Giacomo Alessandro Gerosa

New flux based dose–response relationships for ozone for European forest tree species

To derive O3 dose-response relationships (DRR) for five European forest trees species and broadleaf deciduous and needleleaf tree plant functional types (PFTs), phytotoxic O3 doses (PODy) were related to biomass reductions. PODy was calculated using a stomatal flux model with a range of cut-off thresholds (y) indicative of varying detoxification capacities. Linear regression analysis showed that DRR for PFT and individual tree species differed in their robustness. A simplified parameterisation of the flux model was tested and showed that for most non-Mediterranean tree species, this simplified model led to similarly robust DRR as compared to a species- and climate region-specific parameterisation. Experimentally induced soil water stress was not found to substantially reduce PODy, mainly due to the short duration of soil water stress periods. This study validates the stomatal O3 flux concept and represents a step forward in predicting O3 damage to forests in a spatially and temporally varying climate.

Nutritional Traits of Bean (Phaseolus vulgaris) Seeds from Plants Chronically Exposed to Ozone Pollution

The effect of chronic exposure to ozone pollution on nutritional traits of bean ( Phaseolus vulgaris L. cv. Borlotto Nano Lingua di Fuoco) seeds from plants grown in filtered and nonfiltered open-top chambers (OTCs) has been investigated. Results showed that, among seed macronutrients, ozone significantly raised total lipids, crude proteins, and dietary fiber and slightly decreased total free amino acid content, although with a significant reduction of asparagine, lysine, valine, methionine, and glycine, compensated by a conspicuous augmentation of ornithine and tryptophan. Phytosterol analysis showed a marked increase of beta-sitosterol, stigmasterol, and campesterol in seeds collected from nonfiltered OTCs. With regard to secondary metabolites, ozone exposure induced a slight increase of total polyphenol content, although causing a significant reduction of some flavonols (aglycone kaempferol and its 3-glucoside derivative) and hydroxycinnamates (caffeic, p-coumaric, and sinapic acids). Total anthocyanins decreased significantly, too. Nevertheless, ozone-exposed seeds showed higher antioxidant activity, with higher Trolox equivalent antioxidant capacity (TEAC) values than those measured in seeds collected from filtered air.

Comparison of seasonal variations of ozone exposure and fluxes in a Mediterranean Holm oak forest between the exceptionally dry 2003 and the following year

Ozone and energy fluxes have been measured using the eddy covariance technique, from June to December 2004 in Castelporziano near Rome (Italy), and compared to similar measurements made in the previous year. The studied ecosystem consisted in a typical Mediterranean Holm oak forest. Stomatal fluxes have been calculated using the resistance analogy and by inverting the Penmann-Monteith equation. Results showed that the average stomatal contribution accounts for 42.6% of the total fluxes. Non-stomatal deposition proved to be enhanced by increasing leaf wetness and air humidity during the autumnal months. From a comparison of the two years, it can be inferred that water supply is the most important limiting factor for ozone uptake and that prolonged droughts alter significantly the stomatal conductance, even 2 months after the soil water content is replenished. Ozone exposure, expressed as AOT40, behaves similarly to the cumulated stomatal flux in dry conditions whereas a different behaviour for the two indices appears in wet autumnal conditions. A difference also occurs between the two years.

Validation of the stomatal flux approach for the assessment of ozone visible injury in young forest trees. Results from the TOP (transboundary ozone pollution) experiment at Curno, Italy

This paper summarises some of the main results of a two-year experiment carried out in an Open-Top Chambers facility in Northern Italy. Seedlings of Populus nigra, Fagus sylvatica, Quercus robur and Fraxinus excelsior have been subjected to different ozone treatments (charcoal-filtered and non-filtered air) and soil moisture regimes (irrigated and non-irrigated plots). Stomatal conductance models were applied and parameterised under South Alpine environmental conditions and stomatal ozone fluxes have been calculated. The flux-based approach provided a better performance than AOT40 in predicting the onset of foliar visible injuries. Critical flux levels, related to visible leaf injury, are proposed for P. nigra and F. sylvatica (ranging between 30 and 33 mmol O(3) m(-2)). Soil water stress delayed visible injury appearance and development by limiting ozone uptake. Data from charcoal-filtered treatments suggest the existence of an hourly flux threshold, below which may occur a complete ozone detoxification.

