玉米/大豆套作系统氮素高效利用的根际微生态机理研究

Maize/soybean relay intercropping system, a main technology of high utilization of arable land and nutrient, is used and extended widely in China. But the mechanism of efficient nutrient utilization is not clear. In the preliminary research, we found that the efficient absorption of nitrogen was closely related with the microbial diversity in rhizosphere soil and the nitrogen transformation process. Maize and soybean monoculture and maize/soybean relay intercropping will be compared, so do different nitrogen levels.15N isotope tracing will be used to test the nitrogen absorption properties and nitrogen cycling characters. Simultaneously, diversities of community structure and characters on variation in nitrogen-fixing bacteria, ammonia oxidizing bacteria and denitrifying bacteria will be analyzed deeply. Terminal restriction fragment length polymorphism (T-RFLP), clone library and quantitative polymerase chain reaction (qPCR) will be used to explore gene diversities and dynamic variations in gene abundance of nitrogenase, ammonia monooxygenase and nitrite reductase encoding genes (nifH, amoA and nirS), and to identify dominant bacteria and specific bacteria in soil nitrogen cycling. Through the research, we hope to clarify relationships between variation in bacteria and soil nitrogen absorption and conversion in maize/soybean relay intercropping, and to reveal rhizosphere microecology mechanism of efficient nitrogen utilization. In addition, it has great scientific significance for efficient nutrient utilization and great application prospects for reasonable fertilization and development of bacterial fertilizer.

玉米/大豆套作是提高资源利用率和土地产出率的有效途径，是农业部的主推技术，其养分高效利用机理尚不明确。本课题组前期研究发现玉米/大豆套作系统氮素的高效吸收与根际土壤微生物多样性及土壤氮素转化密切相关。本研究以玉米/大豆套作为对象，通过15N同位素示踪、T-RFLP、克隆文库和qPCR等方法，对单套作及不同施氮水平下作物的氮素吸收特性、土壤的氮素循环特征，及固氮菌、氨氧化细菌和反硝化细菌的群落结构差异和变化特征进行研究；探索套作系统下固氮酶(nifH）、氨单加氧酶(amoA）和亚硝酸盐还原酶(nirS)编码基因多样性及丰度的动态变化规律，鉴定调节土壤氮素循环的优势菌群和特异菌群。通过本项目研究，不但可阐明玉米/大豆套作系统下菌群数量变化与土壤氮素转化和作物氮素吸收的关系，揭示其氮素高效利用的根际微生态机理，还可为其它间套作模式的养分高效利用研究提供借鉴依据，为科学施肥和生物菌肥研发奠定基础。

玉米/大豆套作是提高资源利用率和土地产出率的有效途径，本研究以玉米/大豆套作为对象，结合四年长期定位试验，通过15N同位素示踪、T-RFLP、克隆文库和qPCR等方法，研究了玉米/大豆套作系统的氮素吸收利用特性与土壤氮素循环特征，解析了与土壤氮素循环相关的细菌群落结构与功能，可为解析豆科与禾本科间套作模式的养分高效利用机制提供理论借鉴，为完善玉米/大豆套作模式的施肥方法及生物菌肥开发提供理论参数。.（1）玉米/大豆套作内作物对N素吸收存在形态与数量差异。玉米的总N吸收量无显著变化，15N-NO3或15N-NH4吸收量显著增加23.18%，大豆总N15吸收与根瘤固氮量显著提高21.26%和9.42%，套作系统的周年氮肥利用率提高100.95%，土壤N素贡献率降低10.94%。.（2）玉米/大豆套作促进了土壤N循环，降低N损失。套作相对单作降低了土壤NO3-N淋溶、氨挥发和N2O损失，提高了土壤硝化作用和固氮作用强度，降低了土壤氨化作用强度；与常量施氮相比，减量施氮下套作大豆的土壤硝化作用强度提高12.69%，玉米与大豆的土壤氨化作用强度降低23.69%与7.93%，玉米与大豆的土壤固N作用强度提高26.31%与32.53%。.（3）玉米/大豆套作增加了根际土壤微生物数量，丰富了细菌群落组成。玉米的根际土壤细菌、真菌、放线菌数量在与大豆共生后提高2.6%、15.5%和8.6%，大豆的细菌、放线菌、固氮菌数量提高12.9%、5.6%和2.2%。玉米/大豆套作的根际土壤细菌群落多样性高于玉米与大豆单作，减量施氮提高了共生大豆的细菌群落丰度，其Shannon 指数显著高于休闲处理。.（4）玉米/大豆套作增强了土壤氮素循环相关细菌特异基因表达。套作相对单作提高了土壤中amoA、nifH和nirS基因型微生物多样性指数和基因丰度。套作玉米amoA基因的OTU数高于单作，而套作大豆的OTU数则低于单作，但基因丰度共生后比共生前增加了164.8%；套作玉米和大豆的nifH基因丰度相对单作提高88.9%和34.15%；套作玉米nirS基因优势OTUs有26个，单作玉米有18个，套作玉米nirS基因丰度较单作高84.8%；套作大豆优势OTUs有3个，单作下有2个。