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When plants colonized the terrestrial environment they were morphologically
simple, without vessels drivers and water-dependent for reproduction,
therefore occupying humid habitats (mosses and ferns). With the
transformation of the climate on Earth plants evolved not to depend on water
for reproduction but on the wind, developing open ovaries for pollination and
producing a naked seed (Gymnosperms).
When the Earth's climate became cooler the plants that now dominate
emerged, completely independent of water for reproduction. These plants
have ovaries enclosed in flowers adapted to a specific agent of pollination in
order to optimize reproduction. A fruit is then produced protecting the seeds
inside (Angiosperms).
Gymnosperms: From the greek gimn "naked" and sperma "seed", i.e. plants with "naked seeds"
not having the seed protected by the walls of the ovary, not forming a true fruit.
These plants are already independent of the water for reproduction since the wind takes the
pollen to the female gametophyte (anemophilous pollination). In pine trees (Pinaceae) the male
and the female cones are spatially separated on the same tree (monoecious) in order to prevent
self fertilization - the female strobilus are at the top of the tree while the male are on the base.
The leaves are mostly needle-like (an adaptation for dry and cold) although there may be some
broad-leaved groups. Gymnosperms are evergreen plants (except Ginkgo and Gnetophyta) and
they all produce strobilus that are commonly called cones.
Gymnosperms are distributed among 65 genera and 720 species. Divisions: Coniferophyta
(conifers); Cycadophyta (cicads); Ginkgophyta (Ginkgo); Gnetophyta (Gnetum, Ephedra,
Welwitschia).
Angiosperms: From the greek angio "urn" and sperma "seed", i.e. plants with seeds
protected by a fruit.
This is the dominant group of plants and they are well adapted to the environment
conditions. Their reproduction is completely independent of water: the flowers are
adapted to pollination by the wind or by specific pollinators, allowing a breeding
success. The protection of the seed is made by a fruit. Each family is characterized by a
specific floral morphology. Angiosperms are distributed among 13,678 genera and
257,400 species.
According to Darwin, there are variations among a population of individuals of the same
species. The environment will exert a natural selection that will favor individuals that possess
specific characteristics allowing survival, i.e., those which are best adapted to the environment.
Individuals with those characteristics have the opportunity to pass them to their offspring.
Thus, the relationship between plant habitat and plant adaptations is of extreme importance for
the survival of species.
Habitat: "Place or environment used for the normal life of any living being."
An habitat is a place or part of the environment suitable for the life of a biological community.
Its characteristics are related with a set of intrinsic and extrinsic properties that individualize
each one.
The habitats are influenced by the climatic characteristics of each region.
Tropical forests have hot and humid climates and a luxurious flora that represent
the most biodiverse ecosystem. In temperate forests and coniferous habitats there
are constant climate variations and species must be adapted to it. In the deserts,
due to the low rainfall and consequent lack of water, plants are highly specialized in
capturing it underground.
The savanna is a grassland ecosystem characterized by the trees being sufficiently
small or widely spaced. Savannas are frequently in a transitional zone between
forest and desert or prairie. The biodiversity of the mountains is influenced by the
microclimate due to different altitudes. The tundra, with low levels of biodiversity, is
common in the polar regions where the vegetation is submerged by ice in the winter
.
Plants occupy different habitats according to their needs and are dependent on many factors
such as humidity, light, temperature, soil and biotic factors like the intra and interspecific
relations in a ecosystem (competition for space and nutrients, symbiosis, parasitism, etc.. ).
To survive, plants adapt in different ways, e. g., 1) anti-herbivore adaptations (trichomes,
spines, resins, toxins); 2) adaptations to the lack of space finding ways to grow in dense
forests; 3) reproduction adaptations which depend on factors such as water, wind and animals
for pollination and seed dispersal (colored flowers and fruits and with intense aromas;
reproductive organs in strategic locations for pollen to be carried by the wind).
Plants success depends on a good adaptation to the environment.
Adaptation: "Set of changes through which a species is fit to the conditions of the
environment.“
These changes may be physiological or morphological and allow living
beings to survive in the occupied habitat promoting colonization.
Adaptations to Water
Halophyte plants colonize salty swamps and are adapted to reduce their water loss or store
water during periods of dryness (xeromorphic), supporting high percentages of salinity (ex.
mangroves).
Mesophyte plants live in well-drained soils and are adapted to changes in ecological conditions.
Hydrophyte plants grow partially or totally submerged in water. Their adaptations may be:
Structural: development of intracellular air spaces (aerenchyma) in roots and stems that
allow the diffusion of oxygen from the plant canopy to the roots. This modification allows the plant to
float in the water, enabling the capture and delivery of oxygen to the root tissue (ex. Cyperus cyperus;
Eicchornia crassipes). They can also develop adventitious roots that allow the gas exchange above the
flooded soil, for example through the formation of pneumatophores. (Taxodium distichum).
Reproductive: there is no reproduction competition since germination happens in the
presence of excessive water. Some of these plants have the ability to become numbness in
the soil, or even float. Other plants have the ability to bloom before the flood.
Xerophyte plants grow in areas where water is the limiting factor.
