Vegetation restoration facilitates belowground microbial network complexity and recalcitrant soil organic carbon storage in southwest China karst region

Soil organic carbon (SOC) is an important component of soil ecosystems, and soils are a hotbed of microorganisms playing critical roles in soil functions and ecosystem services. Understanding the interaction between SOC and soil microbial community is of paramount significance in predicting the C fate in soils following vegetation restoration. In this study, high-throughput sequencing of 16S rRNA and ITS genes combined with C-13 NMR spectroscopy analysis were applied to characterize SOC chemical compounds and elucidate associated soil microbial community. Our results indicated that the contents of SOC, total nitrogen, total phosphorus, microbial biomass carbon and biomass nitrogen, dissolved organic carbon, available potassium, exchangeable calcium and soil moisture increased significantly (P < 0.05) along with the vegetation restoration processes from corn land, grassland, shrub land, to secondary and primary forests. Moreover, the Alkyl C and O-alkyl C abundance increased with vegetation recovery, but no significant differences of Alkyl C were observed in different successional stages. In contrast, the relative abundance of Methoxyl C showed an opposite trend. The dominate phyla Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota and Basidiomycota were strongly related to SOC. And, SOC was found to be the determining factor shaping soil bacterial and fungal communities in vegetation restoration processes. The complexity of soil bacteria and fungi interactions along the vegetation restoration chronosequence increased. Determinism was the major assembly mechanism of bacterial community while stochasticity dominated the assembly of fungal community. Bryobacter, Haliangium, and MND1 were identified as keystone genera in co-occurrence network. Besides, the dominant functional groups across all vegetation restoration processes were mainly involved in soil C and N cycles and linked to the enhanced recalcitrant SOC storage. Our results provide invaluable reference to advance the understanding of microbe response to vegetation restoration processes and highlight the impact of microbes on recalcitrant SOC storage.

Automated summary

Soil organic carbon (SOC) is an important component of soil ecosystems, and understanding its interaction with soil microbial community is crucial for predicting carbon fate in soils following vegetation restoration. In this study, high-throughput sequencing and spectroscopy analysis were used to characterize SOC compounds and elucidate associated microbial community. The results showed that SOC, total nitrogen, total phosphorus, microbial biomass, dissolved organic carbon, available potassium, calcium, and soil moisture increased significantly with vegetation restoration. The abundance of certain carbon compounds and the dominant phyla of microorganisms were strongly related to SOC. The composition and assembly mechanisms of bacterial and fungal communities varied along the vegetation restoration chronosequence. Certain keystone genera and functional groups were identified in the microbial community, which were associated with enhanced recalcitrant SOC storage. Overall, this study provides valuable insights into microbe response and the impact of microbes on SOC storage in vegetation restoration processes.