Abstract:
In the aseasonal tropical alpine environment, plants experience frequent oscillations of air temperature around zero, but little is known about the leaf temperatures of different plant growth forms in dry versus humid climatic conditions. During July-August 2007, we measured air temperature at 100 cm and 20 cm above the ground, soil temperature at 1 cm and 10 cm depth, and temperatures of leaves and stems of tropical alpine plants on the eastern (windward and cloudy) and western (leeward and sunny) sides of the Antisana volcano (Ecuador) between 4100 m and 4600 m, with the aim of examining the effects of climate and growth forms on leaf temperature. The sunnier climate on the western side of the mountain provided a much broader thermal envelope, in which only leaves of low-statured plants showed significant departure from air temperature during the day. In contrast, most plants had warmer leaves than was the air temperature on the eastern side, and except for cushion plants, the difference in temperature was progressively greater in leaves of taller plants. Plants warmed up significantly faster on the western side and at higher elevations, with the fastest warming rates of 13-15 K h-1 observed in erect herbs. Night cooling rates did not differ between the opposite mountain sides or between elevations. Erect herbs cooled at the fastest rates (3 K h-1), whereas cushion plants cooled at the slowest rates (about 1 K h–1). Height aboveground along with aspect (west vs. east) were the most significant determinants of the leaf thermal microclimate during the day, with elevation having no effect. Low-statured plants experienced more extreme and more variable microclimates than taller plants in sunnier and drier conditions, but the effect of plant height was almost negligible in humid and cloudy climates. In all climatic conditions, cushion plants performed better than any other growth form by achieving higher temperature during the day and preventing rapid cooling during the night.
