Soil bacterial and archaeal communities are driven by labile organic carbon fractions along natural and cultivated systems

Microbial communities and soil physicochemical properties are highly heterogeneous and vary widely in short distances. Understanding these microbial patterns across various environmental conditions is critical for predictive ecosystem models, as well as the study of early biological indicators of soil health degradation. Although labile soil organic carbon (SOC) fractions have emerged as standardized indicators because of their potential to detect early SOC trends over time, the relationships between microbial attributes and labile SOC remain poorly understood. Here we investigated topsoil Bacteria-Archaea community patterns across 28 sites with different land uses and climate conditions in Chile. We applied Illumina sequencing at the 16S rRNA to examine shifts in the relative abundance, diversity, and composition of these soils microbial communities. Additionally, labile SOC fractions such as permanganate oxidizable carbon (POXC) and light fraction organic matter (LFOM), and soil physicochemical properties were analyzed. The results demonstrate that among all the soil environmental factors tested, pH and POXC/SOC ratio were the most important drivers when explaining the microbial community composition. Moreover, POXC/SOC was closely related to microbial richness and diversity. Additionally, LFOM, C/N ratio, water stable soil aggregates (WSA) and geographic distance also contributed to explain variation in microbial community composition. Consistent changes were observed in community composition across soils represented by higher POXC/SOC ratio and lower LFOM content. Under these conditions, Bacteroidetes (Adhaeribacter, Skermanella, Flavisolibacter and Niastella), Proteobacteria (Skermanella, Ramlibacter and Sphingomonas), and Archaea Thaumarchaeota were found to be the most dominant groups. Our results provide evidence that soil microbial communities are largely modulated by labile SOC fractions.