A lack of focus on data sharing, stakeholders, and economic benefits in current global green infrastructure planning.

Green infrastructure (GI) is increasingly popular in solving urban environmental challenges and enhancing ecosystem services. Yet the research status and challenges of GI planning have not been comprehensively benchmarked to date. We explored the GI types, actions, goals, and spatiotemporal characteristics of GI planning cases worldwide based on the available literature. The challenges of GI planning were also investigated by the cases included in this manuscript. Additionally, the urban governance solutions to address these challenges were proposed. We found that multi-type GI planning is the most popular. Data sharing, stakeholder participation, economic benefits and research funding for GI planning research were generally inadequate, although they have improved trend over time. Multiple-goal GI planning frequently has higher levels of data sharing, stakeholder participation and economic benefits than GI planning that just takes into account one purpose. We conclude that the future transformation of GI planning requires efficient data sharing mechanisms, effective co-design among stakeholders, systematic business models, and available research funding.

Optimal stomatal theory predicts CO2 responses of stomatal conductance in both gymnosperm and angiosperm trees.

Optimal stomatal theory predicts that stomata operate to maximise photosynthesis (Anet ) and minimise transpirational water loss to achieve optimal intrinsic water-use efficiency (iWUE). We tested whether this theory can predict stomatal responses to elevated atmospheric CO2 (eCO2 ), and whether it can capture differences in responsiveness among woody plant functional types (PFTs). We conducted a meta-analysis of tree studies of the effect of eCO2 on iWUE and its components Anet and stomatal conductance (gs ). We compared three PFTs, using the unified stomatal optimisation (USO) model to account for confounding effects of leaf-air vapour pressure difference (D). We expected smaller gs , but greater Anet , responses to eCO2 in gymnosperms compared with angiosperm PFTs. We found that iWUE increased in proportion to increasing eCO2 in all PFTs, and that increases in Anet had stronger effects than reductions in gs . The USO model correctly captured stomatal behaviour with eCO2 across most datasets. The chief difference among PFTs was a lower stomatal slope parameter (g1 ) for the gymnosperm, compared with angiosperm, species. Land surface models can use the USO model to describe stomatal behaviour under changing atmospheric CO2 conditions.

A meta-analysis of mesophyll conductance to CO2 in relation to major abiotic stresses in poplar species.

Mesophyll conductance (gm) determines the diffusion of CO2 from the substomatal cavities to the site of carboxylation in the chloroplasts and represents a critical component of the diffusive limitation of photosynthesis. In this study, we evaluated the average effect sizes of different environmental constraints on gm in Populus spp., a forest tree model. We collected raw data of 815 A-Ci response curves from 26 datasets to estimate gm, using a single curve-fitting method to alleviate method-related bias. We performed a meta-analysis to assess the effects of different abiotic stresses on gm. We found a significant increase in gm from the bottom to the top of the canopy that was concomitant with the increase of maximum rate of carboxylation and light-saturated photosynthetic rate (Amax). gm was positively associated with increases in soil moisture and nutrient availability, but was insensitive to increasing soil copper concentration and did not vary with atmospheric CO2 concentration. Our results showed that gm was strongly related to Amax and to a lesser extent to stomatal conductance (gs). Moreover, a negative exponential relationship was obtained between gm and specific leaf area, which may be used to scale-up gm within the canopy.

Comparing i-Tree Eco Estimates of Particulate Matter Deposition with Leaf and Canopy Measurements in an Urban Mediterranean Holm Oak Forest.

Trees and urban forests remove particulate matter (PM) from the air through the deposition of particles on the leaf surface, thus helping to improve air quality and reduce respiratory problems in urban areas. Leaf deposited PM, in turn, is either resuspended back into the atmosphere, washed off during rain events or transported to the ground with litterfall. The net amount of PM removed depends on crown and leaf characteristics, air pollution concentration, and weather conditions, such as wind speed and precipitation. Many existing deposition models, such as i-Tree Eco, calculate PM2.5 removal using a uniform deposition velocity function and resuspension rate for all tree species, which vary based on leaf area and wind speed. However, model results are seldom validated with experimental data. In this study, we compared i-Tree Eco calculations of PM2.5 deposition with fluxes determined by eddy covariance assessments (canopy scale) and particulate matter accumulated on leaves derived from measurements of vacuum/filtration technique as well as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (leaf scale). These investigations were carried out at the Capodimonte Royal Forest in Naples. Modeled and measured fluxes showed good overall agreement, demonstrating that net deposition mostly happened in the first part of the day when atmospheric PM concentration is higher, followed by high resuspension rates in the second part of the day, corresponding with increased wind speeds. The sensitivity analysis of the model parameters showed that a better representation of PM deposition fluxes could be achieved with adjusted deposition velocities. It is also likely that the standard assumption of a complete removal of particulate matter, after precipitation events that exceed the water storage capacity of the canopy (Ps), should be reconsidered to better account for specific leaf traits. These results represent the first validation of i-Tree Eco PM removal with experimental data and are a starting point for improving the model parametrization and the estimate of particulate matter removed by urban trees.

