CONSTRAINTS ON PLANTS IMPOSED BY CLIM, CONDITIONS

Growth and development of plants are largely dependent on constraints imposed by climatic conditions. For each type of plant and each stage in its cycle of growth there exists an optimum value and extreme values for the action of each climatic factor. This study is concerned with four essential factors for plant production: two energy factors, light and heat; and two tropic factors particularly linked to the climate, water and carbon dioxide. In fact the problem is complex, since the plant integrates the actions of these factors, and optimal conditions of growth are dependent as much on the interaction between these factors as on their individual levels.

We have to take account of the needs of each species and to recognise a certain balance between temperature and light: a night temperature lower than the day temperature is favourable to growth. A temporary water deficiency can sometimes be favourable to the normal development of a crop.

Also, there always exists a limiting factor which can be difficult to detect. For example, during a period of high photosynthetic activity, carbon dioxide is usually limiting.

For these reasons, we do not know sufficient to be able, in each particular situation, to define precisely what are the ideal conditions. The aim of greenhouses and shelters is to change the climatic conditions in a favourable direction, but the control of growing crops under these conditions remains a delicate affair requiring much study to bring about an improvement.