Disentangling thermal acclimation and substrate limitation effects on C and N cycling in peatlands

Temperature and substrate availability are among the key factors controlling microbial metabolism. Therelative importance of these two drivers on soil organic matter turnover is, however, hotly debated. Inthis study, we investigated the effect of temperature changes on the potential enzyme activities involvedin C (phenol-oxidase) and N (protease and amidase) cycling by incubating peat soils collected in winterand summer at the two typical temperatures recorded in the field during these two distinct periods (4and 19 C, respectively). In addition, to evaluate the effect of substrate limitations, we also compared therespiration rates of the thermally adapted soils with and without plant litter additions. Results showedthat both collection season and incubation temperature had a significant effect on the two enzymesinvolved in N-cycling, with summer and increasing temperatures having detrimental effects on thepotential activities of protease and amidase, whereas none of these factors affected phenol-oxidase activity.Furthermore, while adding readily decomposable substrate accelerated decomposition rates, CO2flux rates were similar for all temperature conditions. Interestingly, the greatest contribution of litter toCO2 emissions occurred in the summer samples incubated at the lower temperature, whereas for thewinter samples the stimulating effect on soil respiration was observed under warmer conditions. Thesefindings suggest that the responses of soil microbial communities to temperature and substrate availabilityseem to strongly depend on the long-term temperature conditions and its interaction withsubstrate availability.Conservation Biolog