Spectral reflectance of Betula ermanii at different altitudes in the Changbai mountains.

The leaf spectral reflectance of the Betula ermanii along an altitudinal gradient in the Changbai mountains was measured in an attempt to reveal underlying physiological mechanisms of environmental adaptation of Betula ermanii. The results showed significant differences in the spectral reflectance at different elevations, and the spectral indices also varied significantly. From 1 750 m to 2 000 m, the chlorophyll normalized difference index (chlNDI) indicated that chlorophyll concentrations increased at first and then decreased. Photochemical reflectance index (PRI) indicated lower PAR use efficiency at 2 000 m than lower elevations. Carotenoid index (CAI) indicated that the carotenoid concentrations at 1 750, 1 900 and 2 000 m had no significant difference. In addition, both chlorophyll concentrations and PAR use efficiency in the timberline were higher than those at 2 000 m, while the carotenoid concentration was lower than that at 2 000 m. Hence, we conclud that physiological conditions and stress are different at different elevations, and near 1 900 m is the best region for the growth of B. ermanii; the surroundings above the timberline is unsuitable for the growth and development, thus, higher elevation limits its distribution.