Umbilicaria Mammulata and Nitrogen Deposition at Harvard Forest 2006

Atmospheric N has quadrupled due to anthropogenic inputs and is projected to double again by 2050. The lichen Umbilicaria mammulata relies primarily on atmospheric deposition for nutrients, including N. Much of this species’ geographic distribution coincides with the N deposition gradient in the eastern US. We were interested in the potential impacts of N deposition on this species under realistic field conditions. Lichens were collected at six sites, ranging from Maine (low deposition) to West Virginia (high deposition). Thalli were analyzed for %C, %N, C:N, specific thallus weight (a measure of thickness), chlorophyll content, and chlorophyll fluorescence. Using stepwise regression we identified the most predictive model(s) using N deposition, environmental variables, and climate to predict differences in lichen ecophysiology and biochemistry across the gradient. While N deposition was important in predicting some responses, the model that best predicted %N in lichen only included mean minimum temperature, mean annual precipitation, and substrate slope. In controlled experiments at Grandfather Mountain (Linville NC) lichens were fertilized in situ with N to mimic deposition projected for 2050. There were no significant differences between control and fertilized thalli for any response variables, but differences did exist among sites. The results of this study highlight the complexities associated with sampling along a gradient of one factor in a multivariate environment.