Reading tea leaves worldwide: Decoupled drivers of initial litter decomposition mass-loss rate and stabilization

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models.

Detection and attribution of an anomaly in terrestrial photosynthesis in Europe during the COVID-19 lockdown

Carbon dioxide (CO2) uptake by plant photosynthesis, referred to as gross primary production (GPP) at the ecosystem level, is sensitive to environmental factors, including pollutant exposure, pollutant uptake, and changes in the scattering of solar shortwave irradiance (SWin) - the energy source for photosynthesis. The 2020 spring lockdown due to COVID-19 resulted in improved air quality and atmospheric transparency, providing a unique opportunity to assess the impact of air pollutants on terrestrial ecosystem functioning. However, detecting these effects can be challenging as GPP is influenced by other meteorological drivers and management practices. Based on data collected from 44 European ecosystem-scale CO2 flux monitoring stations, we observed significant changes in spring GPP at 34 sites during 2020 compared to 2015-2019. Among these, 14 sites showed an increase in GPP associated with higher SWin, 10 sites had lower GPP linked to atmospheric and soil dryness, and seven sites were subjected to management practices. The remaining three sites exhibited varying dynamics, with one experiencing colder and rainier weather resulting in lower GPP, and two showing higher GPP associated with earlier spring melts. Analysis using the regional atmospheric chemical transport model (LOTOS-EUROS) indicated that the ozone (O3) concentration remained relatively unchanged at the research sites, making it unlikely that O3 exposure was the dominant factor driving the primary production anomaly. In contrast, SWin increased by 9.4 % at 36 sites, suggesting enhanced GPP possibly due to reduced aerosol optical depth and cloudiness. Our findings indicate that air pollution and cloudiness may weaken the terrestrial carbon sink by up to 16 %. Accurate and continuous ground-based observations are crucial for detecting and attributing subtle changes in terrestrial ecosystem functioning in response to environmental and anthropogenic drivers.

Temperature dependence of emission of volatile organic compounds (VOC) from litters collected in two Mediterranean ecosystems determined before the flaming phase of biomass burning

Fire represents a major threat to Mediterranean terrestrial ecosystems because of the high temperatures reached during summer. While massive loads of organic, inorganic compounds and particulate matter are known to be emitted into the atmosphere from forest wildfires, less is known about the emission from vegetation surrounding fires where air temperatures higher than 100 °C can be reached. Little information exists on the emission from dead vegetation accumulated as litter over forest soils, from which fires often starts. In this study, the response of litter to heatwaves generated by nearby fires was investigated under controlled conditions. Litter samples collected in a Mediterranean maquis and a Holm oak stand during summer were placed in an enclosure flushed with a continuous flow of air, the temperature of the enclosure was progressively risen to 125 °C, until some smog developed but no flaming occurred. The gas from the enclosure was analysed for the content of CO2, H2O, and volatile organic compounds (VOC) to assess the dependence of emission from the air temperature. VOC emission was continuously determined by Proton-Transfer-Reaction mass spectrometry with time of flight (PTR-TOF-MS). Data obtained were complemented with those obtained by collecting VOC on traps that were later analysed by Gas chromatography-mass spectrometry (GC-MS). Results provided useful information to understand the emission mechanism of VOC and other gases from dead vegetation present in the litter of two Mediterranean ecosystems, both dominated by evergreen vegetation species. The study demonstrated that low molecular weight VOC and aromatic hydrocarbons (arenes) produced mostly by thermal oxidation of the wood biopolymers are emitted in addition to isoprenoids typically associated to storage organs and photosynthetic pathway. Moreover, our results support parameterization of litter VOC emission processes in air quality models.

Monitoring of carbon-water fluxes at Eurasian meteorological stations using random forest and remote sensing

Simulating the carbon-water fluxes at more widely distributed meteorological stations based on the sparsely and unevenly distributed eddy covariance flux stations is needed to accurately understand the carbon-water cycle of terrestrial ecosystems. We established a new framework consisting of machine learning, determination coefficient (R2), Euclidean distance, and remote sensing (RS), to simulate the daily net ecosystem carbon dioxide exchange (NEE) and water flux (WF) of the Eurasian meteorological stations using a random forest model or/and RS. The daily NEE and WF datasets with RS-based information (NEE-RS and WF-RS) for 3774 and 4427 meteorological stations during 2002-2020 were produced, respectively. And the daily NEE and WF datasets without RS-based information (NEE-WRS and WF-WRS) for 4667 and 6763 meteorological stations during 1983-2018 were generated, respectively. For each meteorological station, the carbon-water fluxes meet accuracy requirements and have quasi-observational properties. These four carbon-water flux datasets have great potential to improve the assessments of the ecosystem carbon-water dynamics.

Leaf-level coordination principles propagate to the ecosystem scale

Fundamental axes of variation in plant traits result from trade-offs between costs and benefits of resource-use strategies at the leaf scale. However, it is unclear whether similar trade-offs propagate to the ecosystem level. Here, we test whether trait correlation patterns predicted by three well-known leaf- and plant-level coordination theories - the leaf economics spectrum, the global spectrum of plant form and function, and the least-cost hypothesis - are also observed between community mean traits and ecosystem processes. We combined ecosystem functional properties from FLUXNET sites, vegetation properties, and community mean plant traits into three corresponding principal component analyses. We find that the leaf economics spectrum (90 sites), the global spectrum of plant form and function (89 sites), and the least-cost hypothesis (82 sites) all propagate at the ecosystem level. However, we also find evidence of additional scale-emergent properties. Evaluating the coordination of ecosystem functional properties may aid the development of more realistic global dynamic vegetation models with critical empirical data, reducing the uncertainty of climate change projections.

Cell wall ester modifications and volatile emission signatures of plant response to abiotic stress

Growth suppression and defence signalling are simultaneous strategies that plants invoke to respond to abiotic stress. Here, we show that the drought stress response of poplar trees (Populus trichocarpa) is initiated by a suppression in cell wall derived methanol (MeOH) emissions and activation of acetic acid (AA) fermentation defences. Temperature sensitive emissions dominated by MeOH (AA/MeOH <30%) were observed from physiologically active leaves, branches, detached stems, leaf cell wall isolations and whole ecosystems. In contrast, drought treatment resulted in a suppression of MeOH emissions and strong enhancement in AA emissions together with volatiles acetaldehyde, ethanol, and acetone. These drought-induced changes coincided with a reduction in stomatal conductance, photosynthesis, transpiration, and leaf water potential. The strong enhancement in AA/MeOH emission ratios during drought (400%-3500%) was associated with an increase in acetate content of whole leaf cell walls, which became significantly ¹³ C₂ -labelled following the delivery of ¹³ C₂ -acetate via the transpiration stream. The results are consistent with both enzymatic and nonenzymatic MeOH and AA production at high temperature in hydrated tissues associated with accelerated primary cell wall growth processes, which are downregulated during drought. While the metabolic source(s) require further investigation, the observations are consistent with drought-induced activation of aerobic fermentation driving high rates of foliar AA emissions and enhancements in leaf cell wall O-acetylation. We suggest that atmospheric AA/MeOH emission ratios could be useful as a highly sensitive signal in studies investigating environmental and biological factors influencing growth-defence trade-offs in plants and ecosystems.

