Endophyte symbiosis with tall fescue: how strong are the impacts on communities and ecosystems?

We have investigated community and ecosystem consequences of endophyte symbiosis with tall fescue over the past 13 y. Lolium arundinaceum is the most abundant plant in the eastern USA, and most is infected by the wild-type KY-31 endophyte Neotyphodium coenophialum. We established two large experimental grasslands (in 1994 and in 2000) with endophyte-infected or endophyte-free seed sown on recently plowed herbaceous vegetation. Other plant species established by seed or vegetative fragments. No other treatments were applied and plots were subject to natural biotic and abiotic variation. A third experiment examined ecological influences on endophyte infection dynamics starting from an intermediate infection frequency. Finally, we synthesized recent literature investigating the impacts of the tall fescue endophyte on the abundance of associated arthropod species. We found wide-ranging consequences of the endophyte from significant effects on soil feedback and decomposition rates, to plant-plant competition, diversity, productivity, invasibility and succession, to plant-herbivore interactions and energy flow through the food web. Further, we found that herbivore pressure caused rapid increases in infection frequency. Our results suggest that endophyte symbiosis in tall fescue can have a transforming effect on ecological systems.