Even after death the endophytic fungus of Schedonorus phoenix reduces the arbuscular mycorrhizas of other plants

Abstract

Summary 1.Plants can host microbial communities whose integrated functions are often responsible for their success. Understanding mechanisms regulating such functions is thus a major goal in ecology. 2. Fungal endophytes of grasses, particularly of the genus Neotyphodium , have been reported to reduce colonization of their host plant by arbuscular mycorrhizal (AM) fungi. However, it is unclear which mechanism(s) may explain the effects produced by the endophyte and whether these effects are present in nature. 3. We used Schedonorus phoenix (syn. Lolium arundinaceum ) plants that were endophyte-free or infected with one of two strains of Neotyphodium coenophialum known to produce different putative allelochemicals to test the hypotheses that (i) allelopathic effects of the endophyte reduce AM fungal spore germination; and (ii) the allelochemical compound(s) are leached into the soil even after the death of S. phoenix , where they reduce AM fungal colonization of other plants. 4. In a first experiment, aqueous extracts from the shoots of S. phoenix were applied onto spores of the AM fungus Glomus intraradices to test germination effects. Both endophyte strains reduced spore germination by approximately 10% relative to endophyte-free controls. 5. In a second experiment, we placed dried shoot material ('thatch') on the soil surface of pots containing Bromus inermis , which were either inoculated with G. intraradices or not. We watered the plants through the thatch, relying upon leaching to translocate potential allelochemicals to the soil. AM fungal colonization of B. inermis was significantly reduced when thatch was infected with the common strain, but not with AR542, compared to the endophyte-free thatch. Furthermore, the arbuscule : vesicle ratio was 11-fold smaller when thatch was infected with the common strain compared to endophyte-free thatch, suggesting that G. intraradices was stressed by the presence of common strain-leachate. 6. We observed situations whereby two ecologically widespread plant-microbe symbioses interact. Potential mechanisms may include allelopathic effects, although other factors are also possible, and leaching is a mode of entry of putative endophyte-induced AM fungal inhibitors in soil. Understanding these processes is important as they affect AM fungal communities which contribute to plant success and, consequentially, grassland ecosystem dynamics.

Evidence for leaf endophyte regulation of root symbionts: effect of Neotyphodium endophytes on the pre-infective state of mycorrhizal fungi

“…Nevertheless, other mechanisms, such as leaching and decomposition, are not discarded and probably may be occurring simultaneously. In this sense, Antunes et al (2008) have proposed that endophyte chemical compounds are leached into the soil after the death of the plant host.…”

“…According to Antunes et al (2008) there are at least three ecologically relevant mechanisms by which endophyte compounds are released into the soil and might influence AM fungi. One mechanism could be through both the guttation fluid and 'cut leaf fluid' of endophyte infected plants (Koulman et al 2007).…”

“…Another possible way is via the processes of leaching and decomposition. This hypothesis was tested by Antunes et al (2008), who suggested that leaching is a mechanism by which putative endophyteinduced AM fungal inhibitors may reach the soil, when the dead leaves of endophyte infected plants are detached. Antunes et al (2008) tested in in vitro experiments, aqueous extracts from shoot on the spores germination of AM fungi, however, the direct effect of endophytes exudates by leaching and decomposition have not been investigated.…”

Soil microbial community responses to the fungal endophyte Neotyphodium in Italian ryegrass

“…Endophyte negative effects on soil biota activity have been generally associated to the aboveground litter inputs of the host plants (Antunes et al 2008;Lemons et al 2005;Omacini et al 2004). Instead, this study demonstrates that 7 months, one growing season for an annual host, was enough to detect significant changes in the soil functional capacity (by using catabolic response profiles) and perceptible differences in the activity of soil fungi (by using selective inhibition with antibiotics) as well as in the structure of bacterial communities in relation to Table 1 Mean values for soil parameters and above and below ground biomass of Lolium multiflorum infected or uninfected with Neotyphodium occultans (+E and −E, respectively) at the end of the growing season (n=12) endophyte infection level.…”

“…For example, endophyte presence can modify litter decomposition by changing the quality of the litter produced by infected plants and by altering micro-environmental conditions (Lemons et al 2005;Omacini et al 2004). Moreover, previous studies indicated that the endophyte may reduce colonization by arbuscular mycorrhizal fungi either in the host plant (Mack and Rudgers 2008;Omacini et al 2006) or in the plants growing in next generation after the death of host plants (Antunes et al 2008).…”