Will heterotrophic soil respiration be more sensitive to warming than autotrophic respiration in subtropical forests?

Understanding the responses of heterotrophic (R-h) and autotrophic (R-a) components of soil respiration (R-s) to warming is important in evaluating and modelling the effects of changes in climate on soil carbon (C) cycling in terrestrial ecosystems. We used a mesocosm system with buried heating cables (5 degrees C warming) to investigate the responses of R-s, R-h and R-a to warming in a subtropical forest in southern China. Soil CO2 effluxes were measured with a portable automatic soil CO2 flux system from March 2014 to July 2015. We found that warming increased mean R-s and R-h from 788 to 1036 g C m(-2) year(-1) (+31%) and from 512 to 707 g C m(-2) year(-1) (+38%), respectively. There was no difference in R-a between the warming treatment and the control. The lack of response of R-a to warming was probably because the fine root biomass did not change with warming treatment. Soil warming also increased available dissolved organic carbon, microbial biomass carbon, actinomycetal biomass and arbuscular mycorrhizal biomass. Our results suggest that R-h might be more sensitive to climate warming than R-a, and future climate warming could increase soil C loss from increased R-h in subtropical forest ecosystems. Highlights A field warming experiment with partitioning of soil respiration in a humid subtropical forest. Warming increased R-s and R-h without significantly altering soil microbial substrate availability. Heterotrophic respiration appeared more sensitive to warming than autotrophic respiration. Warming increased Actinomycetes bacteria and Arbuscular mycorrhizal fungi.