氮素形态对玉米锌吸收及其向籽粒转移的影响机制

Nitrogen (N) application is one of the important ways to improve grain yield of maize, which is sensitive to zinc (Zn) deficiency. Combining application of N and Zn fertilizers is being paid more and more attention. But most studies mainly focus on the yield and Zn nutritional status of maize as affected by varied application levels of N and Zn fertilizers and their interactions rather than different N forms. Studies have showed that application of NH4-N fertilizer could further improve Zn concentration of shoot and grain in maize compared to that of urea and NH3-N fertilizer. But the underlying physiological and molecular mechanisms remain unclear regarding the changes of shoot Zn nutritional status of maize as affected by different N forms. In this study, a two-year field experiment of maize under Zn-sufficient and Zn deficient conditions was conducted to examine the effects of different N forms on (1) root growth dynamics and root spatial and temporal distribution, (2) root Zn uptake, root-to-shoot Zn translocation and Zn allocation to grain and related contents of nitrogenous compounds and organic acids as well as relative expression levels of genes related with Zn uptake (ZIP family), root-to-shoot Zn translocation (HMA family) and Zn retranslocation within shoot parts (YSL family), (3) grain Zn chemical speciation and its bioavailability. The purpose of this study is to reveal the related physiological and molecular mechanisms of Zn uptake and its allocation to maize grain as affected by different N forms. These results will also give insights into the interactions between N and Zn and finally establish a promising management of N and Zn fertilizers for higher yield and Zn bioavailability of maize grain, which is very important for food security and human health.

氮肥施用是提高玉米产量重要途径之一。玉米对锌缺乏非常敏感。氮锌肥配合施用受到人们高度重视。但大多数研究主要关注氮锌施用水平及其交互作用对玉米产量和锌营养的影响，很少关注氮肥施用形态。研究表明，与尿素和硝态氮肥相比，铵态氮肥能进一步提高玉米植株和籽粒锌浓度。但不同氮素形态引起玉米锌营养变化的相关生理和分子机理不清楚。本项目拟开展2年玉米田间试验，重点研究土壤足锌和缺锌条件下，不同氮素形态（1）对玉米根系生长动态和时空分布的影响，（2）对玉米锌吸收、转运和分配的影响及与此过程相关含氮化合物和有机酸的含量以及相关基因（ZIP, HMA, YSL基因家族）表达差异，（3）对玉米籽粒锌化学形态和生物有效性的影响。初步揭示不同氮素形态影响玉米锌吸收及其向籽粒转移的生理和分子机理，对深入理解氮-锌交互作用和实现玉米高产富锌的氮锌肥调控提供重要理论指导意义，为保证我国粮食安全和人体健康提供重要技术支撑。

在两种土壤类型下（棕壤土和盐碱土）分别开展2年田间定位试验。并结合室内砂培试验，揭示了氮素形态对玉米根系形态（根长、根重）、根系氮锌吸收、氮锌从根系向地上部转运、氮锌在籽粒累积和籽粒锌生物有效性影响机理，并提出实现玉米籽粒高产富锌的氮锌肥调控措施，为保证我国粮食安全和人体健康提供重要技术支撑。主要结论如下：. （1）棕壤土条件下，氮素供应形态和品种对玉米氮素吸收和转移有显著交互作用。晚熟品种登海605产量和花后吸氮量总体表现为控释氮肥和硝酸铵钙高于尿素和硫酸铵，主要因为控释氮肥和硝酸铵钙从乳熟期至成熟期向土壤中释放了大量氮素，与其较高花后氮素吸收实现匹配。对于早熟品种鲁单981，尿素处理的产量和氮素吸收能力高于其他3种氮肥形态。不同氮肥种类对两个品种吐丝前和吐丝后锌吸收、转运、籽粒锌浓度及锌生物有效性均无显著影响。. （2）盐渍土条件下，不同氮肥种类增产效果表现为尿素<硫酸铵<硝酸铵钙。尽管硫酸铵可降低生育期内表层土壤pH，但并不能提高土壤DTPA-Zn浓度。相反有降低土壤DTPA-Zn浓度趋势，不利于根系锌吸收。最终导致籽粒锌浓度下降（稀释效应）。硫酸铵和硝酸铵钙较尿素处理籽粒锌浓度两年平均下降8.7%。为实现玉米籽粒高产优质，迫切需求氮肥优化管理配施锌肥才能得以实现。. （3）室内砂培试验表明，不论哪种氮素形态，与缺锌相比，供锌可使玉米地上部植株、根系和总干物质积累量（地上部和根系之和）分别增加22.4%–125.9%、0.5%–91.8%和15.3%–118.4%；使氮积累量分别增加13.6%–45.8%、-9.9%–44.0%（其中在硫酸铵时根系氮积累量下降）和10.8%–45.6%；使锌积累量分别增加137.0%–387.4%、44.4%–206.8%和194.0%–343.4%。其中地上部植株和根系干物质、氮积累量和锌积累量均在混合氮条件下增幅最大。以上结果表明足锌时，氮锌间有明显协同作用，其中混合氮可实现干物质累积最大化，主要因为混合氮配施锌肥可促进根系生长（提高根系干物质累积、各级根系根长及总根长），同步提高根系氮锌吸收能力、提高地上部叶片光合速率，进而提高地上部植株干物质累积。