微生物介导的海水稻根际不同毫米级土壤氨氧化过程

Ammonia oxidation process in rice rhizosphere is the key to the nitrogen cycle in paddy soil. There are few researches on the evolution characteristics and biological mechanism of ammonia-oxidizing bacteria in the rhizosphere soil of sea rice, because of blind spots and technical deficiencies. This project plans to select the sea rice as the research object, which was found in Zhanjiang area. We design to research the functional microbial community characteristics of ammonia oxidation process in sea rice rhizosphere soil of the salinized rice fields ecosystem. On the basis of clarifying the process and difference of soil ammonia-oxidation in rhizosphere between sea rice and conventional rice, isotopic probe techniques (DNA - SIP) will be used to study ammonia oxidizing microorganism characteristics of succession in different millimeter rhizosphere soil of sea rice, which aim to find "active" ammonium oxidation function microorganism, especially unknown ammonia oxidizing archaea. The evolution of microbial abundance of ammonia oxidation will be also studied by real-time fluorescence quantitative PCR (RT-qPCR). We try to reveal effects of root exudates on soil ammonia-oxidation process mediated by microorganisms by analyzing root exudate composition in different growth stages of sea-rice. This project will reveal the comprehensive mechanism of ammonia oxidation microorganism and root secretion activity in rhizosphere ammonia oxidation process, and provide the theoretical support of key nitrogen cycle process in seawater rice field ecosystem.

水稻根际氨氧化过程是稻田土壤氮循环的关键过程。限于研究盲点和技术不足，沿海滩涂等盐碱化土壤中，海水稻根际土壤氨氧化微生物群落的演变特征与生物学机制仍少有报道。据此，本项目以湛江地区发现的海水稻为研究对象，研究盐碱化稻田生态系统里海水稻根际土壤氨氧化过程的功能微生物群落演替特征。在明确海水稻和常规水稻根际区域土壤氨氧化过程的差异基础上，利用DNA-SIP技术，着重研究优选海水稻根际不同毫米级土壤中氨氧化微生物（AOB和AOA）的群落演替特征，挖掘“活跃的”氨氧化功能微生物，尤其是未知的氨氧化古菌。运用RT-qPCR技术，研究发现的关键氨氧化微生物丰度的变化。对海水稻根系分泌物成分分析，研究根系分泌物对微生物介导的土壤氨氧化过程的影响。为揭示氨氧化微生物在海水稻根际氨氧化过程的综合机制，探明海水稻田生态系统的关键氮循环过程提供理论支撑。

采用海水稻盆栽试验，研究微生物介导海水稻根际不同毫米级土壤氨氧化过程。研究结果表明：低盐浓度处理下耐盐碱水稻根际土壤硝化过程更强烈。耐盐碱水稻根际效应是通过改变土壤环境改变AOB群落结构，而对AOA群落结构的影响不大。在盐碱土壤环境中，盐分对AOA和AOB的丰度和活性都存在显著的抑制作用， AOA的丰度大于AOB的丰度，但是AOA的活性却远低于AOB的活性，在盐碱土壤中对硝化过程的贡献也小于AOB，但在极端高盐的环境中，对土壤起硝化作用主要是由AOA来完成。在氨氧化微生物生态环境得到改善，例如盐分降低，氨浓度高的情况下，AOB的丰度和活性会快速升高，在土壤硝化过程中占优势地位。Nitrosocaldus是AOA群落中相对丰度最高的菌属， Nitrosospira是AOB群落中相对丰度最高的菌属，最高占到整个群落结构的98%，是AOB中起氨氧化过程最主要的一个分支。Nitrosomonas在盐碱稻田中也被检测出，其相对丰度随盐分升高而升高，推测在高盐环境下盐碱稻田土壤中发挥着极其重要的作用。靠近根际的土壤（根际距离<3 mm）AOA和AOB群落多样性、均匀度和物种总数均高于远根际土壤。AOB在靠近非根际土壤时（根际距离>5 mm）时多样性又开始升高。Nitrosocosmicus和Nitrosocaldus（亚硝化暖菌属）为不同处理AOA群落的优势菌属，且随着根际距离的增大，其相对丰度逐渐下降。Nitrososphaera为水稻根际特有的AOA菌属，Nitrosotenuis为根际4-5mm处独有的AOA菌属。在海水稻根际土壤AOB群落属水平中，各处理均以Nitrosospira（硝化螺菌）和Nitrosovibrio（亚硝化弧菌属）为优势菌属。与远根际土壤相比，水稻根际土壤促进Nitrosospira和Nitrosovibrio的生长，抑制Nitrosomonas的相对丰度。