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

Abstract

In 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 populations of Platanus orientalis, 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.

Leaf Shedding and Non-Stomatal Limitations of Photosynthesis Mitigate Hydraulic Conductance Losses in Scots Pine Saplings During Severe Drought Stress

“…Also, it would be more convincing that loss in xylem conductance is a driving force for drought responses if it would have been directly measured instead of indirectly calculated from water potential and transpiration. It should also be noted that the additional parameters required to describe the new model features are yet uncertain with respect to their generality; thus, further studies are needed to evaluate their precision, speciesdependency, or relationship to wood or leaf anatomical traits (Schumann et al, 2019, Velikova et al, 2020.…”

A comparative study on the leaf anatomical structure of Camellia oleifera in a low-hot valley area in Guizhou Province, China

“…The palisade tissue (0.48) and the spongy tissue (0.45) both displayed high plasticity, and these indices determined leaf thickness (r = 0.724 and 0.819, respectively). Under short-term drought stress, Canarium album and Platanus orientalis maintain moisture by increasing leaf thickness [ 3 , 38 ] while Lycopersicon esculentum decreases leaf thickness under long-term drought stress [ 39 ]. Under short-term drought stress, the decrease in the water content of leaves exhibits a certain pattern: The water content of non-functional leaves (lower leaves, morphologically) continuously decreases, whereas that of functional leaves (upper leaves) is maintained to keep biomass accumulation [ 40 ].…”

“…After rehydration, functional leaves maintain their strategy for drought. Platanus orientalis maintains moisture by increasing leaf thickness while Platanus orientalis exerts antioxidant protection by increasing non-enzymatics [ 38 ], which indicate the diversity of different species in dealing with even the same stress. In our study, the excellent individual plants underwent rehydration after short-term drought, and their drought resistance was assessed based on leaf anatomic structure.…”

The Potential Roles of Unique Leaf Structure for the Adaptation of Rheum tanguticum Maxim. ex Balf. in Qinghai–Tibetan Plateau

“…The phenotypic plasticity index (PI) was calculated for each measured variable as the difference between the maximum and the minimum value divided by the maximum value. PI ranges from 0 (no plasticity) to 1, indicating high plasticity [16].…”

“…In addition to leaf size, leaf shape is also a highly plastic trait in plants. Phenotypic plasticity is referred to as the expression of different phenotypes in one species depending on growing conditions [15]; it is crucial for the adaptation and survival of plants [16]. The phenotypic plasticity of the leaves often reflects the balance between the need to maximize the capture of light quanta during photosynthesis and minimizing the damage caused by environmental stresses [4].…”