POS0825 CLINICAL CHARACTERISTICS AND TREATMENT MANAGEMENT OF NON-INFECTIOUS SCLERITIS WITH CORTICOSTEROID-SPARING THERAPY. A RETROSPECTIVE STUDY FROM A TERTIARY EYE CARE CENTER

Background

Non-infectious scleritis refers to a rare and sight-threatening scleral inflammation. An association with an underlying systemic disease is noted in 30% to 40% of cases. Their management may require the use of nonsteroidal anti-inflammatory drugs, oral corticosteroids, and sometimes steroid-sparing immunosuppressive agents. Because of the low incidence and prevalence of scleritis, treatment guidelines are currently not available.

Objectives

We analyzed in a retrospective observational study patients with scleritis referred to the Foundation Rothschild Hospital (Paris) from March 2011 to June 2021.

Methods

Characteristics, visual outcomes, ocular complications, associations with systemic diseases and efficacy of treatment were assessed in patients with non-infectious scleritis who needed steroid-sparing immunosuppressive agents.

Results

Among 731 patients diagnosed with scleritis, 54 patients (71 eyes, 7%) were treated by steroid-sparing immunosuppressive agents. Mean follow up was 111.9 ± 84.5 weeks. Mean age was 48.4 years ± 18.3, and 31 patients (57%) were female. Scleritis was anterior in 51 eyes (72 %), including 25 (35%) with diffuse scleritis, 24 (34%) with nodular scleritis and 2 (3%) with necrotizing scleritis. Scleritis was posterior in 20 eyes (28%). Bilateral involvement was noted in 17 patients (32 %). Ocular complications were observed in 52 eyes (73 %): scleral thinning in 25 eyes (35%), anterior uveitis in 24 eyes (34 %), loss of vision in 20 eyes (28%), posterior segment ocular complications in 18 eyes (25%), ocular hypertension in 17 eyes (24%) and corneal involvement in 16 eyes (23%). An underlying systemic disease was identified in 28 patients (52 %), and scleritis was the first manifestation of the systemic disease in 17 out of 28 patients. Rheumatoid arthritis was the most frequently identified disease (n=12), followed by granulomatosis with polyangiitis (n=8) and relapsing polychondritis (n=4). All patients received at least one immunosuppressive agent. Corticosteroid sparing with a daily dose ≤ 5 mg of prednisone was achieved in 85% of patients. Conventional immunosuppressive agents were used as the first steroid-sparing agent in 38 patients (70%) (methotrexate n=33, azathioprine n=4, mycofenolate mofetil (MMF) n=1) and as second steroid-sparing agent in 1 patient (MMF). This treatment led to control scleral inflammation in 23 (59%) patients after a mean delay of 10.0 ± 6.0 weeks. Biologic therapy was used in 33 (61%) patients (TNF alpha inhibitor n=17, IL6-R inhibitor n=7, anti-CD20 n=9), and as the first steroid-sparing agent in 16 (30%) (TNF alpha inhibitor n=4, IL6-R inhibitor n=4, anti-CD20 n=8). This treatment led to control scleral inflammation after a mean delay of 4,9 ± 3,7 weeks in 29 patients (87.9%).

Conclusion

Scleritis is a severe ocular inflammatory disease that requires repeated and thorough ophthalmologic and general examinations given the high frequency of complications and the possibility of an underlying systemic disease. This study reports real-life experience in management of non-infectious scleritis. Biological therapies seemed to be associated with a better outcome and a quicker reponse than conventional immunosuppressive agents. Further studies are warranted to develop specific guidelines

Disclosure of Interests

None declared

Exploring new strategies for ozone-risk assessment: A dynamic-threshold case study

Tropospheric ozone is a dangerous atmospheric pollutant for forest ecosystems when it penetrates stomata. Thresholds for ozone-risk assessment are based on accumulated stomatal ozone fluxes such as the Phytotoxic Ozone Dose (POD). In order to identify the effect of ozone on a Holm oak forest in central Italy, four flux-based ozone impact response functions were implemented and tested in a multi-layer canopy model AIRTREE and evaluated against Gross Primary Productivity (GPP) obtained from observations of Eddy Covariance fluxes of CO₂. To evaluate if a clear phytotoxic threshold exists and if it changes during the year, six different detoxifying thresholds ranging between 0 and 5 nmol O₃ m^-2 s^-1 were tested. The use of species-specific rather than more general response functions based on plant functional types (PFT) increased model accuracy (RMSE reduced by up to 8.5%). In the case of linear response functions, a threshold of 1 nmol m^-2 s^-2 produced the best results for simulations of the whole year, although the tolerance to ozone changed seasonally, with higher tolerance (5 nmol m^-2 s^-1 or no ozone impact) for Winter and Spring and lower thresholds in Summer and Fall (0-1 nmol m^-2 s^-1). A "dynamic threshold" obtained by extracting the best daily threshold values from a range of different simulations helped reduce model overestimation of GPP by 213 g C m^-2 y^-1 and reduce RMSE up to 7.7%. Finally, a nonlinear ozone correction based on manipulative experiments produced the best results when no detoxifying threshold was applied (0 nmol O₃ m^-2 s^-1), suggesting that nonlinear functions fully account for ozone detoxification. The evidence of seasonal changes in ozone tolerance points to the need for seasonal thresholds to predict ozone damage and highlights the importance of performing more species-specific manipulative experiments to derive response functions for a broad range of plant species.

Warming homogenizes apparent temperature sensitivity of ecosystem respiration

Warming-induced carbon loss through terrestrial ecosystem respiration (Re) is likely getting stronger in high latitudes and cold regions because of the more rapid warming and higher temperature sensitivity of Re (Q ₁₀). However, it is not known whether the spatial relationship between Q ₁₀ and temperature also holds temporally under a future warmer climate. Here, we analyzed apparent Q ₁₀ values derived from multiyear observations at 74 FLUXNET sites spanning diverse climates and biomes. We found warming-induced decline in Q ₁₀ is stronger at colder regions than other locations, which is consistent with a meta-analysis of 54 field warming experiments across the globe. We predict future warming will shrink the global variability of Q ₁₀ values to an average of 1.44 across the globe under a high emission trajectory (RCP 8.5) by the end of the century. Therefore, warming-induced carbon loss may be less than previously assumed because of Q ₁₀ homogenization in a warming world.

Testing Removal of Carbon Dioxide, Ozone, and Atmospheric Particles by Urban Parks in Italy

Cities are responsible for more than 80% of global greenhouse gas emissions. Sequestration of air pollutants is one of the main ecosystem services that urban forests provide to the citizens. The atmospheric concentration of several pollutants such as carbon dioxide (CO₂), tropospheric ozone (O₃), and particulate matter (PM) can be reduced by urban trees through processes of adsorption and deposition. We predict the quantity of CO₂, O₃, and PM removed by urban tree species with the multilayer canopy model AIRTREE in two representative urban parks in Italy: Park of Castel di Guido, a 3673 ha reforested area located northwest of Rome, and Park of Valentino, a 42 ha urban park in downtown Turin. We estimated a total annual removal of 1005 and 500 kg of carbon per hectare, 8.1 and 1.42 kg of ozone per hectare, and 8.4 and 8 kg of PM₁₀ per hectare. We highlighted differences in pollutant sequestration between urban areas and between species, shedding light on the importance to perform extensive in situ measurements and modeling analysis of tree characteristics to provide realistic estimates of urban parks to deliver ecosystem services.

