Light Intensity as an Inhibiting Factor in the Fixation of Atmospheric Nitrogen by Manchu Soybeans 1

R biochemical studies indicate that the symbiotic association of rhizobia and leguminous plants is intimately related to the carbon-nitrogen balance in the plants. The results from many types of experiments (3)3 indicate that an increase in carbohydrate synthesis favors fixation of nitrogen. A discussion of the literature on this subject is given by Wilson (7). In most of the previous work emphasis is laid upon the stimulating effect of carbohydrate synthesis on nitrogen fixation; and the conclusion may be reached that any factor, e. g., light intensity or day length, that will increase the carbohydrate level in the plant will likewise increase nodule formation and nitrogen fixation. Conversely, any method which decreases the carbohydrate concentration, such as short exposure to light and addition of combined nitrogen to the substrate, will also lower nodule production and total nitrogen fixed. In view of the evidence that nodule formation and nitrogen fixation are related to the photosynthetic activity of the plant, and since photosynthesis within limits is apparently proportional to light conditions, it appears reasonable to assume that light conditions and nitrogen fixation should have a positive correlation. The experiments reported in this paper were designed to measure the relation between light conditions and nitrogen fixation.