Grass species and their fungal symbionts affect subsequent forage growth

Abstract

Persistence of forage grasses is enhanced through the deliberate and selective use of symbiotic fungal endophytes that confer benefits, particularly pest resistance. However, they have also been implicated in reduced plant community diversity as a result of directly or indirectly enhancing competitive ability. A relatively underexplored mechanism by which endophytes might influence pasture plant composition is by altering the biotic or abiotic soil conditions. To examine the soil conditioning effects of forage grass species and their fungal symbionts we tested the responses of three pasture plants, perennial ryegrass, prairie grass, and white clover in nine different soils that had been conditioned by monocultures of endophyte-containing (E+), or endophyte-free (E−), perennial ryegrass, tall fescue, or meadow fescue. Conditioning grass species had little effect on the responses of perennial ryegrass and prairie grass regardless of E+ or E− treatments. In contrast, conditioning species had a strong effect on the response of white clover, resulting in reduced biomass when grown in perennial ryegrass conditioned soils. The presence of endophyte also had significant growth consequences for white clover, but was either positive or negative depending on the conditioning grass species. In comparison to their respective E− treatments, E+ tall and meadow fescue conditioned soils resulted in reduced biomass of white clover, whereas E+ perennial ryegrass conditioned soils resulted in increased biomass of white clover. Among the conditioning strains (AR1, AR37, NEA2, WE) of E+ perennial ryegrass, white clover showed significantly different responses, but all responses were positive in comparison to the E− treatment. By examining the effects of several grass species and endophyte strains, we were able to determine the relative importance of grass species vs. fungal symbiont on soil conditioning. Overall, the conditioning effect of grass species was stronger than the effects associated with endophyte, particularly with regard to the response of white clover. We conclude that both grass species and their fungal endophytes can influence pasture plant community composition through plant–soil feedback.