Microorganisms are the main drivers of soil carbon mineralization and changes in their growth and activity with increased temperature could have important feedbacks to climate change. Soil carbon feedbacks to changing temperatures are difficult to model. One reason for this is that the contribution of microbial taxa to the temperature sensitivity (Q10) of soil carbon decomposition is unknown. Here we used soil samples from four ecosystems representative of arctic, boreal, temperate and tropical climates and measured microbial growth rates through quantitative stable isotope probing (qSIP) with 18O as well as soil respiration. Soil from each ecosystem was incubated at 5, 15, 25, and 35℃ for five days. The temperature sensitivity (Q10) of growth was calculated for individual microbial phylotypes and taxonomic groups for comparison with the temperature sensitivity of soil respiration.
Results/Conclusions
We found that both the microbial growth rate and the respiration rate generally increased with temperature. On average microbial growth was most responsive to changes in temperature between 5 and 25℃ and the Q10 of microbial taxa had a significantly non-random phylogenetic distribution. For example, members of Bacilli, Planctomycetacia, Sphingobacteriia and Betaproteobacteria were most sensitive at lower temperatures (5-15 ℃), while Nitrospira and Subgroup 2 in phyla Acidobacteria were most sensitive at higher temperatures (25-35 ℃). Because taxa differ in their temperature sensitivity, variation in microbial community composition may influence the sensitivity of soil carbon to rising temperatures. Indeed, when taxon-specific measurements were aggregated to the community level, microbial growth Q10 was strongly predictive (r2=0.62) of soil respiration Q10 across ecosystems, suggesting the temperature sensitivity of microbial growth and respiration are coupled. Our results emphasize the importance of taxon-specific temperature sensitivity of microbial activity on soil carbon dynamics, which has important implications for predicting the changes in soil carbon store under global warming.