Temperate coniferous forest soils are considered important sinks of soil organic carbon (C).Fresh C inputs may,however,affect soil microbial activity,leading to increased organic matter decomposition and carbon dioxide production.Litter consists of labile and recalcitrant fractions which are thought to be utilized by distinct microbial communities and at different rates during the growing season.In this study,we incubated the whole litter (LC + RC),the labile (LC) and the recalcitrant (RC) fractions with the coniferous soil at two temperatures representing spring/autumn (10 ℃) and summer (20 ℃)for one month.Soil respiration and microbial community composition were regularly determined using phospholipid fatty acids as biomarkers.The LC fraction greatly increased soil respiration at the beginning of the incubation period but this effect was rather short-term.The effect of the RC fraction persisted longer and,together with the LC + RC fraction,respiration increased during the whole incubation period.Decomposition of the RC fraction was more strongly affected by higher temperatures than decomposition of the more labile fractions (LC and LC + RC).However,when we consider the relative increase in soil respiration compared to the dH2O treatment,respiration increased more at a lower temperature,suggesting that available C is more important for microbial metabolism at lower temperatures.Although C was added only once in our study,no changes in microbial community composition were detected,possibly because the microbial community is adapted to relatively low amounts of additional C such as the amounts naturally found in litter.