减量施氮对玉米/大豆套作系统中作物氮素吸收及土壤氨氧化与反硝化细菌多样性的影响

【目的】揭示玉米/大豆套作系统下作物根际土壤细菌数量及群落多样性变化特征与土壤总氮含量、作物氮素吸收之间的关系,为禾/豆间(套)作减肥增效生产提供理论和技术支撑。【方法】大田试验于2013—2015年进行,采用两因素裂区设计,主因素为种植模式,设玉米单作(MM)、大豆单作(SS)和玉米/大豆套作(IMS);副因素为玉米、大豆施氮总量,设不施氮(NN:0)、减量施氮(RN:180 kg·hm~(-2))和常量施氮(CN:240 kg·hm~(-2))。在玉米V12期、VT期和R6期,大豆V5期、R2期、R5期和R8期,利用稀释平板法和凯氏定氮法测定各作物根际土壤细菌数量、非根际土壤和植株总氮含量;结合克隆文库和荧光定量PCR技术研究各处理氨氧化细菌(amo A基因)、反硝化细菌(nir S基因)多样性及其基因丰度。【结果】与相应的单作相比,套作玉米(IM)的作物根际土壤细菌数量提高2.6%,套作大豆提高12.9%;套作玉米土壤总氮含量和植株吸氮量分别提高13.39%和2.10%,大豆的分别降低5.81%和3.24%;套作玉米、大豆的amo A基因丰度比单作增加了38.5%、64.8%,nir S基因丰度比单作提高57.77%、126.39%。各施氮水平间,RN的玉米根际土壤细菌数量比NN和CN的分别提高9.6%和9.8%,大豆的分别提高11.7%和11.0%;施氮提高了玉米、大豆植株吸氮量和土壤总氮含量,单作玉米随施氮量的增加而增加,套作玉米及单、套作大豆的均在RN下最高;减量施氮提高了玉米、大豆amoA基因多样性指数和单作玉米nir S基因多样性指数,降低了套作玉米和单套作大豆nirS基因多样性指数。【结论】减量施氮有利于增加玉米/大豆套作系统中作物根际土壤细菌数量,调节氨氧化细菌和反硝化细菌群落结构及多样性,改善土壤氮素转化过程,促进玉米、大豆对氮素的吸收,实现节肥增效。

Effects of Reduced N Fertilization on Crop N Uptake,Soil Ammonia Oxidation and Denitrification Bacteria Diversity in Maize/Soybean Relay Strip Intercropping System

【Objective】The aim of this study is to reveal the variation characteristics of soil bacteria quantity and community in crop rhizosphere, and the relationship among bacteria quantity and community, soil total N content, crops N uptake in maize/soybean relay strip intercropping system, which will provide theoretical and technology support to reduce fertilizer input and efficient production in cereal/legumes intercropping system.【Method】Field experiments were conducted with two factors split-plot designed from 2013 to 2015, the main factor was planting patterns which included monoculture maize (MM), solo soybean (SS) and maize/soybean relay strip intercropping system (IMS), and the sub-factor total N for maize and soybean were no nitrogen 0 (NN), reduced nitrogen 180 kg N·hm^-2 (RN), conventional nitrogen 240 kg N·hm^-2 (CN), respectively. At V12, VT, R6 stages of maize and V5, R2, R5, R8 stages of soybean, the rhizosphere bacteria quantity was investigated by dilution-plate method, non-rhizosphere soil and crops shoot total N contents were determined by Kjeldahl method, and the diversity and gene abundance of ammonia oxdizing bacteria (amoA) and denitrifying bacteria (nirS) under different N fertilization rates were measured by combining clone library with FQ-PCR. 【Result】 The bacteria quantity in the rhizosphere of intercropped maize (IM) was 2.6% higher, and that of intercropped soybean (IS) was 12.9% higher compared with the corresponding monoculture. The total soil and shoot N contents of intercropped maize were increased by 13.39% and 2.10%, and that of intercropped soybean were decreased by 5.81% and 3.24% in contrast with corresponding monoculture, respectively. The gene abundance of ammonia oxdizing bacteria (amoA) of intercropped maize and soybean was 38.5% and 64.8% higher, and the gene abundance of denitrifying bacteria (nirS) of intercropped maize and soybean was 57.77% and 126.39% higher in contrast with corresponding monoculture, respectively. Under different N fertilization rates, the bacteria quantity in the rhizosphere of maize was 9.6% and 9.8% higher, and that of soybean was 11.7% and 11.0% greater in RN compared NN with CN, respectively. In addition, reduced N fertilization increased the diversity index of amoA gene in the rhizosphere of maize and soybean, and increased the diversity index of nirS of monoculture maize, moreover, reduced N fertilization decreased the diversity index of nirS of intercropped maize and soybean. 【Conclusion】 Reduced N fertilization contributed to increase bacteria quantity in the rhizosphere under maize/soybean relay strip intercropping system, improved the progress of soil N transfer, promoted the N uptake of maize and soybean thereby achieved saving fertilizer.