Contribution of above ground litterfall and roots to the soil CO2 efflux of two sub-tropical Cunninghamia lanceolata and Castanopsis carlesii forests

Abstract Soil respiration (RS) is the largest terrestrial carbon (C) flux to the atmosphere, and it can be influenced by changing input of plant C from above- and/or below ground. Especially in tropical and sub-tropical ecosystems, the contributions of litter respiration (RL), autotrophic respiration (RA) and mineral soil respiration (RM) are still poorly understood. In the present study, RS was measured under untreated control (CT), root exclusion (NR), litterfall exclusion (NL), and combined litterfall and root exclusion (NRNL) in a subtropical Cunninghamia lanceolata plantation and a secondary Castanopsis carlesii forest for three years. In addition, litter input, litter and soil chemistry, and microbial biomass and community structure (PLFAs) were assessed. RS was significantly higher in the C. carlesii forest than in the coniferous C. lanceolata forest. RL and RA were significantly higher in the C. carlesii forest than in the C. lanceolata forest, while there was no significant difference in RM. RM, RA, and RL contributed 55%, 29%, and 16% to RS under C. lanceolata, and 39%, 32%, and 29% under C. carlesii, respectively. Above ground litter input and microbial biomass were lower in the coniferous C. lanceolata forest. Soil microbial biomass was significantly lower in NL, NR and NRNL in both forests. NL had most pronounced effects on the microbial community composition in the C. carlesii soil, whereas NR and NRNL affected the community composition in C. lanceolata soil. Overall, the unexpectedly small and only insignificant additive effects of litter exclusion and root exclusion in the combined treatment (NRNL) suggest that yet unresolved interactions had accelerated the decomposition of mineral soil organic matter and RM under this lowest plant C-input scenario. Hence, in the case that above and below ground plant C inputs change simultaneously, effects on RS and its components might be more complex than suggested by single-C-source manipulation studies.