Abstract
It is necessary to make nitrogen fertilization and nitrogen fixation compatible in order to obtain a large quantity of nitrogen absorption, which is a main contributor to the yield of soybean. However, it is known that the specific activity of soybean nodules is inversely proportional to the nitrogen concentration of the leaves. It is important to understand the control mechanism of nodule activity. Therefore, we examined the relationship between sugar content, as the photosynthetic product, and nodule activity in soybean. The results are summarized as follows. 1) When the nitrogen concentration of the leaves was increased by nitrogen fertilization, the photosynthetic ability of the lower node leaf of the main stem was extremely decreased and nodule activity of the soybean declined. 2) The relationship between leaf nitrogen concentration and root glucose concentration showed negative linear regression, but root glucose concentration and specific activity of the nodule showed positive linear regression. The following was estimated from above the results. Because the nitrogen concentration of the leaves was increased by nitrogen fertilization, the photosynthetic ability of the lower node leaf of the main stem was decreased. This decrement of photosynthetic ability caused the decrement of glucose concentration in the roots, resulting in a decline in nodule activity. It is believed that the mechanism of the feedback control system of nodule activity is managed by the host plant.
