Intraspecific Variation on Thermal Acclimation of Phragmites australis, a Widespread Wetland Plant Species in Response to Multiple Time-Scale Temperature Changes.

The temperature sensitivity of photosynthesis remains a significant uncertainty in wetland plants, critically impacting predictions of vegetation dynamics and ecosystem functions under global warming scenarios. This study investigates the photosynthetic responses of Phragmites australis, a model wetland plant with a broad geographic distribution, to temperature variations across three distinct temporal scales. We analysed short-term responses using net photosynthesis rate temperature curves, medium-term acclimation across three growth temperature regimes, and long-term adaptation of phylogeographical groups to their genotypic origins' climate. We demonstrated that the overall photosynthetic performance of P. australis is principally driven by thermal acclimation to growth temperature, comparing with local adaptation to climate of origin. Genotypes from diverse geographical regions demonstrated varied physiological strategies: those from higher latitudes exhibited remarkable plasticity, adjusting rapidly to optimise photosynthetic performances under changing thermal conditions. These intraspecific differences highlighted the role of evolutionary history in shaping species' potential resilience and adaptive capacity. This study also underscored the complex interplay between temperature, O₂ sensitivity and photosynthetic efficiency, advancing our understanding of how widespread wetland species respond to ongoing global climate dynamics.