Abstract
Global climate change represents a moving target for plant acclimation and/or adaptation, especially in the Mediterranean basin. In this study, the interactions of severe drought (20% of the effective daily evapotranspiration) and O3 fumigation (80 ppb, 5 h day−1, for 28 consecutive days) on (i) photosynthetic performance, (ii) cell membrane stability, (iii) hydric relations, (iv) accumulation of compatible solutes, and (v) lipophilic antioxidant compounds were investigated in young Quercus cerris plants. In addition to the typical drought-induced stomatal closure, imposition of water withholding dramatically influenced the profile of stress-associated metabolites, i.e., abscisic acid (ABA), proline, and lipophilic antioxidants. However, plants were not able to delay or prevent the negative effects of water deficit, the greatest impacting factor in this study. This translated into a steep decline of photosynthetic efficiency, leaf hydration, and membrane fluidity and permeability. When water stress was coupled with O3, plants orchestrated cross-talk among ABA, proline, and sugar in fully-expanded mature leaves, partially leading to a premature senescence.
Highlights
Climate change, encompassing shifts in temperature, precipitation, and atmospheric composition, represents a moving target for plant acclimation and/or adaptation [1]
No injury was observed due to O3 alone, nor in WS/O3 + plants given that the symptoms were the same to those found in the WS/O3 − leaves
Weekly profiles of leaf gas exchanges confirm the main results observed with the imposition of prolonged and moderate water withholding [6]: (i) drought induced severe impairments of photosynthetic process; (ii) no further reductions were observed when O3 was added to drought; and (iii) stomata posed the predominant limitation to CO2 assimilation in both drought- and O3 -stress conditions, which corroborates the anisohydric behavior of Q. cerris [15,34]
Summary
Climate change, encompassing shifts in temperature, precipitation, and atmospheric composition, represents a moving target for plant acclimation and/or adaptation [1]. The Mediterranean basin is considered a global biodiversity hotspot [2], even though natural (i.e., increase in the average temperature, heat waves, drought), as well as anthropogenic factors, such as increased tropospheric ozone (O3 ), are expected to be harsher in this area in the near future [3]. Mediterranean plants have already adapted to climate change through morpho-anatomical, physiological, and molecular responses [4]. Progress has been made in understanding the effects of single stress factors on tree performance (e.g., drought and O3 ). Much remains to be elucidated on combined stresses, whose overall effect is far from being deducible from the combination of unifactorial plant responses [6]
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