The microbial community composition in subsoils remains understudied, and it is largely unknown whether subsoil microorganisms show a similar response to global warming as microorganisms at the soil surface do. Since microorganisms are the key drivers of soil organic carbon decomposition, this knowledge gap causes uncertainty in the predictions of future carbon cycling in the subsoil carbon pool (> 50 % of the soil organic carbon stocks are below 30 cm soil depth).In the Blodgett Forest field warming experiment (California, USA) we investigated how +4 ^∘C warming in the whole-soil profile to 100 cm soil depth for 4.5 years has affected the abundance and community structure of microorganisms. We used proxies for bulk microbial biomass carbon (MBC) and functional microbial groups based on lipid biomarkers, such as phospholipid fatty acids (PLFAs) and branched glycerol dialkyl glycerol tetraethers (brGDGTs). With depth, the microbial biomass decreased and the community composition changed. Our results show that the concentration of PLFAs decreased with warming in the subsoil (below 30 cm) by 28 % but was not affected in the topsoil. Phospholipid fatty acid concentrations changed in concert with soil organic carbon. The microbial community response to warming was depth dependent. The relative abundance of Actinobacteria increased in warmed subsoil, and Gram+ bacteria in subsoils adapted their cell membrane structure to warming-induced stress, as indicated by the ratio of anteiso to iso branched PLFAs. Our results show for the first time that subsoil microorganisms can be more affected by warming compared to topsoil microorganisms. These microbial responses could be explained by the observed decrease in subsoil organic carbon concentrations in the warmed plots. A decrease in microbial abundance in warmed subsoils might reduce the magnitude of the respiration response over time. The shift in the subsoil microbial community towards more Actinobacteria might disproportionately enhance the degradation of previously stable subsoil carbon, as this group is able to metabolize complex carbon sources.

中文翻译：

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全土变暖降低了底土中微生物的丰度并改变了微生物群落结构，但不会改变表层土壤中的微生物群落结构

底土中的微生物群落组成仍未得到充分研究，并且在很大程度上未知底土微生物是否对全球变暖表现出与土壤表面微生物类似的反应。由于微生物是土壤有机碳分解的关键驱动因素，这种知识差距导致对地下碳库中未来碳循环的预测存在不确定性（>  50% 的土壤有机碳储量低于 30 厘米土壤深度）。在 Blodgett森林田间增温实验（美国加利福尼亚州）我们研究了+ 4  ^∘ C如何在整个土壤剖面中升温至 100  cm4.5 年的土壤深度影响了微生物的丰度和群落结构。我们使用基于脂质生物标志物的大量微生物生物量碳 (MBC) 和功能微生物组的代理，例如磷脂脂肪酸 (PLFA) 和支链甘油二烷基甘油四醚 (brGDGT)。随着深度的增加，微生物量减少，群落组成发生变化。我们的结果表明，PLFAs 的浓度随着底土（低于 30 cm）中的变暖而降低 了 28%，但在表土中没有受到影响。磷脂脂肪酸浓度随土壤有机碳而变化。微生物群落对变暖的反应是深度依赖的。温暖的底土中放线菌的相对丰度增加，革兰氏+在底土菌适于其细胞膜结构变暖引起的应力，通过的比率所指示的反异向异支链的磷脂脂肪酸。我们的结果首次表明，与表层土壤微生物相比，地下土壤微生物受变暖的影响更大。这些微生物反应可以通过观察到的变暖地块中底土有机碳浓度的降低来解释。随着时间的推移，温暖的底土中微生物丰度的减少可能会降低呼吸反应的幅度。底土微生物群落向更多放线菌的转变可能会不成比例地增强先前稳定的底土碳的降解，因为该组能够代谢复杂的碳源。