| Abstract: | The productivity of a given area of land depends on the amount of light falling on that area, the area of plant available to intercept the light, and a series of factors reflecting the varying efficiency of partial processes of photosynthesis. These factors include the rate of flux of carbon dioxide into the leaf, photochemical events, carbon fixation, dark respiration, photorespiration, partitioning and other metabolic events which together determine the net assimilation rate. In addition, productivity is decreased by lack of nutrient or water, disease and other stresses induced by the environment. As a result, the efficiency of trapping of solar energy into agricultural products is often less than 1% when expressed in terms of the total incident energy available. This contrasts with a theoretical efficiency of about 10% for carbon dioxide assimilated into carbohydrate, and a potential productivity of about 5% for most temperate plants. On the basis of current knowledge of carbon metabolism, the relative importance of some of the above factors in reducing the high initial rates of carbon assimilation to cause low final yields, are assessed. |