Emission of constitutive isoprene, induced monoterpenes, and other volatiles under high temperatures in Eucalyptus camaldulensis: A 13 C labelling study.

Eucalypts are major emitters of biogenic volatile organic compounds (BVOCs), especially volatile isoprenoids. Emissions and incorporation of 13 C in BVOCs were measured in Eucalyptus camaldulensis branches exposed to rapid heat stress or progressive temperature increases, in order to detect both metabolic processes and their dynamics. Isoprene emission increased and photosynthesis decreased with temperatures rising from 30°C to 45°C, and an increasing percentage of unlabelled carbon was incorporated into isoprene in heat-stressed leaves. Intramolecular labelling was also incomplete in isoprene emitted by heat-stressed leaves, suggesting increasing contribution of respiratory (and possibly also photorespiratory) carbon. At temperature above 45°C, a drop of isoprene emission was mirrored by the appearance of unlabelled monoterpenes, green leaf volatiles, methanol, and ethanol, indicating that the emission of stored volatiles was mainly induced by cellular damage. Emission of partially labelled acetaldehyde was also observed at very high temperatures, suggesting a double source of carbon, with a large unlabelled component likely transported from roots and associated to the surge of transpiration at very high temperatures. Eucalypt plantations cover large areas worldwide, and our findings may dramatically change forecast and modelling of future BVOC emissions at planetary level, especially considering climate warming and frequent heat waves.

How Does the Amount and Composition of PM Deposited on Platanus acerifolia Leaves Change Across Different Cities in Europe?

Particulate matter (PM) deposited on Platanus acerifolia tree leaves has been sampled in the urban areas of 28 European cities, over 20 countries, with the aim of testing leaf deposited particles as indicator of atmospheric PM concentration and composition. Leaves have been collected close to streets characterized by heavy traffic and within urban parks. Leaf surface density, dimensions, and elemental composition of leaf deposited particles have been compared with leaf magnetic content, and discussed in connection with air quality data. The PM quantity and size were mainly dependent on the regional background concentration of particles, while the percentage of iron-based particles emerged as a clear marker of traffic-related pollution in most of the sites. This indicates that Platanus acerifolia is highly suitable to be used in atmospheric PM monitoring studies and that morphological and elemental characteristics of leaf deposited particles, joined with the leaf magnetic content, may successfully allow urban PM source apportionment.

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.

Does long-term cultivation of saplings under elevated CO2 concentration influence their photosynthetic response to temperature?

BACKGROUND AND AIMS: Plants growing under elevated atmospheric CO2 concentrations often have reduced stomatal conductance and subsequently increased leaf temperature. This study therefore tested the hypothesis that under long-term elevated CO2 the temperature optima of photosynthetic processes will shift towards higher temperatures and the thermostability of the photosynthetic apparatus will increase. METHODS: The hypothesis was tested for saplings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for 4-5 years to either ambient (AC; 385 µmol mol(-1)) or elevated (EC; 700 µmol mol(-1)) CO2 concentrations. Temperature response curves of photosynthetic processes were determined by gas-exchange and chlorophyll fluorescence techniques. KEY RESULTS: Initial assumptions of reduced light-saturated stomatal conductance and increased leaf temperatures for EC plants were confirmed. Temperature response curves revealed stimulation of light-saturated rates of CO2 assimilation (Amax) and a decline in photorespiration (RL) as a result of EC within a wide temperature range. However, these effects were negligible or reduced at low and high temperatures. Higher temperature optima (Topt) of Amax, Rubisco carboxylation rates (VCmax) and RL were found for EC saplings compared with AC saplings. However, the shifts in Topt of Amax were instantaneous, and disappeared when measured at identical CO2 concentrations. Higher values of Topt at elevated CO2 were attributed particularly to reduced photorespiration and prevailing limitation of photosynthesis by ribulose-1,5-bisphosphate (RuBP) regeneration. Temperature response curves of fluorescence parameters suggested a negligible effect of EC on enhancement of thermostability of photosystem II photochemistry. CONCLUSIONS: Elevated CO2 instantaneously increases temperature optima of Amax due to reduced photorespiration and limitation of photosynthesis by RuBP regeneration. However, this increase disappears when plants are exposed to identical CO2 concentrations. In addition, increased heat-stress tolerance of primary photochemistry in plants grown at elevated CO2 is unlikely. The hypothesis that long-term cultivation at elevated CO2 leads to acclimation of photosynthesis to higher temperatures is therefore rejected. Nevertheless, incorporating acclimation mechanisms into models simulating carbon flux between the atmosphere and vegetation is necessary.