Ozone impairs the response of isoprene emission to foliar nitrogen and phosphorus in poplar

Tropospheric ozone (O₃) impairs physiological processes of plants while nitrogen (N) deposition may cause imbalances in soil N and other nutrients such as phosphorus (P) suggesting an increase of P demand for plants. However, the combined effect of O₃, soil N and P on isoprene emission from leaves has never been tested. We therefore examined isoprene emission in leaves of Oxford poplar clone exposed to O₃ (ambient, AA [35.0 nmol mol^-1 as daily mean]; 1.5 × AA; 2.0 × AA), soil N (0 and 80 kg N ha^-1) and soil P (0, 40 and 80 kg P ha^-1) in July and September in a Free-Air Controlled Exposure (FACE) facility. We also investigated the response of isoprene emission to foliar N, P and abscisic acid (ABA) contents in September because the 2-C-methylerythritol-5-phosphate (MEP) pathway of isoprenoid biosynthesis produces ABA. We found that O₃ increased isoprene emission in July, which was associated to increased dark respiration, suggesting an activation of metabolism against O₃ stress as an initial response. However, O₃ decreased isoprene emission in September which was associated to reduced net photosynthesis. In September, isoprene emission was positively correlated with leaf N content and negatively correlated with leaf P content in AA. However, no response of isoprene emission to foliar N and P was found in elevated O₃, suggesting that the isoprene responses to foliar N and P depended on the O₃ exposure levels. Isoprene emission rate in 1.5 × AA and 2.0 × AA increased with increasing leaf ABA content, indicating accelerated senescence of injured leaves to favor new leaf growth when high O₃ and nutritional availability in the soil were combined. Even though foliar N and P usually act as a proxy for isoprene emission rate, the impact of recent abiotic factors such as O₃ should be always considered for modeling isoprene emission under climate change.

Current and future impacts of drought and ozone stress on Northern Hemisphere forests

Rising ozone (O₃ ) concentrations, coupled with an increase in drought frequency due to climate change, pose a threat to plant growth and productivity which could negatively affect carbon sequestration capacity of Northern Hemisphere (NH) forests. Using long-term observations of O₃ mixing ratios and soil water content (SWC), we implemented empirical drought and O₃ stress parameterizations in a coupled stomatal conductance-photosynthesis model to assess their impacts on plant gas exchange at three FLUXNET sites: Castelporziano, Blodgett and Hyytiälä. Model performance was evaluated by comparing model estimates of gross primary productivity (GPP) and latent heat fluxes (LE) against present-day observations. CMIP5 GCM model output data were then used to investigate the potential impact of the two stressors on forests by the middle (2041-2050) and end (2091-2100) of the 21st century. We found drought stress was the more significant as it reduced model overestimation of GPP and LE by ~11%-25% compared to 1%-11% from O₃ stress. However, the best model fit to observations at all the study sites was obtained with O₃ and drought stress combined, such that the two stressors counteract the impact of each other. With the inclusion of drought and O₃ stress, GPP at CPZ, BLO and HYY is projected to increase by 7%, 5% and 8%, respectively, by mid-century and by 14%, 11% and 14% by 2091-2100 as atmospheric CO₂ increases. Estimates were up to 21% and 4% higher when drought and O₃ stress were neglected respectively. Drought stress will have a substantial impact on plant gas exchange and productivity, off-setting and possibly negating CO₂ fertilization gains in future, suggesting projected increases in the frequency and severity of droughts in the NH will play a significant role in forest productivity and carbon budgets in future.

Response of isoprene emission from poplar saplings to ozone pollution and nitrogen deposition depends on leaf position along the vertical canopy profile

We investigated isoprene (ISO) emission and gas exchange in leaves from different positions along the vertical canopy profile of poplar saplings (Populus euramericana cv. '74/76'). For a growing season, plants were subjected to four N treatments, control (NC, no N addition), low N (LN, 50 kg N ha^-1year^-1), middle N (MN, 100 kg N ha^-1year^-1), high N (HN, 200 kg N ha^-1year^-1) and three O₃ treatments (CF, charcoal-filtered ambient air; NF, non-filtered ambient air; NF + O₃, NF + 40 ppb O₃). Our results showed the effects of O₃ and/or N on standardized ISO rate (ISO_rate) and photosynthetic parameters differed along with the leaf position, with larger negative effects of O₃ and positive effects of N on ISO_rate and photosynthetic parameters in the older leaves. Expanded young leaves were insensitive to both treatments even at very high O₃ concentration (67 ppb as 10-h average) and HN treatment. Significant O₃ × N interactions were only found in middle and lower leaves, where ISO_rate declined by O₃ just when N was limited (NC and LN). With increasing light-saturated photosynthesis and chlorophyll content, ISO_rate was reduced in the upper leaves but on the contrary increased in middle and lower leaves. The responses of ISO_rate to AOT40 (accumulated exposure to hourly O₃ concentrations > 40 ppb) and POD_Y (accumulative stomatal uptake of O₃ > Y nmol O₃ m^-2 PLA s^-1) were not significant in upper leaves, but ISO_rate significantly decreased with increasing AOT40 or POD_Y under limited N supply in middle leaves but at all N levels in lower leaves. Overall, ISO_rate changed along the vertical canopy profile in response to combined O₃ and N exposure, a behavior that should be incorporated into multi-layer canopy models. Our results are relevant for modelling regional isoprene emissions under current and future O₃ pollution and N deposition scenarios.

Sensitivity of gross primary productivity to climatic drivers during the summer drought of 2018 in Europe

In summer 2018, Europe experienced a record drought, but it remains unknown how the drought affected ecosystem carbon dynamics. Using observations from 34 eddy covariance sites in different biomes across Europe, we studied the sensitivity of gross primary productivity (GPP) to environmental drivers during the summer drought of 2018 versus the reference summer of 2016. We found a greater drought-induced decline of summer GPP in grasslands (-38%) than in forests (-10%), which coincided with reduced evapotranspiration and soil water content (SWC). As compared to the 'normal year' of 2016, GPP in different ecosystems exhibited more negative sensitivity to summer air temperature (Ta) but stronger positive sensitivity to SWC during summer drought in 2018, that is, a stronger reduction of GPP with soil moisture deficit. We found larger negative effects of Ta and vapour pressure deficit (VPD) but a lower positive effect of photosynthetic photon flux density on GPP in 2018 compared to 2016, which contributed to reduced summer GPP in 2018. Our results demonstrate that high temperature-induced increases in VPD and decreases in SWC aggravated drought impacts on GPP. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

Altered energy partitioning across terrestrial ecosystems in the European drought year 2018

Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO₂ exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004-2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosphere compared to the mean of the reference period. In general, drought decreased net CO₂ uptake by 17.8%, but did not significantly change net evapotranspiration. The response of these fluxes differed characteristically between ecosystems; in particular, the general increase in the evaporative index was strongest in peatlands and weakest in croplands. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

