Variation in foliar nitrogen and albedo in response to nitrogen fertilization and elevated carbon dioxide

It has recently been demonstrated that foliar nitrogen is positively correlated with surface albedo over a broad range of plant functional types. However, the mechanism(s) driving the nitrogen-albedo relationship remain elusive. This study investigated leaf spectral properties from three deciduous species subjected to either nitrogen or CO2 fertilization and compared results to measured chemical and structural properties. We measured reflectance and transmittance, foliar nitrogen, leaf mass per unit area, water content, and d13C values for stacks of 1, 2, 4, and 8 leaves. Nitrogen was the best predictor of leaf-level albedo of the traits that we measured. There were no significant differences in albedo between CO2 or nitrogen treatments. Across all species there was a negative relationship between albedo and foliar nitrogen, suggesting that the previously observed nitrogen-albedo relationship is not caused by leaf-level interactions, but is likely due to structural properties at the canopy or stand level