Abstract
Multispecies interactions can be important to the expression of phenotypes and in determining patterns of individual fitness in nature. Many plants engage in symbiosis with arbuscular mycorrhizal fungi (AMF), but the extent to which AMF modulate other species interactions remains poorly understood. We examined multispecies interactions among plants, AMF, and insect herbivores under drought stress using a greenhouse experiment and herbivore choice assays. The experiment included six populations of Clarkia xantiana (Onagraceae), which span a complex environmental gradient in the Southern Sierra Nevada of California. Clarkia xantiana's developing fruits are commonly attacked by grasshoppers at the end of the growing season, and the frequency of attack is more common in populations from the range center than range margin. We found that AMF negatively influenced all metrics of plant growth and reproduction across all populations, presumably because plants supplied carbon to AMF but did not benefit substantially from resources potentially supplied by the AMF. The fruits of plants infected with AMF did not differ from those without AMF in their resistance to grasshoppers. There was significant variation among populations in damage from herbivores but did not reflect the center‐to‐margin pattern of herbivory observed in the field. In sum, our results do not support the view that AMF interactions modulate plant–herbivore interactions in this system.
Highlights
Organisms in natural ecosystems participate in a web of mutualistic and antagonistic species interactions
We examined multispecies interactions among plants, Arbuscular mycorrhizal fungi (AMF), and herbivores using six populations of the annual plant Clarkia xantiana ssp. xantiana
We found that all aspects of growth and reproductive effort were reduced in AMF inoculated plants, suggesting that the net effect of AMF inoculation on xantiana was parasitic in our experiment
Summary
Organisms in natural ecosystems participate in a web of mutualistic and antagonistic species interactions. Plants inoculated with AMF often show improved growth under water stress (Augé, 2001) This symbiosis is thought to be largely mutualistic in natural populations, the outcome of AMF–plant interactions is often context dependent (Hoeksema et al, 2010; Johnson, Graham, & Smith, 1997; Klironomos, 2003). Previous experiments on plant–microbe–herbivore interactions have produced highly variable results (Gehring & Bennett, 2009), with the net outcome depending on factors such as herbivore feeding specialization (Koricheva, Gange, & Jones, 2009) and various abiotic stresses (Pineda, Dicke, Pieterse, & Pozo, 2013). With the complex gradient in abiotic and biotic factors across xantiana’s range, the outcome of interactions between plants, microbial symbionts, and insect herbivores may change across geographic space and among plant populations. We ask the following questions: 1. Does AMF inoculation affect xantiana growth and phenology under low water availability?
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