The FLUXNET2015 dataset provides ecosystem-scale data on CO₂, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

Measurement(s)	net ecosystem exchange • carbon dioxide • water • energy
Technology Type(s)	eddy covariance • measurement device
Sample Characteristic - Environment	terrestrial biome • atmosphere
Sample Characteristic - Location	Earth (planet)

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12295910

Dry Deposition of Ozone over Land: Processes, Measurement, and Modeling

Dry deposition of ozone is an important sink of ozone in near surface air. When dry deposition occurs through plant stomata, ozone can injure the plant, altering water and carbon cycling and reducing crop yields. Quantifying both stomatal and nonstomatal uptake accurately is relevant for understanding ozone's impact on human health as an air pollutant and on climate as a potent short-lived greenhouse gas and primary control on the removal of several reactive greenhouse gases and air pollutants. Robust ozone dry deposition estimates require knowledge of the relative importance of individual deposition pathways, but spatiotemporal variability in nonstomatal deposition is poorly understood. Here we integrate understanding of ozone deposition processes by synthesizing research from fields such as atmospheric chemistry, ecology, and meteorology. We critically review methods for measurements and modeling, highlighting the empiricism that underpins modeling and thus the interpretation of observations. Our unprecedented synthesis of knowledge on deposition pathways, particularly soil and leaf cuticles, reveals process understanding not yet included in widely-used models. If coordinated with short-term field intensives, laboratory studies, and mechanistic modeling, measurements from a few long-term sites would bridge the molecular to ecosystem scales necessary to establish the relative importance of individual deposition pathways and the extent to which they vary in space and time. Our recommended approaches seek to close knowledge gaps that currently limit quantifying the impact of ozone dry deposition on air quality, ecosystems, and climate.

Water use strategy affects avoidance of ozone stress by stomatal closure in Mediterranean trees-A modelling analysis

Both ozone (O₃ ) and drought can limit carbon fixation by forest trees. To cope with drought stress, plants have isohydric or anisohydric water use strategies. Ozone enters plant tissues through stomata. Therefore, stomatal closure can be interpreted as avoidance to O₃ stress. Here, we applied an optimization model of stomata involving water, CO₂ , and O₃ flux to test whether isohydric and anisohydric strategies may affect avoidance of O₃ stress by stomatal closure in four Mediterranean tree species during drought. The data suggest that stomatal closure represents a response to avoid damage to the photosynthetic mechanisms under elevated O₃ depending on plant water use strategy. Under high-O₃ and well-watered conditions, isohydric species limited O₃ fluxes by stomatal closure, whereas anisohydric species activated a tolerance response and did not actively close stomata. Under both O₃ and drought stress, however, anisohydric species enhanced the capacity of avoidance by closing stomata to cope with the severe oxidative stress. In the late growing season, regardless of the water use strategy, the efficiency of O₃ stress avoidance decreased with leaf ageing. As a result, carbon assimilation rate was decreased by O₃ while stomata did not close enough to limit transpirational water losses.

Ozone-induced impairment of night-time stomatal closure in O3-sensitive poplar clone is affected by nitrogen but not by phosphorus enrichment

Nocturnal transpiration may be a key factor influencing water use in plants. Tropospheric ozone (O₃) and availability of nutrients such as nitrogen (N) and phosphorus (P) in the soil can affect daytime water use through stomata, but the combined effects of O₃, N and P on night-time stomatal conductance (g_s) are not known. We investigated the effects of O₃ and soil availability of N and P on nocturnal g_s and the dynamics of stomatal response after leaf severing in an O₃-sensitive poplar clone (Oxford) subjected to combined treatments over a growing season in an O₃ free air controlled exposure (FACE) facility. The treatments were two soil N levels (0 and 80 kg N ha^-1; N0 and N80), three soil P levels (0, 40 and 80 kg P ha^-1; P0, P40 and P80) and three O₃ levels (ambient concentration, AA [35.0 ppb as hourly mean]; 1.5 × AA; 2.0 × AA). The analysis of stomatal dynamics after leaf severing suggested that O₃ impaired stomatal closure execution. As a result, nocturnal g_s was increased by 2.0 × AA O₃ in August (+39%) and September (+108%). Night-time g_s was correlated with POD₀ (phytotoxic O₃ dose) and increased exponentially after 40 mmol m^-2 POD₀. Such increase of nocturnal g_s was attributed to the emission of ethylene due to 2.0 × AA O₃ exposure, while foliar abscisic acid (ABA) or indole-3-acetic acid (IAA) did not affect g_s at night. Interestingly, the O₃-induced stomatal opening at night was limited by N treatments in August, but not limited in September. Phosphorus decreased nocturnal g_s, although P did not modify the O₃-induced stomatal dysfunction. The results suggest that the increased nocturnal g_s may be associated with a need to improve N acquisition to cope with O₃ stress.

Toward stomatal-flux based forest protection against ozone: The MOTTLES approach

European standards for the protection of forests from ozone (O₃) are based on atmospheric exposure (AOT40) that is not always representative of O₃ effects since it is not a proxy of gas uptake through stomata (stomatal flux). MOTTLES "MOnitoring ozone injury for seTTing new critical LEvelS" is a LIFE project aimed at establishing a permanent network of forest sites based on active O₃ monitoring at remote areas at high and medium risk of O₃ injury, in order to define new standards based on stomatal flux, i.e. POD_Y (Phytotoxic Ozone Dose above a threshold Y of uptake). Based on the first year of data collected at MOTTLES sites, we describe the MOTTLES monitoring station, together with protocols and metric calculation methods. AOT40 and POD_Y, computed with different methods, are then compared and correlated with forest-health indicators (radial growth, crown defoliation, visible foliar O₃ injury). For the year 2017, the average AOT40 calculated according to the European Directive was even 5 times (on average 1.7 times) the European legislative standard for the protection of forests. When the metrics were calculated according to the European protocols (EU Directive 2008/50/EC or Modelling and Mapping Manual LTRAP Convention), the values were well correlated to those obtained on the basis of the real duration of the growing season (i.e. MOTTLES method) and were thus representative of the actual exposure/flux. AOT40 showed opposite direction relative to PODY. Visible foliar O₃ injury appeared as the best forest-health indicator for O₃ under field conditions and was more frequently detected at forest edge than inside the forest. The present work may help the set-up of further long-term forest monitoring sites dedicated to O₃ assessment in forests, especially because flux-based assessments are recommended as part of monitoring air pollution impacts on ecosystems in the revised EU National Emissions Ceilings Directive.

