Functional and Structural Leaf Plasticity Determine Photosynthetic Performances during Drought Stress and Recovery in Two Platanus orientalis<i> </i>Populations from Contrasting Habitats

• Main Authors: Violeta Velikova, Carmen Arena, Luigi Gennaro Izzo, Tsonko Tsonev, Dimitrina Koleva, Massimiliano Tattini, Olympia Roeva, Anna De Maio, Francesco Loreto
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: International Journal of Molecular Sciences
• Subjects: climate change; phenotypic plasticity; drought; photosynthesis; leaf structure
• Online Access: https://www.mdpi.com/1422-0067/21/11/3912

In<b> </b>the context of climatic change, more severe and long-lasting droughts will modify the fitness of plants, with potentially worse consequences on the relict trees. We have investigated the leaf phenotypic (anatomical, physiological and biochemical) plasticity in well-watered, drought-stressed and re-watered plants of two<i> </i>populations of <i>Platanus</i><i> </i><i>orientalis</i>, an endangered species in the west of the Mediterranean area. The two populations originated in contrasting climate (drier and warmer, Italy (IT) population; more humid and colder, Bulgaria (BG) population). The IT control plants had thicker leaves, enabling them to maintain higher leaf water content in the dry environment, and more spongy parenchyma, which could improve water conductivity of these plants and may result in easier CO₂ diffusion than in BG plants. Control BG plants were also characterized by higher photorespiration and leaf antioxidants compared to IT plants. BG plants responded to drought with greater leaf thickness shrinkage. Drought also caused substantial reduction in photosynthetic parameters of both IT and BG plants. After re-watering, photosynthesis did not fully recover in either of the two populations. However, IT leaves became thicker, while photorespiration in BG plants further increased, perhaps indicating sustained activation of defensive mechanisms. Overall, our hypothesis, that plants with a fragmented habitat (i.e., the IT population) lose phenotypic plasticity but acquire traits allowing better resistance to the climate where they became adapted, remains confirmed.