Measurement and Control of the Rate of Carbon Dioxide Assimilation by Glasshouse Crops

Abstract

IN recent experiments on the effect of environment on glasshouse crops, the net assimilation rate¹ and other indices of growth are found by measuring the dry weight and leaf area of plants sampled from the crop at intervals of the order of 10 days. During this time the intensity of the solar radiation reaching the plants fluctuates over the whole range between zero and the maximum value, so that a series of different combinations of light intensity and plant temperature occurs even if the air temperature and content of carbon dioxide are successfully maintained constant. Such experiments are thus difficult to interpret, especially as the rate of uptake of carbon dioxide by individual leaves is not related linearly to light intensity at all levels of temperature and carbon dioxide concentration², and even when light and all other environmental factors are held constant the rate may vary with time of day³.