PARENT SESSION
Poster Session 30: Soil Ecology.
Wednesday, August 4 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.
Assessing N availability through multiple resin extractions following the onset of the hemlock woolly adelgid.
Jefts, Sultana*,1, Orwig, David1, 1 Harvard Forest, Harvard University, Petersham, MA, USA
ABSTRACT- Introduced exotic pests can pose serious perturbations to ecosystem function, particularly to nutrient cycling and nutrient availability. Using the context of a natural experiment, the elimination of eastern hemlock (Tsuga canadensis) by the introduced pest the hemlock woolly adelgid (HWA), we are able to obtain a unique insight into the effects this pest has on N availability. This study examined both N availability via ion exchange resins and the efficacy of multiple resin extractions in a set of hemlock stands ranging in HWA damage severity. Overall, heavily infested stands demonstrated higher available nitrate concentrations: 423.49 ėg/g resin in heavily infested stands vs. 283.62 and 55.04 ėg/g resin in recently infested and uninfested stands, respectively. This suggests higher nitrification rates as well as higher nitrate availability possibly leading to nitrate leaching and increased denitrification. Uninfested and recently infested stands exhibited similar ammonium availability when compared with heavily infested stands. Interestingly, two sites that no longer have a hemlock component, exhibited different responses. One previously infested site that was logged now exhibits extremely high ammonium and nitrate availability (1169.40 and 1542.50 ėg/g resin, respectively) indicating lack of plant uptake as well the possibility for high nitrate leaching and denitrification. Another site which lost all hemlocks due to HWA 10 years ago and which previously had high N availability, has been replaced by black birch (Betula lenta) and now exhibits low N availability (88.18 and 108.41 ėg/g resin for ammonium and nitrate) indicating increased plant uptake as black birch continues dominance of the site. The recovery efficiency of using one resin extraction was relatively low in sites with high N availability. This was most pronounced for nitrate indicating that more than one rinse may be needed for sites with expected or known high nitrate availability.
Key words: ion exchange resin, N availability, hemlock woolly adelgid