Effects of NH4+-N/NO3--N ratio on pak-choi nitrogen metabolism and enzyme activity under weak-light Effect of enhanced ammonium nutrition on photosynthesis and nitrate reductase and glutamine synthetase activities of winter wheat Allelopathic Effects of Aquatic Extracts from Solidago canadensis‘‘‘‘s Roots and Rhizospheric Soil on the Seed Germination and Early Seedling Growth of Chinese Cabbage and Radish Studies on the Main Nitrogen Assimilation Enzymes Activities and Nodule Cell Ultrastructure in the Nodule of Alnus cremastogyne Effect of Nitrate Reductase (NR) Inhibitor on NR Activity in Oilseed Rape (Brassica napus L.) and Its Relation to Nitrate Content