Site-level importance of broadleaf deciduous trees outweighs the legacy of high nitrogen (N) deposition on ecosystem N status of Central Appalachian red spruce forests

• Published in: Plant and soil 2016-11, Vol.408 (1/2), p.343-356
• Main Authors: Smith, Kenneth R., Mathias, Justin M., McNeil, Brenden E., Peterjohn, William T., Thomas, Richard B.
• Format: Article
• Language: English
• Subjects: Biogeochemistry; Biomedical and Life Sciences; Deciduous forests; Deciduous trees; Ecology; Environmental aspects; Environmental factors; Forest ecology; Forest ecosystems; Forest litter; Forest soils; Life Sciences; Mineral soils; Nitrification; Nitrogen; Nitrogen (Chemical element); Organic soils; Picea rubens; Plant Physiology; Plant Sciences; Plant species; Regular Article; Retention; Soil composition; Soil nitrogen; Soil Science & Conservation; Species composition; Spruces; Terrestrial ecosystems; Trees
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-016-2940-z

Background and aims Atmospheric nitrogen (N) deposition can influence forest ecosystem N status, and the resilience of forests to the effects of N deposition depends on a number of co-occurring environmental factors that regulate N retention or loss. In this study, we test the idea that N deposition may have important and long-lasting impacts on patterns of N cycling by using field and laboratory techniques to assess N status in seven high-elevation Central Appalachian red spruce (Picea rubens Sarg.) forests located at sites that historically received moderate to high inputs of N atmospheric deposition. Methods During 2011 and 2012, we measured multiple indices of N availability (e.g. foliar/soil C:N and δ ¹⁵N, resin ion-exchange, and N transformation rates) that integrate N cycling over seasonal to decadal time scales. Using a model selection approach, we compared the strength of the association between various environmental factors and temporally-integrated indices of N status in a series of regression models. Results Site-level differences in the relative importance value of broadleaf deciduous (BD) trees consistently explained most of the observed variation in N status. Soil C:N was significantly lower for sites with greater BD importance (R² = 0.67-0.77), and there was a strong positive relationship between BD importance and soil δ ¹⁵N content (R² = 0.64-0.85). Despite a four-fold difference in historic deposition across the seven forest sites, we did not observe any significant relationships between site N status and N deposition. Conclusions These findings suggest that potential legacy effects of N deposition were obscured by the influence of BD importance on N status at these sites. Our results add strong support to the idea that predicting the resilience of forests to the effects of N deposition requires detailed knowledge on the contribution of tree species composition to soil N cycling and retention.