The Effects of Mite Galling on the Ecophysiology of Two Arctic Willows

Deciduous plants in the Arctic are increasing in abundance due to warming trends, and this increase will likely contribute to changes in regional carbon dynamics. One of the dominant deciduous-shrub genera, Salix, is highly susceptible to leaf galls, but the influence of arthropod herbivores on plant-level carbon uptake in the Arctic remains poorly studied. We examined the impacts of galling by two eriophyoid mites on a suite of ecophysiological traits in leaves of two species of willows (Salix pulchra Cham. and Salix glauca L.) in Alaskan arctic tundra. Galled leaves showed significant declines in maximum photosynthetic capacity (A(max)), photosystem II efficiency (F-V/F-M), stomatal conductance (g(s)), and instantaneous water-use efficiency (WUE) in S. pulchra leaves and in A(max) and F-V/F-M of S. glauca leaves. Neighboring gall-free leaves on the same shoot as galled leaves had higher A(max) and g(s)than nearby controls suggesting compensatory responses. Gall-infested tissue had significantly higher concentrations of glucose and fructose compared to gall-free leaves, suggesting a possible preference for these metabolites. Alternatively, this variation in metabolite concentrations in the area of wounding may be associated with the production of defense compounds. To unravel the specific variation in metabolic concentrations related to gall infestation, additional studies are needed. Our findings do suggest that galling mites-ubiquitous but poorly examined in the tundra-have significant impacts on photosynthetic processes that are likely to affect whole-plant functioning in arctic willows.