间作优势的地下部机理解析-"根分泌物-微生物-氮转化过程"互作

The wheat and broad bean intercropping system has some obvious advantages, which make it distributes widely in Yunnan agricultural zones. The mechanism research for intercropping superiority- - improving crop productivity, nutrient efficiency and disease resistance in the intercropping system - - has been mainly focused on the overground part of it, such as the crop combinations, utilization of light, heat and nutrition, and disease resistance mechanism. The aims of this study were to explain the intercropping superiority mechanism from "root exudates - microorganisms - nitrogen transformation processes" interaction, a new point of view from the underground part of intercropping system, and to provide scientific basis for improving nutrients utilization efficiency, reducing negative environmental effects of nitrogen, and controlling crop diseases sustainably by using intercropping rationally. The study will apply the 15N isotopic dilution methods to determine the gross nitrogen transformation rates in the wheat and broad bean intercropping and corresponding monocropping soils, using isotope labeling experiments in the laboratory and in situ and calculating with the FLUZA model or the MCMC method. The nitrogen transformation will be focused on the processes and gross transformation rates related to nitrogen supply and conservation in order to evaluate the effect of planting patterns change on the conservation and supply capacity of soil nitrogen. The major factors and the mechanism influencing the nitrogen gross transformation rates will be illustrated by analyzing the root exudates, enzymatic activity relating to nitrogen transformation, microbe community composition and function, physical and chemical properties in the wheat and broad bean intercropping and corresponding monocropping system soils. It will help us to understand thoroughly the underground mechanism of intercropping superiority from the essential aspect of nitrogen transformation processes influenced by the rhizospheric micro-ecosystem changes, especially changes of biological properties and root exudates in the rhizosphere under intercropping conditions.

小麦蚕豆间作具有明显的间作优势，广泛分布于云南农区。国内外有关间作增产控病的机理研究主要集中在地上部的作物搭配模式、光热养分资源利用、控病机理等方面，本项目拟从地下部"根分泌物-微生物-氮转化过程"互作的新视角解释间作优势的原因并为合理利用间作提高养分资源利用效率，降低氮肥环境负面效应和持续控制病害提供科学依据。本项目采用15N稀释和富集法，通过室内标记培养试验方法和田间原位标记方法，利用FLUZA模型或MCMC算法，研究小麦蚕豆单、间作体系中土壤氮总转化速率，特别是控制土壤供氮、保氮的转化过程及其总速率，评估种植模式变化对土壤保氮、供氮能力的影响；通过分析单间作系统中根系分泌物、氮转化相关酶活性、微生物群落组成、功能、土壤理化性质，揭示土壤氮总转化速率的主要影响因素及机理；从间作根际微生态的变化，特别是根系分泌物和根际生物学性质的变化影响根际土壤氮转化过程的层面揭示间作优势的地下部机理。

小麦蚕豆间作具有明显的间作优势，但间作对土壤氮总转化速率的影响机理尚不太清楚。本项目采用15N稀释和富集法，利用N转化模型研究小麦蚕豆单间作地下部根际土壤氮总转化速率，评估种植模式变化对土壤保氮、供氮能力的影响；通过分析单间作系统中根系分泌物、酶活性、微生物群落组成功能、土壤理化性质，揭示土壤氮总转化速率的主要影响因素及机理；从间作根际微生态的变化，特别是根系分泌物和根际生物学性质的变化影响根际土壤氮转化过程的层面揭示间作优势的地下部机理。研究结果表明，相对于单作，小麦蚕豆间作改善了土壤理化性质，提高了土壤酶活性，改变了作物根系分泌特性，提高了根系有机酸、氨基酸和糖的分泌量，改变了根系分泌物中有机酸的种类和分泌速率。间作通过改变根系分泌物的数量和种类而影响根际微生物种群组成和活性。间作较相应单作土壤显著促进了根际土壤微生物总量、细菌、真菌、放线菌数量的增加，根系分泌有机酸的量与根际细菌、真菌、革兰氏阳性菌、好氧菌数量存在显著或者极显著的正相关。间作提高了土壤无机氮的产生途径（矿化和硝化作用）的总转化速率，进而增强了间作土壤中无机氮的供应能力。间作也同时增强了无机氮同化途径（NO3-同化作用和 NH4+同化作用）的总转化速率，使得矿化和硝化作用产生的无机氮得以有效保持，降低了氮素损失，提高了对无机氮的固持和保蓄能力。同时，氮素矿化速率和无机氮固持速率均与产量和生物量呈显著正相关。土壤微生物总量和细菌数量的增加是间作根际土壤总矿化和总硝化速率提高的微生物学机理，而间作根际土壤硝化细菌 AOB 数量的增加是间作土壤相对于单作土壤总硝化速率提高的主要原因。综上，间作较单作具有更好的无机氮供应和保蓄能力，从而为作物氮素养分吸收和累积创造了营养物质基础，最终为间作增产提供了氮素养分供给的保障。研究结果为从土壤氮总转化速率层面揭示小麦蚕豆间作具有增产优势的机理提供了科学依据。