Regulation Of Rice Grain Mineral Nutrition By Nitrogen

Rice is one of the main food crops in China and the world.Mineral elements are central to human health.At least 22 mineral nutrients are needed for human body to maintain their basic metabolic needs.The "recessive hunger",which is caused by the insufficient intake of microelements such as iron and zinc,is a universal nutritional problem worldwide,especially in the developing countries and regions with a single diet.Therefore,to improve the quality of mineral nutrition of rice and other staple food is the main way to improve the health conditions of residents.The accumulation of grain mineral elements is a complex physiological process,involving root absorption,transportation of the upper part of the ground,remobiliztion of vegetative organs and storage of grain.Nitrogen plays an important role in the accumulation of mineral elements in rice grain.However,there is still no research on the regulation mechanism of nitrogen at plant level.The effect of nitrogen fertilizer on the accumulation and distribution of mineral elements in different organs of rice and the effect of nitrogen on the remobilization of mineral elements in three source organs of rice leaf,leaf sheath and glume were compared by field experiment and pot experiment,and the effect of nitrogen on the quality of rice mineral nutrition and its physiological mechanism were investigated.In order to provide reference for the cultivation technology research of rice yield and quality coordination.The main conclusions are as follows:1.Effects of nitrogen fertilizer on accumulation and distribution of mineral nutrients in rice plants.To explore the effect of fertilizer nitrogen on uptake and distribution of mineral nutrient in the rice plant,twenty cultivars with contrasting agronomic traits were grown with three N rates in a field experiment.Experimental results showed nitrogen,phosphorus and magnesium were mainly allocated in the grain of rice plant at the maturity stage.Potassium,calcium,iron,manganese and copper were mostly accumulated in the stem and sheath of rice plant.The zinc is major accumulated in the stem and grain of rice plant at the maturity stage,and the accumulation ratio is 43.56%and 34.81%,respectively.Nitrogen promotes the absorption of mineral nutrients and increases the proportion of their accumulation in the vegetative organs of rice plants.In addition,two high N applications tended to decrease the harvest index of mineral element.In summary,N increased the mineral absorption,but has a little effect on the improvement of translocation of mineral nutrients.2.Contribution of mineral nutrients from source to sink organs in rice under different nitrogen fertilization.Remobilization of nine mineral nutrients including N,phosphorus(P),potassium(K),calcium(Ca),magnesium(Mg),iron(Fe),zinc(Zn),manganese(Mn),and copper(Cu)was measured from the source organs including bracts,leaf,and sheath to sink rice grain.Experimental results showed considerable contribution of bracts to grain for N,Mg,and Zn,with the averages contributions of 5.96%,12.56%,and 12.34%,respectively,indicating a positive role of rice bracts in N,Mg,and Zn remobilization during grain filling.By contrast,minor contribution of bracts to grain P,K,and Cu was revealed,with the contribution rate being 0.99%,3.90%,and 3.05%,respectively.Further,a net increase in Ca and Fe concentrations of bracts was detected,implying that bracts function as a sink of these mineral nutrients.In addition,grains produced at a moderate level of N topdressing had higher Fe and similar Zn concentration in comparison with those at high N level,suggesting the possibility of N management for maintaining Fe and Zn level under high yielding conditions.3.The distribution characteristics of mineral elements in rice grains between brown rice and polished rice were revealed.Using 20 rice varieties as materials,no nitrogen treatment(CK)and two different nitrogen application treatments(N10-0,N5-5)were set up.At the same time,with Huaidao 5 as the material,a pot experiment with 3 nitrogen levels of low,medium and high levels was set up to determine the dynamic changes of the concentration of mineral elements and the accumulation of phytate phosphorus in rice grains.Phosphorus,magnesium,potassium and iron and manganese are mainly distributed in the outer layer of rice grain,while the calcium,zinc and copper have a high concentration in the milled grain layer.With increasing the application of nitrogen fertilizer,especially the fertilizer application of N5-5,can reduce the mole ratio of phytic acid/calcium,zinc and iron,thus improving the effectiveness of these mineral nutrients to a certain extent.(1)At the same high nitrogen level,N5-5 treatment mainly increased the concentration of calcium,magnesium,manganese and copper in brown rice,but reduced the concentration of each element in milled rice.(2)Under different nitrogen levels,compared with low nitrogen or high nitrogen level,the concentration of mineral elements in brown rice can be increased and the concentration and distribution ratio of phosphorus,calcium,iron,zinc,manganese and copper in milled rice can be increased.In summary,nitrogen has a significant effect on the mineral nutrition quality of rice grain.Nitrogen application can improve the mineral elements,especially the concentration and accumulation of iron and zinc in the vegetative organs of leaf,leaf sheath and glume.Excessive nitrogen application can inhibit the remobilization of mineral nutrition to grain,and reduce the mineral nutrient concentration of rice grain.The results of this study provide a theoretical reference for the research and development of nitrogen fertilizer technology for regulating the mineral nutrition quality of rice.