Strong spatial and temporal turnover of soil bacterial communities in South Africa's hyperdiverse fynbos biome

Soil bacteria play an important role in ecosystem functioning and regulate the health and diversity of aboveground plant communities. South Africa's fynbos vegetation, part of a global biodiversity hotspot with a well-characterised flora, is highly threatened and fragmented. Surprisingly, very little is known about the belowground communities that underlie the region's exceptional botanical diversity. Next-generation sequencing was used to investigate the diversity and composition of soil bacterial communities spanning diverse fynbos sites and across different seasons, and how these relate to spatial and environmental attributes. Fynbos soils were characterised by high bacterial diversities and strong spatial turnover, i.e. unique bacterial assemblages at sites, characterised by specific dominant taxa (e.g. Acidobacteria for acidic soils, Actinobacteria for alkaline soils). This turnover was largely driven by differences in abiotic soil conditions (particularly pH and NH₄ ⁺) and spatial separation. Seasonality also played a significant role in shaping fynbos soil bacterial community diversity and composition. The high diversity and turnover of fynbos soil bacterial communities mirrors previously reported diversity patterns of aboveground plant communities, often also driven by abiotic soil conditions. Thus, future habitat degradation and loss that alter abiotic soil conditions could strongly affect these bacterial communities, a crucial component of the functioning of both below- and aboveground terrestrial ecosystems.