长江中下游小麦品种氮素吸收利用的演进特征及其生理机理

Excessive nitrogen(N) fertilizer application in wheat production has become the main factor that induces the lower production benefit and severe environmental pollution. Breeding new cultivars with high yield and nitrogen use efficiency (NUE) can sufficiently improve the NUE and further ensure the food security and preserve ecological environment. Previous studies showed that N uptake and utilization efficiency improved during the cultivars genetic evolution, while their physiological mechanisms are still unclear. In this study, wheat cultivars share similar genetic background and have been widely planted in the Middle-Lower Yangtze River Basin in different decade were investigated in order to understand the mechanisms of root-shoot balance characteristics and formation of root population with high N uptake; To understand the relationship between nitrogen utilization and root morphology, phytohormone content and their relationships with root-shoot matter balance. Moreover, the characteristics of genetic evolution on root senescence and activity will be analyzed to reveal genetic evolution and regulation mechanism of root NO3- uptake carrier NRTs expression characteristics, root uptake ability, N assimilation and high utilization. The evolution of photosynthesis and carbon metabolism will be further analyzed to understand the relationship between N uptake and assimilation and to clarify the physiological and molecular mechanisms of genetic evolution on N uptake and utilization. Results could provide theoretical basis and technical support for breeding high yield and N efficiency cultivars and efficient production regulation in wheat.

小麦生产中过量施用氮肥导致生产效益降低、环境污染加剧，选育高产高效品种是提高氮肥利用率、确保粮食安全、保护生态环境的重要手段。研究表明，小麦品种演进过程中氮素吸收利用效率提高，但其机理尚不明确。本项目拟以长江中下游麦区有相似遗传背景的不同年代主推品种为材料，系统分析小麦根系形态的演变规律，明确植株内源激素平衡的变化特征及其对根系形态和根-冠物质分配的调控效应，探明氮素高效吸收利用的根系群体和根-冠平衡特征及其形成机理；分析根系衰老和生理活性的演变特征，明确小麦根系NO3-转运蛋白基因表达的演变规律及其调控机制，阐明根系吸收功能和氮素同化的演变机理，明晰氮素高效吸收利用的关键生理特性及其调控机制；分析品种更替中光合性能和碳代谢的演变规律，揭示光合性能演变与氮素吸收利用的关系，阐明小麦品种演进过程中氮素吸收利用演变的生理机理。研究结果将为小麦高产高效品种选育和栽培管理优化提供重要的理论依据。

小麦生产中过量施用氮肥导致生产效益降低、环境污染加剧，选育高产高效品种是提高氮肥利用率、确保粮食安全、保护生态环境的重要手段。项目以长江中下游麦区有相似遗传背景的不同年代主推品种为材料，采用大田、土柱和砂培试验相结合的方法，研究了不同小麦品种改良过程中小麦根系形态学和吸收功能、植株氮素同化、光合特性的演变规律及其与氮素吸收利用的关系。结果表明，小麦品种改良过程中氮素吸收利用效率提高，氮效率提高主要归因于植株花前氮素吸收能力和氮素转运能力增强。小麦品种改良过程中花前根系生物量、总根长、表面积显著提高，且现代品种根系在上层土壤的分布显著高于早期品种，现代品种花前根系活力、根系NO3-转运蛋白基因表达量显著高于早期品种，说明品种改良提高了根系群体和根系对氮素的吸收能力。现代小麦品种花前叶片NR、GS活性和GS1、GS2表达量显著高于早期品种，而花后显著低于早期品种，表明小麦氮素同化能力的改良主要表现在开花前。随着品种育成年代的推进，小麦旗叶花后的光合性能、旗叶叶面积、比叶重逐步提高、叶绿素含量、可溶性蛋白、Rubisco酶含量及活性、最大光化学效率（Fv/Fm）和实际光化学效率（φPSII）随品种育成年代逐步提高，说明品种改良提高小麦光合性能和光系统活力。小麦花前磷酸蔗糖合成酶（SPS）和蔗糖合成酶（SS）活性的提高促进了旗叶可溶性糖和蔗糖含量的提高，从而有利于增强光合产物转化为蔗糖的能力，为籽粒蔗糖含量的提高奠定基础。倒二叶和倒三叶的净光合速率提高幅度旗叶显著高于旗叶，现代小麦品种旗叶高浓度的氮含量使Rubisco酶活化酶相关基因表达下调导致含量及活性降低，使旗叶净光合速率提高幅度小于倒二叶和倒三叶。因此，提高NR、GS活性和叶片光合能力、增加根系吸收面积、改善开花期氮含量在叶片和非叶器官中的分配是品种氮效率改良的基础，也是未来氮高效品种选育和栽培调控的重要目标。