Effect of temperature on soil microbial structure and fractionation during C mineralisation

International audience; Microbial carbon mineralization in soils leads to the production of different gaseous or dissolved components that have environmental impacts. Our study deals with the influence of soil temperature on the production of gaseous and dissolved carbon components during carbon mineralization in forest soils in France. After an incubation of soil samples for 42 days at 4 different temperatures, we determined both size and 13C isotopic signature of dissolved organic carbon and CO2 pools. We also characterised the soil microbial community structure (PLFA profiles). While temperature clearly increases the CO2 production, a low decrease of the dissolved organic carbon pool was observed whatever the temperature of incubation. The isotopic fractionation of the dissolved organic pool was not affected by temperature while a correlation was observed between temperature and isotopic fractionation of the produced CO2. The soil microbial structure was observed to change during incubation. Changes were affected by the soil temperature, specially the relative proportion of fungi decreased with temperature incubation. Correlations between the relative proportion of fungi and isotopic fractionation of the CO2 pool were observed. This result suggests that soil microbial structure can control fractionation during C mineralization.