围垦植稻对崇明东滩湿地产甲烷微生物的影响

滨海湿地是CH4排放的重要自然源,受人类活动的影响较为强烈。本研究选择长江入海口崇明东滩自然湿地(光滩湿地和芦苇湿地)为对照,以空间代替时间变化,比较研究不同围垦年限(27、51、86年)的稻田耕作土壤产甲烷速率演替规律及其微生物数量变异特征。结果表明,围垦稻田的产甲烷速率平均值为13.8ngCH4 g-1 d-1,是自然滩涂湿地的3.3倍,且随着围垦年限增加而显著增加。围垦稻田中产甲烷菌的mcrA基因拷贝数为1.101×108~1.443×108copies g-1,也随围垦年限增长而增加,比光滩湿地中的基因拷贝数高出一个数量级。光滩湿地产甲烷菌的相对丰度显著低于芦苇湿地和围垦稻田,围垦稻田中相对丰度值随围垦年限增长而显著增加。其中,H2/CO2营养型产甲烷菌的相对丰度随内陆方向和围垦年限增长而数量级水平增加,而甲基营养型产甲烷菌的相对丰度在光滩中最高,随内陆方向和围垦年限增长而数量级水平减小。各采样点中的乙酸营养型产甲烷菌相对丰度同处于一个数量级,其在3个围垦稻田中没有显著差异。相关性分析表明,产甲烷速率与H2/CO2营养型产甲烷菌丰度值呈显著正相关,而与甲基营养型产甲烷菌呈显著负相关。因此,围垦种稻的熟土作用促进了滨海湿地甲烷产生过程,H2/CO2营养型产甲烷菌数量的大幅增加是产甲烷速率升高的主控因素之一。

Effects of reclamation and cultivating rice on CH4-producing microorganisms in Chongming Dongtan Wetland, China

Coastal wetlands are an important natural source of CH₄ emission, which is strongly influenced by human activities. In this study, Chongming Dongtan Natural Wetland(bare, flat wetland and reed-vegetated wetland)in the estuary of Yangtze River was selected as the control, and CH₄ production potential and the related microbial quantity and characteristics were investigated in the paddy field soils with different reclamation years(27, 51, 86 years). The results showed that the average rate of CH₄ production in reclaimed paddy fields was 13.8 ng CH₄·g^-1·d^-1, which was 3.3 times higher than that in natural wetlands and increased significantly with the increase in reclamation years. The average copy number of mcrA gene in the methanogens was 1.101×10⁸~1.443×10⁸ copies·g^-1 in reclaimed paddy fields, which was an order of magnitude higher than that in bare, flat wetland and increased with the increase in reclamation years. The relative abundance of the methanogens(as a percentage of the whole archaea)was significantly lower in bare, flat wetland than in reed wetland and reclaimed paddy field, and the relative abundance in reclaimed paddy field increased significantly with the increase in reclamation years. More importantly, the relative abundance of H₂/CO₂ trophic methanogens increased in order of magnitude with the increase in reclamation years, whereas the relative abundance of methylamine trophic methanogens decreased in order of magnitude with the increase in reclamation years. In addition, the relative abundance of acetic acid trophic methanogens was in the same order of magnitude in the five sampling sites, and there was no significant difference among the three reclaimed paddy fields. The correlation analysis showed that the production rate of CH₄ was positively correlated with the abundance of H₂/CO₂ trophic methanogens, but negatively correlated with methylamine trophic methanogens. Therefore, mellowing the soil using reclamation and cultivating rice promote the production of CH₄ in coastal wetlands, and the significant increase in the number of H₂/CO₂ trophic methanogens is one of the main factors controlling the increased CH₄ production rate.