Effects of the Epichloë fungal endophyte symbiosis with Schedonorus pratensis on host grass invasiveness

Effects of nutrient addition on endophyte-associated grass invasion in a long-term, old-field community experiment

Strictly vertically transmitted (hereditary) Epichloë spp. fungal endophytes are symbionts with cool-season pooid host grasses. Such endophytes may increase host invasiveness in the non-native, introduced ranges. However, because costs and benefits for the host can vary with the growing conditions, the endophyte may become locally or temporally extinct when costs outweigh benefits. Our long-term field experiment involved the introduction of seven Schedonorus pratensis (meadow fescue) cultivars hosting Epichloë uncinata endophyte, which represent host-grass populations differing in genetic backgrounds and Epichloë infection frequencies, to an unmanaged old field. In the first 6 years, the host grasses persisted but did not become invasive in the plant community, regardless of their endophyte infection frequency. Subsequently, we hypothesized that increasing nutrient availability would decrease endophyte costs and thus increase the host's success and abundance. We fertilized half of the plots for four additional years and re-examined S. pratensis invasiveness. We predicted that increased nutrient availability would increase S. pratensis abundance and E. uncinata frequency and concentration, as well as decrease plant community diversity, relative to unfertilized plots. Fertilization increased endophyte concentrations in three low-endophyte host populations. However, E. uncinata did not enable S. pratensis populations to achieve high abundance or to reduce plant community diversity in the old field, with or without fertilization. Thus, nutrient availabililty and host invasiveness appear to be decoupled in this study system.

Endophyte species influence the biomass production of the native grass Achnatherum sibiricum (L.) Keng under high nitrogen availability

Research on the interaction of endophytes and native grasses normally takes infection status into account, but less often considers the species of endophyte involved in the interaction. Here, we examined the effect of endophyte infection, endophyte species, nitrogen availability, and plant maternal genotype on the performance of a wild grass, Achnatherum sibiricum. Six different Epichloë-infected maternal lines of A. sibiricum were used in the study; three lines harbored Epichloë gansuensis (Eg), while three lines harbored Epichloë sibirica (Es). These endophytes are vertically transmitted, while Eg also occasionally produces stromata on host tillers. We experimentally removed the endophyte from some ramets of the six lines, with the infected (E+) and uninfected (E-) plants grown under varying levels of nitrogen availability. Eg hosts produced more aboveground biomass than Es hosts only under high nitrogen supply. Endophyte species did not show any influence on the maximum net photosynthetic rate (Pmax), photosynthetic nitrogen use efficiency, or total phenolics of A. sibiricum under all nitrogen conditions. However, the plant maternal genotype did influence the Pmax and shoot biomass of A. sibiricum. Our results show that endophyte species influenced the shoot biomass of A. sibiricum, and this effect was dependent on nitrogen supply. As with most coevolutionary interactions, A. sibiricum that harbored Eg and Es may show pronounced geographic variation in natural habitats with increased nitrogen deposition. In addition, stroma-bearing endophyte (Eg) provides positive effects (e.g., higher biomass production) to A. sibiricum plants during the vegetative growth stage.