Coupled iron oxides and microbial-mediated soil organic carbon stabilization across tea plantation chronosequences

Soil acidification due to long-term tea plantations is a pervasive problem that may affect soil organic carbon (SOC) preservation by altering organo-mineral interactions. Nevertheless, how iron (Fe) minerals and microbes regulate SOC stabilization with increasing years of tea plantation establishment remains unclear. By analyzing the dynamic changes of SOC, Fe fractions and Fe oxide-bound OC (Fe-OC) pools, and associations with microbial communities over tea plantation establishment time-series (1, 7, 16, 25, and 42 years), this study explored the roles of coupled Fe oxides and microbial communities in regulating SOC accumulation and stabilization. The SOC levels significantly increased with years of tea plantation, accompanied by increases in the proportions of macroaggregates, poorly crystalline Fe oxides and organically complexed Fe, but soil pH decreased sharply. The increased soil Fe-OC pool and molar C:Fe ratios were positive correlated with SOC and macroaggregates, indicating that SOC was preserved by physic-chemical protection. Furthermore, these changes induced decreases in microbial biomass C and bacterial diversity with years of tea plantation. The relative abundance of A-strategists (i.e., Acidobacteria, Actinobacteria, Chloroflexi) increased concurrently, with an opposite trend for Y-strategists, suggesting tea plantation-induced environmental changes shifted the Y-strategists towards the predominance of A-strategists. Collectively, these findings provide new insights into the role of Fe oxides and microbial life history traits in SOC accumulation and stabilization in the progression of tea plantation establishment, including (i) physic-chemical protection of SOC through formation of Fe-OC by complexation; and (ii) regulation of the microbial community diversity and composition, especially bacterial life strategies. These results are of great implications for better predicting and accurately controlling the response of OC pools in tea plantations to future changes and disturbances and for maintaining regional C balance.