TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > Factors Affecting Plant Populations
Edaphic Factors
- Texture - this is determined by the proportion of sand, silt and clay particles. These in turn influence the water-holding capacity of soil. Clay soils with their smaller particles hold more water than sandy ones.
- Humus - this constitutes all dead and decaying remains of organisms. It acts like a sponge in retaining water and so improves sandy soils. Equally it lightens clay soils and helps them to break up. As it decomposes, the humus slowly releases minerals and so adds nutrients to the soil.
- Air - Roots derive their oxygen directly from the soil as do most soil animal. If the soil becomes waterlogged, the air is driven out and this can lead to anaerobic conditions and subsequent death of the fauna and flora.
- Water - the water content of the soil is the difference between rainfall and evaporation or other losses such as uptake by plants. Water is an essential metabolite and a medium for the transfer of gametes.
- Minerals - different species require different minerals and so the distribution and size of any population is dependent on the blend of available minerals.
- pH - the pH of the soil directly influences which plants grow: heathers prefer acidic and stonewort prefers alkaline soils. It also affects the physical properties of soils and the uptake of minerals.
- Temperature - this influences other soil factors such as water content as well as activity, germination and growth of organisms in the soil.
- Biotic factors - soils contain vast populations of organisms. These influence aeration and drainage (earthworms burrowing) and mineral content (bacteria breaking down humus) as well as having direct effects such as parasitising plants or feeding on their roots.
Climatic Factors
- Light this is essential for photosynthesis and affects flowering in plants as well as reproduction, hibernation and migration in animals. Three aspects of light are important: wavelength, intensity and duration.
- Water is essential for all organisms and the more plentiful it is, the larger and more varied the community is likely to be.
- Air and water movements both are important in dispersing seeds and spores and so determine the distribution of many species. The intensity of the movements may also influence the shape and survival of organisms, especially plants where transpiration rates are affected.
- Humidity this affects the transpiration rate in plants and the rate of evaporation in animals.
- Temperature - Each species has an optimum temperature at which it lives, and it can only survive within a fixed temperature range. Temperature also indirectly influences distribution by affecting water availability and humidity.
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