Antarctic vascular plants show restrictions in mesophyll CO2 conductance due to morphological leaf adaptations to deal with the harsh climate. Rubisco kinetic parameters, however, compensate by optimizing photosynthesis and carbon balance.

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 the in situ warming effects on photosynthesis, including the underlying diffusive, biochemical and anatomical determinants, and the relative growth of two Antarctic vascular species, Colobanthus quitensis and Deschampsia antarctica, using open top chambers (OTCs) and gas exchange measurements in the field. In C. quitensis, the photosynthetic response to warming relied on specific adjustments in the anatomical determinants of the leaf CO transfer, 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. antarctica showed no response to warming, with a lack of significant differences between plants grown inside OTCs and plants grown in the open field. Overall, the present results are the first reporting a contrasting effect of in situ warming 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.

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Understanding the strategies employed by plant species that live in extreme environments offers the possibility to discover stress tolerance mechanisms. We studied the physiological, antioxidant and metabolic responses to three temperature conditions (4, 15, and 23°C) of Colobanthus quitensis (CQ), one of the only two native vascular species in Antarctica. We also employed Dianthus chinensis (DC), to assess the effects of the treatments in a non-Antarctic species from the same family.Using fused LASSO modelling, we associated physiological and biochemical antioxidant responses with primary metabolism. This approach allowed us to highlight the metabolic pathways driving the response specific to CQ.Low temperature imposed dramatic reductions in photosynthesis (up to 88%) but not in respiration (sustaining rates of 3.0-4.2 lmol CO 2 m À2 s À1 ) in CQ, and no change in the physiological stress parameters was found. Its notable antioxidant capacity and mitochondrial cytochrome respiratory activity (20 and two times higher than DC, respectively), which ensure ATP production even at low temperature, was significantly associated with sulphur-containing metabolites and polyamines.Our findings potentially open new biotechnological opportunities regarding the role of antioxidant compounds and respiratory mechanisms associated with sulphur metabolism in stress tolerance strategies to low temperature.

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