A Double Edge-Sword in Antarctica: In Situ Passive Warming Exacerbates Drought and Heat Stress Differentially in the Native Vascular Species.

We investigated the impact of open-top chamber (OTC) passive warming systems at molecular and ecophysiological levels on Deschampsia antarctica (DA) and Colobanthus quitensis (CQ) in Antarctica. In this field campaign, OTC led to more benign conditions early in the growing season but ultimately intensified drought stress and increased extreme heat events, affecting photosynthetic capacity, metabolism and dehydration tolerance in DA; however, CQ remained relatively unaffected. DA exhibited significant reductions in photosynthesis primarily due to stomatal and mesophyll limitations. Furthermore, DA plants grown under OTC conditions showed a notable 17% decrease in leaf mass per area (LMA), a crucial trait associated with stress tolerance. Metabolic profiling revealed an increased accumulation of osmoprotectants and protein stabilisers (soluble sugars, trehalose, myo-inositol and galactinol), secondary metabolite precursors (tryptophan and nicotinate) and cell wall constituents (xylose) in OTC-grown DA, suggesting a robust metabolic response to stress. However, these metabolic adjustments were insufficient to counteract the decline in LMA and maintain dehydration tolerance. This study thereby provides new insights into the physiological and metabolic limitations of Antarctic vascular plants under future warming and drying scenarios.