Abstract / Summary
Invasive species are predicted to escape their natural enemies, yet whether this release is overcome by co-invasion of specialist enemies and/or gain of diverse assemblages of generalist antagonists remains unresolved. Here we describe a natural experiment where invasive Pinus contorta conifers experienced a die-off in the Mackenzie Basin on the South Island of New Zealand. Using a combination of visual surveys, culturing, and next-generation sequencing, we show that fungal pathogens likely contributed to this mortality event this mortality event. The fungal communities of living pines were significantly more diverse than dead pines, characterized by many low abundance fungal OTUs alongside a few dominant species. Indicator OTUs of living tree communities were most closely related to a diverse suite of putative plant pathogens, some of which are known to infect pines; dead pines were associated with saprotrophic white and brown rot fungi. Critically, no single pathogen explained the mortality; living vs. dead status accounted for less than 3% of fungal community variation. We argue that these invasive conifers have accumulated a disparate assemblage of both co-invasive and novel latent pathogens that act opportunistically in concert with harsh abiotic conditions, suggesting enemy accumulation may predispose invasive species to population-level mortality.