Are endophyte-mediated effects on herbivores conditional on soil nutrients?

Abstract

Neotyphodium endophytes are assumed to have mutualistic relationship with their grass hosts, mainly resulting from mycotoxin production increasing plant resistance to herbivores by the fungus that subsists on the plant. To study importance of often ignored environmental effects on these associations, we performed a greenhouse experiment to examine the significance of endophyte infection and nutrient availability for bird-cherry aphid ( Rhopalosiphum padi) performance on meadow fescue ( Lolium pratense). Naturally endophyte-infected (E+), uninfected (E-), or manipulatively endophyte-free (ME-) half-sib families of meadow fescue were grown on two soil nutrient levels. Endophyte infection reduced aphid performance in general. However, to our knowledge, this is the first study to demonstrate experimentally that herbivore performance decreases on E+ host plants with increasing availability of nutrients in soils. Potential improvement in herbivore performance in high nutrient soils and decreased plant performance in low nutrient soils in ME- plants, compared to E- and E+ plants, suggests that loss of endophyte infection after long coevolutionary relationship may be critical to plant fitness.

Effect of Endophyte Association with Brachiaria Species on Shoot and Root Morpho-physiological Responses under Drought Stress

“…Variable effects of endophytes are related to high dependence of host-endophyte associations on environmental conditions and genetics of both host and endophyte [21][22][23][24]. In the present study, significant three-way and two-way interactions influenced several traits, including leaf area, total root diameter, diameter of cortex, area of stele, number of tillers, shoot elongation, stomatal conductance, shoot biomass, and diameter of xylem vessels (p<0.05).…”

Environmental conditions and host plant origin override endophyte effects on invertebrate communities

“…Because alkaloids are nutrient-rich compounds, their synthesis has cost to other basic plant growth and reproductive functions Faeth and Bultman 2002;Faeth and Fagan 2002). These costs may outweigh the benefits of the endophyte infection in most environments, but particularly so in nutrient-poor environments in nature (Ahlholm et al 2002;Lehtonen et al 2005). Thus, in its native habitat, infected wild tall fescue may produce lower levels and fewer types of alkaloids than its cultivated and selective-bred varieties in nutrient-rich environments in the introduced range (Saikkonen et al 1998Siegel and Bush 1996; but see Piano et al 2005).…”

Endophytic fungus decreases plant virus infections in meadow ryegrass ( Lolium pratense )

“…In turn, the endophyte receives nutrients, carbohydrates and shelter from its host. Recently, it has been acknowledged that the nature of the relationship varies from mutualistic to antagonistic (Saikkonen et al 1998;Faeth 2002), depending on, for example, environmental conditions (Cheplick et al 1989;Lehtonen et al 2005a), the genetic background of the grass and fungus and interacting species in the community (Saikkonen et al 2004;Lehtonen et al 2005b).…”