Invasive plant species can alter ecosystems by co-invading with other organisms. Conifers, especially pines (Pinaceae), are among the most problematic non-native plant species globally and cause major ecological impacts. Pines may simplify soil fungal communities due to a loss of plant species richness and decreased environmental heterogeneity. However, pines also co-invade with symbiotic ectomycorrhizal fungi, which might lead to increased fungal diversity and shifts in soil function. Our aim was to determine whether co-invasion of pine and their ectomycorrhizal fungi 1) increase fungal diversity within location (i.e., alpha diversity) but homogenizes soil fungal communities across locations (i.e., gamma diversity) and 2) alters the dominance of other soil functional groups such as saprotrophic fungi. We established thirteen 20 x 20m plots across a Pinus nigra invasion gradient on the South Island, New Zealand. We recorded total stand basal area (m2/ha) as a measurement of pine density. We sampled twenty-four soil cores from each plot and extracted DNA from each soil core independently. We amplified the DNA using fungal specific primers fITS7 and ITS4 and sequenced using Illumina MiSeq.
Results/Conclusions
Co-invasion of pines and their ectomycorrhizal fungi homogenize soil fungal communities. Contrary to our hypothesis, alpha diversity decreased by 54% as a function of P. nigra density. Beta diversity had a unimodal response to P. nigra density where diversity was highest in plots with intermediate density of pine. Gamma diversity decreased by 33% as a function of P. nigra density. This co-invasion also caused shifts in soil functional groups and soil communities. As P. nigra density increased, the proportion of reads of plant pathogens and arbuscular mycorrhizal fungi decreased. In contrast, the proportion of reads of saprotrophic fungi did not change. The proportion of ectomycorrhizal fungi shifted from less than 5% in plots with no P. nigra to over 50% in plots with high density of P. nigra. As many ectomycorrhizal fungi have their own enzymatic capabilities this co-invasion may lead to changes in soil nutrient cycling and ecosystem functioning. These changes in soil communities may inhibit recovery and restoration of co-invaded ecosystems.