Simulated fire and plant-soil feedback effects on mycorrhizal fungi and invasive plants.

Climate change intensifies fires, raising questions about their impacts on plant invasions via changes in soil biota and plant-soil feedback (plants alter soil conditions, changing plant growth and vice-versa). We explored effects of plant-soil feedback and simulated fire (heat) on mutualistic arbuscular mycorrhizal (AM) fungal communities and invasive plant growth. Soils were collected from a dominant native grass (Chionochloa macra) and two invasive hawkweeds (Hieracium lepidulum, Pilosella officinarum) in a New Zealand grassland and then heated. In our experiment, both hawkweeds exhibited greater biomass in Pilosella soils, which also had the highest AM fungal richness. Heat had little effect on plant biomass or AM fungal community composition and richness. Hawkweeds altered AM fungal communities relative to the dominant native grass, and moderate soil heating increased Hieracium growth. Hieracium plants also grew better in Pilosella soils, suggesting the potential for soil-mediated invasional meltdown whereby one invasive species facilitates invasion by another.