Coniferous Deadwood Decomposition Improves Soil Organic Carbon Storage in a Temperate Forest

Abstract

The decomposition of deadwood is critical for soil organic carbon (C) formation and sequestration in forest ecosystems. However, it is still unclear how soil organic C changes and its underlying mechanisms in response to different stages of deadwood decay. This study investigated soil organic C dynamics, soil properties, exoenzyme activities, and PLFA biomarker based on five decay classes (defined from 1 to 5) of Masson pine (Pinus massoniana Lamb.) downed deadwood in subtropical-temperate ecotonal forests in Central China. The results showed that soil organic C content increased with progressive deadwood decay, and reached the greatest at the last two decay classes. Soil inorganic N, bacterial biomass, fungal biomass, fungal to bacterial biomass ratio, cellulase, and ligninase increased whereas soil pH decreased along with deadwood decay. The structural equation model results demonstrated that soil organic C was directly driven by soil bacterial and fungal biomass, as well as cellulase activity which were negatively regulated by soil pH during deadwood decomposition. This finding points out the importance of cellulase rather than liginase in soil C formation and sequestration during deadwood decomposition. Overall, our study provides the empirical evidence that deadwood greatly contributes to soil organic C accumulation, implying the deadwood management strategy in promoting soil organic C stocks in natural forest ecosystems.

Keywords: Decomposition stage, Microbial biomass, C-degrading enzyme activity, Forest management, Soil carbon pool