不同基因型花生根瘤菌固氮效率差异机制研究

Reducing the use of nitrogen fertilizer which contaminated environment to fulfill agricultural sustainable development is considered to be a global subject of agriculture in 21st century. Rhizobia could intrude into peanut and form nodules in roots. Fixing nitrogen in the atmosphere by root nodules plays an important role in nitrogen supplying of peanut. In our preliminary experiment, nitrogen fixation function of root nodules had significant genetic variation among different genotypes of peanut. Based on the previous screening of peanut variety with nitrogen fixation high efficiency, this study will be conducted with the main index of nitrogen fixation efficiency and the entry point of morphological characters, ultra structure and physiological metabolism. A total of 7 genotypes of peanut are used in pot experiment with 15N isotope tracing analysis from three respects of root, root nodule and leaf to: (1) investigate the relationship between root morphological characters, root system formation, capability of material metabolism of root, and nitrogen fixation efficiency of rhizobia; (2) reveal the relationship between ultra structure of root nodule, conversion and transport of metabolic material of nitrogen fixation, and nitrogen fixation efficiency of rhizobia, quantitative analysis the contribution of root nodule characters to nitrogen fixation; (3) clarify the relationship between supply ability of photosynthate and carbon metabolism capacity of leaves, leaf senescence characteristics, and nitrogen fixation efficiency of rhizobia; (4) explain the physiological mechanism causing the differences of nitrogen fixation efficiency of different peanut genotypes. Results obtained from this study will provide important theoretical value and technical support for selecting and breeding nitrogen high efficiency variety, and saving nitrogen fertilizer cultivation.

减少氮肥用量及其对环境的压力，实现农业可持续发展，被认为是21世纪一个全球性农业研究课题。花生根系着生根瘤，能够直接利用大气中的氮气作为氮源，在花生氮素供应中占有举足轻重的地位。申请人前期研究发现，不同基因型花生根瘤菌固氮效率存在显著差异。本项目在前期根瘤菌高效固氮品种筛选的基础上，以根瘤菌固氮效率为主指标，以形态特征、超微结构和生理代谢为切入点，从根系、根瘤和叶源三个方面，在桶栽条件下，利用15N示踪技术，研究根系形态结构特征及物质代谢能力与根瘤数量、质量以及根瘤菌固氮效率的关系；阐明不同基因型花生根瘤超微结构、根瘤菌固氮产物的转化与转运特点及其与根瘤菌固氮效率的关系；阐明叶源光合产物供应能力、碳代谢水平和生育后期叶片脱落属性与根瘤菌固氮效率的关系。揭示不同基因型花生根瘤菌固氮效率差异机制，提出根瘤菌固氮效率的评价指标，为花生氮高效品种筛选、培育和节氮栽培提供理论依据和技术支撑。

花生根系着生根瘤，可有效供给花生生育所需要的氮素营养，在花生氮素供应中占有举足轻重的地位。减少氮肥施用量，充分发挥根瘤菌固氮潜力来满足花生对氮素的需求，是国内外公认的花生节氮、高效、生态栽培最有效的途径，也是未来花生生产发展的趋势。因此本项目以不同基因型花生为研究材料，从形态建成、超微结构和生理代谢三方面系统阐明根系、根瘤和叶源三者与根瘤菌固氮效率的关系，揭示不同基因型花生根瘤菌固氮效率差异的机制。研究表明：（1）根系形态性状基因型间遗传变异系数均达20%以上，表现为根系长度>根系表面积>根系体积，氮代谢生理活性基因型间遗传变异系数为17.3%~20.7%，表现为硝酸还原酶>谷氨酰胺合成酶>谷氨酸脱氢酶。根系形态性状和氮代谢生理活性均与根瘤菌固氮量极显著正相关，相关系数分别达0.587~0.707和0.953~0.964。（2）单细胞内类菌体数量基因型间遗传变异系数达40.8%，根瘤内根瘤菌固氮产物基因型间遗传变异系数为35.2%~55.3%，根瘤内豆血红蛋白含量和根瘤菌固氮酶活性基因型间差异性达显著水平。根瘤特性指标中，类菌体数量、酰脲含量、尿囊酸含量、根瘤菌固氮酶活性和豆血红蛋白含量均与根瘤菌固氮量极显著正相关，且酰脲含量和根瘤菌固氮酶活性相关性高于其余各指标。（3）不同基因型花生叶片脱落属性存在显著性差异，叶片脱落比例和落叶速率基因型间遗传变异系数分别为41.5%和39.8%。净光合速率、可溶性糖含量、蔗糖合成酶和蔗糖磷酸合成酶活性基因型间差异性均达显著水平，基因型间遗传变异系数分别为21.5%、19.2%、18.4% 和24.3%。花生落叶比例和速率与根瘤菌固氮量极显著或显著负相关，光合产物供应能力与根瘤菌固氮量极显著正相关，相关系数均达0.9以上。（4）根瘤菌固氮效率存在显著遗传变异性，而且与根系形态性状及氮代谢能力、根瘤内类菌体数量、根瘤菌物质代谢能力和叶源碳水化合物的供给能力极显著正相关，通过调控上述相关指标可协同提高根瘤菌固氮效率。研究结果为花生根瘤菌高效固氮品种筛选、培育和高效施氮提供依据。