Biology Department, Indiana University, Bloomington, IN 47405, USA

Background and objectives
The role of fungal parasites as determinants of plant community structure has been of longstanding interest but little experimental research has been conducted. Their effects on plant diversity are of particular interest given that experimental studies show a functional relationship between plant diversity and stability of communities [1]. Tall fescue grass (Festuca arundinacea) is probably the most widely distributed introduced species in the eastern USA and most plants are infected by the seed-transmitted fungal endophyte Neotyphodium coenophialum [2]. The objective of this research was to quantify the effects of fungal endophyte infection on diversity and productivity of experimental tall fescue grasslands


Materials and methods
Eight 20X20 m plots were established in autumn 1994 at the Indiana University Experimental Farm. The site, initially consisting of herbaceous vegetation, was ploughed and disced and then four plots were seeded with endophyte-infected (E+) tall fescue seed and four with uninfected (E-) seed (var KY-31) at a rate of 45 kg/ha. A good stand of fescue resulted, along with other plant species typical of midwestern grasslands. In E+ plots more than 80% of the tall fescue was infected compared with less than 1% in E- plots. Vegetation was sampled from 20 random 0.5X0.5 m blocks from each plot in late spring and early autumn from 1995. All vegetation rooted within the frame was cut off at the soil surface, returned to the lab, sorted by species (or into litter), dried and weighed. Species richness, diversity and productivity were calculated from these data.

Results and conclusions
There were no differences between E+ and E- plots the first year of the study, although there was significant variation among plots within infection type for most variables. In the second and third years a number of significant trends emerged. Species richness and diversity were much lower in E+ than E- plots, largely owing to the near-absence of dicots in E+ plots. Productivity varied among plots but showed no consistent differences between E+ and E- plots. However, tall fescue productivity was consistently higher in E+ plots and comprised a larger proportion of the biomass. These results indicate that endophyte infection supresses plant diversity in grasslands and may therefore alter ecological processes responsive to diversity. Several potential mechanisms by which endophyte infection suppresses diversity are being explored.

1. Tilman D, Downing, JA, 1994. Nature 367, 363-65.
2. Clay K, 1994. Biotechnology of Endophytic Fungi of Grasses. Boca Raton: CRC Press Inc. pp. 73-86.