1. Understanding the extent to which plant genotype influences community composition has important conservation and management value. Here, we add a new layer to current research by testing whether genotypes of plant symbionts influence plant community composition.
2. Tall fescue grass Lolium arundinaceum is planted worldwide for forage, turf, and soil stabilization, has invaded native communities, and commonly hosts the foliar endophytic fungus, Neotyphodium coenophialum. We quantified vegetation development over a 6-year period in replicated field plots of the two most commonly introduced genotypes of the endophyte (KY-31, AR-542) in two tall fescue cultivars (Georgia-5, Jesup). The KY-31 endophyte produces ergot alkaloids toxic to mammalian herbivores, while AR-542 lacks ergots. We expected that the KY-31 endophyte would promote tall fescue dominance by altering mammalian herbivory, that endophyte-free plots would support the highest plant diversity, and that AR-542 endophyte would show intermediate effects.
3. Plots with the KY-31 endophyte supported ∼10% fewer plant species than endophyte-free or AR-542 plots. KY-31 also reduced graminoids and forbs more strongly than AR-542, with the greatest response in Georgia-5. Endophyte genotype did not significantly alter the prevalence of tall fescue; however, absence of the endophyte reduced the biomass of Georgia-5.
4. Both plant and endophyte genetic identity influenced the persistence of endophyte symbiosis. In Georgia-5, the frequency of AR-542 declined more through time than did KY-31; these effects were reversed in Jesup.
5. Endophyte presence reduced herbivory by mammals (voles), but endophyte genotype had no effect, suggesting that voles were not driving endophyte genotype-mediated changes in plant composition, and that other compounds besides ergot alkaloids influenced vole feeding.
6. Synthesis and applications. When endophyte-symbiotic plants are desired, the AR-542 endophyte in the Georgia-5 background would achieve higher native plant diversity and reduce tall fescue invasion of nearby areas. Conversely, Jesup is recommended for increased tall fescue persistence, as both biomass and reproduction exceeded Georgia-5. In summary, our results demonstrate that, like plant genotype, symbiont genotype can also alter vegetation dynamics and plant composition and should be considered when managing for conservation, restoration, forage, turf, re-vegetation or soil stabilization.