Environmental Context of Endophyte Symbioses: Interacting Effects of Water Stress and Insect Herbivory

Abstract

Symbiotic associations between grasses and fungal endophytes are generally regarded as mutualistic, yet benefits to host plants may vary with environmental context. Previous studies have emphasized how endophytes influence plant responses to single stressors. In contrast, the outcome of endophyte-grass interactions under simultaneous biotic and abiotic stresses remains poorly explored. We hypothesized that benefits from endophyte symbiosis become most apparent in ''complex'' environments where hosts experience multiple stresses. We evaluated the performance of endophyte-infected (Eþ) vs. endophyte-uninfected (EÀ) Lolium multiflorum plants in a factorial experiment with water supply (control vs. drought) and insect herbivory (with aphids vs. without aphids). Endophyte infection delayed tiller production in well-watered plants, while water stress reduced tillering in EÀ plants. Endophyte mediation of herbivory tolerance was contingent on water supply. Whereas aphid herbivory was detrimental to Eþ plants in well-watered soils, aphids interacted with drought stress in decreasing the reproductive output of EÀ but not Eþ plants. Moreover, endophyte presence decreased aphid densities on drought-stressed plants only. Thus, endophyte symbiosis enhanced host tolerance to overlapping biotic and abiotic stresses, although infected plants failed to outgrow their uninfected counterparts. These results support the view that mutualistic endophyte effects may not arise in low-stress environments.

Pathogen resistant advantage of endophyte-infected over endophyte-free Leymus chinensis is strengthened by pre-drought treatment

“…The relevance of drought as regulator for plant-microbe interactions has been demonstrated for fungal endophytes (Miranda et al 2011;Vesterlund et al 2011;Yule et al 2011). For instance, Yule et al (2011) found that a moderate water-stress treatment strengthened the positive effect of endophytes on plant biomass and aphid incidence, which was lost under a highwatering regime.…”

Microbes as Targets and Mediators of Allelopathy in Plants

“…A similar mechanism may be behind the results of Vásquez- de-Aldana et al (2011), who showed that root exudates of red fescue (Festuca rubra) had a greater inhibitory effect on the germination and seedling growth of four target species when infected with a fungal endophyte, Epichloë festucae. Endophyte infection can be beneficial to the host plant with respect to many factors including increased resistance to drought, salt stress, nematodes, mammalian and insect herbivores, and bacterial and fungal pathogens (Kimmons et al, 1990;Li et al, 2009;Ownley et al, 2010;Sabzalian and Mirlohi, 2010;Miranda et al, 2011;Rocha et al, 2011). Rudgers and Orr (2009), however, were able to show that soils conditioned by non-native tall fescue (Lolium arundinaceum) that was infected by the fungal endophyte, Neotyphodium coenophialum, were able to reduce the biomass of Elaeagnus umbellata, Fraxinus pennsylvanica, and Platanus occidentalis.…”

A fungal endophyte of a palatable grass affects preference of large herbivores

“…We analysed those traits usually affecting preference by domestic herbivores (Bailey et al 1996;Jung et al 1997) that, in turn, can be also modified by the endophyte (Miranda et al 2011;Soto-Barajas et al 2016). We analysed those traits usually affecting preference by domestic herbivores (Bailey et al 1996;Jung et al 1997) that, in turn, can be also modified by the endophyte (Miranda et al 2011;Soto-Barajas et al 2016).…”