大气CO2浓度升高对乌梁素海湿地土壤有机碳的影响及机制研究

The elevated atmospheric CO2 can increase plant-derived carbon (C) input into soil, enhance microbial activities with subsequent soil organic matter decomposition. These CO2-led changes will finally impact soil C cycle. However, relative experimental studies mainly focused on forest, grassland and cropland ecosystems with few on wetland ecosystems, especially the lake wetland ecosystems. Wetland ecosystems, holding about one-third of the global soil C stock, play important role in global C cycle. Therefore, our project aims to study the impacts of elevated CO2 on soil C and the underlying mechanisms through an open top chamber experiment in Wuliangsuhai lake wetland. We will monitor the dynamics of belowground C (e.g., soil organic C, soil dissolved organic C, soil microbial biomass C) and aboveground C (e.g., plant biomass C, total organic C in the surface water). Meanwhile, plant photosynthesis, root growth and activity, soil C mineralization and microbial characteristics will also be investigated. Besides, we will also study the relationships of C between aboveground and belowground. Based on those results, the impacts of elevated atmospheric CO2 on soil C in the lake wetland will be elucidated. Our research will enhance the knowledge on the relationships between climate change and wetland ecosystems, and therefore, provide theoretical foundation and decision basis for our country mid-long term adaptation to climate change and policy making.

大气CO2浓度升高会增加植物向土壤的碳输出，提高微生物活性，加速有机质分解，从而影响土壤碳循环。然而，相关试验研究多集中于森林、草地、农田等生态系统，较少关注湿地生态系统，尤其是湖泊湿地生态系统。湿地土壤储存着全球陆地土壤1/3以上的碳库，在全球碳循环中作用重要。为此，本项目以乌梁素海湖泊湿地为研究对象，进行野外原位CO2浓度增高的开顶式气室（Open Top Chamber, OTC）试验，研究CO2浓度升高条件下土壤总有机碳、可溶性有机碳、微生物量碳等地下部碳，以及植物生物量碳、水体总有机碳等地上部碳的动态变化；植物光合作用、根系生长和活性、土壤碳矿化动态和微生物学特性等关键过程；以及地上部和地下部碳过程的相互联系与影响等，从而阐明大气CO2浓度升高对湖泊湿地土壤碳的影响及作用机制，以增强对全球气候变化与湿地生态系统关系的认识，为我国中长期应对气候变化与政策制定提供理论参考和决策依据。

大气CO2浓度升高会增加植物向土壤的碳输出，提高微生物活性，加速有机质分解，从而影响土壤碳循环。然而，相关试验研究多集中于森林、草地、农田等生态系统，较少关注湿地生态系统，尤其是湖泊湿地生态系统。湿地土壤储存着全球陆地土壤1/3以上的碳库，在全球碳循环中作用重要。为此，本项目以乌梁素海湖泊湿地为研究对象，进行野外原位CO2浓度增高的开顶式气室（Open Top Chamber, OTC）试验，研究大气CO2浓度升高对湖泊湿地碳循环的影响。结果显示，对于地上部碳动态而言，大气CO2浓度升高提高了湿地植物的光合作用，使植物整个生育期株高比对照平均提高了7.88%，地上部生物量累积量比对照平均提高了19.32%，从而表明大气CO2浓度升高可提高地上部碳累积量。对于地下部碳动态而言，大气CO2浓度升高提高了根系生物累积量，增多了细根数量，使根长变长，根体积变大、根系活跃吸收面积增大。然而，从两年的实验结果来看，大气CO2浓度升高虽然使得土壤可溶性有机碳含量略微提高，但并未达显著水平，而且对土壤可溶性氮含量、总有机碳含量和总氮含量均无影响。结合乌梁素海湿地富营养化水平较高的情况，本研究认为，较短时期内，大气CO2浓度升高可提高富营养化湖泊湿地地上部碳累积量，从而影响地上部碳动态，而对于地下部碳动态则基本无影响。