Abstract
Plant invasions can cause biotic homogenisation which can have cascading effects on the diversity of invaded ecosystems. These impacts on diversity are likely to be scale-dependent and thus affect different aspects of diversity (i.e. beta, gamma and alpha). For example, the widespread invasion of non-native pine trees causes a loss of plant gamma diversity; however, the effects of this invasion and co-invasion by ectomycorrhizal fungi on belowground fungal communities remain unknown. We established thirteen 400 m(2) plots across a Pinus nigra density gradient in Canterbury, New Zealand. We sampled twenty-four soil samples from each plot and extracted and sequenced DNA for fungi from each sample independently, allowing determination of within-sample (alpha) and plot-scale (gamma) diversity and turnover (beta-diversity). Pine invasion was associated with a positive unimodal response in soil fungal beta-diversity, reflected by an increase in saprotroph diversity at low pine density following a loss of this group of fungi at high pine densities. Pine invasion was also associated with an overall 47.7% loss of fungal alpha-diversity and a 50% loss of gamma-diversity. Loss of diversity correlated to a shift from a saprotroph-dominated fungal community in low pine density plots to an ectomycorrhizal-dominated community in high pine density plots. However, despite the resulting dominance of ectomycorrhizal fungi, there was no increase in gamma-diversity of ectomycorrhizal fungi as pine density increased. Our results support the concept that low-density invasions increase ecosystem heterogeneity and therefore beta-diversity, but that as aboveground plant communities become more homogenised there is a dramatic loss of fungal diversity across all scales that could inhibit recovery and restoration of invaded ecosystems.
