Unveiling soil bacterial diversity in the Andes-Amazon transition zone: Impacts of forest conversion to pasture

Abstract

Soil microorganisms play a crucial role in the functioning of ecosystems by performing several essential functions. However, their resilience is tested by disturbances, primarily driven by land use changes. The Andes-Amazon transition zone, renowned for its ecological importance, is experiencing a growing pressure of removing native forests to establish pastures. In the last decades, efforts to characterize biodiversity in this region have been increasing; however, our comprehension of soil microbial communities and their responses to land use changes remains limited. Here, we used a shotgun DNA metagenomic sequencing approach to investigate the composition, diversity, and functions of soil bacterial communities in the litter and topsoil (0–10 cm) of a forest localized in an Andes-Amazon transition zone in Colombia and evaluate how they are affected by pasture establishments. Our findings unveiled the forest litter as a distinct microbial ecosystem, characterized by the highest bacterial richness and diversity. This layer was positively associated with increased availability of carbon (C), nitrogen (N), and phosphorus (P), and enzymatic activity linked to the mineralization of these elements. The transition from forest to pasture altered the microbial community structure, which was accompanied by a reduction of soil acidity. We observed that Proteobacteria, Acidobacteria, and Actinobacteria were the most abundant phyla in all environments, with a predominance of Proteobacteria and Bacteroidetes in forest litter, while forest-pasture conversion increased the abundance of Verrucomicrobia and Firmicutes in the soil. Functional profiles were over-represented in the litter, followed by pasture and forest soils. These results provide a foundational framework for comprehending the microbiome in the Andes-Amazon transition zone and its role in ecosystem functioning. Furthermore, this study sheds light on the far-reaching consequences of land use changes on microbial communities.