Geo word is consist of geological forces, which may be physical or
chemical. Hence, the movement of substances in between along the ecosystem is
called as biogeochemical cycle. Biogeochemical cycle is of two types :
a.
Those cycles in which nutrient is found in gaseous form and atmosphere
plays an important role in this cycle, then these are called as "atmospheric
cycle". Example - Carbon cycle.
b.
Those cycles, which complete in the hydrosphere itself only, then this type of
cycle is called as edaphic cycle or sedimentary cycle.
- 45 -
Carbon Cycle
Carbon is found in every living organism in the organic form, while in the
environment or atmosphere; it is present in the inorganic form. The main source of
carbon is atmosphere, where it is present in the form of CO 2 in the concentration
0.345% or 345 ppm. In the carbon cycle, producers and decomposers are two major
components, which regulate carbon cycle.
In the carbon cycle, two processes are very important :
1.
Immobilization: The process in which inorganic carbon is converted into
organic carbon; then it is called as immobilization. Green plants regulate this
process only, because they convert CO2 into glucose in the presence of
sunlight and chlorophyll.
2.
Minralization:
The process in which organic carbon is converted into
inorganic carbon, is called as Minralization.
This process is regulated by
decomposers, which are bacteria, fungi, nematodes etc.
Carbon cycle is a gaseous cycle, because this cycle goes continuously in
between atmosphere and terrestrial area (lithosphere) and it mainly depends
on CO2. Concentration of CO2 in the atmosphere is 345 ppm. Green plants
absorbs CO2 from atmosphere and converts this CO2 into glucose in the
presence of chlorophyll and sunlight. It is called as photosynthesis.
6CO2 + 12 H2O
ChlorophyII
C6H12O6 + 6H2O + 6O2
Sunlight
In this process, inorganic carbon gets converted into organic carbon i.e. glucose.
This glucose gets transformed into various forms as starch, cellulose, glycogen etc.
In plants it is stored in the form of starch. From plants these substances enter the
- 46 -
food chain and when herbivore eat plants, then organic contents gets into herbivores
and these enter from herbivores to carnivores. Thus, these remain in organic form in
the whole food chain. Although they get transferred from starch to glucose and from
glucose to glycogen, yet in each tropic level these organic compounds gets oxidize
during respiration due to which organic compounds converts into CO2.
C6H12O6 + 6O2
C6H12O6 + 6CO2
This CO2 enters into the atmosphere, but a large part of organic compounds enters
soil in the form of excretory substances. Similarly after death also, this compounds
enter into the soil, where different types of decomposers converts it in the form of
complex organic compounds to simple organic compound like starch and cellulose
get converted into glucose. This gets decomposed in the presence of cellulosic
fungus, later on, during anaerobic decomposition, and then this gets converted into
alcohol and acids.
+ H2O
(C6H10O5)n
n C6H12O6
Cellulase
Cellulose
n C6H12O6
Fermentative bacteria
C6H12O6
2C2H5OH + 2CO2
At last, these gets converted into CO2 by aerobic fungus and bacteria.
2C2H5OH + O2
CH3COOH + H2O
CH3COOH + O2
2CO2 + H2O
This CO2 reacts with water and forms H2CO3, which forms carbonates from rocks.
Along with it, carbon deposits in the form of coke, coal and petroleum, which later on
are used in the form of fuel and are released in the form of CO 2 into the atmosphere
which is called as combustion.
CO2 + H2O
H2CO3
H2CO3 + Ca++
CaCO3 + 2H+
- 47 -
Carbon cycle goes on in between terrestrial zone, atmosphere and hydrosphere, in
which global cycle shows 1015 gm carbon deposition.
Nitrogen Cycle
Nitrogen is an important nutrient for plants and animals. 78% nitrogen is found in
atmosphere normally, but plants cannot absorb nitrogen directly from atmosphere.
They absorb it as ion from the soil. Hence nitrogen can be divided into two forms,
available and unavailable from. Gaseous form is unavailable form like N 2, N2O, NO2,
NO etc., but ionic forms as NO2, NO3- and NH4+ of nitrogen are available form.
Hence, it is necessary for nitrogen to be converted from gaseous to ionic form. Then
only, plants can absorb nitrogen. Nitrogen cycle is also a gaseous cycle. Following
steps are important in nitrogen cycle :
1.
Nitrogen fixation:
The process in which unavailable form of nitrogen
(gaseous) gets converted in to available form (ionic form), is called as
nitrogen fixation. This process takes place by two ways. When nitrogen gets
fixed due to physical factors, then it is called as physical nitrogen fixation. In
this process nitrogen converts into nitrate while if nitrogen gas is converted
into fixed form ammonium nitrogen with the help of living organisms, then it is
called as biological nitrogen fixation. This process is regulated by microbes
e.g.; Rhizobium, pseudomonas, cyanobacteria etc.
2.
