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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 -1- 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.) -2- ------------------------------------------------------------------------------------------------ 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. -3- 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. -4- 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. -5- 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. -6- 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 : -7- (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 - Cold region soil 2. Alluvial soil - 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 - Azonal soil 2. Vertisol - Grumu soil 3. Inceptisol - Brown forest soil 4. Aridisol - Desert redish desert soil 5. Mollisol - Chernozem, chestnut, brunizem 6. Spodosol - Podsol, brown podsolic soil 7. Uttisol - 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 ………………………….. -8- 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 -9- 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. - 10 - 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 - 11 - 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 - 12 - 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 : - 13 - 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 - 16 - 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. - 54 - __________________________________________________________________ 2.8 CHECK YOUR PROGRESS - THE KEY ___________________________________________________________________ 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 - 55 - - 56 -