Harmon, P. F. | bioRxiv Science

bioRxiv2021

Invasive grass litter suppresses native species and promotes disease

Plant litter can alter ecosystems and promote plant invasions by changing resource acquisition, depositing toxins, and transmitting microorganisms to living plants. Transmission of microorganisms from invasive litter to live plants may gain importance as invasive plants accumulate pathogens over time since introduction. It is unclear, however, if invasive plant litter affects native plant communities by promoting disease. Microstegium vimineum is an invasive grass that suppresses native populations, in part through litter production, and has accumulated leaf spot diseases since its introduction to the U.S. In a greenhouse experiment, we evaluated how M. vimineum litter and accumulated pathogens mediated resource competition with the native grass Elymus virginicus. Resource competition reduced biomass of both species and live M. vimineum increased disease incidence on the native species. Microstegium vimineum litter also promoted disease on the native species, suppressed establishment of both species, and reduced biomass of M. vimineum. Nonetheless, interference competition from litter had a stronger negative effect on the native species, increasing the relative abundance of M. vimineum. Altogether, invasive grass litter suppressed both species, ultimately favoring the invasive species in competition, and increased disease incidence on the native species.

ecology↗

bioRxiv2020

Emerging fungal pathogen on an invasive grass differentially affects native species

Infectious diseases and invasive species are strong drivers of biological systems that may interact to shift plant community composition. Disease and invasion can each directly suppress native populations, but variation in responses among native species to disease, invasion, and their combined effects are not well characterized. Here, we quantified the responses of three native North American grass species to experimental inoculation with the fungal pathogen Bipolaris gigantea, which has recently emerged in populations of the invasive grass Microstegium vimineum, causing leaf spot disease. In a greenhouse experiment, we examined the direct effects of disease on the native species and the indirect effects of disease on the native species through altered competition with M. vimineum, which was planted at a range of densities. Pathogen inoculation directly affected each of the three native species in unique ways, by increasing, decreasing, or not changing their biomass relative to mock inoculation. Higher M. vimineum densities, however, reduced the biomass of all three native species, regardless of inoculation treatment, suggesting that disease had no indirect effects through altered competition. In addition, competition with M. vimineum suppressed native plant biomass to a greater extent than disease. The differential impacts of B. gigantea and the consistent impacts of M. vimineum on native species biomass suggest that disease may modify native plant community composition while plant invasion may suppress multiple native plant species in systems where these drivers co-occur.

ecology↗