These plants adapt in different ways: some can avoid the xeric period maintaining
the seed form and limiting their active period to the rainy season, other develop
reserve structures in the soil (bulbs, rhizomes or tubers) or change the shape of its
leaves.
There are different types of Xerophytes:
Xerophyte
Plants
Sensitiv to
drought
Avoid dry seasons
(Annuals. Ephemeral, summer
deciduous)
Drought
resistant
Avoid dessiccation
Tolerate dessiccation
(arid-tolerant)
Efficient in capturing
and conducting
water
(long roots)
Dormant during dry
season
Water reservoirs: Succulent
stems and leaves
(Euphorbia sp., Dracaena sp.)
Leaves reduced to spines;
Photosynthesis in the stem
(Cactus; Euphorbia sp.)
Temperature Adaptations
Plant adaptations may respond to seasons. Some plants are annual, others lose their leaves to survive
to adverse ecological conditions. In autumn many trees present yellow or red leaves, before the loss.
This phenomenon is due to the extraction of chlorophyll from leaves to permanent tissues allowing
other pigments to become more visible, such as carotenoids (responsible for the yellow color) and
anthocyanin (red color). The photosynthetic pigments that still remain have a red tone. Thus, some
deciduous plants exhibit these pigments before reaching the winter in order to save chlorophyll.
Deciduous trees discard their leaves mainly for two reasons:
• To avoid ice accumulation.
•To decrease energy costs with the maintenance of leaves when the rate of photosynthesis is
reduced.
•Mediterranean plants are adapted to heat in summer, their leaves are small in order to reduce the
exposure to the sun and therefore avoiding water loss by transpiration.
•Other plants have "trembling leaves", which swing with the wind to lower the temperature.
Soil / Space / Wind Adaptations
Carnivorous plants live in soils lacking nitrogen and are adapted to obtain
this nutrient from insects. These plants produce a digestive fluid with an
attractive scent, which leads the insects to enter in their traps (modified leaves).
The plant produces enzymes to digest the insects in the traps.
There are four main families of carnivorous plants: Sarraceniaceae, Nepenthaceae, Droseraceae and
Lentibulariaceae. These plants are native to the tropical zone, occurring in Southeast Asia, America and
Australia, southern Europe and Africa. (Drosera sp.; Pinguicula sp.;Sarracenia sp.; Utricularia sp.; Dionaea
muscipula; Heliamphora sp.; Cephalotus follicularis)
Some tropical plants present adaptations to respond to light competition. They germinate on other trees
and develop adventitious roots through the trunk to both climb the tree searching for light and absorb
available nutrients in its surface. These plants are called epiphytes they do not absorb organic matter directly
from the tree above which they grow, so are not parasites, although there is some discussion about it
because the epiphyte ends up strangling the other tree (ex. Ficus macrophylla).
Other tropical species have extremely flexible stems allowing them to survive tornadoes and
hurricanes without breaking (ex. palm trees don't have secondary growth in the trunk forming
only flexible stems, not true trunks).
Biodiversity
The biodiversity concept is often defined as the variety of all forms of life, from genes to
species, through to the broad scale of ecosystems.
Causes of Biodiversity loss:
A species is threatened when its populations decrease over time, eventually resulting in
extinction. The IUCN (International Union for Conservation of Nature) developed the most used
classification for the species conservation status. This classification includes several levels for
conservation status ranging from least concern (LC) to extinct (E).
The decline of species is due to a number of natural and anthropogenic factors that
cause profound changes in ecosystems, directly or indirectly:
Habitat Destruction (deforestation and fragmentation)
Introduction of invasive (exotic) species
Pollution (greenhouse gases emission, contamination of habitats)
Climate Change
Illegal Trade
Under-exploitation of resources
A pro-environmental and sustainable behavior is urgent to reduce the biodiversity loss caused
by human impact. Reducing, reusing and recycling waste, saving water and energy, increasing
the use of renewable energy and the awareness of the population/politicians to native
biodiversity and its preservation are some examples that may promote a more
sustainable management of resources.
Examples
Acacia dealbata (Silver Wattle)
The introduction of acacia in Portugal reports back to 1939 and the species spread across all
country. The initial aim was to use acacia as ornamental and to combat soil erosion. Today, this
species represents 0.6% of the Portuguese forest area (18500ha) in the coastal biogeographic
unit of the north and center. In Portugal, Acacia dealbata is considered one of the most
aggressive invasive species in terrestrial ecosystems.
Eichhornia crassipes (Water Hyacinth):
Aquatic plant, very common in stagnant waters. It reproduces both by seed as easily
vegetatively by rhizomes or small fragments. It grows rapidly, forming mats that can completely
cover the water surface. Reduces water quality, biodiversity, the available light and water flow,
increasing eutrophication.
Other invasive species:
Arundo donax L.; Carpobrotus edulis (L.) ; Ipomoea acuminata (Vahl.) Roem. & Schult.;
Myriophyllum brasiliensis Verdc. ; Opuntia ficus-indica (L.) Miller; Oxalis pes-caprae L.
Curiosities
70% of the known biodiversity remains in forests.
The deforestation contributes about 15% for the global
CO2 emissions.
1.6 billion of people depend on forests.
The deforestation of the rain forest happens in a rate
of 15 million ha / year.