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

Violeta Velikova,Luigi Gennaro Izzo,Olympia Roeva,Carmen Arena,Dimitrina Koleva,Anna De Maio,Massimiliano Tattini,Tsonko Tsonev,Francesco Loreto

doi:10.3390/ijms21113912

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.

Highlights

Physiology and life history of plants can be significantly altered by environmental factors
IT plants from dry habitat had thicker leaves (LT) and spongy parenchyma (SP) (Figure 1A,D), while the relative area of mesophyll occupied by intercellular spaces (InS) and palisade parenchyma thickness (PP) (Figure 1B,C), as well as the epidermises
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Summary

Introduction

Physiology and life history of plants can be significantly altered by environmental factors. Increased frequency of extreme weather events is becoming an important feature of predicted climate changes, especially in the Mediterranean area [1]. The rise of CO2 in the atmosphere proceeds at an rapid speed, and the associated global warming can lead to drastic changes in precipitation and reduction of available freshwater [1]. It is expected that drought in warm periods will become the most frequent climate extreme, negatively affecting terrestrial ecosystems [2]. The impact of drought stress on plants remains largely undetermined [3]. Plants, due to their sessile nature, have developed strategies to respond effectively to environmental changes, and to continually adapt to their local environment, thereby exploring highly diverse habitats [4]

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Results

Discussion

Conclusion