Extreme drought decreases soil heterotrophic respiration but not methane flux by modifying the abundance of soil microbial functional groups in alpine peatland

Extreme drought can have a substantial effect on the soil water content, soil microbial community structure and function, soil heterotrophic respiration (Rh), and soil methane (CH4) flux. However, the effects of extreme drought on Rh and CH4 flux at different plant growth stages (rapid growth, full bloom, and decline stages) and the main factors driving changes in Rh and CH4 flux remain unclear. We conducted an experiment to reveal the responses of Rh, CH4 flux, and the microbial community to extreme drought and the main factors affecting Rh and CH4 flux. Extreme drought significantly decreased Rh (from 69.41 to 31.37 mg m−2h−1) at the decline stage but had no significant effect on CH4 flux. Extreme drought significantly decreased bacterial α-diversity, markedly decreased the relative abundance of Rokubacteria and Chloroflexi at the rapid growth stage and decline stage, and significantly increased the relative abundance of Actinobacteria at the full bloom stage. At the rapid growth and full bloom stages, extreme drought significantly decreased the relative abundance of aromatic hydrocarbon degraders by 50.26% and 64.37%, respectively. At the decline stage, extreme drought significantly decreased the relative abundance of methanol oxidizers and lignin degraders by 81.63% and 82.08%, respectively. A random forest model analysis revealed the most important role of bacterial functional groups in determing Rh and CH4 flux. The aromatic compound degraders and aromatic hydrocarbon degraders amounted to 11.89 % of contribution to Rh, and aromatic compound degraders, aromatic hydrocarbon degraders, aliphatic non-methane hydrocarbon degraders, and methylotrophs amounted to 13.29 % of contribution to CH4 flux. Our findings indicate that microbial functional groups involved in carbon cycles are important factors explaining variation in Rh and CH4 flux and are critical for exploring the possible microbial response mechanism of soil carbon cycling under future scenarios of extreme drought.