Hydraulic and Photosynthetic Performance of Antarctic Plants Under Successive Freeze–Thaw Cycles

Climate change projections predict warming and increased weather variability, mainly in polar regions, altering freeze-thaw patterns. However, the effects of rising temperatures and more frequent freeze-thaw events on the water and CO₂ management of Antarctic plants remain unclear. To address this, we conducted a laboratory experiment to investigate how growth temperature (5°C and 15°C) and successive freeze-thaw cycles influence the hydraulic and photosynthetic performance of Deschampsia antarctica (D. antarctica) and Colobanthus quitensis (C. quitensis). Our results showed that warmer conditions improved hydraulic and photosynthetic performance in both species, driven by anatomical adjustments in leaf xylem vessels. Additionally, plants exposed to successive freeze-thaw cycles exhibited a coordinated decline in whole-plant hydraulic conductivity and leaf gas exchange, regardless of growth temperature. The magnitude of changes (%) in photosynthetic traits after freeze-thaw cycles varied between species, with D. antarctica showing similar responses at both growth temperatures, while C. quitensis experienced more pronounced changes at the lower temperature. Overall, these findings suggest that while Antarctic plants benefit from warmer temperatures, repeated freeze-thaw events could disrupt their hydraulic balance and limit photosynthesis, particularly under natural environmental conditions.