Linking plant lignin components or microbial necromass to soil organic carbon accumulation across different forest types

AbstractSlow cycling organic matter such as plant lignin components or microbial necromass play important roles in soil organic carbon (SOC) accumulation, but their relatively importance are rarely quantified or have been under debate in forest ecosystems. While the traditional hypothesis holds that low-quality litter inputs generally favor more SOC accumulation by selectively storing recalcitrant lignin components, an emerging hypothesis highlights high-quality litter inputs effectively promoting more SOC formation due to faster microbial decomposition leading to more necromass products. Here, we compiled and analyzed a global database of plant lignin components (lignin phenols as biomarker; 126 individual sties) and microbial necromass (amino sugars as biomarker; 137 individual sties) together with SOC in surface mineral soils across coniferous, broad-leaved and mixed forests that represent different litter-quality inputs. Results showed that amino sugars were insignificant predictor for SOC variations across different forest types. SOC contents increased with lignin phenols, but lignin phenols were significantly higher in broad-leaved and mixed forests than in coniferous forests. Therefore, our findings challenge both traditional and emerging hypotheses, and provide new insights for future research on the mechanisms of SOC formation and stabilization from plant and microbial pathways.