红壤旱地根际土壤微生物对氮素转化关键过程的调控机制

Influenced by rhizodeposition, the molecular mechanisms of rhizosphere microorganism on key process of nitrogen transformation in upland red soil is poorly understood. Therefore, this project will focus on “plant-soil-microbe interactions”. Field and incubation experiments combined with 13C/15N isotop tracing will be conducted to monitor N2O production and emission from 0-100cm soil profile and the dynamic change of nitrate and ammonia in soil and leaking water, which may reveal nitrogen migration and transformation in research area. Quantitative PCR, reverse transcription PCR, high-throughput sequencing and enzyme analyzing methods will be conducted to study the nitrogen cycling related microbial community structure, quantity and activity in upland rhizosphere or non-rhizosphere soil under different ratio of chemical fertilizer to organic fertilizer with or without crop planting at DNA and mRNA levels, which will show the key functional microorganism related nitrogen cycling. Combined with DNA/RNA-SIP, the effects of photosynthetic assimilation on the active functional microorganism related nitrogen cycling under rhizosphere or non-rhizosphere soil will be revealed. Statistical analysis will systematically indicate the molecular mechanisms of rhizosphere microorganism on key processes of nitrogen transformation, and find the suitable fertilization measures to decrease nitrogen loss. This project will enrich the understanding of nitrogen cycling process in upland red soil, and also offer the theoretical basis to promote nitrogen use efficiency and improve the ecological environment.

受根际沉积物的影响，农田根际土壤微生物如何调控氮素转化的机制尚不清楚。本项目以“植物-土壤-微生物互作关系”为主线，通过田间试验，盆栽试验结合13C、15N稳定同位素示踪，监测剖面土壤N2O产生和排放，土壤和渗漏水硝态氮和铵态氮动态变化，揭示红壤旱地土壤氮素迁移和转化规律；采用qPCR、RT-PCR、高通量测序结合酶学分析技术，从DNA和mRNA水平研究农田作物种植与不种植，化肥有机肥不同配比，根际与非根际土壤氮素转化关键功能微生物群落结构、数量和活性，明确红壤旱地根际土壤参与氮素转化关键功能微生物；结合DNA/RNA-SIP技术研究光合同化作用对根际与非根际土壤氮素转化关键功能微生物的影响；利用统计分析系统研究根际土壤微生物对氮素转化的调控机制，并从实践上找到调控氮素损失的施肥措施。其结果对于全面认识红壤旱地根际土壤氮素转化机制，提高氮肥利用效率及改善生态环境具有重要影响。

项目以“植物-土壤-微生物互作关系”为主线，通过田间试验和盆栽试验相结合，揭示根际效应影响下的红壤旱地土壤氮素迁移和转化规律。研究发现外援添加根系分泌物促进了N2O排放，且添加葡萄糖增加N2O排放效果高于增加草酸，根系分泌葡萄糖促进nirS型亚硝酸还原菌的生长，并抑制N2O还原菌的生长，可能是根系分泌物调控N2O排放的微生物作用机制；盆栽种植油菜根系分泌物中有机酸和氨基酸所起的生态作用不同，单施化肥养分不均衡诱导根系分泌更多的有机酸缓解营养胁迫，化肥有机肥配施促进根系分泌更多的氨基酸增强土壤活性。有机无机肥配比为1:3可能为油菜生长提供最均衡养分，为油菜施肥管理提供参考。AOA丰度和群落结构均与地上生物量显著相关，AOB则与硝化势显著相关，含nirK基因微生物与反硝化势具有显著的相关关系，而含nirS基因微生物则与地上生物量具有显著的相关关系；田间原位试验明确了NO3--N流失量受渗漏水古菌-amoA和细菌-amoA以及narG和nirK基因型反硝化功能微生物的调控。土壤细菌-amoA是调控NO3--N流失量的主要微生物，但细菌-amoA并不能直接影响NO3--N流失量，而是通过流失至渗漏水中的细菌-amoA的硝化作用和增加土壤NO3--N含量两个渠道来促进NO3--N的流失。其结果对于全面认识红壤旱地根际土壤氮素转化机制，提高氮肥利用效率及改善生态环境具有重要影响。