Sensitivity analysis of a parameterization of the stomatal component of the DO3SE model for Quercus ilex to estimate ozone fluxes

A sensitivity analysis of a proposed parameterization of the stomatal conductance (g(s)) module of the European ozone deposition model (DO(3)SE) for Quercus ilex was performed. The performance of the model was tested against measured g(s) in the field at three sites in Spain. The best fit of the model was found for those sites, or during those periods, facing no or mild stress conditions, but a worse performance was found under severe drought or temperature stress, mostly occurring at continental sites. The best performance was obtained when both f(phen) and f(SWP) were included. A local parameterization accounting for the lower temperatures recorded in winter and the higher water shortage at the continental sites resulted in a better performance of the model. The overall results indicate that two different parameterizations of the model are needed, one for marine-influenced sites and another one for continental sites.

Chlorophyll a fluorescence analysis along a vertical gradient of the crown in a poplar (Oxford clone) subjected to ozone and water stress

An experiment in open-top chambers was carried out in summer 2008 at Curno (Northern Italy) in order to study the effects of ozone and mild water stress on poplar cuttings (Oxford clone). In this experiment direct fluorescence parameters (JIP-test) were measured in leaves from different sections of the crown (L: lower; M: medium; U: upper parts of the crown). The parameters considered were calculated at the different steps of the fluorescence transient, and include maximum quantum yield efficiency in the dark-adapted state (F(v)/F(M)); the L-band, at 100 ∝ s, that expresses the stability of the tripartite system reaction centre-harvesting light complex-core antenna; the K-band, at 300 ∝ s, that expresses the efficiency of the oxygen-evolving complex; the J-phase, at 2 ms, that expresses the efficiency with which a trapped exciton can move an electron into the electron transport chain from Q(A)(-) to the intersystem electron acceptors; the IP-phase, which expresses the efficiency of electron transport around the photosystem 1 (PSI) to reduce the final acceptors of the electron transport chain, i.e., ferredoxin and NADP; and finally the performance index total (PItot) for energy conservation from photons absorbed by PSII to the reduction flux of PSI end acceptors. The main results are: (i) different dynamics were observed between leaves in the lower section, whose PItot decreased over time, and those in the upper sections in which it increased, with a dynamic connected to the leaf age; (ii) ozone depressed all the considered fluorescence parameters in basal leaves of well-watered plants, while it had little or no damaging effect on medium-level or upper-section leaves; (iii) PItot and IP-phase increased in upper leaves of plants subjected to ozone stress, as well as the net photosynthesis; (iv) water stress increased PItot of leaves in all levels of the crown. The results suggest that ozone-damaged poplar plants compensate, at least partially, for the loss of photosynthesis with higher photosynthetic rates in young leaves (in the upper section of the crown), more efficient to fix carbon.

Ozone fluxes and foliar injury development in the ozone-sensitive poplar clone Oxford (Populus maximowiczii × Populus berolinensis): a dose–response analysis

Between 2004 and 2005 a combined open plot and open-top chamber (OTC) experiment was carried out at Curno (Northern Italy) with cuttings of the poplar clone Oxford (Populus maximowiczii Henry x Populus berolinensis Dippel) grown in open plots (OPs, ambient air), charcoal-filtered OTCs (CF, ozone concentration reduced to 50% of ambient) or non-filtered OTCs (NF, ozone concentration reduced to 95% of ambient). Plants in half of the chambers were kept well-watered (WET), and plants in the remaining chambers were not watered (DRY). The onset and development of visible foliar injury and the stomatal conductance to water vapor (g(w)) were assessed during each growing season. A stomatal conductance model was parameterized by the Jarvis approach, allowing the calculation of ozone stomatal fluxes of plants in each treatment. The pattern of visible symptoms was analyzed in relation to ozone exposure (AOT40, accumulated ozone over a threshold of 40 ppb) and accumulated ozone stomatal fluxes (AF(ST)). Symptoms became visible at an AOT40 between 9584 and 13,110 ppb h and an AF(ST) between 27.85 and 30.40 mmol O(3) m(-2). The development of symptoms was more widespread and faster in plants in WET plots than in DRY plots. A slightly higher dose of ozone was required to cause visible symptoms in plants in DRY plots than in WET plots. By the end of each growing season, plants in the CF OTCs had absorbed a high dose of ozone (31.60 mmol O(3) m(-2) in 2004 and 32.83 mmol O(3) m(-2) in 2005, for WET plots), without developing any visible symptoms. A reliable dose-response relationship was defined by a sigmoidal curve model. The shape of this curve expresses the change in leaf sensitivity and physiologic state over a prolonged ozone exposure. After the appearance of the first symptoms, foliar injury increased more rapidly than the increases in ozone exposure and ozone absorbed dose; however, when the injury incidence reached 75%, the plant response declined.

