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As an essential plant micronutrient, copper (Cu) is required as a component of several enzymes, but it can be highly toxic to plants when present in excess quantities. Nitrogen (N) application can help to alleviate the phytotoxic effects of heavy metals, including Cu, and different N forms significantly affect the uptake and accumulation of heavy metals in plants. The aim of this study was to determine the effects of different N forms, i.e., ammonium (NH 4 + ) and nitrate (NO 3 - ), on Cu detoxification in wheat seedlings. The inhibition of seedling growth under excess Cu was more obvious in wheat plants supplied with NO 3 - than in those supplied with NH 4 + . This growth inhibition was directly induced by excess Cu accumulation and reduced absorption of other mineral nutrients by the plants. Compared with seedlings treated with NO 3 - , those treated with NH 4 + showed a decrease in Cu-induced toxicity as a result of increased antioxidant capacity in the leaves and a lower redox potential in the rhizosphere. Furthermore, treatment with NH 4 + decreased the loss of mineral nutrients in wheat seedlings exposed to excess Cu. In conclusion, compared with supplying NO 3 - , supplying NH 4 + to wheat seedlings under Cu stress improved their ability to maintain their nutritional and redox balance and increased their antioxidant capacity, thereby preventing a decline in photosynthesis. According to our results, NH 4 + is more effective than NO 3 - in reducing Cu phytotoxicity in wheat seedlings., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Saline-alkaline stress is one of the most serious global problems affecting agriculture, causing enormous economic and yield losses in agricultural production. Wheat, one of the most important crops worldwide, is often subjected to saline-alkaline stress. In this study, two wheat cultivars with different saline-alkaline tolerance, XC-12 (non-tolerance) and XC-45 (tolerance), were used to investigate the influence of saline-alkaline stress on photosynthesis and nitrogen (N) metabolism through hydroponic experiment with aim of elucidating the mechanism of resistance to salt-alkali. These results showed that saline-alkaline stress significantly reduced biomass accumulation, chlorophyll content, photosynthetic ability and N absorption but increased N utilization efficiency. There was no significant difference in photosynthesis between XC-12 and XC-45 under saline-alkaline stress. In addition, XC-45 had lower ratio of Na + /K + in leaves and Na + -K + selection rate and higher N absorption ability than XC-12, thereby improving physiological metabolism. Moreover, the roots exhibited greater growth performance in response to saline-alkaline stress as a result of increasing glutamine synthetase activity in roots, thus promoting N metabolism in roots. By coordinating the synergistic effect of increasing soluble protein in root, XC-45 exhibited greater tolerance to saline-alkaline stress. All data pinpoint that the root physiological function was more responsible for resistance to saline-alkaline stress in wheat., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest., (© Prof. H.S. Srivastava Foundation for Science and Society 2020.)