Warming-induced microbial decomposition of organic matter in permafrost soils constitutes a climate-change feedback of uncertain magnitude. While physicochemical constraints on soil functioning are relatively well understood, the constraints attributable to microbial community composition remain unclear. Here we show that biogeochemical processes in permafrost can be impaired by missing functions in the microbial community—functional limitations—probably due to environmental filtering of the microbial community over millennia-long freezing. We inoculated Yedoma permafrost with a functionally diverse exogenous microbial community to test this mechanism by introducing potentially missing microbial functions. This initiated nitrification activity and increased CO₂ production by 38% over 161 days. The changes in soil functioning were strongly associated with an altered microbial community composition, rather than with changes in soil chemistry or microbial biomass. The present permafrost microbial community composition thus constrains carbon and nitrogen biogeochemical processes, but microbial colonization, likely to occur upon permafrost thaw in situ, can alleviate such functional limitations. Accounting for functional limitations and their alleviation could strongly increase our estimate of the vulnerability of permafrost soil organic matter to decomposition and the resulting global climate feedback.

气候变暖引起的永久冻土中微生物的有机分解构成了不确定程度的气候变化反馈。尽管对土壤功能的物理化学约束条件了解得比较清楚，但微生物群落组成的约束条件仍不清楚。在这里，我们表明，永久性冻土中的生物地球化学过程可能会由于微生物群落的功能缺失（功能限制）而受损，这很可能是由于微生物群落经过一千年的冷冻而受到环境过滤的结果。我们用功能多样的外源微生物群落接种了永生冻土，以通过引入潜在的微生物功能来测试这种机制。这启动了硝化活性并增加了CO ₂161天的生产量增长了38％。土壤功能的变化与微生物群落组成的变化密切相关，而不是与土壤化学或微生物生物量的变化密切相关。因此，目前的多年冻土微生物群落组成限制了碳和氮的生物地球化学过程，但是可能在永久冻土原位融化时发生的微生物定植可以减轻这种功能限制。考虑到功能性局限性及其减轻的影响，可能会大大增加我们对多年冻土有机物易分解的脆弱性以及由此产生的全球气候反馈的估计。