多年冻土退化对湿地甲烷排放的影响研究进展

全球气候变暖导致北半球大部分多年冻土区的冻土已经开始退化。多年冻土退化对冻土区湿地CH₄排放产生重要影响,可能直接决定冻土区湿地对全球气候变暖的反馈方式。综述了近年来多年冻土退化对湿地CH₄排放影响的研究。多年冻土退化导致的土壤活动层深度增加和植被类型由中生向湿生的转变都可能会大大增加冻土区湿地CH₄排放量,从而可能对全球气候变暖产生正反馈作用。但多年冻土退化导致的水文条件变化、土壤温度变化和微生物组成及活性变化对湿地CH₄排放的影响却存在一定的不确定性。多年冻土退化除了影响湿地CH₄排放量之外,还可能通过改变土壤冻融过程而影响湿地CH₄排放的季节分配模式。最后提出目前研究中存在的问题,并对未来研究方向进行了展望。

Effect of permafrost degradation on methane emission in wetlands: a review

In the northern hemisphere, global warming is resulting in the thawing of permafrost. Permafrost degradation would have a dramatic impact on methane emission from wetlands in the permafrost area and thus regulate the feedback effects of wetlands in relation to global warming. In this paper, we reviewed the effect of permafrost degradation on methane emission in the northern wetland ecosystem. Permafrost degradation increased the active soil layer depth and caused a shift in plant species from neutral-growing to wet-growing, which enhanced methane emission in wetlands and produced positive feedback for global warming. The effect of altered water regimes on methane emission in wetlands was different among different types of permafrost regions. In continuous and discontinuous permafrost regions, wetter soil conditions due to permafrost degradation enhanced methane emission in wetlands. However, in sporadic permafrost regions, island permafrost thawing caused wetland drought conditions, leading to the disappearance of the soil surface water and thus decreasing methane emissions. Increased soil temperature induced by permafrost degradation increased methanogenic activity and thereby accelerated methane production; however, these warmer temperatures also increased methanotrophic activities, concurrently accelerating methane oxidation. Nonetheless, the composition of methanogens and methanotrophs in wetlands was changed dramatically by permafrost degradation; thereby, with the process of permafrost degradation, the ultimate effects of soil temperature and microbial composition and activity on methane emission in wetlands remain uncertain. In addition, permafrost degradation altered the soil freeze-thawing process, and thus seasonal patterns of methane emissions in wetlands. Finally, we addressed existing gaps in the research and identified a prospect for further study.