Effects of severe dwarf mistletoe infection on the ectomycorrhizal community of aPinus contortastand in Yellowstone Park

Abstract

Molecular methods were used to test the hypothesis that severe infection by dwarf mistletoe ( Arceuthobium , a carbon-sink parasite) affects the ectomycorrhizal (EM) communities of its host, lodgepole pine. Results indicate significantly lower EM fungal species richness (2 ± 0.2 SE species per core in uninfected and 1 ± 0.2 species per core in infected blocks; P < 0.005), Shannon–Wiener diversity indices (1.1 in uninfected and 0.6 in infected; P < 0.05), and also differences in species EM fungal composition; uninfected blocks are dominated by a species of Cortinarius while the infected stand is dominated by species of Russula , and Piloderma (26%). By contrast, dwarf mistletoe infection has no apparent effect on evenness (0.65 in controls and 0.47 in infected; 0.05 < P < 0.1), or on EM infection levels (35 ± 7 EM tips per core in uninfected and 21 ± 5 in infected; P > 0.1). Thus, dwarf mistletoe infection may select for EM fungal species that impose a lower carbon demand on the host, or that possess carbon-degrading abilities to augment carbon lost to the parasite, enabling the trees in infected blocks to maintain relatively high EM infection levels. Our results indicate that effects of dwarf mistletoe infection occur not just in the crown of infected but extend into the soil as well, and hence may have much greater implications for ecosystem function than previously thought.