Communities are composed of plants which are adapted to the existing conditions. In fact, plants must be adapted to their environment if they are to survive, and it is this plasticity which is one of the most unusual and fascinating features of the members of the plant kingdom. Adaptations allow some plants to withstand drought, while others can survive waterlogging; some to thrive in extreme cold areas, and yet others to withstand great heat.
Several experiments have been undertaken to determine to what extent a species may adapt. For example, numerous transplants were made along a line across the Sierra Nevada mountains. The experiments were very carefully controlled, ensuring that only physical conditions changed, by transplanting each plant with its original soil. Identical plants were always used, often making sure that this was the case by takingfrom the same plant. They were then planted at different stages along the line; this meant that some were more or less at sea-level, while others were positioned at transplant stations upto 2,200m (7,200ft) above sea-level. The transplants were left to fend for themselves completely in their new and vastly different environments.
The results were staggering; some plants adapted to their new environment so well that after only a few years they would have been identified as a different species. Plants .which had shown luxuriant growth in the lowlands became small and stunted at the higher levels. Their intcrnodes were shorter,were more woody and became smaller. In fact, the plants took on a typical ‘alpine’ growth habit. The plants on the lower slopes were found to be intermediate in form between the lowland and alpine types. Other scientists have repeated these experiments with different species, and this plasticity has been found to be quite common in the plant kingdom.
The ability to change the outward appearance is called phenotypic plasticity and it is very important for the survival of the plant. However, it is non-reversible; for example, in the above experiments, if the alpine plant were grown at sea-level it would not revert to its original form.
Plants of the same species exhibiting phenotypic plasticity appear different but genetically they are identical, and produce offspring of the same appearance. A plant becomes more perfectly suited to its environment when it is genetically adapted, as it will then produce offspring which are also adapted in the same ways. When variations and adaptations become fixed genetically they become characters of that species. This is Darwin’s natural selection in action.
Most adaptations are now believed to arise by selective action of the environment causing genetic variation strictly by chance. Under such conditions, sexual reproduction becomes more important as it offers the chance to exchange genetic material.