Photosynthetic performance and growth vary among populations of Myrsine coriacea under contrasting climatic scenarios

Abstract Key message A warm, high-VPD climatic scenario revealed population-level differences in ecophysiological responses in Myrsine coriacea , highlighting contrasting responses to changing climatic conditions. Abstract Temperature and atmospheric evaporative demand are key drivers of tree performance, while phenotypic plasticity and population-level differentiation shape responses to environmental variation. In tropical montane ecosystems, understanding how populations can physiologically respond to variation in temperature and atmospheric evaporative demand is essential for predicting forest responses to climate change. We investigated the responses of Myrsine coriacea populations along an elevational gradient in the Brazilian Atlantic Forest under contrasting climatic scenarios. Seedlings from seven populations (639–1774 m a.s.l.) were grown in a common garden experiment under Cold-Dry and Warm-Humid scenarios. We evaluated growth, gas exchange, chlorophyll fluorescence, and biochemical traits to assess variation in physiological responses among populations. Low- and mid-elevation populations maintained growth under the warmer, higher-VPD scenario, whereas the highest-elevation population showed increased mortality. Although photosynthetic capacity increased under the warmer scenario, respiratory costs and light compensation points also increased, indicating patterns consistent with reduced net carbon gain. In the highest-elevation population, increased intercellular CO 2 concentration together with reduced quantum efficiency suggested that constraints on carbon assimilation were unlikely to arise solely from CO 2 diffusion. These results demonstrate that phenotypic shifts under the warmer climatic scenario do not necessarily translate into functional resilience. The highest-elevation population exhibited coordinated morphological and physiological adjustments, but these responses were not accompanied by improved growth or survival, suggesting limited acclimation under the warmer, higher-VPD scenario. Together, these findings highlight how population-level differentiation influences photosynthetic performance, growth, and acclimation under contrasting climatic scenarios, emphasizing the importance of intraspecific variation when predicting tropical forest responses to climate change.