Remote sensing of photosynthetic activity of arctic vegetation

Relationship between diurnal changes in photosynthetic activity and canopy reflectance of summer vegetation was studied in Northeast Greenland. 3 types of vegetation were tested including mixture of arctic willow and arctic birch, cottongrass and haircup moss. Photosynthetic activity was tested with PAM fluorometer as Y(II). Canopy reflectance was measured with field spectrometer; in addition Photochemical Reflectance index (PRI) was measured at leaf level with portable PRI-meter. It was found that among existing vegetation indices PRI reveals the best correlation with Y(II) at leaf and canopy levels. Selecting another reference wavelength allowed to increase accuracy but both PRI and the modified index did not correlate with Y(II) in data captured from haircup moss. An alternative “compromise” index was selected providing satisfactory correlation with Y(II) in all 4 plots. The results indicate that optical response to changes in Xanthophyll cycle is the most convenient approach for remote testing of diurnal changes in arctic vegetation.