减施氮肥和增氧灌溉对水稻氮代谢关键酶活性及氮素利用的影响

该研究旨在分析减施氮肥和增氧灌溉对水稻氮代谢关键酶活性及氮素利用的影响。2020年以中旱221（旱稻）、中浙优8号（水稻）和IR45765-3B（深水稻）共3个品种为材料，设常规淹水灌溉（Conventional Flood Irrigation, WL）、微纳米气泡水增氧灌溉（Micro-nano Bubble Water Oxygenation Irrigation, MBWI）2个灌溉模式和常规施氮（195.0 kg/hm2）、减施氮肥（157.5 kg/hm2）2个氮水平，研究了减施氮肥和增氧灌溉对水稻关键生育时期氮代谢相关酶活性、植株含氮量、氮素积累量以及产量和氮肥利用率的影响。结果表明，与常规施氮处理相比，减施氮肥降低了氮代谢酶活性，而增氧灌溉有助于提高硝酸还原酶、谷氨酰胺合成酶、谷氨酸合酶、谷丙转氨酶活性。增氧灌溉和氮肥一定程度上有助于水稻氮素积累，增氧灌溉下减施氮肥处理比淹水灌溉常规施氮量的当季氮肥利用率分别提高15.6%、36.2%、21.5%（P<0.05）。增氧灌溉和增施氮肥显著增加水稻产量，中旱221增氧灌溉下减施氮肥比淹水灌溉常规施氮量处理增产3.5%（P<0.05），而中浙优8号和IR45765-3B增氧灌溉下减施氮肥与淹水灌溉常规施氮量差异不显著（P>0.05）。相关分析表明，氮代谢酶活性与同时期叶片含氮量及氮素积累量大多呈显著或极显著的正相关。可见，增氧灌溉可以显著提高水稻氮素代谢相关酶活性，从而显著提高水稻氮素积累量、产量和当季氮肥利用效率，水稻氮肥减施条件下采用增氧灌溉有助于水稻维持较高氮肥吸收和利用效率，而谷氨酰胺合成酶活性可以用于预测水稻各时期氮素积累量。研究结果可为水稻氮肥减施和提高水稻氮肥利用效率提供理论和技术支持。

Effects of nitrogen fertilizer reduction and oxygen-enhancing irrigation on the key enzyme activities of nitrogen metabolism and nitrogen utilization in rice

A very low utilization rate of nitrogen fertilizer has posed a great challenge to agriculture production in China in recent years. There is an almost half loss rate of nitrogen fertilizer applied to the soil, leading to the ever-increasing surplus of nitrogen in agricultural nitrogen balance. Once the nitrogen content in soil has not yet reached a steady state, a lot of nitrogen loss can occur, as the nitrogen content in soil increases. The dissolved oxygen concentration in soil can reduce the loss of nitrogen runoff for the high yield. The nitrogen use efficiency of rice can depend mainly on the nitrogen forms, microbial community structure, as well as nitrogen uptake and transformation in rhizosphere. This study aims to clarify the effect of reduced nitrogen fertilizer application and aerobic irrigation on the key growth period of rice, including the nitrogen metabolism-related enzyme activities, plant nitrogen content, nitrogen accumulation, yield, and nitrogen use efficiency. A series of experiments were carried out in the network room of the experimental base at China National Rice Research Institute. The test materials were Zhonghan 221 (upland rice), Zhongzheyou 8 (rice), and IR45765-3B (deep rice). Two irrigation modes were set, including Conventional Flood Irrigation (WL), and Micro-Nano Bubble Water Oxygenation Irrigation (MBWI). Two nitrogen levels were set as the conventional (195.0 kg/hm2) and reduced nitrogen fertilizer application (157.5 kg/hm2). The results showed that: 1) The activities of key enzymes of nitrogen metabolism in rice leaves decreased in the reduced nitrogen fertilizer application, compared with the conventional dosage. The MBWI significantly improved the nitrate reduction of rice leaves, Enzyme, glutamine synthase, glutamate synthase, and alanine aminotransferase activity. 2) The MBWI and increased nitrogen fertilizer dosage greatly contributed to the nitrogen accumulation in different organs of rice, whereas, the reduction of nitrogen fertilizer application under MBWI was better than that under WL. The nitrogen fertilizer utilization rate in the season increased by 15.6%, 36.2%, and 21.5% (P<0.05), respectively, for three rice varieties. 3) The grain yield of different rice varieties significantly increased under the oxygen-increasing irrigation with MBWI and increasing nitrogen fertilizer application rate. By contrast, the grain yield increased by 3.5% (P<0.05) via the reduced nitrogen fertilizer application under medium-dry 221 irrigation, compared with conventional nitrogen application under WL. However, there was no significant difference between the reducing and routine nitrogen application under WL (P>0.05). 4) A correlation analysis showed that the activities of key enzymes of nitrogen metabolism in rice leaves were mostly positively correlated with the leaf nitrogen content and nitrogen accumulation in the same period (P<0.05) or extremely significantly (P<0.01). Consequently, the oxygenated irrigation under MBWI can significantly improve the activities of nitrogen metabolism-related enzymes in different rice varieties, thereby significantly improving the nitrogen accumulation of rice plants for the high efficiency of nitrogen fertilizer use in the current season, as well as the high grain yield of rice. The MBWI under the condition of fertilization can greatly contribute to maintaining the high absorption of nitrogen fertilizer and utilization efficiency, where the glutamine synthase activity can be used to predict the nitrogen accumulation in rice at various stages. The research results provide theoretical and technical support for reducing nitrogen application in rice and improving nitrogen use efficiency in rice.