根系吸水对多变低水条件下施氮的响应

Negative impacts on agricultural production induced by insufficient water resources are increasing seriously. It has been proved that the recovery of absorption to water by roots after rewatering from drought was vital important to recovery of plant growth and reduce those adverse effects. Importantly, supplying of nitrogen fertilizer can enhance more recovery capacity of plants from water deficiency. However, the mechanisms about this are still not clear completely. Therefore, cotton and wheat grown in nutrient solution, pots soil or PVC tube soil will be selected to study characteristics of root water uptake under partial root-zone nitrogen supplying subjected to variable and low soil water environments. And the aquaporins activity and expression, concentrations of ABA and NO3- and pH value in xylem sap, single root and whole roots system hydraulic conductance, changes of roots' anatomic structures and morphological adaptations, water use efficiency and so on will be measured. The purpose is to establish a conversion relationship between water uptake and water use at different biological level including cells, organ and individual, to reveal a signal mechanism and hydraulic relationship between different level of roots water uptake, to clear adaptation mechanism of water uptake and use to coupling of water and nitrogen as well as the efficient coordination mechanism, and then to clarify response characteristics of root water uptake to nitrogen supplying under variable and low soil water environments. This study is put forward to provide a theoretical basis and technical support for the development of water-saving theory and optimal-nitrogen supplying theory in variable water conditions.

近年来水资源不足对农作生产产生的负面影响日趋严重。现已证实，在旱后水分恢复时根系对水分吸收能力的恢复是植株生长恢复的关键，而给予氮肥供应，可在某种程度上增强植株的这种恢复能力，但相关机制依然没有得到完全理解。本研究采用养液培养、管栽和盆栽控水分根施氮的试验方法，以冬小麦和棉花为材料，针对多变低水条件下施氮后作物根系吸水功能的变化展开研究，旨在从根系水通道蛋白活性表达，木质部ABA、NO3-和pH等化学信号物质调控，根系水力学导度、解剖结构改变和形态适应、地上部水分利用等角度，建立细胞-单根-个体/整株水分吸收过程和水分利用效率的尺度转换关系，揭示根系吸水在不同层次上的信号联动机制和水力学联系，明确作物水分吸收和利用对水氮应用耦合的水分适应机理以及高效协调机制，继而阐明根系吸水对变水条件下施氮的响应特征，为指导农作生产中氮肥合理施用和节水理论的发展提供新的理论依据和技术支撑。

干旱条件下根系对水分吸收能力的维持是植株生长得以持续和旱后生长快速恢复的关键，氮肥供应可在某种程度上增强植株的这种能力，但相关作用机制依然没有得到完全理解。本项目通过养液栽培和土壤栽培冬小麦/棉花植株，设置正常（中）、高和低氮三种施氮量，分根交替供水和常规供水两种水分供应方式，同时设置单次干旱和二次干旱复水两种变水频率或1:3、0:4和2:2三种施肥比例，对不同层次根系水力学导度、解剖和形态特征以及生理生态适应性展开了研究，阐明了根系吸水对环境水分变化和氮素施用的响应特征与适应机制。结果表明：长期或短期干旱、单次或二次干旱或不同生育时期干旱处理均会对棉花/冬小麦的根系吸水、生长和生物量（产量）形成产生明显的抑制，但均可提高WUE。耦合高氮可明显减轻这种抑制效应，减施氮肥则加重了干旱的不利影响。应对水分变化，整株水平上根系形态特征适应性改变，如增大根系总长度和根系表面积等；单根水平上根组织代谢物质含量调节性变化，如抗氧化酶活性和渗透调节物质含量增加等，解剖结构特征适应性改变，如皮层增厚、根系直径增大等；细胞水平上诱导更强的AQPs表达以加强根系吸水；同时，根系吸水受叶片木质部汁液中ABA和NO3-信号与水力信号正向协同调控。水分恢复后，这些形态和生理方面的适应策略在氮的耦合作用下有效的促进了根系吸水补偿效应的产生。氮肥增施未改变根系解剖结构，但与分根交替供水处理以及合理的施肥比例（1:3）一起，可诱导更强的对变水条件的根系形态特征和生理生化适应能力；前期短时干旱处理在根系形态方面的适应性变化亦可显著增强二次干旱时的水分吸收能力。因此，分根交替供水处理耦合中高量氮肥及合理的施肥比例（1:3），适时短时干旱处理植株，可通过上述适应机制获取高的生物量和WUE。研究结果可为指导农作生产中氮肥合理施用和节水理论的发展提供新的理论依据和技术支撑。