Bacterial and nematode communities associated with soybean-cultivated soils from two native Brazilian biomes

The Cerrado and Atlantic Rainforest are two geographically distinct biomes in Brazil that have undergone significant land-use change due to soybean cultivation. These biomes differ greatly in their edaphic and climatic characteristics, driving below-ground biodiversity patterns that remain poorly understood. To address this knowledge gap, 152 soil samples were collected from major soybean-producing areas in the Brazilian Cerrado and Atlantic Rainforest biomes between January and May 2021. This study explored the effect of soybean cultivation on nematode and bacterial communities across both biomes using 18S rRNA and 16S rRNA amplicon sequencing. The results revealed that bacterial diversity did not differ between the biomes, indicating possible biotic homogenization driven by agricultural practices. However, bacterial community composition varied, with the Cerrado having a higher relative abundance of Bacillota, whereas the Atlantic Rainforest had a greater relative abundance of Acidobacteriota. Redundancy analysis (RDA) indicated that bacterial communities were primarily influenced by soil clay content, regardless of biome. In contrast, nematode community structure had distinct patterns between the biomes, with a higher relative abundance of fungivorous nematodes associated with the Cerrado and bacterivorous and omnivorous nematodes associated with the Atlantic Rainforest. RDA also revealed that nematode communities were strongly influenced by mean air temperature, which differed significantly between the biomes. Network analyses highlighted greater complexity in the Cerrado, with both positive and negative correlations between bacteria and nematode trophic groups. In contrast, in the Atlantic Rainforest interactions were limited to negative correlations. This is the first study to consider both the bacterial and nematode communities of Brazilian soils at national scale.