Nitrogen addition stimulates priming effect in a subtropical forest soil

The priming effect (PE) induced by fresh carbon inputs generally stimulates soil organic matter (SOM) mineralization. However, the magnitude of the PE will vary according to the chemical composition of plant litter and nitrogen (N) deposition, due to the effect of these factors on soil microbial community composition and activity. This needs to be considered explicitly in ecosystem models, for more accurate prediction of soil carbon dynamics and stocks. Thus, we conducted a 100-day incubation experiment with additions of three 13C-labeled litters and inorganic N to evaluate the effects of plant litter in combination with N additions on SOM mineralization, PE, microbial community composition and activity in a subtropical Cunninghamia lanceolata forest soil. We found no difference in SOM mineralization and PE among three litter types, but the addition of litter together with N increased the PE by approximately 11–42%, apparently through a microbial stoichiometry decomposition process. When N was added, the PE response, biomass of microbial groups and enzyme activities were related to the litter chemical composition. The direction of PE varied with time, and different microbial mechanisms operated at different decomposition stages. Moreover, microbial activity seemed to be energy-limited by the late decomposition stage, based on the incorporation of litter-derived carbon into soil microbial phospholipid fatty acids with high-lignin litter than other litter types. In conclusion, our findings emphasize that different chemical composition litters in combination with N inputs into soil can have a strong effect on soil carbon stocks by stimulating the priming of native SOM mineralization in subtropical forests. Our results also highlight that changes in litter chemical composition, nutrient availability and microbial processes need to be considered from short to long term, which is of great importance to accurately evaluate the variability of the PE under future climate change scenarios.