Bacterial diversity is positively correlated with soil heterogeneity

Plant and animal diversity generally increases with increasing environmental heterogeneity. Here, we test whether this relationship also holds for bacterial communities in soil. Specifically, we investigate whether invasive annual grasslands have reduced soil heterogeneity and, thereby, decreased bacterial alpha- and beta-diversity. Soils were sampled at nine sites within a 5-km stretch of Southern California, at five depths in three habitats, including non-native invasive annual grassland, native oak woodland, and native coastal sage scrub. We characterized soil heterogeneity as well as bacterial alpha- and beta-diversity by 16S ribosomal RNA sequencing. We found that invasive annual grasslands harbored less soil heterogeneity and reduced bacterial alpha-diversity relative to the two native woody habitats. Further, across all habitats and depths, bacterial alpha- and beta-diversity was positively related to soil heterogeneity. These results suggest that plant invasions associated with soil homogenization may lead to reduced microbial diversity.