Considering mycorrhizal relationships of invasive plants when restoring ecosystems
K. K. TRESEDER , M. R. MALTZ, AND D. C. BAÑUELAS
Department of Ecology and Evolutionary Biology, University of California Irvine, CA 92617 USA

Invasive plants can alter the mycorrhizal community. When we remove invasive plants to restore ecosystems, do we need to intentionally restore the mycorrhizal community as well? Or will they recover on their own once the invasives are removed? We performed two case studies in Southern California. In coastal sage scrub, Brassica nigra (black mustard) can deplete mycorrhizal fungi in the rhizosphere by releasing allelochemicals. We asked whether herbicide applications or mowing to remove the black mustard would lead to an increase in mycorrhizal abundance. We found that glyphosate applications were associated with a significant increase in arbuscular mycorrhizal hyphal abundance, but only in one of two sites. Mowing had no significant effect. In this case, plant-focused restoration may not be accompanied by recovery of the mycorrhizal community. In a riparian ecosystem, S chinus terebinthifolia (Brazilian pepper tree) is displacing Salix (willow). A previous study demonstrated that when Brazilian pepper tree invaded Florida, it increased ectomycorrhizal abundance (Dawkins and Esiobu 2017). A large restoration project fully removed a stand of Brazilian pepper tree, including topsoil and roots to 60 cm depth. Before and after tree removal, we collected soil within the restored area. We performed DNA sequencing of the ITS2 region to identify the soil fungi. We found, surprisingly, that the relative abundance of ectomycorrhizal fungi increased significantly following tree removal. In particular, the ectomycorrhizal genus Geopora displayed the most significant increases. Geopora is a known symbiont on willows. Here, plant-focused restoration may be sufficient. These two case studies demonstrate that although plant-focused restoration can help restore mycorrhizal fungi as well, this response is not consistent. It may be worth intentionally performing mycorrhizal restoration when removing invasive plants that alter the mycorrhizal community.