Litter manipulation effects on microbial communities and enzymatic activities vary with soil depth in a subtropical Chinese fir plantation

Litter manipulation alters soil microbial community biomass and extracellular enzymatic activities due to the alteration of carbon and nutrient inputs. However, it is unclear whether adding or removing litter more significantly effects these characteristics and how they interact with depth and associated soil properties in subtropical Chinese fir (Cunninghamia lanceolata) forests. Soils were collected along 60 cm soil profiles in a Chinese fir plantation that was treated for 6.5 years with litter removal, litter addition, or no treatment (controls) using a completely randomized block experiment. Soil abiotic properties, the biomass of predominant microbial communities, and the activities of five hydrolytic enzymes were measured in 0–10 cm, 10–20 cm, 20–40 cm, and 40–60 cm soil layers. Litter addition generally resulted in positive effects on soil abiotic factors, microbial communities, and enzymatic activities, respectively, while litter removal tended to result in neutral, positive, and negative effects on these properties. Soil nutrients, microbial functional groups, and various enzymatic activities were generally more sensitive to litter addition than litter removal. In contrast, enzymatic stoichiometry depended more on soil depth than litter manipulation. Soil nutrients, microbial biomass, and enzymatic activities, in addition to their internal associations, decreased with increasing profile depths. Soil microbial communities and enzymatic activities exhibited asynchronous responses to litter manipulation with increasing profile depth. Our findings highlight the mechanistic interactions among soil abiotic properties, microbial community characteristics, and enzymatic properties that vary with soil depth.