Contrasting Hydraulic-Photosynthetic Strategies Sustain Antarctic Vascular Plants Under Long-Term Warming

Leaf hydraulics and their coordination with photosynthesis are central to maintaining plant physiological function, especially in plants inhabiting extreme environments. We investigated the hydraulic responses of the only two vascular plant species native to Antarctica, Deschampsia antarctica and Colobanthus quitensis, to long-term in situ warming imposed by open-top chambers (OTCs), and assessed how these responses covary with photosynthesis (A_N). After 7 years under OTC, D. antarctica reduced both leaf hydraulic conductivity (K_leaf) and A_N when compared with plants under natural conditions (OA), whereas C. quitensis increased both. A tight coordination between hydraulics and photosynthesis emerged in both species, supported by structural and ultrastructural leaf adjustments. In D. antarctica, reductions in K_leaf and A_N could be linked to outside-xylem modulation and likely to senescence triggered by more frequent freeze-thaw events inside OTCs, where time below 0°C increased nearly tenfold compared with OA (from 32 to 309 h). Conversely, C. quitensis displayed increased cell wall elasticity, enhanced water transport and CO₂ diffusion, triggered by changes in vascular anatomy, and the growth form that favors heat conservation. These results highlight that the two Antarctic vascular species represent complementary adaptive pathways to environmental change, illustrating two sides of a common adaptive continuum, balancing hydraulic safety and efficiency, stability and plasticity, critical for survival in one of the most stressful environments on Earth.