| To investigate the effects of manganese on assimilation of nitrogen in soybean, sand culture method with 15N tracer technique was employed in this study, using optimal Mn concentration as a control to evaluate the results from four manganese stress treatments including 2 manganese deficiency treatments (including serious stress and light stress which were 1/25 (S1) and 1/5 (S2) of optimal Mn concentration respectively) and 2 excess stress treatments (including serious stress and light stress which were 5 (S3) and 25 (S4) times of optimal Mn concentration respectively). The results showed that manganese stress had no significant effects on the activities of NR at seedling stage, but showed significant inhibitory effects at the other growth stages (P＜0.01) with decreasing rates at 15.26％～53.10％. The higher the stress level was, the more severe the inhibitory effects were. Different manganese stresses inhibited NO3-N content in leaves, stems and roots at seedling and mature stage and in pods at mature stage, and caused promotion effects at other stages. N contents in vegetative organs during the period from seedling to seed filling stage and in toots at mature stage were inhibited by manganese stress, and were promoted in leaves and root at mature stage. Manganese stress had no significant effects on N contents in pod at pod beginning and seed filling stages, but decreased the N level significantly at mature stage. Manganese stress had no significant effect on mineral nitrogen accumulation in leaves at seedling and mature stages, but inhibited that at full flowering and seed filling stages, with a maximal decreasing rate by S4 at 37.34%. Mineral nitrogen accumulation in stems and roots were not affected by different manganese stress during the period from pod bearing and mature stages. Mineral nitrogen accumulations in pod and the whole plant were also inhibited by manganese stress, displaying decreasing rates by S1, S2, S3 and S4 at mature stages as 40.93%, 22.85%, 26.83% and 42.15%, and 34.27%, 18.38%, 22.05% and 34.19%, respectively. The result indicated that assimilation and accumulation of mineral nitrogen were inhibited by deficient and excessive manganese significantly, and inhibitory effects became increased with the increases of stress levels. |