Leaf litter decomposition in the air should not be ignored in subtropical plantations of China

Litter decomposition is an indispensable component of carbon and nutrient cycles in forests. Plant litter is often intercepted by tree branches or understory vegetation in the air, yet aerial litter decomposition dynamics are overlooked in these ecosystems. Here, we collected leaf litter of four common tree species (Liquidambar formosana, Schima superba, Pinus elliottii, and Pinus massoniana) from subtropical plantations of southern China, and used the litterbag method to measure litter mass remaining and microbial respiration on the ground and in the air by reciprocally transplanting leaf litter in the four plantations. The main objectives were to compare the differences in litter decomposition rates and the home-field advantage between on the ground and in the air over 360 days of decomposition. Irrespective of decomposition habitats and incubation periods, litter mass remaining was slightly higher in the air (37.0%) than on the ground (32.0%), and microbial respiration was much lower in the air (2.2 mu g CO2-C h-1 g-1) than on the ground (18.2 mu g CO2-C h-1 g-1). Litter mass remaining correlated negatively with microbial respiration on the ground, despite no significant relationship in the air. In addition, the home-field advantage during decomposition only occurred on the ground (4.86-12.33%), but disappeared in the air. These contrasting patterns indicated that litter decomposition was driven by microbial processes on the ground and abiotic processes in the air. Our findings highlight that decomposition position predominantly regulates leaf litter decomposition patterns, and suggest that litter decomposition in the air should not be neglected in subtropical forests.