Ozone and particle fluxes in a Mediterranean forest predicted by the AIRTREE model

Mediterranean forests are among the most threatened ecosystems by the concurrent effects of climate change and atmospheric pollution. In this work we parameterized the AIRTREE multi-layer model to predict CO₂, water, ozone, and fine particles exchanges between leaves and the atmosphere. AIRTREE consists of four different modules: (1) a canopy environmental module determines the leaf temperature and radiative fluxes at different levels from above to the bottom of the canopy; (2) a hydrological module predicts soil water flow and water availability to the plant's photosynthetic apparatus; (3) a photosynthesis module estimates the net photosynthesis and stomatal conductance, and (4) a deposition module estimates ozone and PM deposition sinks as a function of the resistances to gas diffusion in the atmosphere, and within the canopy and leaf boundary layer. We describe the AIRTREE model framework, accuracy and sensitivity by comparing modeling results against long-term continuous Eddy Covariance measurements of ozone, water, and CO₂ fluxes in a Mediterranean Holm oak forest, and we discuss potential application of AIRTREE for ozone-risk assessment in view of availability of a large observational database from ecosystems distributed worldwide.

Ozone flux and ozone deposition in a mountain spruce forest are modulated by sky conditions

In order to understand the main driving factors of ozone (O₃) deposition we tested the hypothesis that sky conditions (cloudy, partly cloudy, and clear sky) modulate O₃ flux in forest ecosystems via stomatal regulation. The hypothesis is based on the fact that complex microclimate conditions under cloudy sky usually stimulate stomatal conductance. O₃ fluxes were inferred from a concentration gradient in a mountainous Norway spruce forest in the Czech Republic (Central Europe) for years 2012-2016 and measured directly by eddy-covariance during the summer of 2017. Daily and seasonal O₃ depositions were calculated separately for days with cloudy, partly cloudy, and clear sky conditions. The data show unequivocally that more O₃ is taken up under cloudy and partially cloudy skies. Moreover, we found significant interactive effects of sky conditions and season on O₃ flux. Though there are other mechanisms and pathways involved in the transport of O₃ to the plant-soil system, the highest O₃ deposition was associated to the highest stomatal conductance during partly cloudy and cloudy sky conditions in all seasons, while lower O₃ ecosystem fluxes were observed under clear sky conditions despite the highest O₃ concentrations at this time. These findings suggest that forests growing at sites where conditions are predominantly cloudy are expected to deposit higher extent of O₃ than less-cloudy forests being thus more threatened by phytotoxic O₃.

Isoprene is more affected by climate drivers than monoterpenes: A meta-analytic review on plant isoprenoid emissions

Isoprene and monoterpenes (MTs) are among the most abundant and reactive volatile organic compounds produced by plants (biogenic volatile organic compounds). We conducted a meta-analysis to quantify the mean effect of environmental factors associated to climate change (warming, drought, elevated CO₂ , and O₃ ) on the emission of isoprene and MTs. Results indicated that all single factors except warming inhibited isoprene emission. When subsets of data collected in experiments run under similar change of a given environmental factor were compared, isoprene and photosynthesis responded negatively to elevated O₃ (-8% and -10%, respectively) and drought (-15% and -42%), and in opposite ways to elevated CO₂ (-23% and +55%) and warming (+53% and -23%, respectively). Effects on MTs emission were usually not significant, with the exceptions of a significant stimulation caused by warming (+39%) and by elevated O₃ (limited to O₃ -insensitive plants, and evergreen species with storage organs). Our results clearly highlight individual effects of environmental factors on isoprene and MT emissions, and an overall uncoupling between these secondary metabolites produced by the same methylerythritol 4-phosphate pathway. Future results from manipulative experiments and long-term observations may help untangling the interactive effects of these factors and filling gaps featured in the current meta-analysis.

Basic and Continuing Education Needs of Nurses Instrument: Development and Validation

AIM

To develop and psychometrically test the Basic and Continuing Education Needs of Nurses Instrument.

BACKGROUND

Nurses need to keep updating their knowledge through engaging in continuing education and professional development activities. Continuing education should be based on needs assessment.

METHODS

Items generated were devised from a comprehensive literature review guided by Morrel-Samuels' guidelines. Psychometric analysis was then performed on data from 3632 registered nurses across 74 Lebanese hospitals. Two-factor structures were evaluated: the one-dimensional structure including all items and a six-dimensional structure proposed by the authors. Reliability, exploratory and confirmatory factor analyses were used. Associations between the total knowledge score and nurses' characteristics were assessed using linear regression.

RESULTS AND DISCUSSION

The total scale had Cronbach's alpha of 0.93 and the six subscales between 0.74 and 0.82. Exploratory factor analysis on the first randomly drawn sample of the data supported the one-factor structure. Confirmatory factor analysis on the second randomly drawn sample revealed that both structures were acceptable with better fit for the six-dimensional structure. Linear regression showed significant associations between total score and nurses' age, income, education and gender. The tool has satisfactory psychometric properties for registered nurses in Lebanon and demonstrated relevance to the Lebanese context of nursing practice.

CONCLUSION

We developed a locally adaptable and psychometrically sound instrument to assess the perceived learning needs of Lebanese nurses. Evidence of the validity and reliability of the instrument was provided.

IMPLICATIONS FOR NURSING AND HEALTH POLICY

At a practice level, the Instrument allows nurse leaders to assess knowledge gaps and respond accordingly to nurses perceived learning needs at the national level thus improving practice and protecting people's health. At a policy level, this study has implications for developing policies, regulations and guidelines in support of nurses' continuing education needs and their professional development.

Impacts of air pollution on human and ecosystem health, and implications for the National Emission Ceilings Directive: Insights from Italy

Across the 28 EU member states there were nearly half a million premature deaths in 2015 as a result of exposure to PM_2.5, O₃ and NO₂. To set the target for air quality levels and avoid negative impacts for human and ecosystems health, the National Emission Ceilings Directive (NECD, 2016/2284/EU) sets objectives for emission reduction for SO₂, NOx, NMVOCs, NH₃ and PM_2.5 for each Member State as percentages of reduction to be reached in 2020 and 2030 compared to the emission levels into 2005. One of the innovations of NECD is Article 9, that mentions the issue of "monitoring air pollution impacts" on ecosystems. We provide a clear picture of what is available in term of monitoring network for air pollution impacts on Italian ecosystems, summarizing what has been done to control air pollution and its effects on different ecosystems in Italy. We provide an overview of the impacts of air pollution on health of the Italian population and evaluate opportunities and implementation of Article 9 in the Italian context, as a case study beneficial for all Member States. The results showed that SO₄^2- deposition strongly decreased in all monitoring sites in Italy over the period 1999-2017, while NO₃^- and NH₄⁺ decreased more slightly. As a consequence, most of the acid-sensitive sites which underwent acidification in the 1980s partially recovered. The O₃ concentration at forest sites showed a decreasing trend. Consequently, AOT40 (the metric identified to protect vegetation from ozone pollution) showed a decrease, even if values were still above the limit for forest protection (5000 ppb h^-1), while PODy (flux-based metric under discussion as new European legislative standard for forest protection) showed an increase. National scale studies pointed out that PM10 and NO2 induced about 58,000 premature deaths (year 2005), due to cardiovascular and respiratory diseases. The network identified for Italy contains a good number of monitoring sites (6 for terrestrial ecosystem monitoring, 4 for water bodies monitoring and 11 for ozone impact monitoring) distributed over the territory and will produce a high number of monitored parameters for the implementation of the NECD.

