增温对大兴安岭泥炭湿地土壤碳、氮循环的影响及微生物机制

Northern high-latitude peatlands contain a large proportion of carbon and nitrogen and play important roles in carbon and nitrogen cycling in terrestrial ecosystem. Global warming is expected to have greater impacts on northern peatland in coming decade than most other ecosystems. Plant litters release carbon and nitrogen during the leaching and decomposition processes. Soil microorganisms and enzyme are driving indicators of soil biochemical reaction. Warming may result in significant variation of litter quality, soil microbial activity, community composition and function (enzyme activity) and further influence the decomposition of soil organic carbon and release of inorganic nitrogen, change the soil carbon and nitrogen pool and composition. However, the transformation of soil carbon and nitrogen and interaction with soil microorganism in peatland ecosystem under climate warming is uncertain, especially, the microbial mechanism is poorly understood. We will carry out field experiments and incubation experiments using 13C and 15N-label and molecular biology technology. The aim is to assess the potential impacts of climate warming on litter decomposition, soil carbon and nitrogen mineralization, carbon and nitrogen fractions, as well as soil microbial and enzyme activities. This will help to investigate the response of soil carbon and nitrogen cycle processes to the elevated temperature in a cool-temperate peatland and reveal the dynamic of soil carbon and nitrogen pool change to climate change.

北方高纬泥炭湿地是碳和氮的重要贮存库，对全球碳、氮生物地球化学循环具有重要作用，同时该地区也是对气候变化响应较为敏感的区域。土壤有机碳、氮主要来源于植被枯落物。微生物和酶是土壤碳、氮转化的重要推动者。温度升高会改变植被枯落物性质及土壤微生物群落结构、代谢活性和功能（酶活性），进而影响土壤有机碳分解和无机氮的释放，改变土壤碳库、氮库量和组成。以往关于泥炭湿地土壤碳、氮转化及其与微生物相互作用关系的系统研究较少，特别是在气候变暖背景下土壤碳、氮循环的微生物机制还不明确。本项目拟通过野外原位控制及室内模拟实验，结合同位素技术和分子生物学手段研究温度升高对大兴安岭泥炭湿地枯落物分解、土壤碳氮矿化及土壤碳氮组分、微生物、酶活性等的影响，初步探讨寒温带泥炭湿地土壤碳、氮循环过程对增温的响应及其微生物机制，以期为探明气候变暖情境下泥炭湿地土壤碳、氮动态提供基础资料和科学依据。

本项目以大兴安岭泥炭湿地为研究对象，基于野外原位增温实验和室内模拟实验，研究了连续多年冻土区泥炭湿地土壤碳、氮循环过程对增温的响应及其微生物机制。结果表明：增温能够促进连续多年冻土区泥炭湿地典型植被白毛羊胡子草和笃斯越橘对土壤中的氮营养的吸收，促进氮在植物地上部分的累积，进而降低植物碳氮比。短期增温（3年）导致0-10cm，10-20cm土壤微生物量碳含量和20-30cm土壤溶解有机碳含量降低，能够促进植物生长并吸收更多的氮，进而导致土壤氨氮和全氮含量降低。受土壤温度的影响，深层土壤古菌数量、表层和深层土壤氨氧化菌数量增加，但由于受碳、氮活性基质的限制，表层土壤总细菌、深层土壤反硝化细菌、表层和深层土壤甲烷氧化菌数量降低。增温3年降低了参与碳循环的土壤酶活性、提高了与磷循环有关的酶活性，但是对氮循环相关的酶活性没有显著影响。连续增温6年显著提高了泥炭湿地典型植物柴桦的重要值，显著降低笃斯越橘密度、盖度、重要值及生物量，降低了灌木非根际土壤溶解有机碳含量，提高了灌木根际表层土壤微生物数量和表层苔草、灌木根际细菌丰度和表层苔草土壤产甲烷菌数量。连续增温对甲烷氧化菌和古菌丰度的影响主要表现在中层苔草和灌木根际土壤。连续增温显著提高了表层灌木根际土壤蔗糖酶、脲酶活性和表层苔草、灌木根际β-葡萄糖苷酶活性。随着温度升高土壤微生物呼吸作用增强，表层土壤和深层土壤碳矿化量均显著增加。温度升高能够提高土壤反硝化细菌数量，有利于土壤反硝化过程。在室内培养环境下，由于缺少外源碳输入，受碳源基质有效性降低的影响，温度升高导致大多数的表层土壤微生物数量降低。根系添加可为土壤微生物提供能源和基质，进而提高土壤碳矿化量。可利用有机碳添加能够提高土壤微生物数量，并促进土壤微生物分泌蔗糖酶和β-葡萄糖苷酶，进而加速土壤碳氮循环。本项目研究对于明确未来气候变暖背景下冻土区泥炭湿地生态系统碳氮循环过程，并为预测其土壤碳、氮动态提供了重要的科学依据。