Consequences of fungal endophytes on host plant invasion and the structure of plant community.

CASAS,C; GUNDEL, PE; SEMMARTIN, M.; OMACINI, M.

Congreso; 7th International Symbosis Society Congress.; 2012

Species invasion is a central issue in ecology because exotic species may severely impact on fundamental ecological processes. Systemic fungi of the genus Neotyphodium (Clavicipitacea) are present in many grasses forming a symbiosis that is dispersed by host seeds into new areas and might improve host ability to invade. The annual grass Lolium multiflorum (Lm), commercialized worldwide as forage, commonly hosts this endophyte in naturalized populations of Pampean grasslands (Argentina). Here we evaluated endophyte impact on Lm ability to grow and its consequences on community structure, in Pampean grasslands with different grazing histories. The field experiment consisted in the addition, or not (C), of Lm seeds with high and low level of symbiotic seeds (+E: 79% and -E: 4% respectively), in grazed and ungrazed (i.e. ten year-old exclosures) grasslands. After removing all Lm plants emerged from the soil bank and temporarily excluding cattle, we assigned the seed addition treatment to ~0.6 m2 plots, in a split-plot design (early autumn), and we estimated plant cover per species during and after the host growing season (spring and summer). Seed addition increased overall Lm cover. A positive effect of endophyte on Lm cover was detected only in ungrazed plots (interaction: P<0.0001). During spring, E+ seeded plots had lower cover of other exotic grasses than unseeded plots (P=0.01) meanwhile the cover of native grasses was reduced only in ungrazed plots sown with E+ seeds (interaction: P=0.002). These latter effects were vanished in summer (P>0.05). Dicots cover was low (<10%) and not modified by seed addition (P>0.05). Our work shows that endophytes which are often overlooked can increase the invasive behaviour in an annual host grass. Understanding human-induced changes in the appearance and functioning of entire ecosystems still requires knowledge of the long-term impact of these symbionts on different above- and belowground ecosystem components.