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.
Bibliographical noteFunding Information:
We thank the National Science Foundation for supporting our research on Clarkia xantiana (DEB-1255141 to Moeller including an REU supplement for LGB and DEB-1701072 to Moeller and Benning), and Stefan Jaronski of the USDA ARS Northern Plains Agricultural Research Laboratory for generously providing a grasshopper colony for our experiment. The manuscript was much improved by discussions with A. Pringle, M. Hart, and M. Keller-Pearson, and from thoughtful comments by J. Lau, the Lau lab, and the Moeller lab.
- aboveground–belowground interactions
- arbuscular mycorrhizal fungi
- flowering phenology
- geographic range
- parasitism mutualism continuum
- soil microbial community
- tripartite multispecies interactions