Variations in physiological and biochemical traits of oak seedlings grown under drought and ozone stress

Abstract

Despite the huge biodiversity characterizing the Mediterranean environment, environmental constraints, such as high sunlight and high temperatures alongside with dry periods, make plant survival hard. In addition, high irradiance leads to increasing ozone (O3 ) concentrations in ambient air. In this era of global warming, it is necessary to understand the mechanisms that allow native species to tolerate these environmental constraints and how such mechanisms interact. Three Mediterranean oak species (Quercus ilex, Quercus pubescens and Quercus cerris) with different features (drought tolerant, evergreen or deciduous species) were selected to assess their biometrical, physiological and biochemical responses under drought and/or O3 stress (80-100 nl l(-1) of O3 for 5 h day(-1) for 77 consecutive days). Leaf visible injury appeared only under drought stress (alone or combined with O3 ) in all three species. Drought × O3 induced strong reductions in leaf dry weight in Q. pubescens and Q. cerris (-70 and -75%, respectively). Alterations in physiological (i.e. decrease in maximum carboxylation rate) and biochemical parameters (i.e. increase in proline content and build-up of malondialdehyde by-products) occurred in all the three species, although drought represented the major determinant. Quercus ilex and Q. pubescens, which co-occur in dry environments, were more tolerant to drought and drought × O3 . Quercus ilex was the species in which oxidative stress occurred only when drought was applied with O3 . High plasticity at a biochemical level (i.e. proline content) and evergreen habitus are likely on the basis of the higher tolerance of Q. ilex.

Cross-Talk between Physiological and Metabolic Adjustments Adopted by Quercus cerris to Mitigate the Effects of Severe Drought and Realistic Future Ozone Concentrations

“…The O 3 concentration applied in this experiment was known to induce changes in the main photosynthetic parameters in Turkey oak plants subjected to prolonged exposure [6]. The entire methodology of O 3 exposure has been performed according to Lorenzini et al [24].…”

“…To date, progress has been made in understanding the effects of single stress factors on tree performance (e.g., drought and O 3 ). However, much remains to be elucidated on combined stresses, whose overall effect is far from being deducible from the combination of unifactorial plant responses [6].…”

“…Both drought and O 3 have the potential to cause (i) a reduction of plant growth and photosynthesis, (ii) stomatal closure, (iii) cell dehydration, (iv) excess of excitation energy with massive production of reactive oxygen species (ROS), and, eventually, (v) leaf necrosis [6]. However, the simultaneous imposition of O 3 and drought can induce responses considerably different from those observed when each stressor is applied independently.…”

“…In a previous experiment [6], the behavior of Q. cerris saplings exposed to moderate drought and/or O 3 throughout the whole summer season was evaluated. The tolerance of the Mediterranean sympatric Q. ilex (evergreen), Q. pubescens (deciduous), and Q. cerris (deciduous) species to these environmental conditions was compared, focusing on their different phenotypic plasticity.…”

“…The tolerance of the Mediterranean sympatric Q. ilex (evergreen), Q. pubescens (deciduous), and Q. cerris (deciduous) species to these environmental conditions was compared, focusing on their different phenotypic plasticity. The present work was performed to test if a shorter and severe drought might further limit O 3 uptake, thereby inducing different responses of Q. cerris, the species that had shown to be the least drought tolerant [6]. In particular, here we would like to analyze, in greater depth, the leaf-intrinsic and osmotic adjustments adopted by Q. cerris.…”