季节冻融对泥炭沼泽碳排放的影响研究进展

Research advances in the influence of seasonal freeze-thaw on carbon emissions from peatlands

泥炭沼泽是至关重要的陆地碳库,同时对气候变化极其敏感,其碳动态受到全球范围的广泛关注.季节冻融作为重要的地表过程,对泥炭沼泽碳库构成最集中和强烈的干扰.大量野外监测与室内冻融模拟研究显示,泥炭沼泽在季节冻融期间出现碳排放高峰,这与土壤水热条件及生物学过程发生剧烈变化紧密相关,相关程度受到冻结期与冻融交替期长短、日冻融循环频次和强度等的影响.冻结和融化过程中,土壤水分向相变界面附近运移,泥炭土的导热率增大,引起热通量的变化;季节冻融会改变泥炭土微生物活性、群落结构和部分微生物生物量,进而影响微生物作用的碳排放;季节冻融会破坏土壤结构,对土壤团聚体稳定性造成影响,进而影响团聚体有机碳的释放;季节冻融中冻融交替过程会增加溶解性有机碳(DOC)含量,降低微生物量碳(MBC)含量,并显著影响活性有机碳含量,从而影响泥炭碳排放.目前,大量机理研究能够对部分野外监测结果作出解释,但仍然存在一定的局限性,已有研究存在注重现象而忽略机制、实验参数缺乏原位性、不同冻融模式下的研究不足等问题.另外,鉴于高海拔泥炭沼泽在区域碳平衡中的关键作用,以及高海拔条件下季节冻融过程的特殊性,季节冻融对高海拔泥炭沼泽碳排放的影响值得深入研究.(图1表1参117)

As a significant terrestrial carbon pool that is extremely sensitive to climate change, peatlands, with their potential for carbon emission, play an important role in Earth’s climatic system. Seasonal freeze-thaw, as a critical surface process, constitutes the most concentrated and strongest influence on the carbon pool of peatlands. Many data sets from outdoor field monitors, as well as indoor incubation research, show that the emission peak from the carbon pool happens during the freeze-thaw period. First, the dramatic variations of both hydrological and thermal factors during this period are thought to be responsible for the variations in carbon emissions. The degree of correlation is affected by the length of the freeze-thaw cycles, as well as the frequency and intensity of the daily freeze-thaw cycles. During freezing and thawing, the soil water moves to the phase interface. This movement, along with an increase in the thermal conductivity of the peat, results in a change of heat flux. Second, the seasonal freeze-thaw cycle changes the microbial activity, community structure, and some microbial quantity, and then affects the carbon emission of the microbial population. In the end, the seasonal freeze-thaw cycle destroys the soil structure, affects the stability of soil aggregates, and then affects the release of organic carbon(OC) from aggregates. Freeze-thaw cycles increase dissolved organic carbon(DOC) content, reduce microbial biomass carbon(MBC) content, and significantly affect active organic carbon content. Therefore, freeze-thaw cycles affect peat carbon emissions. Many mechanism studies explain some of the field monitoring results, but there are limitations, such as inconsistent test conditions and insufficient research under different freeze-thaw modes. The researchers have tended to pay attention to the phenomenon but ignore the mechanism. In addition, because of the key role of high-altitude peatlands in regional carbon balance and the special seasonal freeze-thaw process under such conditions, the influence of seasonal freezethaw cycles on carbon emissions of high-altitude peatlands requires further study.