On Photosynthesis and Free Nitrogen Assimilation by Leguminous Plants

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Abstract
Data from many types of experiments indicate a definite correlation between the nitrogen-fixing, photo-synthetic and respiratory functions of inoculated leguminous plants. The environmental methods used to change the carbohydrate-N relation of the plant include: variation in pCO2, pN2, and pO2 of the atmospheres supplied to inoculated leguminous plants and regulation of the quantity of combined N supplied such plants. Nitrogen fixation and development of nodules are usually limited by the carbohydrate synthesis in the plant but under certain conditions there may accumulate an excess of carbohydrate which inhibits these functions of the symbiotic process. The distribution of nodules on the plant is conditioned to a great extent by the supply of carbohydrate; a plant high in carbohydrate will have a large number of nodules on the lateral roots, whereas nodules on plants low in carbohydrate are concentrated near the tap-root. The detrimental effects of combined N on N fixation and nodule formation can be explained at least in part because of a narrowing of the carbohydrate-N relation of the plant.