Tree diversity shapes soil bacterial community structure under low abiotic heterogeneity in the Atlantic forest

The Brazilian Atlantic Forest, a critical biodiversity hotspot, plays a vital role in climate regulation and water conservation. To explore the relationship between tree diversity and soil bacterial communities, soil samples were collected along an edapho-climatic gradient. We hypothesized that tropical forest soils, among Earth’s most complex biological environments, exhibit predictable microbial community assembly patterns driven by deterministic processes. Specifically: (i) tree composition influences bacterial communities more strongly than abiotic factors when environmental heterogeneity is low, following niche-based assembly rules; (ii) specific tree taxa function as keystone species, shaping bacterial communities through microhabitat modification. Our findings indicate that tree diversity had a greater influence on shaping bacterial communities than soil attributes. Of the 72 tree species identified, Senegalia recurva , Araucaria angustifolia , Styrax acuminatus , Ilex paraguaiensis , Eugenia subterminalis , and Pisonia ambigua were key drivers of soil bacterial diversity. Additionally, late-successional tree species that require high light were closely linked to predicted microbial cycling of carbon, nitrogen, sulfur, and phosphorus. These results offer a hypothesis-generating framework for evaluating species selection in Atlantic Forest restoration projects, suggesting that these species represent candidates whose effects can enhance soil health and ecosystem functionality in reforestation programs.