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Ozone (O3) pollution poses a significant threat to global crop productivity, particularly for wheat, one of the most important staple foods. While bread wheat (Triticum aestivum) is unequivocally considered highly sensitive to O3, durum wheat (Triticum durum) was often found to be more tolerant. This study investigated the O3 dose–response relationships for durum wheat in the Mediterranean region, focusing mainly on grain yield losses, and utilizing the phytotoxic ozone dose (POD) metric to describe the intensity of the stressor. The results from two experiments with Open-Top Chambers performed in 2013 and 2014 on two relatively sensitive durum wheat cultivars confirmed that this wheat species is far more tolerant than bread wheat. The use of a local parameterization of a stomatal conductance model based on field measurements did not significantly improve the dose–response relationships obtained in comparison to the generic parameterization suggested by the Mapping Manual of the United Nations Economic Commission for Europe (UNECE). The POD6 critical level of 5 mmolO3 m−2 for 5% grain yield loss was remarkably higher than the one established for bread wheat with analogous experiments, highlighting that O3 risk assessments based on bread wheat may largely overestimate the damage in the Mediterranean region where durum wheat cultivation prevails. [ABSTRACT FROM AUTHOR]

In this study a comparison of the soil CO2 fluxes emitted from two maize (Zea mays L.) fields with the same soil type was performed. Each field was treated with a different tillage technique: conventional tillage (30 cm depth ploughing) and no-tillage. Measurements were performed in the Po Valley (Italy) from September to October 2012, covering both pre- and postharvesting conditions, by means of two identical systems based on automatic static soil chambers. Main results show that no-tillage technique caused higher CO2 emissions than conventional tillage (on average 2.78 and 0.79 μmol CO2 m−2 s−1, resp.). This result is likely due to decomposition of the organic litter left on the ground of the no-tillage site and thus to an increased microbial and invertebrate respiration. On the other hand, fuel consumption of conventional tillage technique is greater than no-tillage consumptions. For these reasons this result cannot be taken as general. More investigations are needed to take into account all the emissions related to the field management cycle.

Dry deposition is an important ozone sink that impacts ecosystem carbon and water cycling. Ozone dry deposition in forests is regulated by vertical transport, stomatal uptake, and non‐stomatal processes including chemical removal. However, accurate descriptions of these processes in deposition parameterizations are hindered by sparse observational constraints on individual sink terms. Here we quantify the contribution of canopy‐atmosphere turbulent exchange and chemical ozone removal by soil‐emitted nitric oxide (NO) to ozone deposition in a North‐Italian broadleaf deciduous forest. We apply a multi‐layer canopy exchange model to interpret campaign observations of nitrogen oxides (NOx = NO + NO2) and ozone exchange above and inside the forest canopy. Two state‐of‐science parameterizations of in‐canopy vertical diffusivity, based on above‐canopy wind speed or stability, do not reproduce the observed exchange suppressed by canopy‐top radiative heating, resulting in overestimated dry deposition velocities of 10%–19% during daytime. Applying observation‐derived vertical diffusivities in our simulations largely resolves this overestimation. Soil emissions are an important NOx source despite the observed high background NOx levels. Soil NOx emissions decrease the gradient between canopy and surface layer NOx mixing ratios, which suppresses simulated NOx deposition by 80% compared to a sensitivity simulation without soil emissions. However, a sensitivity analysis shows that the enhanced chemical ozone sink by reaction with soil‐emitted NO is offset by increased vertical ozone transport from aloft and suppressed dry deposition. Our results highlight the need for targeted observations of non‐stomatal ozone removal and turbulence‐resolving deposition simulations to improve quantification and model representation of forest ozone deposition. Plain Language Summary: Ozone is a harmful air pollutant that impacts human and ecosystem health. Ozone can be removed by forest ecosystems as a result of air transport into forests followed by plant ozone uptake or chemical removal, but quantifying these individual processes is difficult. We combine model simulations and treetop measurements to study the role of vertical forest‐atmosphere air transport and chemical ozone removal inside the forest. We find that our model can only reproduce surface ozone removal if we account for suppressed transport as derived from observations. The soil is a substantial source of nitric oxide (NO) that reacts with ozone. According to our analysis, the presence of a soil NO source does not lead to increased ozone removal because other ozone sinks are reduced. Our results suggest that individual ozone removal processes in forests can best be studied using targeted observations and models that better resolve forest‐atmosphere exchange. Key Points: We use a multi‐layer canopy‐atmosphere exchange model to interpret ozone flux observations inside and above a North‐Italian forestTwo state‐of‐science vertical exchange parameterizations do not capture in‐canopy stable stratification suppressing ozone depositionSoil nitric oxide emissions do not increase ozone deposition due to compensating effects by deposition and transport [ABSTRACT FROM AUTHOR]

