COS 18-2 - The microbial associations of a widespread invader, Taeniatherum caput- medusae, across a precipitation gradient.

Abstract: Invasive plants threaten biological communities globally, and research has increasingly found plant-microbe interactions to influence invasion. Plants cultivate species-specific microbial communities in soils and within their roots, and invading plants can alter these communities by associating with distinct microbes, often decreasing mutualists and increasing pathogens. This can promote invader competitive advantage and alter long-term soil communities, which may inhibit restoration. The widespread invasion of Medusahead (Taeniatherum caput-medusae) in the American west is well documented, but our understanding of its plant-soil interactions is minimal. The role of precipitation in Medusahead invasion has not been tested, despite drought being the key environmental stress in this system and Medusahead occupying a wide precipitation gradient. Using a landscape-scale survey, I will identify the soil and root microbiome of Medusahead and co-occurring local grasses across a precipitation gradient. I hypothesize that Medusahead cultivates fungal communities distinct from local grasses in that they contain fewer beneficial symbionts and more pathogens. I predict that these differences will be accentuated at high precipitation, with Medusahead having the lowest symbiont and highest pathogen relative abundance under high precipitation.

A survey of roots and soils across northern California was conducted in spring 2021 at seven sites across a precipitation gradient. Soils and plant roots were collected in three plant community types: local forage grasses, Medusahead, and their intersection (mixed). The fungal community was amplified and sequenced on Illumina miseq and sequences were processed using an ASV approach. Fungal guilds (symbiont, pathogen, etc.) were identified with Funguild. Ordinations and mixed effect models were used to assess fungal communities across the invasion and precipitation gradient.

Results show a significant difference in fungal composition across plant community type, precipitation levels (low, medium, or high), and their interaction in both roots and soils. This indicates that the microbiomes of Medusahead and local grasses are different and that they change independently across precipitation levels. However, there was no clear pattern of decreased symbionts and increased pathogens in Medusahead with increased precipitation, as predicted. Interestingly, the low precipitation soils had the lowest symbiont and the highest pathogen relative abundance, contrary to my predictions. When further broken down, Medusahead soils had the lowest symbiont and highest pathogen abundances at low precipitation compared to the other community types. These results suggest that Medusahead invasion is most threatening under low precipitation as Medusahead seems to accentuate the low symbionts and high pathogens abundance for local species.