Linkage between temperature sensitivity of SOM decomposition and microbial communities depends on soil fractions

The magnitude of terrestrial carbon (C)-climate feedback largely depends on the temperature sensitivity of soil organic matter (SOM) decomposition (Q(10)). However, our understanding of determinants of Q(10) for SOM fractions such as particulate and mineral-associated organic matter (POM and MAOM, respectively) is still inadequate. Particularly, it remains unclear whether microbial effects on Q(10) are fraction-dependent, which induces large uncertainties in projecting soil C dynamics. Here, we conducted large-scale topsoil sampling on the Tibetan Plateau, in combination with SOM fractionation and 300-day laboratory incubation to assess SOM fraction-dependent linkages between Q(10) and microbial properties. We found that compared with MAOM, POM had larger Q(10) and greater microbial diversity, and also structured distinct microbial communities as well as their co-occurrence patterns. Furthermore, associations of Q(10) with microbial properties differed between the two SOM fractions. Bacterial community composition and relative abundance of bacterial keystone taxa affected Q(10) for POM and MAOM respectively, while bacterial alpha diversity showed opposite relationships with Q(10) for POM and MAOM. These findings highlight the necessity of incorporating SOM fraction-dependent microbial properties and their linkages with Q(10) into Earth system models to accurately predict terrestrial C-climate feedback.