玉米/大豆套作氮素高效吸收的根系生理调控机制研究

Legume-cereal intercropping systems are effective approaches to enhance nitrogen use efficiency. However, the mechanisms of physiological ecology involve rhizosphere allelopathy and root development are still unclear. Previously, we found that intercropping maize with soybean can optimize crop root distribution and promote nitrogen uptake. Additionally, the rhizosphere microorganisms and allelopathy are important factors which impact soil nitrogen cycle and root growth in the relay intercropping.We will use methods including high performance liquid chromatography (HPLC), quantitative polymerase chain reaction (qPCR), transmission electron microscope (TEM), enzyme activity detection to research crop root growth and exudates. Here, we will determine crop root morphology, root bleeding saps, and nitrogen uptake curve to analyze the ability of nitrogen acquisition. In addition, we will determine the variation of soil physical structure, root exudates and component. We are also to test phytohormones and corresponding response genes in the root which are induced by rhizosphere environment variation to analyze the effects of increasing root surface by elongation lateral root. We will test the root physiological function and respiration intensity, and the ultrastructure of root mitochondria to analyze the effects of reinforcing energy by enhancing mitochondrial respiration. Finally, we will determine the antioxidants content, and activities of antioxidases and coding genes in the root to analyze the effects of increasing validity period by delaying senescence.Through the research, we hope to reveal the physiological mechanisms of root involve nitrogen efficient acquisition in maize-soybean relay intercropping systems. Additionally, this study will offer opportunities for further utilize nitrogen efficiently, and will provide a theoretical basis for technical development to root growth regulators for intercropping.

豆科与禾本科间套作是提高氮素利用率的有效途径，但其氮素高效吸收受根际化感与根系发育调控的生理生态机制尚不明确。前期研究发现，玉米/大豆套作可改善根系分布、促进氮素吸收，根际微生物与根系分泌物是影响土壤氮素循环与根系吸氮的重要因素。在此基础上，本研究拟通过HPLC、qPCR、电镜观察、酶学检测等方法，对玉豆套作的根系可塑性与伤流强度、植株氮素吸收曲线进行测定，分析根系的吸氮能力；监测土壤物理结构与特异根系分泌物的变化规律，并对其诱导产生的根系内源激素含量及其响应基因表达量、根系呼吸强度及线粒体的超微结构与生理功能、根系中抗氧化物质的含量与抗氧化酶活性及其编码基因的表达水平进行检测，分析根系吸氮的“伸长侧根扩面积、增强呼吸补能量、延缓衰老增时间”效应；最终揭示玉豆套作下根系高效吸氮的生理机制，完善间套作的氮高效利用理论，为间套作根系生长与营养调控提供理论依据。

本研究以大豆玉米带状套作系统为研究对象，结合四年长期定位试验，通过动态环境监测、表型特征提取、生理生化分析等方法，调查根区土壤通气环境变化、根系分泌物分泌特性与组分差异、根系形态与空间分布特征、作物氮素与物质吸收积累变化，检测根系线粒体超微结构、根系活力、呼吸强度、活性氧与抗氧化代谢变化，阐明套作环境下根系发育及延衰机制，为完善禾本科/豆科间套作系统养分高效利用的根系调控机制提供理论依据。.(1)玉米大豆套作优化根系分布与氮素吸收，促进物质积累与产量形成。套作增加玉米在垂直方向40～60cm的根系分布，根长、根表面积、根体积较单作增加18.91%、12.89%、9.77%；大豆后期根系生长与单作差异不显著。套作使玉米、大豆的平均氮素吸收率和最大氮素吸收速率分别提高18.47%、33.78%和18.47%、45.87%。与单作相比，套作增加物质积累及氮素吸收，且土地当量比均在 1.32以上。.(2)玉米大豆套作改善土壤通气环境与根系分泌特征，促进根系形成发育。玉米大豆套作增加作物根系附近＞2mm土壤水稳性团聚体分布，增加土壤孔隙度，降低容重。提高伤流液重量，增加伤流液中可溶性糖、硝态氮、铵态氮含量。套作增加玉米、大豆黄酮和黄酮醇分泌，大豆川陈皮素、桔皮素和山奈酚分泌量增加247%、209%和262%；玉米地奥司明、尼泊尔鸢尾异黄酮7-O-β-D-葡萄糖苷、檬黄素O-己糖苷和芹菜素C-戊糖苷分泌增加100%，180%，142%和270%。.(3)玉米大豆套作促进根系生长，增强根系呼吸，延缓根系衰老，提高根系养分吸收能力。根系分泌物浇灌能使玉米、大豆根系中IAA含量分别增加38.93%和26.5%，使其响应因子ZmARF1和GmARF分别上调49.32%和53.32%；玉米根系的一级侧根长、根系生物量提高23.58%、30.68%，大豆的主根长、根系体积比率增加27.09%、68.24%。套作能维持根系在发育后期仍呈较密集的线粒体分布，提高根系呼吸强度。套作增加根系中抗氧化物酶（SOD、CAT、POD）的活性，相关基因GmSOD、GmCAT1、GmPOD表达增加109.02%、98.45%、100.64%，促进抗氧化物质（GSH、AsA）合成，降低活性氧积累，延缓根系衰老。

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