Cross-talk between physiological and biochemical adjustments by Punica granatum cv. Dente di cavallo mitigates the effects of salinity and ozone stress

Plants are exposed to a broad range of environmental stresses, such as salinity and ozone (O₃), and survive due to their ability to adjust their metabolism. The aim of this study was to evaluate the physiological and biochemical adjustments adopted by pomegranate (Punica granatum L. cv. Dente di cavallo) under realistic field conditions. One-year-old saplings were exposed to O₃ [two levels denoted as ambient (AO) and elevated (EO) O₃ concentrations] and salinity [S (salt, 50 mM NaCl)] for three consecutive months. No salt (NS) plants received distilled water. Despite the accumulation of Na⁺ and Cl^- in the aboveground biomass, no evidence of visible injury due to salt (e.g. tip yellow-brown lesions) was found. The maintenance of leaf water status (i.e. unchanged values of electrolytic leakage and relative water content), the significant increase of abscisic acid, proline and starch content (+98, +65 and +59% compared to AO_NS) and stomatal closure (-24%) are suggested to act as adaptive mechanisms against salt stress in AO_S plants. By contrast, EO_NS plants were unable to protect cells against the negative impact of O₃, as confirmed by the reduction of the CO₂ assimilation rate (-21%), accumulation of reactive oxygen species (+10 and +225% of superoxide anion and hydrogen peroxide) and malondialdehyde by-product (about 2-fold higher than AO_NS). Plants tried to preserve themselves from further oxidative damage by adopting some biochemical adjustments [i.e. increase in proline content (+41%) and induction of catalase activity (8-fold higher than in AO_NS)]. The interaction of the two stressors induced responses considerably different to those observed when each stressor was applied independently. An analysis of the antioxidant pool revealed that the biochemical adjustments adopted by P. granatum under EO_S conditions (e.g. reduction of total ascorbate; increased activities of superoxide dismutase and catalase) were not sufficient to ameliorate the O₃-induced oxidative stress.

Increased docosahexaenoic acid and n-3 polyunsaturated fatty acids in milk from mothers of small for gestational age preterm infants

The study aimed to test whether or not milk fatty acid composition in mothers of small for gestational age (SGA) infants is similar to that in mothers of adequate for gestational age (AGA) infants. Thirty three mothers of SGA preterm infants and 66 mothers of AGA preterm infants were included. Milk and plasma fatty acids were analyzed using capillary gas chromatography. Milk DHA (0.68 ± 0.37 vs. 0.44 ± 0.24; p < 0.01) was higher and n-6:n-3 PUFA ratio (12.0 ± 4.64 vs. 16.0 ± 6.32; p < 0.05) was lower in mothers of SGA infants. Plasma ARA and DHA were increased in mothers of SGA infants and decreased in their infants. Milk ARA or DHA was positively related to the correspondent fatty acid in plasma (r = 0.374, p = 0.010 for ARA and r = 0.690, p < 0.001 for DHA). Breast milk in mothers of preterm infants born SGA is enriched in DHA and n-3 PUFA. Breastfeeding SGA preterm infant with own mother's milk is recommended.

Plants for Sustainable Improvement of Indoor Air Quality

Indoor pollution poses a serious threat to human health. Plants represent a sustainable but underexploited solution to enhance indoor air quality. However, the current selection of plants suitable for indoors fails to consider the physiological processes and mechanisms involved in phytoremediation. Therefore, the capacity of plants to remove indoor air pollutants through stomatal uptake (absorption) and non-stomatal deposition (adsorption) remains largely unknown. Moreover, the effects of the indoor plant-associated microbiome still need to be fully analyzed. Here, we discuss how a combination of the enhanced phytoremediation capacity of plants together with cutting-edge air-cleaning and smart sensor technologies can improve indoor life while reducing energy consumption.

Modeling ozone uptake by urban and peri-urban forest: a case study in the Metropolitan City of Rome

Urban and peri-urban forests are green infrastructures (GI) that play a substantial role in delivering ecosystem services such as the amelioration of air quality by the removal of air pollutants, among which is ozone (O₃), which is the most harmful pollutant in Mediterranean metropolitan areas. Models may provide a reliable estimate of gas exchanges between vegetation and atmosphere and are thus a powerful tool to quantify and compare O₃ removal in different contexts. The present study modeled the O₃ stomatal uptake at canopy level of an urban and a peri-urban forest in the Metropolitan City of Rome in two different years. Results show different rates of O₃ fluxes between the two forests, due to different exposure to the pollutant, management practice effects on forest structure and functionality, and environmental conditions, namely, different stressors affecting the gas exchange rates of the two GIs. The periodic components of the time series calculated by means of the spectral analysis show that seasonal variation of modeled canopy transpiration is driven by precipitation in peri-urban forests, whereas in the urban forest seasonal variations are driven by vapor pressure deficit of ambient air. Moreover, in the urban forest high water availability during summer months, owing to irrigation practice, leads to an increase in O₃ uptake, thus suggesting that irrigation may enhance air phytoremediation in urban areas.

Ozone flux in plant ecosystems: new opportunities for long-term monitoring networks to deliver ozone-risk assessments

Ozone (O₃) is a photochemically formed reactive gas responsible for a decreasing carbon assimilation in plant ecosystems. Present in the atmosphere in trace concentrations (less than 100 ppbv), this molecule is capable of inhibiting carbon assimilation in agricultural and forest ecosystems. Ozone-risk assessments are typically based on manipulative experiments. Present regulations regarding critical ozone levels are mostly based on an estimated accumulated exposure over a given threshold concentration. There is however a scientific consensus over flux estimates being more accurate, because they include plant physiology analyses and different environmental parameters that control the uptake-that is, not just the exposure-of O₃. While O₃ is a lot more difficult to measure than other non-reactive greenhouse gases, UV-based and chemiluminescence sensors enable precise and fast measurements and are therefore highly desirable for eddy covariance studies. Using micrometeorological techniques in association with latent heat flux measurements in the field allows for the partition of ozone fluxes into the stomatal and non-stomatal sinks along the soil-plant continuum. Long-term eddy covariance measurements represent a key opportunity in estimating carbon assimilation at high-temporal resolutions, in an effort to study the effect of climate change on photosynthetic mechanisms. Our aim in this work is to describe potential of O₃ flux measurement at the canopy level for ozone-risk assessment in established long-term monitoring networks.

Postnatal RBC arachidonic and docosahexaenoic acids deficiencies are associated with higher risk of neonatal morbidities and mortality in preterm infants

Arachidonic (AA) and docosahexaenoic (DHA) acids are essential for the health and development of the neonate. Red blood cell (RBC) fatty acids were analyzed in 583 very low birth weight (VLBW) infants and 274 term infants using capillary gas chromatography. VLBW infants exhibited significantly lower RBC AA (13.0 ± 0.89 vs. 13.5 ± 0.98) and DHA (3.77 ± 0.60 vs. 3.80 ± 0.62), but higher n6:n3 ratio (3.97 ± 0.46 vs. 3.63 ± 0.37) than term infants. In VLBW infants, DHA was lower in those born with small for gestational age (3.69 ± 0.57 vs. 3.86 ± 0.58) and those who suffered from neonatal sepsis (3.73 ± 0.60 vs. 3.86 ± 0.55). Both AA and DHA were significantly lower in infants who developed respiratory distress syndrome or intraventricular hemorrhage, and those who died during the hospital stay. VLBW infants had lower postnatal RBC AA and DHA levels than term infants did. These deficits are associated with higher risk of neonatal morbidities and mortality.

