SOIL MICROBIOTA INTERACTION WITH SOIL ORGANIC MATTER AND ENZYMATIC ACTIVITY IN TROPICAL SEASONAL FOREST SUCCESSION AFTER DISTURBANCES.

Tropical forests play a crucial role in biogeochemical cycles. These ecosystems strongly depend on soil organic matter (SOM) and on transformation of elements in the soil, processes largely mediated by soil microbial communities. SOM plays a key role on soil physical, chemical, and biological properties, and complex feedbacks exist among SOM, vegetation, and soil microorganisms. These interactions are especially relevant in tropical seasonal forests with different successional trajectories. In this study, we evaluated soil microbiome composition, SOM, soil enzymatic activity, and chemical attributes in seasonal Atlantic Forests across three stages of ecological succession: a) Old-growth Forests, with no recorded disturbances for at least the last century); b) Logged Forests, subjected to selective timber extraction until the 1970s); and Secondary Forests, resulting from natural succession following pasture abandonment in the 1980s). A pasture was also sampled as outgroup. Our results showed strong associations among SOM, clay content, β-glucosidase activity, and the nutrients Ca, Cu, Mg, and N. These attributes were positively associated with eutrophic microbial phyla, including Thaumarchaeota, Actinobacteria, Nitrospirae, and Planctomycetes, and negatively associated with oligotrophic, generalist phyla Acidobacteria and Proteobacteria. The phylum Firmicutes was considerably more abundant in pasture than in forest soils, reflecting its adaptability to disturbed environments. Thaumarchaeota were detected exclusively in forests, highlighting their ecological importance in these systems. The strong association between clay content, SOM, and nutrient availability underscores the role of soil physical properties which, together with forest cover, drive soil microbial succession in parallel with forest successional dynamics.