Warming inhibited new soil organic carbon formation with higher bacterial necromass contribution

Abstract

Warming has been consistently observed to reduce soil carbon (C) storage by accelerating soil organic matter (SOM) decomposition. While soil C fraction may differentially respond to warming, and microbial necromass has been considered an important contributor to persistent soil C pool. However, how warming regulates microbial necromass formation and their potential contribution to new soil organic carbon (SOC) fractions is not fully understood. In this study, we examined the effects of elevated temperature on newly formed amino sugar C (i.e., indicative of fungal and bacterial-derived microbial necromass C) and its allocation in particulate organic matter (POM) and mineral-associated organic matter (MAOM) fractions in alpine soils of Southwest China, based on 37-day incubation experiments at 15 ℃ and 25 ℃ by adding 13C labeled glucose and oxalic acid. The results showed that warming significantly reduced the formation of new SOC by lowering the incorporation of new C into both POM and MAOM fractions. Glucose addition was found to enhance new SOC formation more effectively than oxalic acid addition regardless of temperature. Warming also significantly decreased the new microbial necromass in both soil fractions with more bacterial necromass associated with mineral particles, which was primarily attributed to a higher abundance of bacterial community. In addition, glucose addition significantly promoted the fungal necromass contribution to newly formed SOC. Overall, this study revealed that warming significantly altered the allocation of newly-formed SOC and microbial necromass, highlighting the different microbial responses in soil C sequestration with implications for predicting and managing soil C stocks in forest ecosystems under climate change.