Particular physiological traits allow the vascular plants Deschampsia antarctica Desv. and Colobanthus quitensis (Kunth) Bartl. to inhabit Antarctica. The photosynthetic performance of these species was evaluated in situ, focusing on diffusive and biochemical constraints to CO₂ assimilation. Leaf gas exchange, Chl a fluorescence, leaf ultrastructure, and Rubisco catalytic properties were examined in plants growing on King George and Lagotellerie islands. In spite of the species- and population-specific effects of the measurement temperature on the main photosynthetic parameters, CO₂ assimilation was highly limited by CO₂ diffusion. In particular, the mesophyll conductance (g_m)—estimated from both gas exchange and leaf chlorophyll fluorescence and modeled from leaf anatomy—was remarkably low, restricting CO₂ diffusion and imposing the strongest constraint to CO₂ acquisition. Rubisco presented a high specificity for CO₂ as determined in vitro, suggesting a tight co-ordination between CO₂ diffusion and leaf biochemistry that may be critical ultimately to optimize carbon balance in these species. Interestingly, both anatomical and biochemical traits resembled those described in plants from arid environments, providing a new insight into plant functional acclimation to extreme conditions. Understanding what actually limits photosynthesis in these species is important to anticipate their responses to the ongoing and predicted rapid warming in the Antarctic Peninsula.

Summary: The Antarctic Peninsula has experienced a rapid warming in the last decades. Although recent climatic evidence supports a new tendency towards stabilization of temperatures, the impacts on the biosphere, and specifically on Antarctic plant species, remain unclear. We evaluated thein situwarming effects on photosynthesis, including the underlying diffusive, biochemical and anatomical determinants, and the relative growth of two Antarctic vascular species,Colobanthus quitensisandDeschampsia antarctica, using open top chambers (OTCs) and gas exchange measurements in the field. InC. quitensis, the photosynthetic response to warming relied on specific adjustments in the anatomical determinants of the leafCO₂transfer, which enhanced mesophyll conductance and photosynthetic assimilation, thereby promoting higher leaf carbon gain and plant growth. These changes were accompanied by alterations in the leaf chemical composition. By contrast,D. antarcticashowed no response to warming, with a lack of significant differences between plants grown insideOTCs and plants grown in the open field. Overall, the present results are the first reporting a contrasting effect ofin situwarming on photosynthesis and its underlying determinants, of the two unique Antarctic vascular plant species, which could have direct consequences on their ecological success under future climate conditions.

The effects of in vitro environmental conditions, ventilation of culture vessels and light level, on water loss control and photosynthetic capacity of Castanea sativa during in vitro culture were assessed. C. sativa microshoots were cultured in ventilated (V) and non ventilated (NV) vessels, using two photon flux density (PFD) levels, 50 and 150 μmol photons m⁻² s⁻¹ (L₅₀ and L₁₅₀, respectively). The use of ventilation and the increase in irradiance improved the performance of the microshoots with respect to traditional in vitro culture of C. sativa (NVL₅₀). Microshoots grown under VL₁₅₀ showed an increase in stomatal density and improved their functional characteristics, showing a more elliptical shape and lower percentage of open stomata. This paralleled a significantly lower transpiration rate and stomatal conductance. Increasing light level and using ventilated vessels increased the microshoots’ capacity to harmlessly dissipate excess absorbed energy, water use efficiency and photosynthetic activity, resulting in a greater production of new microshoots. These improvements during in vitro culture generate microshoots with anatomical and functional characteristics similar to those observed in seedlings, which could help reduce the stress observed during ex vitro transfer.

Antarctic flowering plants have become enigmatic because of their unique capability to colonize Antarctica. It has been shown that there is not a single trait that makes Colobanthus quitensis and Deschampsia antarctica so special, but rather a set of morphophysiological traits that coordinately confer resistance to one of the harshest environments on the Earth. However, both their capacity to inhabit Antarctica and their uniqueness remain not fully explained from a biological point of view. These aspects have become more relevant due to the climatic changes already impacting Antarctica. This review aims to compile and update the recent advances in the ecophysiology of Antarctic vascular plants, deepen understanding of the mechanisms behind their notable resistance to abiotic stresses, and contribute to understanding their potential responses to environmental changes. The uniqueness of Antarctic plants has prompted research that emphasizes the role of leaf anatomical traits and cell wall properties in controlling water loss and CO₂ exchange, the role of Rubisco kinetics traits in facilitating efficient carbon assimilation, and the relevance of metabolomic pathways in elucidating key processes such as gas exchange, nutrient uptake, and photoprotection. Climate change is anticipated to have significant and contrasting effects on the morphophysiological processes of Antarctic species. However, more studies in different locations outside Antarctica and using the latitudinal gradient as a natural laboratory to predict the effects of climate change are needed. Finally, we raise several questions that should be addressed, both to unravel the uniqueness of Antarctic vascular species and to understand their potential responses to climate change.