Depth‐dependent effects of short‐term whole‐soil warming on microbial necromass and plant lignin

Abstract The changes in the origins and storage of soil organic carbon (SOC) under a warming climate are closely related to SOC decomposition and the feedbacks to climate change. Yet, the responses of plant‐ and microbial‐derived carbon (C) to warming and their depth dependence remain unclear. In this study, using a field whole‐soil warming experiment (+4°C, 80 cm depth) in a subtropical forest, the short‐term (13 months) impacts on plant‐ and microbial‐derived SOC constituents across depth were investigated. Lignin phenols and amino sugars were utilized to indicate plant lignin and microbial necromass, respectively. Our findings indicate that lignin phenol content declined with soil depth, while its degradation extent increased. Combined with constrained nutrient availability and alleviated microbial C limitation, these factors collectively controlled the depth‐dependent restriction on microbial necromass C concentration. Warming decreased lignin phenol content by 31.8% and increased bacterial necromass C by 81.3% in topsoil (0–20 cm). Concentration of fungal necromass C was promoted by 15.7%–91.5% under warming across the subsoil layers (20–80 cm), while lignin phenol content remained unchanged. The warming effects on SOC constituents were primarily driven by microbial biomass C in topsoil, whereas in subsoil, they were positively associated with substrate availability, including soil ammonium and dissolved organic C. Overall, this study suggests that the composition of SOC may have changed even if the total content remains stable under climate warming, with implications for the prediction of soil C dynamics in future. Read the free Plain Language Summary for this article on the Journal blog.