Leaf gas exchange in Espeletia schultzii Wedd, a giant caulescent rosette species, along an altitudinal gradient in the Venezuelan Andes

Abstract

Abstract Gas exchange studies along low altitudinal gradients (0–2 500 metres above sea level) suggest an increase in plant CO2 assimilation with increasing altitude. The question arises however, will this hold true for higher altitudinal ranges? The purpose of this work was to characterize carbon and water relationships in Espeletia schultzii along an extreme altitudinal gradient. Gas exchange characteristics under field conditions during wet and dry seasons were documented for Espeletia schultzii, a giant caulescent rosette species, along an altitudinal gradient (2 950, 3 550 and 4 200 m) in the Venezuelan Andes. Significant differences in CO2 assimilation rates between seasons were found for all studied sites. Low assimilation rates obtained during the dry season were a consequence of: low leaf conductances to counteract low leaf water potentials and/or high vapour pressure differences between leaf and air, and to high leaf temperatures measured during the dry season. Important differences in A P i curve parameters were obtained between wet and dry seasons. A decrease in Amax was observed for the two lower populations, while a similar value was obtained for both wet and dry seasons at the higher altitude. A decrease in the relation P i P a and an increase in stomatal limitation and leaf temperature were measured from wet to dry season. There was a differentiation in CO2 assimilation with increasing altitude. At 2 950 m, maximum rates were above 5 μmol · m−2 · s−1, at 3 550 m 3 μmol · m−2 · s−1, while at 4 200 m maximum CO2 assimilation rate was below 3 μmol ·m−2 · s−1. This decrease may be explained by: an increase in leaf pubescence, lower leaf conductances and/or lower leaf nitrogen content at higher altitude.