滨海湿地土壤微生物驱动氮素转化与消除研究

Soil microbe-driven conversion and elimination of nitrogen in coastal wetlands play an important role in maintaining the nitrogen level and mitigating nitrogen pollution in coastal and offshore waters. During the process of nitrogen transformation in soil microbes in coastal wetlands, it is necessary to deeply understand the ecological characteristics of Comammox bacteria in ammonia oxidation process and main ways to eliminate nitrogen in nitrate reduction process. We selected the coastal wetlands of the Yellow River Delta, which are located in the coastal waters of China, as the target research area. The main types of wetlands in the area for 3 consecutive years would be sampled to quantitatively analyses the distribution and community characteristics of microbes involved in nitrogen conversion in coastal wetland soils. Furthermore, using molecular biology and stable isotope tracer technique, the species composition and abundance of Comammox bacteria in the coastal wetland system would be clarified. And then the conversion rates of denitrification, Anammox and DNRA pathways of soil microbe-driven denitrification in the study area would be analysed. The possible cooperative or competitive relationships among these three pathways that might drive denitrification, as well as master the main pathway of nitrogen removal by microorganisms in coastal wetlands would be further considered. The mechanisms by which nitrogen conversion by soil microbes respond to environmental factors in coastal wetlands as well as the potential of soil microbes to drive nitrogen pollution in coastal wetlands would be revealed. Our findings would provide baseline data for future work to reduce nitrogen levels in coastal areas and control pollution in coastal waters.

滨海湿地土壤微生物驱动的氮转化与消除对维持滨海地区和近岸海域水环境中氮素水平，缓解氮素污染起着重要的作用。针对滨海湿地土壤微生物驱动氮转化过程中需要深入认知氨氧化过程Comammox菌生态学特征和硝酸盐还原过程氮素消除主要途径的问题，本项目拟选取位于我国近岸海域水体无机氮污染显著的黄河三角洲滨海湿地作为研究区域，对其主要湿地类型进行连续三年采样。系统运用分子生物学与稳定同位素示踪技术，分析滨海湿地土壤氮转化微生物数量分布与群落特征，明确滨海湿地Comammox菌种类组成和丰度，解析滨海湿地土壤微生物驱动硝酸盐还原过程反硝化、Anammox和DNRA三个途径的转化速率与可能存在的协同、竞争等相互作用关系，掌握滨海湿地土壤微生物驱动氮素消除的主要通路，揭示滨海湿地土壤氮转化微生物对环境因子的响应机制。结合滨海湿地土壤微生物驱动氮素消除的潜力，为滨海地区氮素减排和近岸海域水污染控制提供科学支撑。

本研究选取黄河三角洲滨海湿地四种典型样地，分别在四个不同季节采集了四种样地0-20cm根系层的土壤样本。研究结果表明：（1）土壤理化指标分析发现在芦苇与柽柳混生群落样地中根系土壤的质量整体高于其他样地，此样地中全氮、有机质和速效磷的含量最高。翅碱蓬群落样地中速效氮的含量最高，滩涂裸地中速效钾、阳离子交换量（CEC）和pH值最高。植物根系作用、植物凋落物、微生物作用活性与土壤理化性质之间是相互影响的。（2）微生物群落分析结果表明，微生物组成存在的时空差异明显，芦苇与翅碱蓬混生群落样地土壤中微生物的多样性在春季和冬季最高，而在芦苇与柽柳混生群落样地中夏季和秋季最高。微生物组成在门水平上，放线菌门（Actinbacteria）在夏季相对丰度升高，秋冬季逐渐减少。在纲水平上，放线菌纲（Actinomycetes ）和酸微菌纲（Acidimicrobiia）的相对丰度也在夏季升高。科水平上的厌氧绳菌科（Anaerolineaceae）和芽单胞菌科（Gemmatimonadaceae）占主导地位。属水平的优势菌主要有盐单胞菌属（Halomonas）、浮霉菌属（Planctomyces）等。（3）功能微生物相对丰度结果分析表明，随这季节的变化，固氮菌相对丰度变化较大，而氨氧化细菌（AOB）、完全氨氧化细菌（Comammox）、亚硝酸氧化细菌（NOB）和反硝化细菌（DNB）四个季节均在芦苇与柽柳混生群落样地中的相对丰度最高。聚类分析发现，与碳氮相关的功能基因丰度随着季节产生明显变化。春季在滩涂裸地中功能基因的丰度最高。夏季在芦苇与翅碱蓬混生群落样地中功能基因的丰度最高。秋季在滩涂裸地和芦苇与翅碱蓬混生群落样地中的功能基因的丰度都较高。冬季在芦苇与翅碱蓬混生群落样地和芦苇与柽柳混生群落样地中功能基因的丰度最高。（4）土壤中氨氧化速率与样地微生物群落多样性指数成正比。夏季氨氧化速率降低，冬季氨氧化速率升高，并且土壤反硝化速率表现出与氨氧化速率相同的趋势。春季土壤微生物反硝化速率和氨氧化速率与完全氨氧化细菌（Comammox）和亚硝酸盐氧化菌（NOB）相关性最大。夏季硝化螺旋菌属（Nitrospira）与土壤氨氧化速率呈正相关，而与反硝化速率呈负相关。秋季硝酸盐异化还原成铵（DNRA）作用菌与土壤氨氧化速率呈显著正相关，而与反硝化速率呈负相关。