Influences of genes, herbivory and drought on mortality and ectomycorrhizal community of a foundation tree

Understanding the influences of both genetic variation and climate change on population structure, community dynamics and ecosystem functioning has become a major frontier in ecological research. While recent work has demonstrated the importance of genetics and climate change in altering plant populations and their associated above-ground communities, little research has examined below-ground community responses. Furthermore, many of these studies have focused on pair wise interactions even though the importance of studying complex interactions is critical in understanding species responses to drought and genetic variation. Here I use pinyon pine (Pinus edulis ) that show chronic resistance or susceptibility to an herbivore as a model system to examine the influence of genetic variation and drought on both the tree population, and complex host-herbivore-mutualist interactions with associated ectomycorrhizal fungi.;First I show, using both field observations and a greenhouse experiment, that: (1) The mortality of adult Pinus edulis resistant to the moth was three times higher than that of trees susceptible to the moth. (2) When grown under drought conditions in the greenhouse, seedlings from resistant mothers died sooner than seedlings from susceptible mothers. (3) Adult moth resistant trees experienced significantly greater water stress than adult moth susceptible trees. (4) Differential mortality caused a shift in stand structure from 3:1 resistant dominated, to 1:1 resistant: susceptible.;Next, I compared ectomycorrizal fungi (EMF) communities of herbivore resistant trees, herbivore susceptible trees and herbivore susceptible trees from which insects were removed at two collection dates 10 years apart; a very wet year and a very dry year, and found: (1) EMF community composition differed between herbivore resistant and herbivore susceptible trees though EMF species richness was similar. (2) Even after 10 and 20 years of herbivore removal, the EMF community composition of removal trees was similar to that of susceptible trees and different from that of resistant trees. (3) Drought conditions were associated with reduced EMF species richness in all three groups of trees, but EMF community composition changed only in the resistant trees.;Finally, I did a follow up experiment in the greenhouse to test the findings of EMF community patterns found on adult trees. In this experiment I found: (1) The seedlings derived from insect resistant and susceptible trees also support different mycorrhizal communities, regardless of the inoculum source of the soil. Seedlings derived from herbivore removal trees did not differ from seedlings derived from susceptible trees, supporting the pattern found in the adults. (2) Seedling performance is in part determined by the composition of EMF community suggesting a feedback on tree performance.