Microbial decomposition of soil organic carbon (SOC) has a strong impact on future atmospheric greenhouse gas concentrations, which, in turn, serve as important feedbacks to climate warming. However, the underlying mechanisms of this relationship remain poorly understood. Previous research has assessed the impact of warming on the phylogenetic and structural composition of microbial communities and uncovered positive relationships between warming and CO2 emissions derived from microbial communities. Nevertheless, the underlying mechanisms of active microbial carbon (C) degradation induced by warming remain elusive, which impairs our ability to predict future C dynamics. Here, we used stable isotope probing to examine the active bacteria in a tallgrass prairie ecosystem. Soil from a long-term in situ warming experiment were incubated with 13C-labelled Avena fatua (common wild oat) straw to simulate grass litter. Our overarching hypothesis is that long-term warming stimulates the degradation of both fresh C and native SOC by altering the abundance and composition of the communities to enhance the C-degrading capacities of the active bacterial community. Therefore, we utilized a number of cutting-edge technologies, including quantitative PCR (qPCR), high-throughput sequencing, the GeoChip functional gene microarray, and Biolog EcoPlates, to examine the diversity, identity, and metabolic functions of the bacteria actively involved in C degradation.
Results/Conclusions:
C degradation rates of both straw and native SOC were higher under warming. The phylum Firmicutes, known to be efficient in degrading chemically labile and recalcitrant C compounds, increased to 18.5% of the total bacterial abundance under warming. Within this phylum, the order Bacillales was specifically induced by the warming treatment. Additionally, warming increased the phylogenetic β-diversity among the active bacterial communities, revealing a divergent pattern. Since warming stimulated soil respiration by 13.3% and the priming effect on native SOC by 14.4%, we conclude that warming accelerates soil C degradation by increasing the abundance of the active bacterial fraction, restructuring the community composition, and increasing the community’s C-degrading potential. In summary, identification of active bacterial taxa involved in C degradation may provide key targets to help reduce the atmospheric C load. Below-ground communities are indispensable for key ecosystem functions, such as soil C sequestration. The higher abundance of active bacterial community members and greater C-degrading potential could contribute to positive feedbacks to climate warming in a tall grass prairie. Our finding of stronger priming effects by warming is alarming, as it reveals an overlooked mechanism of accelerating climate warming in a grassland ecosystem.