Light plays a crucial role for all living creatures. Sunlight is the ultimate source of energy for the biological world. Light is essential for photosynthesis, plays important role in respiration and transpiration, and regulates hormones in plants.
Light also influences the growth and development of flowers, fruiting and distribution of plants. Different plants flower in different seasons, depending on the length of day and night.
This phenomenon is called ‘photoperiodism’. In tropical rain forests, the composition, stratification, life form etc. are very much adjusted to the light intensity received at different layers. Besides, light is an important factor for leaf fall and germination of seeds.
Like light, heat exeats a profound influence on the physiological and biochemical activities of organisms. Generally, organisms are best adopted to have their activities in a temperature region of 20° C to 30° C.
The physiological effects of temperature arc the mineral absorption in plants, water uptake, growth and germination in plants. Plants exhibit morphological, ecological and physiological-adaptation to the variation in temperature. Most ofland plants thrive in quite a wide range of temperature while those of aquatic environments usually show much less tolerance.
Water is most important for life. All the physiological processes need water. The availability of water in an eco-system affects the distribution, growth and development of species.
Rainfall determines the types of vegetation in any region. The evergreen forest in tropical regions is due to heavy rainfall throughout the year. The grasslands are found in regions where there is heavy rainfall in summer and low rainfall in winter. In fact, vegetation in an area is closely associated with quantity of rainfall.
Thus we find different types of vegetation in lakes, flooded river valleys, swamps, marshes and bogs.
Wind is strong moving current of air. Wind has played an important role in the evolution of shape, size and anatomy of plant structures. Excessive transpiration due to wind leads to desiccation and death of plants.
Thus they adopt themselves to become dwarf, possess small leaves and more branches. On the mountains, due to the danger of uprooting, the vegetation is composed of species having prostrate growth, with long underground roots.
Many of the physiological activities of plants, like transpiration, absorption of water etc. are greatly influenced by humidity. Humidity plays an important role in the life of plants especially epiphytes and lichens that absorb directly from the air. pi I can be a deciding factor in aquatic ecosystem, as far as distribution of organisms is concerned. For every species, there is an optimum pi I level where they can survive.
Large-scale industrialization and the discharge of effluents into water bodies or the soil, change the pll level endangering the lives of organisms.