Soil microbial trait-based strategies drive the storage and stability of the soil carbon pool in Robinia pseudoacacia plantations

Abstract

Soil microorganisms play an essential role in soil carbon sequestration and stability in forest ecosystems. However, how trade-offs in distinct microbial traits affect soil carbon storage and stability remains largely unknown, especially for forest soils that stock significant amounts of organic carbon. Here, we assessed the influences of the chronosequence of Robinia pseudoacacia (8, 18, and 30 years) on soil organic carbon (SOC) fractions and further explored the specific roles of microbial taxa in regulating soil carbon sequestration on the Loess Plateau via high-throughput sequencing techniques and analysis of co-occurrence networks and assembly processes. The results showed that the concentrations of soil easily oxidizable carbon (EOC), recalcitrant organic carbon (ROC), and SOC storage increased with stand age. However, the dissolved organic carbon (DOC) and microbial biomass carbon (MBC) concentrations increased from 8 years to 18 years and then decreased after 30 years. Stand age significantly affected the soil bacterial and fungal structures and diversity. Stochastic processes, especially dispersal limitation, were the main assembly processes affecting the bacterial and fungal communities. Soil pH, DOC and the N:P ratio drove bacterial assembly. However, fungal assembly was not affected by soil properties. Moreover, network analysis showed that three major bacterial modules and one major fungal module (Bac_Mod 1, 3, 4 and Fun_Mod 2) showed strong relationships with soil carbon storage and were considered soil carbon pool-associated modules. These modules based on the co-occurrence network analysis were composed of microbial taxa with different taxonomic and functional traits. Both random forest and correlation analyses indicated that increases or decreases in these modules were strongly correlated to variations in SOC fractions. These results demonstrated that with R. pseudoacacia plantation development, the recalcitrant-related module attributed to SOC became more stable.