Particle deposition in a peri-urban Mediterranean forest

Urban and peri-urban forests provide a multitude of Ecosystem Services to the citizens. While the capacity of removing carbon dioxide and gaseous compounds from the atmosphere has been tested, their capacity to sequestrate particles (PM) has been poorly investigated. Mediterranean forest ecosystems are often located nearby or inside large urban areas. This is the case of the city of Rome, Italy, which hosts several urban parks and is surrounded by forested areas. In particular, the Presidential Estate of Castelporziano is a 6000 ha forested area located between the Tyrrhenian coast and the city (25 km downtown of Rome). Under the hypothesis that forests can ameliorate air quality thanks to particle deposition, we measured fluxes of PM1, 2.5 and 10 with fast optical sensors and eddy covariance technique. We found that PM1 is mainly deposited during the central hours of the day, while negligible fluxes were observed for PM 2.5 and 10. A Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT v4) simulated PM emission from traffic areas in the city of Rome and showed that a significant portion of PM is removed by vegetation in the days when the plume trajectory meets the urban forest.

Interaction of drought and ozone exposure on isoprene emission from extensively cultivated poplar

The combined effects of ozone (O3 ) and drought on isoprene emission were studied for the first time. Young hybrid poplars (clone 546, Populus deltoides cv. 55/56 x P. deltoides cv. Imperial) were exposed to O3 (charcoal-filtered air, CF, and non-filtered air +40 ppb, E-O3 ) and soil water stress (well-watered, WW, and mild drought, MD, one-third irrigation) for 96 days. Consistent with light-saturated photosynthesis (Asat ), intercellular CO2 concentration (Ci ) and chlorophyll content, isoprene emission depended on drought, O3 , leaf position and sampling time. Drought stimulated emission (+38.4%), and O3 decreased it (-40.4%). Ozone increased the carbon cost per unit of isoprene emission. Ozone and drought effects were stronger in middle leaves (13th-15th from the apex) than in upper leaves (6th-8th). Only Asat showed a significant interaction between O3 and drought. When the responses were up-scaled to the entire-plant level, however, drought effects on total leaf area translated into around twice higher emission from WW plants in clean air than in E-O3 . Our results suggest that direct effects on plant emission rates and changes in total leaf area may affect isoprene emission from intensively cultivated hybrid poplar under combined MD and O3 exposure, with important feedbacks for air quality.

Fatty acids profile in preterm Colostrum of Tunisian women. Association with selected maternal characteristics

Fatty acids (FA), especially arachidonic (AA, 20:4ω6) and docosahexaenoic (DHA, 22:6ω3) acids are critical for the health and development of infants. Colostrum FA composition has been examined in 101 lactating Tunisian women delivering prematurely using gas chromatography. Among polyunsaturated FA, linoleic acid predominated whereas each of the other polyunsaturated FA accounted for 1% or less of total FA. Colostrum AA and DHA contents were lower in women aged above 34 years compared to those less than 34 years. Preeclampsia was associated with lower DHA (0.40±0.22 vs. 0.53±0.27; p=0.018), but higher AA (1.14±0.44 vs. 0.93±0.30; p<0.006) and AA:DHA ratio (4.31±4.04 vs. 2.29±2.79; p<0.001). In multivariate analysis, colostrum DHA correlated with plasma DHA (β, 0.417; p=0.002), maternal age (β, -0.290; p=0.028) and preeclampsia (β, -0.270; p=0.042). Preterm colostrum FA profile in Tunisian women is comparable to those of other populations. Colostrum AA and DHA levels are altered in aged and pre-eclamptic women.

BVOC responses to realistic nitrogen fertilization and ozone exposure in silver birch

Emission of BVOC (Biogenic Volatile Organic Compounds) from plant leaves in response to ozone exposure (O3) and nitrogen (N) fertilization is poorly understood. For the first time, BVOC emissions were explored in a forest tree species (silver birch, Betula pendula) exposed for two years to realistic levels of O3 (35, 48 and 69 ppb as daylight average) and N (10, 30 and 70 kg ha(-1) yr(-1), applied weekly to the soil as ammonium nitrate). The main BVOCs emitted were: α-pinene, β-pinene, limonene, ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and hexanal. Ozone exposure increased BVOC emission and reduced total leaf area. The effect on emission was stronger when a short-term O3 metric (concentrations at the time of sampling) rather than a long-term one (AOT40) was used. The effect of O3 on total leaf area was not able to compensate for the stimulation of emission, so that responses to O3 at leaf and whole-plant level were similar. Nitrogen fertilization increased total leaf area, decreased α-pinene and β-pinene emission, and increased ocimene, hexanal and DMNT emission. The increase of leaf area changed the significance of the emission response to N fertilization for most compounds. Nitrogen fertilization mitigated the effects of O3 exposure on total leaf area, while the combined effects of O3 exposure and N fertilization on BVOC emission were additive and not synergistic. In conclusion, O3 exposure and N fertilization have the potential to affect global BVOC via direct effects on plant emission rates and changes in leaf area.

Rapid leaf development drives the seasonal pattern of volatile organic compound (VOC) fluxes in a 'coppiced' bioenergy poplar plantation

Leaves of fast-growing, woody bioenergy crops often emit volatile organic compounds (VOC). Some reactive VOC (especially isoprene) play a key role in climate forcing and may negatively affect local air quality. We monitored the seasonal exchange of VOC using the eddy covariance technique in a 'coppiced' poplar plantation. The complex interactions of VOC fluxes with climatic and physiological variables were also explored by using an artificial neural network (Self Organizing Map). Isoprene and methanol were the most abundant VOC emitted by the plantation. Rapid development of the canopy (and thus of the leaf area index, LAI) was associated with high methanol emissions and high rates of gross primary production (GPP) since the beginning of the growing season, while the onset of isoprene emission was delayed. The highest emissions of isoprene, and of isoprene photo-oxidation products (Methyl Vinyl Ketone and Methacrolein, iox ), occurred on the hottest and sunniest days, when GPP and evapotranspiration were highest, and formaldehyde was significantly deposited. Canopy senescence enhanced the exchange of oxygenated VOC. The accuracy of methanol and isoprene emission simulations with the Model of Emissions of Gases and Aerosols from Nature increased by applying a function to modify their basal emission factors, accounting for seasonality of GPP or LAI.

Early and late adjustments of the photosynthetic traits and stomatal density in Quercus ilex L. grown in an ozone-enriched environment

Quercus ilex L. seedlings were exposed in open-top chambers for one growing season to three levels of ozone (O3 ): charcoal filtered air, non-filtered air supplemented with +30% or +74% ambient air O3 . Key functional parameters related to photosynthetic performance and stomatal density were measured to evaluate the response mechanisms of Q. ilex to chronic O3 exposure, clarifying how ecophysiological traits are modulated during the season in an ozone-enriched environment. Dark respiration showed an early response to O3 exposure, increasing approximately 45% relative to charcoal-filtered air in both O3 enriched treatments. However, at the end of the growing season, maximum rate of assimilation (Amax ) and stomatal conductance (gs ) showed a decline (-13% and -36%, for Amax and gs , respectively) only in plants under higher O3 levels. Photosystem I functionality supported the capacity of Q. ilex to cope with oxidative stress by adjusting the energy flow partitioning inside the photosystems. The response to O3 was also characterised by increased stomatal density in both O3 enriched treatments relative to controls. Our results suggest that in order to improve the reliability of metrics for O3 risk assessment, the seasonal changes in the response of gs and photosynthetic machinery to O3 stress should be considered.

