Energy balance and temperature relations of Azorella compacta, a high-elevation cushion plant of the central Andes.

The environmental relationships and ecophysiology of Azorella compacta, a giant cushion plant, were investigated in Parque Nacional Lauca, Chile (18 degrees 10'-18 degrees 25' S and 69 degrees 16' W, 4400 m asl). The diurnal temperature range can reach 42 degrees C on some days of the year. The surface temperature of A. compacta was 13 degrees C below that of the air temperature of -7 degrees C at dawn, but from midmorning to late afternoon, the plant surface temperature remained within a few degrees of the air temperature. Soil surface temperatures did not differ between north- and south-facing slopes, but a model showed an increase in radiation reception by north-facing slopes throughout most of the year. Gas exchange measurements of A. compacta measured at the onset of the wet season ranged from -0.6662 to 11.4 micromol.m(-2).s(-1), and maximum stomatal conductance (Gs) was 410 mmol.m(-2).s(-1). The estimated light compensation point was 89 micromol.m(-2).s(-1) and estimated light saturation occurred at about 1280 mumol.m(-2).s(-1). Diurnal water potential measurements for A. compacta ranged from -1.67 to -2.65 MPa. This is one of the first ecophysiological studies of a tropical alpine cushion plant.