Soil enzyme activities responded differently to short-term litter input manipulation under coniferous and broad-leaved forests in the subalpine area of Southwest China

Litter plays an irreplaceable role in terrestrial ecosystem carbon (C), nitrogen (N) and phosphorus (P) cycling, and its decomposition is largely regulated by litter quality, soil properties and enzyme activities. However, how soil enzyme activities respond to change in litter input under different forest types remains unsolved. Here, we investigated soil enzyme activities involved in C (beta-glucosidase, BG), N (N-acetyl-beta-glucosaminidase, NAG; leucine aminopeptidase, LAP) and P (acid phosphatase, ACP) under short-term litter manipulations (i.e. Detritus Input and Removal Treatment-DIRT: control, CK; double litter, DL; no roots and double litter, NRDL; no litter, NL; no roots, NR; no roots and no litter, NRNL) and associated influencing drivers in a coniferous forest (Pinus yunnanensis) and a broad-leaved forest (Quercus pannosa) in the subalpine area of Southwest China. Our results showed that litter removal treatment significantly reduced enzyme activities under two forest soils, with the stronger effect of the NR treatment on decreased enzyme activities compared to the NL treatment, possibly because roots could provide more available C sources and nutrient to microorganism and also immediately interact with soil minerals. In contrast, the short-term litter addition did not significantly affect enzyme activities under both two forest soils. Additionally, the BG activities in coniferous forest soil were characterized by a lower effect size compared to those in broad-leaved forest soil under the litter removal (NL and NRNL) treatments, but the higher effect size of LAP and ACP activities were observed under the NRNL treatment in the coniferous forest soil. This finding was attributed to higher organic C sources in the coniferous forest soil which could promote other nutrients utilization by microorganisms, leading to more N and P enzyme productions. We observed that the enzyme activities in the coniferous forest soil were closely related to soil N, P contents and microbial traits (i.e., fungal and bacterial structure), while enzyme activities in the broad-leaved forest soil primarily depended on microclimates (soil temperature and moisture) and soil properties (pH, dissolved organic C and P contents) under short-term litter manipulations. Overall, our results revealed the different pattern and the regulatory mechanism of soil enzyme activities under litter input manipulation of two forests, thereby advancing understanding of soil enzyme dynamics in association with initial litter quality and soil properties under future global change.