Elevation provenance affects photosynthesis and its acclimation to temperature in the high-Andes alpine herb Phacelia secunda.

We analyzed whether Phacelia secunda populations from different elevations exhibit intrinsic traits associated with its diffusive and biochemical components of photosynthesis and if they differ in their acclimation of photosynthesis to warmer temperatures. We hypothesized that P. secunda plants will have similar photosynthetic performances regardless of altitudinal provenance and that plants from high elevations have a lower photosynthetic acclimation capacity to higher temperature than plants from low elevation. Plants from 1600, 2800 and 3600 m elevation in the central Chilean Andes were collected and grown at two thermal regimes (20/16 and 30/26°C day/night). The following photosynthetic traits were measured on each plant at the different growing temperatures: A N , g s , g m , J max , V cmax , Rubisco carboxylation k cat c . Under a common growing environment, plants from the highest elevation showed slightly lower CO 2 assimilation rates compared to lower elevations plants. While diffusive components of photosynthesis increased with elevation provenance, the biochemical component decreased, suggesting compensations that explain the similar photosynthetic rates among elevation provenances. Plants from high elevations showed lower photosynthetic acclimation to warmer temperatures compared to plants from low elevation, and these responses were related with elevational changes in diffusional and biochemical components of photosynthesis. Plants of P. secunda from different elevations maintain their photosynthetic traits when growing in a common environment suggesting low plasticity to respond to future climate changes. The fact that plants from high elevation showed lower photosynthetic acclimation to warmer temperature suggest a higher susceptibility to the increase in temperature associated with global warming.