Minralization: The process in which organic nitrogen is converted into
inorganic nitrogen, is called as Minralization. Since in this process, the first
- 48 -
product is ammonia, so it is called as ammonification.
This process is
anaerobic and is regulated by ammonifying bacteria.
3.
Nitrification: The process in which ammonia is converted in to nitrate, it is
called as nitrification. This is an aerobic process, hence takes place in the
presence of oxygen.
NH3, first of all, converts into nitrite, Nitrosomonas.
Later on it regulates this process, and these nitrites get converted into
nitrates. Nitrobactor regulates this process.
4.
Denitrification:
The process in which nitrate, nitrogen gets converted into
nitrogen gas, is called as denitrification.
Denitrifying bacteria like
pseudomonas denitrificans controls this process. It is an anaerobic process.
The nitrogen present in the atmosphere converts into ammonia or nitrate by
physical or biological nitrogen fixation and enters into the soil.
Cyanobacteria
2 NH4-
N2
Physical nitrogen fixation
NO3--N
N2
In this form NH4+ or NO3--N is absorbed by plants and plants convert it into
organic nitrogen by Immobilization. This organic nitrogen is in the form of
amino acid and proteins in the plants, which enter into animals through food
chains. In the form of different animals and plants, it enters into the soil, or
after death, it enters into the soil. Here, Ammonifying bacteria degrade it and
change it into NH3. This NH3 gets oxidized and forms NO3--N.
Organic -N
NH3
NH3
NO2--N
NO2--N
NO3--N
This NO3--N changes into N2 by denitrifying bacteria, which enters into the
atmosphere in the form of gas. Or NO3--N enters into the underground water by the
process of leaching.
Pseudomonas denitrificans
NO3--N
N2
- 49 -
Sulphur Cycle
Sulphur is an important compound for plants and animals. It is found in some amino
acids like cytosine, methionine etc. It is also an important constituent of proteins,
hormones and vitamins. Sulphur cycle is partially a sedimentary cycle, whose most
of the parts runs in the form of sediments, while SO 2 and SO3 are found in the
atmosphere in the form of H2S gas. Hence, in the soil and sediments, its large
reservoir pool is found and in small reservoir, it is in the form of sediments.
Following steps are involved in this :
1.
Immobilization: In this process, inorganic Sulphur gets converted into organic
Sulphur, which is called as immobilization.
Green plants regulate this
process.
2.
Minralization: In this process organic Sulphur gets converted into inorganic
Sulphur. This process takes place in the presence of microbes.
3.
Reduction-Oxidation: In this process, SO2 or SO3 gets reduced in the form of
H2S or H2S gets oxidized in the form of SO2 or SO3.
In Sulphur cycle, sediments play the major role. Due to microbial activity, organic
Sulphur gets converted into H2S and SO2 or SO3, which being water-soluble
represents upward movement, which can be absorbed by plants. This process is
called as microbial recovery. This recovery is taking place mainly in the form of SO 2
or SO3.
- 50 -
Similary, SO2 and SO3 are produced due to combustion of fossil fuels. Volcano
activation is the other source of SO2. This SO2 form SO3 in the atmosphere by
oxidation, which mixes with rainy water to form H2SO4.
This H2SO4 gives SO4-- ions, which later on enters the soil and form the salts in the
soil. Thus, Sulphur again reaches back into the soil in the form of SO 4-- from the
atmosphere.
Organic S
H2S
2H2S + 3O2
2H2O + 2SO2
O2 + 2SO2
2SO3
H2O + SO3
H2SO4
H2SO4
2H + SO4-
Ca++ + SO4-
CaSO4
Plants in the ionic form as S- or SO4-, which is known as fixed Sulphur form, while
SO2 and SO3 are gaseous form, which cannot be absorbed by plants, also absorb
Sulphur. Mainly, Sulphur cycle depends on erosion, sedimentation, leaching, rain
adsorption like physical process and production and decomposition like biological
process.
- 51 -
Phosphorus Cycle
It is the simplest biogeochemical cycle. Mainly, it is related with lithosphere and
hydrosphere, and atmosphere plays a negligible role in this cycle.
Actually,
phosphorous is present in the form of PO4-3. It is called inorganic form. A large
amount of phosphorous is found in the form of sedimentary deposit, which is 1000
times more than the soil and ocean. Mainly, the flow of phosphorous takes place in
between the soil and ocean.
Mainly living organisms take the inorganic form present inside the soil and after it is
converted into organic phosphorous by the process of biosynthesis. But after the
death of organism or after the excretion, dead organic matter enters into the soil,
where it is converted into inorganic phosphorous by microbial activity. During rain,
this organic or inorganic phosphorous reaches in the water and it enters into the
ocean by the flow of river. In ocean, dead organic phosphorous decomposes due to
microbial activity, and when this inorganic phosphorous is present in upper part of
ocean, then it gets absorbed by living organisms, but when it enters into the deep
ocean, then its sedimentation takes place, and then it forms the phosphate rocks.
