COS 120-7
Plant-soil feedback in abandoned agricultural fields contributes to plant community assembly and limits successful restoration
The conversion of habitat to agriculture is one of the dominant forms of land degradation and loss of biodiversity throughout the world. The subsequent abandonment has led to some of the most dramatic plant invasions. Strong soil legacies, such as increased pathogens and decreased mycorrhizal activity, in abandoned agriculture may limit successful reestablishment of native plant species and contribute to invasive species success. We examined the combined effects of pathogens and altered arbuscular mycorrhizal fungal (AMF) inoculum in abandoned agriculture on the exotic annual grass Bromus diandrus and restoration of native plant species. Four native forbs with varying abundance and sizes were chosen for study: Amsinckia menziesii, Layia platyglossa, Lasthenia californica, and Plantago erecta. In a controlled greenhouse environment, native forbs and Bromus were grown in monoculture, 2-species mixture (grass and forb), and 5-species mixture in sterile soil and inoculum soil from abandoned citrus agricultural lands. Soil feedback in native versus invasive plants was determined using AMF, pathogenic/saprophytic fractions, and whole soil inoculum from agricultural soil compared to sterile soil. Roots of native and invasive species were stained and examined for hyphal infection. Fungal DNA was extracted from plant roots and will be sequenced for species level identification.
Results/Conclusions
The four native species experienced neutral to positive feedbacks with agricultural soils, with each species responding differently. In competition with Bromus all native forb species experienced reduced biomass, but the presence of inoculum resulted in greater biomass compared to sterile soil. Bromus experienced neutral feedback with agricultural soils. This indicates that native forbs are poor competitors with Bromus, but that AMF may have the ability to partially alleviate competitive effects from Bromus. Both native and invasive species were infected with coarse and fine endophyte AMF, although the abandoned agriculture soil has an unusually large component of fine endophyte. Regression analyses were used to identify whether plant biomass was positively correlated with an index of mycorrhizal activity (= % infection x root biomass). Higher mycorrhizal activity correlated to greater total plant biomass P<<0.001. Though high levels of potential pathogens were found infecting the roots of native forbs, no relationship between biomass and percent non-mycorrhizal fungal infection was found. A surprising finding was the hyphae of an oomyecete morphologically resembling Phytophthora infecting the roots of Amsinckia menziesii, Lasthenia californica, and Layia platyglossa. Continued work on identifying potential pathogens using high-throughput sequencing is underway, as well as plant responses to pathogen infection.