A Fungal Endosymbiont Affects Host Plant Recruitment Through Seed- and Litter-mediated Mechanisms

Authors: OMACINI, MARINA - Universidad De Buenos Aires; CHANETON, ENRIQUE - Universidad De Buenos Aires; BUSH, LOWELL - University Of Kentucky; GHERSA, CLAUDIO - Universidad De Buenos Aires

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2009
Publication Date: 6/1/2009
Citation: Omacini, M., Chaneton, E.J., Bush, L., Ghersa, C.M. 2009. A Fungal Endosymbiont Affects Host Plant Recruitment Through Seed- and Litter-mediated Mechanisms. Functional Ecology 2009. 23:1148-1156.

Interpretive Summary: 1. Many grass species are associated with maternally transmitted fungal endophytes. Increasing evidence shows that endophytes enhance host plant success under varied conditions, yet studies have rarely considered alternative mechanisms whereby these mutualistic symbionts may affect regeneration from seed. 2. We performed a microcosm experiment to evaluate whether infection with Neotyphoclium occuptans affects recruitment in the annual grass Lolium mult(orum either directly, by infecting the seeds, or indirectly, by altering the suitability of recruitment microsites through the litter shed by host plants. Endophyte effects on establishment were tested for different litter depths and watering regimes under natural herbivory by leaf-cutting ants. 3. Seed infection increased seedling emergence through the litter as well as final recruitment, irrespective of microsite conditions. However, litter produced by infected plants delayed emer-gence and decreased density of both infected and non-infected grass populations. 4. Individual plant biomass did not change with seed infection but was increased under deep lit-ter from endophyte-infected plants. Although seed infection did not protect establishing plants from leaf-cutting ants, herbivory was reduced in the presence of deep litter shed by infected plants. 5. We conclude that fungal endophytes may affect host plant recruitment across subsequent generations not only by infecting the seeds but also through the host's dead remains. While the former effect entailed an advantage to infected plants, litter-mediated effects did not discriminate by infection status, and generally promoted the establishment of fewer and larger plants. Thus hidden foliar symbionts may play an underappreciated role in maintaining host species domi-nance through the litter produced by prior patch occupants.

Technical Abstract: 1. Many grass species are associated with maternally transmitted fungal endophytes. Increasing evidence shows that endophytes enhance host plant success under varied conditions, yet studies have rarely considered alternative mechanisms whereby these mutualistic symbionts may affect regeneration from seed. 2. We performed a microcosm experiment to evaluate whether infection with Neotyphoclium occuptans affects recruitment in the annual grass Lolium mult(orum either directly, by infecting the seeds, or indirectly, by altering the suitability of recruitment microsites through the litter shed by host plants. Endophyte effects on establishment were tested for different litter depths and watering regimes under natural herbivory by leaf-cutting ants. 3. Seed infection increased seedling emergence through the litter as well as final recruitment, irrespective of microsite conditions. However, litter produced by infected plants delayed emer-gence and decreased density of both infected and non-infected grass populations. 4. Individual plant biomass did not change with seed infection but was increased under deep lit-ter from endophyte-infected plants. Although seed infection did not protect establishing plants from leaf-cutting ants, herbivory was reduced in the presence of deep litter shed by infected plants. 5. We conclude that fungal endophytes may affect host plant recruitment across subsequent generations not only by infecting the seeds but also through the host's dead remains. While the former effect entailed an advantage to infected plants, litter-mediated effects did not discriminate by infection status, and generally promoted the establishment of fewer and larger plants. Thus hidden foliar symbionts may play an underappreciated role in maintaining host species domi-nance through the litter produced by prior patch occupants.