Nitrogen is the main limiting nutrient after carbon, hydrogen and oxygen for photosynthetic process, phyto-hormonal, proteomic changes and growth-development of plants to complete its lifecycle. Excessive and inefficient use of N fertilizer results in enhanced crop production costs and atmospheric pollution. Atmospheric nitrogen (71%) in the molecular form is not available for the plants. For world’s sustainable food production and atmospheric benefits, there is an urgent need to up-grade nitrogen use efficiency in agricultural farming system. The nitrogen use efficiency is the product of nitrogen uptake efficiency and nitrogen utilization efficiency, it varies from 30.2 to 53.2%. Nitrogen losses are too high, due to excess amount, low plant population, poor application methods etc., which can go up to 70% of total available nitrogen. These losses can be minimized up to 15–30% by adopting improved agronomic approaches such as optimal dosage of nitrogen, application of N by using canopy sensors, maintaining plant population, drip fertigation and legume based intercropping. A few transgenic studies have shown improvement in nitrogen uptake and even increase in biomass. Nitrate reductase, nitrite reductase, glutamine synthetase, glutamine oxoglutarate aminotransferase and asparagine synthetase enzyme have a great role in nitrogen metabolism. However, further studies on carbon–nitrogen metabolism and molecular changes at omic levels are required by using “whole genome sequencing technology” to improve nitrogen use efficiency. This review focus on nitrogen use efficiency that is the major concern of modern days to save economic resources without sacrificing farm yield as well as safety of global environment, i.e. greenhouse gas emissions, ammonium volatilization and nitrate leaching.

中文翻译：

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氮在农业和环境中的命运：提高氮利用效率的农艺、生态生理和分子方法


氮是继碳、氢和氧之后植物光合作用过程、植物激素、蛋白质组变化和生长发育以完成其生命周期的主要限制养分。氮肥的过度和低效使用导致作物生产成本增加和大气污染。大气中分子形式的氮（71%）不能被植物利用。为了世界可持续粮食生产和大气效益，迫切需要提高农业耕作系统的氮利用效率。氮素利用效率是氮素吸收效率和氮素利用效率的乘积，为30.2%～53.2%。由于施氮量过多、植株数量少、施用方法不当等原因，氮素损失过高，可达总有效氮的70%。通过采用改进的农艺方法，例如最佳施氮剂量、使用冠层传感器施氮、维持植物种群、滴灌施肥和豆类间作，可以将这些损失降至 15-30%。一些转基因研究表明氮吸收有所改善，甚至生物量有所增加。硝酸还原酶、亚硝酸还原酶、谷氨酰胺合成酶、谷氨酰胺氧化戊二酸转氨酶和天冬酰胺合成酶在氮代谢中起很大作用。然而，还需要利用“全基因组测序技术”进一步研究碳氮代谢和组学水平上的分子变化，以提高氮素利用效率。本综述重点关注氮的利用效率，这是当今社会最关心的问题，即在不牺牲农业产量和全球环境安全的情况下节省经济资源，即 温室气体排放、铵挥发和硝酸盐浸出。