Tri-trophic interactions: The role of mycorrhizal fungi on plant compensation following ungulate herbivory

Background/Question/Methods Previous studies on the interactions between ungulate herbivores and the compensatory responses of scarlet gilia, Ipomopsis aggregata, demonstrated a range of plant fitness responses dependent upon climatic conditions (ranging from under to over-compensation under severe drought to non-drought conditions, respectively). In spite of all we know about fitness compensation in scarlet gilia no one has studied the effects of mycorrhizae on compensation in scarlet gilia or, for that matter, any other plant species showing patterns of growth compensation following herbivory. In the San Francisco Peaks of Flagstaff, Arizona, a summer long study was conducted across a natural population of scarlet gilia to assess the compensatory (fitness) response of mycorrhizal removal treatments under drought conditions. Results/Conclusions Results clearly demonstrate that mycorrhizal fungi play an important role in growth compensation. Mycorrhizal removal experiments demonstrated that mycorrhizal fungi negatively influenced the fitness of browsed plants. Naturally browsed and experimentally clipped (simulating ungulate herbivory) plants combined with a fungicide treatment exhibited higher fitness than those without the fungicide treatment. Conversely, for uneaten controls, fungicide treatment had no effect. Overall, drought conditions and the negative effects of mycorrhizal fungi combined to restrict plant compensatory responses to that of equal compensation following ungulate herbivory; likely due to competition for limiting resources in a drought year. Whether the relationship between mycorrhizal fungi and plant compensation is altered in better (i.e. more precipitation) years remains to be assessed.