Hence, it is clear that very small amount of phosphorous takes part in this cycle.
Thus, its larger amount is present in ocean or in soil. Its quality is very less in fresh
water. Similarly, amount of phosphorous in the different biomass is very less.
Although more amount of phosphorous is present in aquatic biomass as compared
to terrestrial biomass.
- 52 -
It means that maximum part of phosphorous is found in lithosphere and major part
between or among the available P is soluble in the ocean, which is absorbed by
marine plants and animals, excreted in the ocean itself. But this phosphorous is
taken out in the form of ocean plant and animal by the human activity, which are
used as weeds. These are also used as fertilizers and on the land, if phosphorous
enters into the plants and animals or fertilizers are made from phosphate rocks and
these fertilizers enter from insects into the soil, among which is maximum part gets
deposited. Thus, phosphorous cycle is related only with lithosphere and
hydrosphere.
2.7 IMPACT OF ADDITIONAL PHOTON ON
PHOTOSYNTHETIC EFFICIENCY AND
ECOSYSTEM
Energy enters the biological system as light energy, or photons, is transformed into
chemical energy in organic molecules by cellular processes including photosynthesis
and respiration, and ultimately is converted to heat energy. This energy is dissipated,
meaning it is lost to the system as heat; once it is lost it cannot be recycled. Without
the continued input of solar energy, biological systems would quickly shut down.
Thus the earth is an open system with respect to energy.
Elements such as carbon, nitrogen, or phosphorus enter living organisms in a variety
of ways. Plants obtain elements from the surrounding atmosphere, water, or soils.
Animals may also obtain elements directly from the physical environment, but usually
they obtain these mainly as a consequence of consuming other organisms. These
materials are transformed biochemically within the bodies of organisms, but sooner
or later, due to excretion or decomposition, they are returned to an inorganic state.
Often bacteria complete this process, through the process called decomposition or
mineralization.
During decomposition these materials are not destroyed or lost, so the earth is a
closed system with respect to elements (with the exception of a meteorite entering
the system now and then). The elements are cycled endlessly between their biotic
and abiotic states within ecosystems. Those elements whose supply tends to limit
biological activity are called nutrients
- 53 -
Check Your Progress - 4
Notes: i) Write your answer in the space given below.
ii) Compare your answer with those given at the end of the unit.
Describe the process in the given space below :
a) Denitrification ………………………………………………………………….
…………………………………………………………………………………..
…………………………………………………………………………………..
…………………………………………………………………………………..
b) Immobilization : …………………………………………………………….
…………………………………………………………………………………..
…………………………………………………………………………………..
…………………………………………………………………………………..
2.7 Let Us Sum Up
The scientist A.G. Tansley used the term Ecosystem at the place of Ecological
system.
He defined an Ecosystem is the dynamic stage of Ecology in which
contents flow of energy and nutrients goes on.
The amount of food i.e. either
produced or taken from other factors is known as Productivity.
The important
components that can synthesize food itself are known as Producers. The Biotic
component represent dynamic state of Ecosystem and in which continuous flow of
energy takes place in the form of food. The efficiency of Ecosystem through which it
can conserve maximum amount of energy is known as Ecological Efficiency. The
Ecological efficiency can be studied in various steps i.e. amount of Solar energy,
amount of energy used by Green plants and quantity produced by energy flow.
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2.8 CHECK YOUR PROGRESS - THE KEY
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1.
a) Aquatic ecosystem, Chaparral, Coral reef, Desert, Human ecosystem
Littoral zone, Marine ecosystem, Rainforest, Savanna, Tundra
2.
a) Gross Primary Productivity
b) Net Primary Productivity
c) CH2O + 4S + 3H2O
d) Gross Secondary Productivity
3.
a) Ecological efficiency is defined as the energy supply available to trophic
level N + 1, divided by the energy consumed by trophic level N.
b) Energy enters the biological system as light energy, or photons, is
transformed into chemical energy in organic molecules by cellular
processes including photosynthesis and respiration, and ultimately is
converted to heat energy.
4.
a) Denitrification: The process in which nitrate, nitrogen gets converted into
nitrogen gas, is called as denitrification.
b) The process in which inorganic carbon is converted into organic carbon;
then it is called as immobilization. Green plants regulate this process
only, because they convert CO2 into glucose in the presence of sunlight
and chlorophyll
2.9 ASSIGNMENT / ACTIVITIES
1.
To study Flora of Bhopal and find out frequency, density and abundance of
any 10 dominating grasses of Bhopal flora.
2.
To study and aquatic / forest ecosystem near about Bhopal.
3.
Write a brief account on Ecological efficiency and Litterfall Decomposition.
4.
Global Biogeochemical Cycles - Describe with any 2 examples.
2.10 REFERENCES :
1.
Plant Ecology by Roy & Chapman
2.
Plant Ecology by S. Sundara Rajan
3.
Plant Ecology by Ambust
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