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Abstract: Cultivation techniques in the nursery aimed to improve tolerance to abiotic stresses after planting in the landscape may have great ecological value. Here we tested the hypothesis that the irradiance at which plants grow in the nursery may impact on their responses to a subsequent drought stress. Measurements of relevant morpho-anatomical, physiological and biochemical traits were conducted in Fraxinus ornus, a member of the Oleaceae family of increasing interest as an urban tree. Leaves developed under moderate shade displayed a lower ability to preserve water balance, thus suffering from a greater decline in net CO2 assimilation than leaves acclimated to full sunlight, when subsequently exposed to drought stress. Shaded leaves also displayed an inherently lower capacity to dissipate excess radiant energy through nonphotochemical quenching, thus suffering from greater oxidative damage than sun leaves under drought. These results indicate that sunlight irradiance at which container-grown ash trees grow in the nursery may tightly affect the tolerance to subsequent drought stress. This may have great value for enhancing the establishment of container-grown plants in the landscape, as fully leaved plants may suffer from severe drought stress during early stages of acclimation in the landscape. [Copyright &y& Elsevier]

Two bean cultivars with different sensitivity to ozone, i.e. the O3-sensitive Cannellino and the O3-tolerant Top Crop, were exposed to acute O3-stress (165nLL−1) with the aim of evaluating physiological and biochemical traits that may confer O3-tolerance. Stomatal conductance was smaller and the ability to dissipate excess energy, via regulated and unregulated nonphotochemical quenching mechanisms was greater in Top Crop than in Cannellino. These morphological and physiological-traits allowed the O3-tolerant cultivar to compensate for the light-induced declines in ΦPSII, to preserve photosystem II from excitation-energy, and likely to prevent the generation of ROS to a superior degree than the O3-sensitive cultivar. Furthermore, the potential capacities to reducing the superoxide anion and H2O2 were significantly greater in Top Crop than in Cannellino. These findings are consistent with the early accumulation of H2O2, the almost complete disruption of cell structure, and irreversible damages to the photosynthetic apparatus observed in the O3-sensitive cultivar. [Copyright &y& Elsevier]

The presence of Psidium guajava in polluted environments has been reported in recent studies, suggesting that this species has a high tolerance to the metal stress. The present study aims at a physiological characterization of P. guajava response to high nickel (Ni) concentrations in the root-zone. Three hydroponic experiments were carried out to characterize the effects of toxic Ni concentrations on morphological and physiological parameters of P. guajava , focusing on Ni-induced damages at the root-level and root ion fluxes. With up to 300 μM NiSO 4 in the root-zone, plant growth was similar to that in control plants, whereas at concentrations higher than 1000 μM NiSO 4 there was a progressive decline in plant growth and leaf gas exchange parameters; this occurred despite, at all considered concentrations, plants limited Ni 2+ translocation to the shoot, therefore avoiding shoot Ni 2+ toxicity symptoms. Maintenance of plant growth with 300 μM Ni 2+ was associated with the ability to retain K + in the roots meanwhile 1000 and 3000 μM NiSO 4 led to substantial K + losses. In this study, root responses mirror all plant performances suggesting a direct link between root functionality and Ni 2+ tolerance mechanisms and plant survival. Considering that Ni was mainly accumulated in the root system, the potential use of P. guajava for Ni 2+ phytoextraction in metal-polluted soils is limited; nevertheless, the observed physiological changes indicate a good Ni 2+ tolerance up to 300 μM NiSO 4 suggesting a potential role for the phytostabilization of polluted soils. [ABSTRACT FROM AUTHOR]