Studies on the relationship between photosynthesis and nitrogen fixation in the symbiotic system of soybean and nodule bacteria (Rhizobium)

The relationship between photosynthesis of soybean and nitrogen fixation of the nodules by symbiotic Rhizobium was studied. The contents of total nitrogen and chlorophyll; the net photosynthetic rate and seed yield of soybean were much higher in either hydroponically cultivated or field-grown plants inoculated with Rhizobium B16-11C (or Clark nodulating strain) than in control without inoculation (or Clark non-nodulating strain). These results showed that the symbiotic nitrogen fixation had a beneficial effect on photosynthesis. However, the effect was indirect and show so that there was no change in the net photosynthetic rate of the soybean roots. On the other hand, decreasing the photosynthate supply to nodule by shade, defoliation or shoot removal of the soybean, the nodule activity declined significantly. It seemed that the supply of photosynthate to root nodule is a limiting factor for symbiotic nitrogen fixation