• We hypothesized that poplar can be useful for the extraction of zinc (Zn) from contaminated soils and water. However, the physiological response and the base of tolerance of poplar plants to th...

Forest functionality and productivity are directly related to canopy light interception and can be affected by potential damage from high irradiance. However, the mechanisms by which leaves adapt to the variable light environments along the multilayer canopy profile are still poorly known. We explored the leaf morphophysiological and metabolic responses to the natural light gradient in a pure European beech (Fagus sylvatica L.) forest at three different canopy heights (top, middle and bottom). Structural adjustment through light-dependent modifications in leaf mass per area was the reason for most of the variations in photosynthetic capacity. The different leaf morphology along the canopy influenced nitrogen (N) partitioning, water- and photosynthetic N-use efficiency, chlorophyll (Chl) fluorescence and quali-quantitative contents of photosynthetic pigments. The Chl a to Chl b ratio and the pool of xanthophyll-cycle pigments (VAZ) increased at the highest irradiance, as well as lutein and β-carotene. The total pool of ascorbate and phenols was higher in leaves of the top and middle canopy layers when compared with the bottom layer, where the ascorbate peroxidase was relatively more activated. The non-photochemical quenching was strongly and positively related to the VAZ/(Chl a + b) ratio, while Chl a/Chl b was related to the photochemical efficiency of photosystem II. Along the multilayer canopy profile, the high energy dissipation capacity of leaves was correlated to an elevated redox potential of antioxidants. The middle layer gave the most relevant contribution to leaf area index and carboxylation capacity of the canopy. In conclusion, a complex interplay among structural, physiological and biochemical traits drives the dynamic leaf acclimation to the natural gradients of variable light environments along the tree canopy profile. The relevant differences observed in leaf traits within the canopy positions of the beech forest should be considered for improving estimation of carbon fluxes in multilayer canopy models of temperate forests.

Increasing global background concentrations of tropospheric ozone (O₃) are expected to affect both crops and forest ecosystems negatively. The phytotoxic effects of O₃ are mainly associated with the O₃-induced production of reactive oxygen species (ROS) in excess of the ability of the plant to maintain ROS below the tolerance threshold. It is the balance between O₃ uptake and cellular antioxidant potential that determines O₃ effects on vegetation. The greater sensitivity to ambient O₃ exposure (60 nl l⁻¹ O₃, 15 days, 5 h a day) of poplar clone Eridano (Populus deltoides × maximowiczii) compared with clone I-214 (P. × euramericana) was reflected in a lower photosynthetic efficiency, higher stomatal conductance and hydrogen peroxide (H₂O₂) accumulation and more pronounced leaf tissue membrane injury in Eridano than in I-214. We checked if the differences in clonal responses to O₃ fumigation were related to differing capacities for antioxidant defense and phenylpropanoid metabolism and found that the increases in foliar ascorbate and phenolic concentrations and phenylpropanoid metabolism in Eridano were insufficient to counteract H₂O₂ accumulation and the consequent oxidative stress. This was probably because the higher influx of O₃ into Eridano leaves compared with I-214 leaves resulted in a lower potential detoxification capacity per unit of O₃ influx.