ABSTRACT
In Chapter 2 we denned environmental stress as any factor which tends to reduce the efficiency of functioning of one or more key physiological processes in the organisms occupying a given ecosystem. The organisms which occupy such ecosystems have to have the right combination of adaptive characteristics to meet the challenges which the environment offers to survival there. In the case of green plants, which rely absolutely on photosynthesis to produce the food they need to survive, anything which reduces the efficiency or rate of photosynthate-accumulation is a source of stress. Ecosystems which impose this sort of stress on plants include
• the understorey habitat of forest ecosystems (where shade is the main source of stress)
• high mountain ecosystems (where cold and high wind combine to stress the plants by coupling low metabolic activity with so-called 'physiological drought' produced by the desiccating effect of the wind)
• salty ecosystems, like salt marshes and salinised irrigated farmland (where, again, accumulation of too much salt in the cells of the plants causes them to dry out through osmotic processes)
• hot desert ecosystems (where direct drought stress is the biggest problem for plant survival)
• nutrient-stressed systems, such as oligotrophic lakes, where plant growth nutrients are in limiting supply.
