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°10′-18°25′ S and 69°16′ W, 4400 m asl). The diurnal temperature range can reach 42 °C on some days of the year. The surface temperature of A. compacta was 13 °C below that of the air temperature of -7 °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 μmol·m -2·s-1, and maximum stomatal conductance (Gs) was 410 mmol·m-2·s-1. The estimated light compensation point was 89 μmol·m-2·s-1 and estimated light saturation occurred at about 1280 μmol·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. © 2008 German Botanical Society and The Royal Botanical Society of the Netherlands