Ecological consequences of fungal endophytes on host plant invasion and plant community structure.

CASAS C., GUNDEL P.E., SEMMARTIN M. & M OMACINI.

Krakow

Congreso; 7th International Symbiosis Society Congress; 2012

International Symbiosis Society Congress

Understanding species invasion is a central problem in ecology because exotic species may severely impact ecosystems and invasions underlie fundamental ecological processes. Asexual fungi of the genus Neotyphodium (Clavicipitacea) are present in many grasses forming a symbiosis that is carried into host seeds during dispersal into new areas. The annual grass Lolium multiflorum (Lm), promoted as forage world-wide, commonly host this endophyte in naturalized populations of pampean grasslands (Argentina). Here we evaluate the impact of endophyte presence on Lm ability to overcome colonization barriers in grasslands with different grazing histories and symbiosis effects on community structure. We performed a field experiment that consisted in the addition or not of Lm seeds with high and low level of endophyte frequency (+E: 79% and -E: 4% of symbiotic seeds) in grazed and ungrazed (i.e. ten year-old exclosures) grasslands of the Flooding Pampa. After removing all Lm plants emerged from the soil bank and excluding cattle, we assigned to ~0.6m2 plots, in a split-plot design, the three treatments of sowing (early autumn) and we estimated plant cover per species during and after the host growing season (spring and summer). Sowing increased Lm cover in grasslands with different history of grazing (F2,32: 23,8; P<0.0001). Endophyte effects on its colonization ability were only detectable in ungrazed sites (F2,34: 24.1; P<0.0001) where this species reached 60% of cover after the addition of E+ seeds. The cover of other grasses varied with the recipient community and the sowing treatment only during the spring. Because in grazed and ungrazed there was a significant reduction in the cover of native and exotic grasses comparing E+ and unsown plots ( P<0.001). Those differences were erased during the summer. Part of these effects persisted when Lm cover was used as a covariable. Dicots cover was lesser than 10% throughout the experiment and was not modified by treatments. Fungal endophytes are often overlooked in studies of plant community. However, their presence in exotic grass such as Lm may explain host success as invader in natural communities. Although, this symbiosis is not toxic for cattle, it can modify the structure and dynamic of plant communities which, in turn, may affect forage availability and quality/invasibility.