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.