Altitudinal and seasonal variation of protective and photosynthetic pigments in leaves of the world's highest elevation trees Polylepis tarapacana (Rosaceae)

In the present study we analyzed both photosynthetic and UV-B absorbing pigment variations in Polylepis tarapacana (Rosaceae) during two contrasting seasons (winter and summer) at two altitudes (4300 and 5000 m a.s.l.) in the Sajama volcano (Oruro, Bolivia). UV-B absorbing pigments, chlorophyll a, b and carotenoids contents as well as the chlorophyll a to chlorophyll b ratio showed clear differences in both seasons. UV-B absorbing pigments, total chlorophyll and chlorophyll a contents as well as chlorophyll a/b values were higher in winter than in summer at both altitudes, while chlorophyll b content and the total chlorophyll to carotenoids ratio showed an opposite pattern. Carotenoids content exhibited not only an increase with altitude but also a significant variation between seasons, the highest value being recorded in winter. We discuss the results in relation to the radiation regime of the Sajama region rather than to the water status of the plant studied, since the latter was similar for both seasons and altitudes.