How does position affect the decomposition of fine woody debris in subtropical forest?

Fine woody debris (FWD: 1 cm ≤ diameter ≤ 10 cm) may be intercepted by understory vegetation (including the branches of canopy trees). However, the decay dynamics of aerial FWD are often overlooked. In this study, we collected wood from four different tree species (Platycarya strobilacea, Lithocarpus glaber, Pinus massoniana, and Cryptomeria japonica) from four forests in subtropical China, and the mesh bag method was used to measure the remaining mass and microbial respiration by reciprocally transplanting mesh bags filled with different species among the four forests. The main objectives of this study were to reveal the influence of position (the ground and the air) on the decay rates of FWD and the home-field advantage (HFA) effect during a two-year experimental period. Irrespective of the experimental periods and decay fields, the mass loss of FWD was significantly higher on the ground (58.05%) than in the air (45.74%), and the microbial respiration of wood was significantly higher on the ground (18.87 μg CO2 h−1 g−1) than in the air (7.79 μg CO2 h−1 g−1). Microbial respiration was negatively correlated with wood remaining mass on the ground during the entire decay period and in the air only during the late decay period. The HFA effect was observed only on the ground (5.03–23.86%). Our study highlights that soil contact predominantly regulated the decomposition patterns and the HFA effect of fine woody debris and suggests that we should not neglect the decay of fine woody debris in the air due to the interception of understory vegetation in subtropical Chinese forests.