Progressive dehydration stress limits survival and growth of native Antarctic flowering plants: species-specific physiological and biochemical responses

Rapid climate warming in Antarctica has driven increased abundance and range expansion of the only two native flowering plants, Deschampsia antarctica and Colobanthus quitensis . Sustained warming and glacial retreat are expected to increase climatic uncertainty, including the frequency and severity of drought episodes, which may impose significant physiological constraints on these two species. To characterize adaptive strategies under water deficit, we subjected both plants to a 40-day dehydration treatment at 16°C. Both species exhibited progressive water loss, with declines in photosynthetic activity and biomass accumulation preceding severe dehydration (relative water content < 20%). Despite experiencing more negative soil water potentials, D. antarctica adopted an opportunistic strategy, sustaining growth and maintaining photosynthetic activity longer into the stress gradient. This was associated with elevated antioxidant enzyme activities, changes in chlorophyll concentration, and higher soluble sugar accumulation. In contrast, C. quitensis employed a conservative strategy, characterized by early root-to-shoot allocation, rapid suppression of gas exchange, stronger non-photochemical quenching, and progressive proline accumulation. Both species exhibited partial survival after 30 days of dehydration, but complete mortality after 40 days of stress treatment. These results demonstrate that while D. antarctica can sustain greater biomass accumulation under moderate drought stress, both species share similar survival thresholds, revealing fundamental physiological constraints that may determine Antarctic plant community responses to increasing aridity. • Progressive dehydration reveals species-specific physiological strategies in Antarctic plants • Deschampsia antarctica demonstrates opportunistic growth persistence • Colobanthus quitensis exhibits conservative stress avoidance • Divergent strategies converge: relative water content <10% is lethal to both species