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Harvard Forest REU Symposium Abstract 2007
- Title: Linking foliar nitrogen concentrations to long-term carbon uptake at Harvard Forest
- Author: Leland K Werden (Harvard University)
- Abstract:
Measurements of CO2 exchange and ground-based measurements of C pools at Harvard Forest have shown that C-uptake has systematically increased over the last 18 years, mostly due to the growth of red oak (Quercus rubra). This increase in C-uptake cannot be explained by climatic variables over the long term and is unexpected because it is believed that trees of this age have matured. Foliar N concentration is positively correlated with photosynthetic rates at the leaf level and could be one of the factors contributing to C-uptake. We investigated whether N has been involved in the observed increases in C-uptake by measuring N concentrations in fresh foliage samples collected from the footprint of the eddy-flux tower over several years since 1998. We found that that the mean foliar N concentration of hardwood species has increased significantly (p < 0.05) since 1998. No relationship was found between growth rates and foliar N concentrations of individual trees. Our results suggest that interannual variation in foliar N concentration follows a similar pattern of interannual variation in C sequestration, although a causal relationship between the two is not supported. N concentration measurements of other components of the forest are needed to develop a more detailed analysis of N-cycling at this site. Measurements in future years will help us to determine if canopy N concentration is in fact increasing at this site or if the early measurements taken for this study were made in an abnormally N-poor year.
- Research Category: Forest-Atmosphere Exchange; Large Experiments and Permanent Plot Studies
- Figures: percent.N.vs. species.jpg
Growth rate vs. percent N 2006.jpg
