围垦对崇明东滩湿地全程氨氧化微生物的影响

全程氨氧化微生物（comammox）的发现根本改变了学术界对硝化过程的认识，但其地理分异规律及对氮转化过程的贡献仍不清楚。本研究选择长江口崇明东滩不同围垦年限（0、27、51、86年）稻田表层耕作土壤，采用好氧培养试验测定土壤硝化潜力；通过标靶功能基因amoA实时荧光定量硝化微生物的数量变异特征，包括全程氨氧化细菌（comammox）、氨氧化细菌（AOB）和古菌（AOA）。结果表明，与围垦0年的自然滩涂湿地相比，围垦27、51、86年的水稻土净硝化速率从2.24mg N /(kg·d)分别增加至19.3、11.6和11.4mg N /(kg·d)，增幅高达5.1-8.7倍。土壤氨氧化古菌AOA的丰度与围垦年限显著正相关。自然滩涂湿地中氨氧化古菌AOA和AOB的数量分别为0.34×107 copies/g和1.14×107 copies/g，围垦86年后增幅最高可达27.9倍。自然滩涂湿地中comammox Clade A和Clade B amoA基因拷贝数高于围垦稻田土壤，且Clade A随着围垦年限增加其丰度显著增加。统计分析发现，氨氧化细菌AOB与土壤硝化速率显著正相关，可能在围垦水稻土氨氧化过程中发挥了重要作用；而全程硝化细菌comammox Clade A和Clade B与土壤总有机碳（TOC）、铵含量（NH4+）呈显著负相关关系，可能更适应于营养贫瘠的滩涂自然湿地土壤。

Effect of Reclamation on Abundance of Comammox Microorganism in Chongming Wetland

The discovery of comammox broadens our understanding of the nitrification process, but little is known about its natural geographical distribution and its contribution to the nitrogen conversion process. In this study, the surface soils of the paddy field in the Chongming wetland of the Yangtze River estuary (0, 27, 51, 86 years of reclamation) were selected. The aerobic incubation was used to determine the soil nitrification rate and its influencing factors. The target functional gene amoA was analyzed by real-time fluorescent quantitative PCR to analyze the quantitative variation characteristics of comammox, ammoxidox bacteria (AOB) and ammonia archaea (AOA). The results showed that the net nitrification rate of paddy soil in the 40, 75 and 120 years of reclamation was 19.26 mg N /(kg·d), 11.63 mg N /(kg·d) and 11.43 mg N /(kg·d), which was significantly 5.1-8.7 times higher than that of natural tidal wetland (0 year of reclamation). The amoA gene copy number of soil ammonia archaea AOA was between 0.34×107 and 9.95×107 copies/g, which increased significantly with the increase of reclamation year. The amoA gene copy number of soil ammonia bacteria AOB ranged from 1.14×107 - 8.43×107 copies/g, which was significantly positively correlated with soil nitrification rate (r = 0.96*), indicating that AOB might play a dominated role in nitrification process. The comammox Clade A and Clade B copy number of the soil in the paddy fields (27, 51, 86 years) were lower than that of tidal flat wetland soil (no reclamation), and Clade A increased significantly with the increase of the reclamation year. Correlation analysis showed that there was a significant negative correlation between comammox Clade A/Clade B and soil total organic carbon (TOC) and ammonium content (NH4+), indicating that the ammonia-oxidizing microorganisms (Clade A, Clade B) is more suitable for nutritional infertility. In summary, it can be seen that comammox bacteria is widely present in the coastal wetland soil layer of the Yangtze River estuary, which possibly may play an important role in the nitrogen transformation process of tidal flat natural wetlands.