| The function of anthocyanin pigment in deciduous senescing leaves is not resolved. To examine whether anthocyanic pigmentation protects photosynthesis or nitrogen (N) resorption, warms the leaf, or instead is repressed by high N concentrations, photosynthetic performance of green and red leaves, and the dynamics of N and of anthocyanin through senescence, were compared in three species: Arctous alpina (L.) Nied., Chamerion angustifolium (L.) Holub, and Cornus canadensis L. In addition, I measured leaf temperatures in A. alpina and added foliar N to C. angustifolium and C. canadensis. Foliar N concentrations were determined with an elemental analyzer. Foliar anthocyanin concentrations were estimated with a color index using pixel data from digital images and spectral reflectance measurements. Photosynthesis was measured with an infrared gas analyzer and leaf temperatures with an infrared thermometer. Maximum potential absorbed solar radiation of individual leaves was modeled in different solar conditions using spectrometer and pyranometer data.;Results did not support the photoprotective, N resorption or warming hypotheses. Photosynthesis declined markedly as red pigmentation increased, suggesting no photoprotection. Foliar N concentrations were negatively correlated with anthocyanin concentrations. Anthocyanin concentrations peaked and persisted after N resorption was complete. There was no evidence of warming in matched red and green leaves nor did potential absorption of solar radiation differ between leaf colors. Where foliar N was added, experimental leaves had less anthocyanin than controls in C. angustifolium. The data are consistent with the hypothesis that anthocyanin accumulation is repressed by higher N concentrations. Red pigmentation is a phenological marker of completed N resorption in these species, and thus may be useful in tracking temporal changes in the N cycle. |