Ecological impacts of atmospheric pollution and interactions with climate change in terrestrial ecosystems of the mediterranean basin: Current research and future directions

Mediterranean Basin ecosystems, their unique biodiversity, and the key services they provide are currently at risk due to air pollution and climate change, yet only a limited number of isolated and geographically-restricted studies have addressed this topic, often with contrasting results. Particularities of air pollution in this region include high O3 levels due to high air temperatures and solar radiation, the stability of air masses, and dominance of dry over wet nitrogen deposition. Moreover, the unique abiotic and biotic factors (e.g., climate, vegetation type, relevance of Saharan dust inputs) modulating the response of Mediterranean ecosystems at various spatiotemporal scales make it difficult to understand, and thus predict, the consequences of human activities that cause air pollution in the Mediterranean Basin. Therefore, there is an urgent need to implement coordinated research and experimental platforms along with wider environmental monitoring networks in the region. In particular, a robust deposition monitoring network in conjunction with modelling estimates is crucial, possibly including a set of common biomonitors (ideally cryptogams, an important component of the Mediterranean vegetation), to help refine pollutant deposition maps. Additionally, increased attention must be paid to functional diversity measures in future air pollution and climate change studies to establish the necessary link between biodiversity and the provision of ecosystem services in Mediterranean ecosystems. Through a coordinated effort, the Mediterranean scientific community can fill the above-mentioned gaps and reach a greater understanding of the mechanisms underlying the combined effects of air pollution and climate change in the Mediterranean Basin.

Short and long term photosynthetic adjustments in sun and shade leaves of Fagus sylvatica L., investigated by fluorescence transient (FT) analysis

Abstract Fluorescence transient (FT) analysis (fast kinetics) was carried out on sun and shade leaves of beech seedlings in an experimental field at Curno (North Italy), during the 2008 growing season (June–August). The aim of the research was to determine: (1) morphology in sun leaves as long term acclimation to high light; (2) short term responses to high light, i.e. during the course of the day; (3) evolution of responses during the growing season and the ageing process. Sun leaves differ from shade leaves by their lower trapping capacity (expressed by the ratio FV/FM) and higher capacity to reduce end acceptors beyond PSI (expressed by phase I–P of the FT). These features were assessed at pre-dawn, when the entire plant is fully dark-adapted. Short term responses (differences between midday and pre-dawn assessments) occur especially in sun leaves, indicating that the photosynthetic machinery reacts to the high excitation pressure by increasing photochemical and non-photochemical de-excitation processes. Other responses concern the inactivation of the oxygen evolving system and a stability loss of the tripartite system reaction centre (RC) – harvesting light complex – core antenna, expressed by the onset of K and L-bands at midday. Sun leaves are well acclimated to high light from a structural and functional point of view, however, the irradiance at midday provokes conditions of instability in the photosynthetic machinery, possibly through reactive oxygen species (ROS) production at both PSII and PSI sides. The temporal patterns across the growing season indicate the progression of senescence processes, that are more pronounced in sun leaves which present a permanent (chronic) condition of photoinhibition. Differences between sun and shade leaves decrease over time.

Responses to ozone on Populus "Oxford" clone in an open top chamber experiment assessed before sunrise and in full sunlight

The effects of ambient levels of ozone and summer drought were assessed on a poplar clone (Populus maximowiczii Henry X P. × berolinensis Dippel — Oxford clone) in an open top chamber experiment carried out at the Curno facilities (Northern Italy). Chlorophyll (Chl) a fluorescence parameters (from both modulated and direct fluorescence) were assessed at different hours of the day (predawn, morning, midday, afternoon, and evening), from June to August 2008. This paper compares the results from predawn (PD, before sunrise) and afternoon (AN, in full sunlight) measurements, in order to evaluate the role of high sunlight as a factor influencing responses to ozone stress. Sunlight affected the maximum quantum yield of primary photochemistry (decrease of Fv/Fm) thus indicating photoinhibition. The effective quantum yield (ΦPSII) and the photochemical quenching (qP) were enhanced in the afternoon with respect to the predawn, whereas the nonphotochemical quenching (NPQ) was reduced. The effect of ozone was detected with fluorescence on well watered plants in the first week of July, before the onset of visible symptoms. As far as Fv/Fm are concerned, the differences between ozone-treated and control plants were statistically significant in the predawn, but not in the afternoon. Ozone exerted only minor effects on drought exposed plants because of the reduced stomatal ozone uptake, but effects on the IP phase of the fluorescence transient were observed also in drought-stressed plants.