Elevation and intraseasonal variation of in situ photosynthesis in high-Andean peatland (bofedal) species of central Chile

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 (g m ), increasing the diffusional limitation of CO₂ and reducing photosynthetic rates (A N ). Results indicate that plants in the low-elevation site exhibited significant reductions in A N and g m late in the growing season. In contrast, plants in the high-elevation site maintain stable A N , highlighting adaptations to cooler climates. While LMA increased across species at the end of the growing season, it showed low correlation with A N . Instead, g m 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 g m as an important factor mediating photosynthetic adaptation in Andean plants and highlight the complexity of their responses to elevation and intraseasonal changes. • This work highlights that mesophyll conductance (g m ) emerges as a principal regulator of photosynthesis in high-Andean peatland plants • Seasonal decrease in temperatures reduces photosynthesis mainly through internal CO₂ diffusion constraints • Leaf mass per area shows weak functional linkage with photosynthetic performance • Species differ in their capacity to maintain mesophyll conductance across elevations • Temperature sensitivity of mesophyll conductance shapes alpine plants photosynthetic capacity