Background/Question/Methods Mycorrhizal associations could impact plant fitness by altering floral traits that attract pollinators and/or floral antagonists. In our study system research shows that flower size and fragrance influence visitation by bumblebee pollinators and nectar-thieving ants to Polemonium viscosum. In this study we examined the effects of mycorrhizae on this well-studied pollination web. In particular, we asked the following questions: 1) Do mycorrhizae affect floral traits known to influence interactions in the web? 2) Do mycorrhizae affect the behavior of bumblebees and ants? 3) Do the effects of mycorrhizae on floral traits and insect behavior affect reproductive fitness?  We conducted our study in 2008 -2009 on Pennsylvania Mountain (Park County, CO, USA) at krummholz (3500m) and tundra (3700m) sites. Each year we selected 15 replicates of 6 plants per site. In 2009 we continued to treat and monitor plants from the first year.  Within each replicate plants were divided into two treatments groups and were sprayed with a systemic fungicide (I0.25% Iprodione) to reduce mycorrhizal colonization or with water as a control.  We measured flower size, nectar production, fragrance emission, pollen deposition, pollen production, and seed set.  We also observed pollinator visitation and ant damage to control and fungicide-treated plants.
Results/Conclusions The fungicide treatment reduced arbuscular mycorrhizal colonization by 34%.  Reduced AM colonization affected several floral traits and reproductive fitness; however, these effects depended on the year and site.  Fungicide-treated plants produced smaller flowers, except at the tundra site in 2009.  Fungicide –treated plants also produced more nectar and more seeds, but only at the krummholz site in 2009.  The fungicide treatment affected both the amount and composition of fragrance produced by tundra plants in 2009. After two years of treatment, fungicide-treated plants produced more fruits. Reduced AM colonization also affected pollinator and ant behavior.  Fungicide-treated plants were visited by more pollinators at both sites in 2009, and were more likely to experience ant damage in both years.  In conclusion, mycorrhizae affect a number of plant traits related to reproductive fitness; however, different traits respond to mycorrhizae at different temporal scales, and environmental conditions can influence the strength of these effects.    Our results also show that mycorrhizae influence plant-insect interactions by altering traits that act as signals as well as components of reproductive success.