Effetti di ozono e carenza idrica su fotosintesi e accrescimento in cloni di pioppo

High concentrations of tropospheric ozone and limited water availability adversely affect plant productivity and growth. Ozone critical concentrations are frequently exceeded and a general trend toward increasing background ozone levels is expected. Ozone is already an important part of the chemical climate with potentially significant implications for the response of ecological system to changes in temperature and precipitation patterns. Ozone and drought are environmental factors that can act simultaneously on plant physiology, with antagonistic action (both factors lead the stomata closure, with reduce ozone uptake and a water loss transpiration), and synergic effects (produced a strong pressure oxidation within the leaf tissues). Growth reduction is considered one of the most important response indicator in trees subjected to ozone exposure. Growth reduction is an overall and integrated physiological response to functional disturbances, in particular to those affecting photosynthesis. The most harmful ecological effect of ozone is that, by reducing growth, it also reduces carbon fixing, which makes forests less effective in protecting themselves against climate change. The effects of ozone and drought have been detected in two open-top chambers (OTCs) experiment at the facility of Curno (Northen Italy) in 2008 and 2009. In the first year, plants of the poplar clone Populus maximowiczii Henry x P. x berolinensis Dippel (Oxford clone), grown in pots, were exposed at two ozone levels (50% ambient ozone in charcoal-filtered OTCs, CF, and 95% ambient ozone in non-filtered OTCs, NF) and with two water soil regimes (well-water, WET, and non-watered, DRY). Physiological measures (net photosynthesis, stomatal conductance, chlorophyll a fluorescence, leaf water content, carbon and oxygen isotopic analysis) and biomass (above-ground and root biomass) have been carried on 1 year old seedlings during and at the end of the vegetation season. In the second experiment, we investigated the acclimation process in relation to stress in Populus maximowiczii Henry x P. x berolinensis Dippel (Oxford clone) and in Populus nigra cv. Jean Pourtet. The experiment comprised three water soil regimes (well-watered, W1, watered, W2 and dry, W3, with, respectively, 60% and 20% of water availability respect to W1). The plants were grown within the OTCs NF and CF. Physiological measures (net photosynthesis, stomatal conductance, chlorophyll a fluorescence, leaf water content, carbon and oxygen isotopic analysis) were have been carried to analyze the plant responses to episodic water stress during the season. The effects on growth were detected at the end of experiment. The water shortage was revealed as the main factor influencing the photosynthetic efficiency and growth of plants. Effects of ozone were detected on specific features of photosynthetic apparatus and on the leaf and root biomass. The comparison of the two clones, Oxford clone showed a drastically reduction of net photosynthesis and of stomatal conductance at the beginnig of water stress, while in P. nigra the reduction of the gas exchange was more gradual. Differences in growth between the two clones were not significant, although P. nigra showed greater sensitivity to ozone in term of leaf symptoms. We confirmed the sensibility of poplar clones to ozone, with effects on biomass production, allocation of resources and growth