稻田干湿交替(alternate wetting and drying,AWD)是提高水稻水、氮利用率的重要水分管理措施。水稻品种、生态环境、氮肥运筹和土壤落干强度是影响AWD下水稻氮素利用率(nitrogen use efficiency,NUE)的主要因素。AWD通过改变土壤水-气环境而影响土壤中生物化学过程,进而影响土壤氮素营养的有效性。轻度AWD促进水稻根系的生长和活力,促进水稻氮素的吸收、同化和转移而提高NUE。轻度AWD不仅提高水稻光合作用,还促进干物质向籽粒的分配,从而提高水稻产量和氮素利用率。AWD还引起植物激素的变化,植物激素也可能参与了对水稻氮素利用的调控。该文从根际氮素营养与环境、根系形态功能、氮素同化和再转移,以及碳同化和分配、植物激素调控等方面综述了AWD对水稻氮素利用率的影响与调控,并提出了一些值得深入探讨的问题。
英文摘要:
Since Green Revolution in 1960s, rice yield has increased dramatically worldwide due to extensive application of chemical fertilizer, particularly nitrogen fertilizer. In fact, farmers always obtain high rice yield by excessive application of nitrogen fertilizer. This raises environmental problems and causes low nitrogen use efficiency (NUE) in rice. Improvement of rice NUE is one of the most efficient ways to resolve those problems, and it has been one of the most concerned research subjects in the field of rice science. Rice production consumes about 80% of agricultural irrigation water in Asia, which is the largest rice planting area in the world. However, seasonal water deficit caused by climate change is becoming a major threat in rice production in many areas. Paddy alternate wetting and drying (AWD) is an important water management technology in counteraction of water deficit and improvement of rice water use efficiency (WUE). It has been accepted as an efficient water regime in main rice planting countries. It is also found that AWD is an effective approach to improve the NUE. Nevertheless, rice NUE is influenced by many factors under AWD irrigation condition, including rice variety, ecological environment, nitrogen fertilizer management, and soil drying intensity. Drying and re-watering cycle in AWD affects biochemical and physical processes such as nitrification, denitrification, mineralization, percolation, and leaching in soil by changing soil water and air equilibrium, which in turn affect the availability of nitrogen nutrition. However, the processes are complex, involving the interactions of soil pH and Eh values, and microbe community and quantity. Proper AWD (e.g. alternate wetting and moderate drying, WMD) facilitates the growth of rice root, improves its ultrastructure and activity, and promotes nitrogen absorption, assimilation, and transference in rice. As a result, NUE of rice is increased. Nitrate reductase (NR), glutamine synthetase (GS), and glutamate: oxo-glutarate aminotransferase (GOGAT) are the most important enzymes in nitrogen assimilation. Their activities are positively correlated with NUE and improved under appropriate AWD condition. WMD has no adverse effects on rice photosynthesis that is the main source of dry matter for rice yield. In addition, it accelerates the transference of dry matter from vegetative organs to seeds developing, and increases harvest index (HI) of rice. Therefore, both rice yield and NUE are enhanced. AWD leads to the change of phytohormone in rice, which might participate in the regulation of rice NUE. Cytokinin is an essential phytohormone in the regulation of nitrogen metabolism. Many studies observed the increase of cytokinin content in both rice roots and leaves under WMD condition. Cytokinin content was positively correlated with net photosynthetic rate. However, the regulative mechanism of cytokinin on photosynthesis and NUE has remained to be elucidated. In this paper, we reviewed the main factors that impact rice NUE under AWD conditions, with emphasis on the influence mechanisms of AWD on rice NUE in the aspects of rhizosphere nitrogen nutrition and environment, root morphology and function, nitrogen assimilation and re-transference, carbon assimilation and allocation, and regulation of phytohormone. Finally, we proposed some suggestions for further research in the field of the relationship between AWD and NUE.