Responses of soil bacterial communities to invasive Australian Acacia species over large spatial scales

The impacts of invasive plants on soil bacterial communities are less well understood than are their impacts on the above-ground components of the communities they invade. This is surprising given the important roles that below-ground communities play in ecosystem functioning. An example is South Africa's Cape fynbos, a global biodiversity hotspot which is highly fragmented and threatened. We use next-generation sequencing data to investigate how invasive Australian Acacia species ('wattles') impact broad-scale composition and turnover of soil bacterial communities. Our comparisons of bacterial communities across different fynbos habitats, in both wattle-invaded and uninvaded (pristine) soils, and sampled across multiple seasons, found invasion to signifcantly change the composition and turnover of these communities. Differences in soil bacterial communities between invaded and pristine soils were primarily driven by differences in soil pH and NH₄⁺ as well as seasonality. Finally, we found that the presence of invasive wattles reduces the spatial structure of bacterial community composition in fynbos soil by weakening the pattern of distance decay of compositional similarity in pristine soil communities. Consequently, restoration efforts of wattle-invaded and degraded fynbos habitats should account for the important functional links between below- and above-ground terrestrial ecosystems, especially altered bacterial communities.