Removal of Ozone by Urban and Peri-Urban Forests: Evidence from Laboratory, Field, and Modeling Approaches

A crucial issue in urban environments is the interaction between urban trees and atmospheric pollution, particularly ozone (O). Ozone represents one of the most harmful pollutants in urban and peri-urban environments, especially in warm climates. Besides the large interest in reducing anthropogenic and biogenic precursors of O emissions, there is growing scientific activity aimed at understanding O removal by vegetation, particularly trees. The intent of this paper is to provide the state of the art and suggestions to improve future studies of O fluxes and to discuss implications of O flux studies to maximize environmental services through the planning and management of urban forests. To evaluate and quantify the potential of O removal in urban and peri-urban forests, we describe experimental approaches to measure O fluxes, distinguishing laboratory experiments, field measurements, and model estimates, including recent case studies. We discuss the strengths and weaknesses of the different approaches and conclude that the combination of the three levels of investigation is essential for estimating O removal by urban trees. We also comment on the implications of these findings for planning and management of urban forests, suggesting some key issues that should be considered to maximize O removal by urban and peri-urban forests.

Atmospheric benzenoid emissions from plants rival those from fossil fuels

Despite the known biochemical production of a range of aromatic compounds by plants and the presence of benzenoids in floral scents, the emissions of only a few benzenoid compounds have been reported from the biosphere to the atmosphere. Here, using evidence from measurements at aircraft, ecosystem, tree, branch and leaf scales, with complementary isotopic labeling experiments, we show that vegetation (leaves, flowers, and phytoplankton) emits a wide variety of benzenoid compounds to the atmosphere at substantial rates. Controlled environment experiments show that plants are able to alter their metabolism to produce and release many benzenoids under stress conditions. The functions of these compounds remain unclear but may be related to chemical communication and protection against stress. We estimate the total global secondary organic aerosol potential from biogenic benzenoids to be similar to that from anthropogenic benzenoids (~10 Tg y⁻¹), pointing to the importance of these natural emissions in atmospheric physics and chemistry.

Bidirectional Flux of Methyl Vinyl Ketone and Methacrolein in Trees with Different Isoprenoid Emission under Realistic Ambient Concentrations

Methyl vinyl ketone (MVK) and methacrolein (MAC) are key oxidation products (iox) of isoprene, the most abundant volatile organic compound (VOC) emitted by vascular plants in the atmosphere. Increasing attention has been dedicated to iox, as they are involved in the photochemical cycles ultimately leading to ozone (O3) and particle formation. However, the capacity of plants to exchange iox under low and realistic ambient concentrations of iox needs to be assessed. We hypothesized that a foliar uptake of iox exists even under realistic concentrations of iox. We tested the capacity of iox exchange in trees constitutively emitting isoprene (Populus nigra) or monoterpenes (Quercus ilex), or that do not emit isoprenoids (Paulownia imperialis). Laboratory experiments were carried out at the leaf level using enclosures under controlled environmental factors and manipulating isoprene and reactive oxygen species (ROS) production by using the isoprene specific inhibitor fosmidomycin, acute O3 exposure (300 ppbv for 4 h), and dark conditions. We also tested whether stress conditions inducing accumulation of ROS significantly enhance iox formation in the leaf, and their emission. Our results show a negligible level of constitutive iox emission in unstressed plants, and in plants treated with high O3. The uptake of iox increased linearly with exposure to increasing concentrations of ambient iox (from 0 to 6 ppbv of a 1:1 = MVK/MAC mixture) in all the investigated species, indicating iox fast removal and low compensation point in unstressed and stressed conditions. Plant capacity to take up iox should be included in global models that integrate estimates of iox formation, emission, and photochemical reactions in the atmosphere.

Comparing i-Tree modeled ozone deposition with field measurements in a periurban Mediterranean forest

Ozone flux estimates from the i-Tree model were compared with ozone flux measurements using the Eddy Covariance technique in a periurban Mediterranean forest near Rome (Castelporziano). For the first time i-Tree model outputs were compared with field measurements in relation to dry deposition estimates. Results showed generally a good agreement between predicted and measured ozone fluxes (least sum square=5.6 e(-4)) especially when cumulative values over the whole measurement campaign are considered. However at daily and hourly time-step some overestimations were observed in estimated values especially in hot dry periods. The use of different m values in the Ball-Berry formula in the different periods, produced the best fit between predicted and measured ozone fluxes. This suggests that a variable value for the coefficient m accounting for water availability may be appropriate to improve model estimates for Mediterranean and drought prone regions.

Bidirectional exchange of biogenic volatiles with vegetation: emission sources, reactions, breakdown and deposition

Biogenic volatile organic compound (BVOC) emissions are widely modelled as inputs to atmospheric chemistry simulations. However, BVOC may interact with cellular structures and neighbouring leaves in a complex manner during volatile diffusion from the sites of release to leaf boundary layer and during turbulent transport to the atmospheric boundary layer. Furthermore, recent observations demonstrate that the BVOC emissions are bidirectional, and uptake and deposition of BVOC and their oxidation products are the rule rather than the exception. This review summarizes current knowledge of within-leaf reactions of synthesized volatiles with reactive oxygen species (ROS), uptake, deposition and storage of volatiles, and their oxidation products as driven by adsorption on leaf surface and solubilization and enzymatic detoxification inside leaves. The available evidence indicates that because of the reactions with ROS and enzymatic metabolism, the BVOC gross production rates are much larger than previously thought. The degree to which volatiles react within leaves and can be potentially taken up by vegetation depends upon compound reactivity, physicochemical characteristics, as well as upon their participation in leaf metabolism. We argue that future models should be based upon the concept of bidirectional BVOC exchange and consider modification of BVOC sink/source strengths by within-leaf metabolism and storage.

Environmental controls on ozone fluxes in a poplar plantation in Western Europe

Tropospheric O3 is a strong oxidant that may affect vegetation and human health. Here we report on the O3 fluxes from a poplar plantation in Belgium during one year. Surprisingly, the winter and autumn O3 fluxes were of similar magnitude to ones observed during most of the peak vegetation development. Largest O3 uptakes were recorded at the beginning of the growing season in correspondence to a minimum stomatal uptake. Wind speed was the most important control and explained 44% of the variability in the nighttime O3 fluxes, suggesting that turbulent mixing and the mechanical destruction of O3 played a substantial role in the O3 fluxes. The stomatal O3 uptake accounted for a seasonal average of 59% of the total O3 uptake. Multiple regression and partial correlation analyses showed that net ecosystem exchange was not affected by the stomatal O3 uptake.