Growth characteristics and nitrogen use efficiency in a supernodulating soyabean mutant, En6500, derived from the variety Enrei

摘要

The supernodulating soyabean (Glycine max) mutant, En6500, derived from the variety Enrei, produces many root nodules, but has a low growth rate. This study examined the characteristics of nodulation and plant growth in En6500 in order to elucidatethe mechanism of its low growth rate. The relative growth rate was low in En6500 compared with Enrei. The dry weight of the nodules per unit root mass was greater in En6500 than in Enrei, suggesting that the root of En6500 is supporting too many or an excess of nodules, which presumably leads to a reduction of plant growth rate. Reduced growth rate was associated with low net assimilation rate and low leaf photosynthesis. Moreover, the reduced leaf photosynthesis was associated with low partitioning ofnitrogen to leaves in En6500. High allocation of nitrogen to the plant organs, besides the leaves, resulted in low photosynthesis and reduced nitrogen-use efficiency for dry matter production. This might be a potential mechanism for the low growth rate of En6500.