A chlorophyll fluorescence (ChlF) assessment was carried out on oak seedlings (Quercus ilex L. Quercus pubescens Willd. Quercus frainetto Ten.) of Italian and Greek provenance, during the years 2017 and 2018, in a common garden in central Italy planted in 2017. This trial aimed to test the relative performances of the oak species in the perspective of assisted migration as part of the actions for the adaptation of forests to climate change. The assessment of the photosynthetic performance of the tree species included the analysis of the prompt chlorophyll fluorescence (PF) transient and the modulated reflection (MR) at 820 nm, leaf chlorophyll content, leaf gas exchange (net photosynthesis, stomatal conductance), plant growth (i.e. height) and mortality rate after 2 years from the beginning of the experiment. The assessment of the performance of the three oak species was carried out 'in vivo'. Plants were generated from seeds and exposed to several environmental factors, including changing seasonal temperature, water availability, and soil biological and physical functionality. The results of PF indicate a stable functionality of the photosynthetic system PSII (expressed as F V/ F M) across species and provenances and a decline in photochemistry functionality at the I–P phase (Δ V IP) in Q. frainetto , thus indicating a decline of the content of PSI in this species. This result was confirmed by the findings of MR analysis, with the speed of reduction and subsequent oxidation of PSI (V RED and V OX) strongly correlated to the amplitude of Δ V IP. The photosynthetic rates (net photosynthesis, P N) and growth were correlated with the parameters associated with PSI content and function, rather than those related to PSII. The low performance of Q. frainetto in the common garden seems to be related to early foliar senescence with the depletion of nitrogen, due to suboptimal climatic and edaphic conditions. Chlorophyll fluorescence allowed discrimination of populations of oak species and individuation of the less (or/and best) suitable species for future forest ecology and management purposes. [ABSTRACT FROM AUTHOR]

A 1-month field campaign of ozone (O3) flux measurements along a five-level vertical profile above, inside and below the canopy was run in a mature broadleaf forest of the Po Valley, northern Italy. The study aimed to characterize O3 flux dynamics and their interactions with nitrogen oxides (NOx) fluxes from the forest soil and the atmosphere above the canopy. Ozone fluxes measured at the levels above the canopy were in good agreement, thus confirming the validity of the constant flux hypothesis, while below-canopy O3 fluxes were lower than above. However, at the upper canopy edge O3 fluxes were surprisingly higher than above during the morning hours. This was attributed to a chemical O3 sink due to a reaction with the nitric oxide (NO) emitted from soil and deposited from the atmosphere, thus converging at the top of the canopy. Moreover, this mechanism was favored by the morning coupling between the forest and the atmosphere, while in the afternoon the fluxes at the upper canopy edge became similar to those of the levels above as a consequence of the in-canopy stratification. Nearly 80 % of the O3 deposited to the forest ecosystem was removed by the canopy by stomatal deposition, dry deposition on physical surfaces and by ambient chemistry reactions (33.3 % by the upper canopy layer and 46.3 % by the lower canopy layer). Only a minor part of O3 was removed by the understorey vegetation and the soil surface (2 %), while the remaining 18.2 % was consumed by chemical reaction with NO emitted from soil. The collected data could be used to improve the O3 risk assessment for forests and to test the predicting capability of O3 deposition models. Moreover, these data could help multilayer canopy models to separate the influence of ambient chemistry vs. O3 dry deposition on the observed fluxes. [ABSTRACT FROM AUTHOR]

Regional estimates of the effects of ozone pollution on forest growth depend on the availability of reliable injury functions that estimate a representative ecosystem response to ozone exposure. A number of such injury functions for forest tree species and forest functional types have recently been published and subsequently applied in terrestrial biosphere models to estimate regional or global effects of ozone on forest tree productivity and carbon storage in the living plant biomass. The resulting impacts estimated by these biosphere models show large uncertainty in the magnitude of ozone effects predicted. To understand the role that these injury functions play in determining the variability in estimated ozone impacts, we use the O-CN biosphere model to provide a standardised modelling framework. We test four published injury functions describing the leaf-level, photosynthetic response to ozone exposure (targeting the maximum carboxylation capacity of Rubisco (Vcmax) or net photosynthesis) in terms of their simulated whole-tree biomass responses against data from 23 ozone filtration/fumigation experiments conducted with young trees from European tree species at sites across Europe with a range of climatic conditions. Our results show that none of these previously published injury functions lead to simulated whole-tree biomass reductions in agreement with the observed dose-response relationships derived from these field experiments and instead lead to significant over- or underestimations of the ozone effect. By re-parameterising these photosynthetically based injury functions, we develop linear, plant-functional-typespecific dose-response relationships, which provide accurate simulations of the observed whole-tree biomass response across these 23 experiments. [ABSTRACT FROM AUTHOR]

