Symbiosis between plants and microorganisms is widespread, but research into its effects on the composition of a plant community is in its infancy. Such studies require patience. Jennifer Rudgers and colleagues have spent six years investigating the relative performance of cultivars of tall fescue grass with different forms of a symbiont, and now report the results and their recommendations for the use of this versatile yet vexatious grass (J. A. Rudgers et al. J. Appl. Ecol. doi:10.1111/j.1365-2664.2010.01788.x).

Tall fescue could well be the plant that makes a lawn near you. It is also grown for forage (pictured). It is highly invasive, however, and counts as a weed in situations in which plant diversity is desirable. Like many plants, it does not live alone, and has what might be called the X factor — symbionts that in the case of tall fescue often include the fungus Neotyphodium coenophialum. Like the grass, the fungus comes in different genotypic forms. For example, one common form (KY-31) produces alkaloids that are toxic to certain herbivores; another form (AR-542) does not.

Credit: CAPMC

By planting experimental plots, Rudgers et al. set out to test, among other things, how two cultivars of the tall fescue Lolium arundinaceum inoculated with KY-31, AR-542 or neither, affect the plant species composition of the plots. The two cultivars chosen were Georgia-5 and Jesup.

The authors' salient finding is that Georgia-5 plus AR-542 allows greatest growth of other grasses and herbaceous flowering plants, and produces fewest inflorescences (and so fewer seeds). Those characteristics would be appropriate for applications in which tall fescue has a job to do but where diversity of vegetation is the aim, for example in preventing soil erosion. There would also be reduced fescue spread from the planting site. Jesup with either symbiont is preferable for monoculture.

The significance of this line of research extends well beyond the specific performance and application of tall fescue. Plant breeders are becoming ever-more imaginative in exploring the intricate options offered by different genotypic mixes of plants and symbionts. Ecologists have a big task on their hands in checking the ecosystem consequences — and in taking into account the many other conditions that affect vegetation growth and invasiveness.