Shifts in microbial trophic strategy explain different temperature sensitivity of C[O.sub.2] flux under constant and diurnally varying temperature regimes

Understanding soil C[O.sub.2] flux temperature sensitivity ([Q.sub.10]) is critical for predicting ecosystem-level responses to climate change. Yet, the effects of warming on microbial C[O.sub.2] respiration still remain poorly understood under current Earth system models, partly as a result of thermal acclimation of organic matter decomposition. We conducted a 117-day incubation experiment under constant and diurnally varying temperature treatments based on four forest soils varying in vegetation stand and soil horizon. Our results showed that [Q.sub.10] was greater under varying than constant temperature regimes. This distinction was most likely attributed to differences in the depletion of available carbon between constant high and varying high-temperature treatments, resulting in significantly higher rates of heterotrophic respiration in the varying high-temperature regime. Based on 16S rRNA gene sequencing data using Illumina, the varying high-temperature regime harbored higher prokaryotic alpha-diversity, was more dominated by the copiotrophic strategists and sustained a distinct community composition, in comparison to the constant-high treatment. We found a tightly coupled relationship between [Q.sub.10] and microbial trophic guilds: the copiotrophic prokaryotes responded positively with high [Q.sub.10] values, while the oligotrophs showed a negative response. Effects of vegetation stand and soil horizon consistently supported that the copiotrophic vs oligotrophic strategists determine the thermal sensitivity of C[O.sub.2] flux. Our observations suggest that incorporating prokaryotic functional traits, such as shifts between copiotrophy and oligotrophy, is fundamental to our understanding of thermal acclimation of microbially mediated soil organic carbon cycling. Inclusion of microbial functional shifts may provide the potential to improve our projections of responses in microbial community and C[O.sub.2] efflux to a changing environment in forest ecosystems. Keywords: microbial trophic strategy; temperature sensitivity ([Q.sub.10]); constant vs varying temperature regimes; decomposition; 16S rRNA gene sequencing