玉米不同优势杂交种密植群体光胁迫对叶片早衰的影响及其调控

Increased maize planting density is the major way in improving the yield. With the increase of planting density and that population environment is deteriorated gradually, changing quantity and quality of light are the basic reasons why maize leaf senescence of high planting density are caused. Genetic improvement of maize varieties has made a significant contribution to density-tolerance for increasing yield. At present, the mechanism and differences about the effects of different heterotic of maize crossbreed in high planting density with light stress in China on maize leaf senescence are still not clear. This project is basing on the study of the alternating of maize hybrids varieties in China. Selecting two representative heterotic patterns of maize currently production with different planting density, nitrogen and shading treatment to study the dynamics of maize functional leaf senescence of different heterotic patterns in the field condition. Comparing the difference of physical index included photosynthetic parameters, endogenous hormone and chlorophyll ultrastructure. Using 14C isotope-labelling method, the relationship of assimilation distribution and transportation of different organs with leaf senescence is clarified. It is to reveal the mechanism of the effects of root activity, respiration rate, ATP- enzymatic activity with different heterotic in maize on leaf senescence. Comparative analysis of regulation effect of nitrogen fertilizer on maize leaf senescence under light stress can be made. By comprehensive analysis, the mechanism and regulation ways of light stress in high planting density population on leaf senescence of maize hybrids with different heterotic are revealed. That can provide reference theory and technology for China's and maize resistance breeding and high-yielding planting.

群体密度的增加是玉米提高单产的主要途径，随着种植密度提高，群体内环境恶化，光量及光质改变是玉米密植群体叶片早衰的根本原因。玉米品种遗传改良对耐密增产贡献较大，而目前对于我国不同优势玉米杂交种密植群体光胁迫对叶片早衰影响的差异性及其机制尚不清楚。本项目在对我国玉米品种更替研究的基础上，以目前生产上两类优势杂交种（郑单958和先玉335及其改良品种）为材料，设置不同种植密度，辅助遮光和氮素处理，大田条件下比较研究不同优势玉米杂交种密植群体叶片衰老动态规律以及相关的光合参数、叶绿素超微结构等生理指标的差异，采用14C标记明确不同器官同化物运转与叶片早衰的关系，揭示不同优势玉米根系活力、激素含量、ATP酶活性对叶片早衰的影响机制，比较分析氮肥对光胁迫下密植群体叶片早衰的调控效应，阐明玉米不同优势杂交种密植群体光胁迫对叶片早衰的影响机制及其调控途径，为我国玉米密植高产和抗逆育种提供理论和技术借鉴。

玉米群体密度的增加是提高单产的主要途径，但随着种植密度提高，群体内环境恶化、群体质量变差是玉米密植群体叶片早衰的根本原因，同时玉米品种遗传改良对耐密增产贡献较大。本项目以目前生产上代表性的两类优势杂交种（郑单958和先玉335及其改良品种）为材料，大田两年研究表明，先玉335品种的最高籽粒产量均高于郑单958，且在高密度条件下优势更大，产量提高主要是密植条件下穗粒数增加所致。同时研究证明玉米密植条件下冠层结构和叶片衰老特性存在明显差异，先玉335具有较大的茎叶夹角、上部节间及上层叶片的叶向值（+18.42%），中上层叶片PAR截获率显著高于郑单958，节间增长明显拓展了植株上部空间，良好的冠层结构协调了中上部叶片光氮匹配程度，灌浆期具有良好的叶绿体超微结构和较高的光合能力，因此协同提高了植株的光能利用率、氮利用效率和叶片生理质量。研究表明，高密度条件下先玉335品种的干物质积累量、花后干物质量及干物质运转效率明显提高，13C同位素研究表明，而成熟期密植条件下先玉335籽粒中碳素分配率显著高于郑单958。综合措施可以改善花后的C、N代谢，促进了维管束系统的分化发育和功能，提高花后物质运转效率（+11-42%）。同时灌浆期高密度群体先玉335品种具有较高根系总量和深层根系数量，正常氮肥下先玉335根系活力和根系伤流量均大郑单958，同时明显提高了高密条件下的群体根冠比例，协调了地上与地下矛盾，有助于植株对氮素的高效吸收与利用。研究表明最优施氮量条件下，两密度处理的氮素利用效率和氮素吸收效率先玉335均显著高于郑单958，而氮农学利用率和氮肥偏生产力差异不显著。对不同层次叶片研究表明，先玉335类型品种中上部叶片硝酸还原酶（NR）、谷氨酰胺合成酶（Gs）等氮代谢关键酶活性具有较高水平，这有助于延缓植株叶片的衰老和提高及氮素代谢能力；对不同生育阶段叶片研究表明，先玉335类型品种灌浆前、中期具有较高的NR及Gs酶活性，明显提高了高密度下叶片生理质量和物质生产能力，有利于籽粒产量和氮效率的协同提高。