高氮肥用量下水稻根系铵冗余吸收及其与氮肥利用效率的关系

In submerged paddy field, the application of N fertilizer and soil N mainly absorbed in the form of ammonium, previous study showed that rice could be affected negatively by elevated ammonium because of root redundant ammonium absorption. In this project, in order to study the affect of root redundant ammonium absorption on nitrogen use efficiency, a high-NUE (Qilishimiao ) and a low-NUE (Shuanchao 25) rice cultivar will be used as materials in hydroponic experiments and field trials. In hydroponic experiments, varying ammonium concentrations will supplied, and growth, root morphology, total N and ammonium concentration, root oxygen consumption, and transmembrane ammonium fluxes in the root meristem and elongation zones will determined to analysis the impact of redundant ammonium absorption on rice growth,and it relation to nitrogen use efficiency. In field trials, varying nitrogen fertilizer amount will applied to study the relationship among nitrogen aplication amount, rhizosphere ammonium concentration and root redundant ammonium absorption, and root respiration, root morphology, transmembrane ammonium fluxes in the root will analyzed under high nitrogen application treatment, in order to demonstrate the influence of root redundant ammonium absorption on nitrogen use efficecy under high nitrogen aplicaton. The results of the project will provide helpful knowledge to clarify the process of nitrogen absorption, reveal the mechanism of nitrogen use efficiency among varieties and enviroment, as well as to provide new theoretical fundation and guide way to nitrogen fertilizer application in rice production.

水田淹水条件下，施用的N肥和土壤中的N主要以铵的形式被水稻吸收，为探明高氮肥用量下水稻根系的铵冗余吸收及其与氮肥利用效率的关系，本项目以氮肥利用效率差异的常规中籼稻品种齐粒丝苗和双朝25为材料，进行铵浓度的水培试验和施氮量的大田试验。通过水培试验对不同铵浓度下水稻根际酸化、铵和钾离子的吸收，铵无效循环以及根系形态的分析，探明铵冗余吸收对水稻生长的影响及品种间差异，氮肥利用效率的品种间差异与铵冗余吸收的关系。进而进行大田氮肥用量试验，分析施氮量对水稻根际铵浓度的影响及其与根系铵冗余吸收的关系，比较高氮肥用量下氮肥利用效率差异水稻品种的根系铵冗余吸收及根系形态，揭示高氮肥用量下水稻根系铵冗余吸收与氮肥利用效率的关系。研究结果，有助于揭示品种间、环境间氮肥利用差异的机理，深化水稻氮肥吸收理论，为水稻氮肥施用技术的优化提供依据。

水田淹水条件下，施用的N肥和土壤中的N主要以铵的形式被水稻吸收，为探明高氮肥用量下水稻根系的铵冗余吸收及其与氮肥利用效率的关系，本项目以氮肥利用效率差异的常规中籼稻品种齐粒丝苗和沪科3号为材料，进行铵浓度的水培试验和施氮量的大田试验，研究不同铵浓度下水稻根系对铵的吸收，分析铵冗余吸收对水稻生长的影响及品种间差异，氮肥利用效率的品种间差异与铵冗余吸收的关系。研究结果表明：1）在不同外界铵浓度下，N高效的品种和N低效的品种根系分生区和伸长区铵离子的跨细胞膜运输的速率存在显著差异。在0-1mM NH4+ 浓度范围内，NH4+的吸收主要通过高亲和运转系统，水稻对NH4+ 的吸收曲线符合Michaelich-Menten动力学方程，高氮肥利用效率水稻QL由于细胞膜上的NH4+转运离子载体数量多，铵吸收速率明显高于低氮肥利效率品种HK3。当外界铵浓度高于1mmol L-1时，水稻根系对铵的吸收呈现不饱和的特征，在高铵下，过量吸收的铵会在根系的伸长区排出，其中氮低效的品种根系伸长区的铵外排现象比氮高效品种明显。2）在大田生产中，田面水和土壤溶液铵态氮浓度在施肥后2-4天显著增加，基肥施后田面水和土壤溶液中的铵浓度明显高于蘖肥和穗肥施用后的铵浓度峰值，因此基肥施后的苗期是水稻最易发生铵冗余吸收的时期。3）高铵下氮高效和氮低效品种的根系呼吸强度都增加，说明伸长区的铵外排是一耗能过程。铵冗余吸收影响水稻的生长发育，氮低效品种根系和地上部的铵含量和铵积累量增加，株高、分蘖、根系总长度、总根尖数和单株叶面积显著降低，出现铵中毒现象；而氮高效品种QL由于根部的谷氨酸合成酶（GOGAT）活性随着铵浓度的增加显著增加，因此根部NH4+ 含量和NH4+ 积累量并未显著升高，株高、分蘖的变化也不明显。本研究结果证实高铵下水稻存在铵冗余吸收，且水稻品种间的氮肥利用效率差异与根系的铵冗余吸收有关，有助于揭示品种间、环境间氮肥利用差异的机理，深化水稻氮肥吸收理论，为水稻氮肥施用技术的优化提供依据。