Litter addition and understory removal influenced soil organic carbon quality and mineral nitrogen supply in a subtropical plantation forest

Aims Aboveground litter inputs have been modified by global changes in plantation forests, where understory management is also prevalent, which may alter soil fertility and stand productivity. This study aimed to quantify the specific roles of litter and understory in affecting soil carbon (C) and nitrogen (N) dynamics. Methods A field experiment was established with four treatments, namely, litter addition (LA), understory removal (UR), litter addition and understory removal (LA + UR), and a control, in a subtropical Cunninghamia lanceolata plantation. Topsoil delta C-13, organic C concentration, storage and decomposition, mineral N, N mineralization, and C and N hydrolase activities were analyzed. Results Litter addition significantly increased soil organic C, macro-particulate organic C (macro-POC) and mineral N at a 0-5 cm depth, but decreased delta C-13(macro-POC) at 0-5 cm and 5-10 cm depths. Understory removal significantly increased soil NH4+-N, the rates of nitrification and net N mineralization as well as the soil organic C respiration rate at the two depths, while it decreased the C storage in bulk soil, especially in mineral protected pools. The activities of beta-glucosidase and beta-N-acetylglucosaminidase increased with litter addition and understory removal, respectively. Conclusions Litter addition tends to improve soil C quantity and quality due to fresh organic C inputs, while understory removal helps increase the N supply via the acceleration of N mineralization and the absence of understory plant uptake.