Abstract

Alpine ecosystems present significant challenges for plant photosynthesis due to fluctuating temperatures, water availability, and reduced CO2 partial pressure at higher elevations. We studied the photosynthetic and leaf morphological responses of three high-Andean (alpine) wetland species: Colobanthus quitensis, Oxychloe andina, and Plantago barbata early and late in the growing season, at two sites at different elevations (2600 m and 3550 m a.s.l.). We hypothesized that the decrease in temperature towards higher elevation and the end of the growing season will result in higher leaf mass area (LMA) and lower mesophyll conductance (gm), increasing the diffusional limitation of CO2 and reducing photosynthetic rates (AN). Results indicate that plants in the low-elevation site exhibited significant reductions in AN and gm late in the growing season. In contrast, plants in the high-elevation site maintain stable AN, highlighting adaptations to cooler climates. While LMA increased across species at the end of the growing season, it showed low correlation with AN. Instead, gm emerged as the dominant diffusional component within the Harley-based framework. Species-specific strategies were observed, with higher LMA buffering O. andina against environmental stress, while low-LMA species (C. quitensis and P. barbata) were more sensitive to thermal variability. These findings emphasize gm as an important factor mediating photosynthetic adaptation in Andean plants and highlight the complexity of their responses to elevation and intraseasonal changes.