During a two-year Open-Top Chamber experiment performed in 2012 and 2013, young trees of hornbeam ( Carpinus betulus L.) were exposed to four levels of ozone (O 3 ) (−40% of ambient O 3 in charcoal-filtered OTCs, −5% in non-filtered OTCs, +30% and +75% in O 3 -enriched OTCs) and two levels of Nitrogen (N) wet deposition (CoN = tap water and +N = tap water + 70 kg N ha −1  yr −1 ). Stomatal conductance at leaf level and growth parameters (stem diameter and height) were measured during the two years of experimentation, while at the end of each growing season plants dry biomass partition between the roots and the stem was assessed. Hornbeam plants resulted highly tolerant to O 3 , which did not cause any significant negative effects on the biomass yield of plants grown in CoN conditions. Furthermore, the dose-response relationships based on the Phytotoxic Ozone Dose (POD 1 ) indicated that the stem biomass increased under high levels of O 3 (+1.48% per 1 mmol O 3  m −2 absorbed by CoN plant), while root biomass was not affected. Nitrogen alone caused a general increase of total biomass in both years of the experiment (+14.8% and +38.1% on average in 2012 and 2013, respectively). However, in 2013 plants subject to the highest level of O 3 showed an opposite behavior, with a −11% decrease of total biomass in +N conditions. Ozone and Nitrogen in combination caused a statistically significant negative effect on the stem biomass and stem diameter of plants. Dose-response relationships based on POD 1 for plants in +N conditions revealed significant linear regressions for stem, roots and total biomass, which decreased by −1.04%, −0.80% and −0.92% for each mmol m −2 of O 3 absorbed, respectively. These results show that on a long-term scale, an increase of N wet deposition could significantly modify C. betulus response to O 3 stress, playing a potential role in the risk assessment of O 3 impact on the growth of this species. [ABSTRACT FROM AUTHOR]

Regional estimates of the effects of ozone pollution on forest growth depend on the availability of reliable damage functions that estimate a representative ecosystem response to ozone exposure. A number of such damage functions for forest tree species and forest functional types have recently been published and subsequently applied in terrestrial biosphere models to estimate regional or global effects of ozone on forest tree productivity and carbon storage in the living plant biomass. The resulting impacts estimated by these biosphere models show large uncertainty in the magnitude of ozone effects predicted. To understand the role that these damage functions play in determining the variability of estimated ozone impacts, we use the O-CN biosphere model to provide a standardised modelling framework. We test four published damage functions describing the leaf-level, photosynthetic response to ozone exposure (targeting Vcmax or net photosynthesis) in terms of their simulated whole-tree biomass responses against field data from 23 ozone filtration/fumigation experiments conducted with European tree species at sites across Europe with a range of climatic conditions. Our results show that none of these previously published damage functions lead to simulated whole-tree biomass reductions in agreement with the observed dose-response relationships derived from these field experiments, and instead lead to significant over- / or underestimations of the ozone effect. By re-parameterising these photosynthetic based damage functions we develop linear, plant functional type specific dose-response relationships, which provide accurate simulations of the observed whole-tree biomass response across these 23 experiments. [ABSTRACT FROM AUTHOR]

In the framework of the European FP7 project ECLAIRE a joint field campaign was run in Marmirolo, in the northern part of the Italy, one of the most polluted areas in Europe due to intense industrial activities and peculiar climate conditions promoting high ozone formation by photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds. The studied ecosystem is a mixed oak-hornbeam forest and the aim of this field campaign was to investigate the processes regulating the gas exchange between the forest and the atmosphere with a focus on ozone flux measurements and the interaction with reactive gases. Measurements were run on a 40 m tower equipped with sonic anemometers and fast ozone analyzers for eddy covariance at five different heights: one at canopy height, two above canopy and two below canopy. NO fluxes were measured above canopy and NOx fluxes were measured with a dynamic chamber system at the soil level. Ozone fluxes measured at different levels above the canopy showed a good agreement between each other, while fluxes at 24 m were surprisingly higher than the above ones. In this paper we discuss the possible reasons for this discrepancies shedding light on the role of NOx and of the coupling between forest and atmosphere will be explained. A partition of the ozone fluxes will be shown too to identify the most relevant sinks in the soil-plant continuum. [ABSTRACT FROM AUTHOR]