Pine invasion drives loss of soil fungal diversity

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 m² 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 (α) and plot-scale (γ) diversity and turnover (β-diversity). Pine invasion was associated with a positive unimodal response in soil fungal β-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 α-diversity and a 50% loss of γ-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 γ-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.