Elevated CO2 increases tree-level intrinsic water use efficiency: insights from carbon and oxygen isotope analyses in tree rings across three forest FACE sites.

Elevated CO2 increases intrinsic water use efficiency (WUE(i) ) of forests, but the magnitude of this effect and its interaction with climate is still poorly understood. We combined tree ring analysis with isotope measurements at three Free Air CO2 Enrichment (FACE, POP-EUROFACE, in Italy; Duke FACE in North Carolina and ORNL in Tennessee, USA) sites, to cover the entire life of the trees. We used δ¹³C to assess carbon isotope discrimination and changes in water-use efficiency, while direct CO2 effects on stomatal conductance were explored using δ¹8O as a proxy. Across all the sites, elevated CO2 increased ¹³C-derived water-use efficiency on average by 73% for Liquidambar styraciflua, 77% for Pinus taeda and 75% for Populus sp., but through different ecophysiological mechanisms. Our findings provide a robust means of predicting water-use efficiency responses from a variety of tree species exposed to variable environmental conditions over time, and species-specific relationships that can help modelling elevated CO2 and climate impacts on forest productivity, carbon and water balances.

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.

Upside down and the game of C allocation.

Non-structural carbohydrates (NSCs) represent the primary carbon (C) reserves and play a crucial role for plant functioning and resilience. Indeed, these compounds are involved in the regulation between C supply and demand, and in the maintenance of hydraulic efficiency. NSCs are stored in parenchyma of woody organs, which is recognized as a proxy for reserve storage capacity of tree. Notwithstanding the importance of NSCs for tree physiology, their long-term regulation and trade-offs against growth were not deeply investigated. This work evaluated the long-term dynamics of mature tree reserves in stem and root, proxied by parenchyma features, and focusing on the trade off and interplay between the resources allocation in radial growth and reserves in stem and coarse root. In a Mediterranean beech forest, NSCs content, stem and root wood anatomy analysis, and eddy covariance data, were combined. The parenchyma fraction (RAP) of beech root and stem was different, due to differences in axial parenchyma (AP) and narrow ray parenchyma (nRP) fractions. However, these parenchyma components and radial growth showed synchronous inter-annual dynamics between the two organs. In beech stem, positive correlations were found among soluble sugars content and nRP, and among starch content and the AP. Positive correlations were found among Net Ecosystem Exchange (NEE) and AP of both organs. In contrast, NEE was negatively correlated to radial growth of root and stem. Our results suggest a different contribution of stem and roots to reserves storage, and a putative partitioning in the functional roles of parenchyma components. Moreover, a long-term trade-off of C allocation between growth and reserve pool was evidenced. Indeed, in case of C source reduction, trees preferentially allocate C towards reserves pool. Conversely, in high productive years, growth represents the major C sink.

Photosynthetic limitations and volatile and non-volatile isoprenoids in the poikilochlorophyllous resurrection plant Xerophyta humilis during dehydration and rehydration.

We investigated the photosynthetic limitations occurring during dehydration and rehydration of Xerophyta humilis, a poikilochlorophyllous resurrection plant, and whether volatile and non-volatile isoprenoids might be involved in desiccation tolerance. Photosynthesis declined rapidly after dehydration below 85% relative water content (RWC). Raising intercellular CO(2) concentrations during desiccation suggest that the main photosynthetic limitation was photochemical, affecting energy-dependent RuBP regeneration. Imaging fluorescence confirmed that both the number of photosystem II (PSII) functional reaction centres and their efficiency were impaired under progressive dehydration, and revealed the occurrence of heterogeneous photosynthesis during desiccation, being the basal leaf area more resistant to the stress. Full recovery in photosynthetic parameters occurred on rehydration, confirming that photosynthetic limitations were fully reversible and that no permanent damage occurred. During desiccation, zeaxanthin and lutein increased only when photosynthesis had ceased, implying that these isoprenoids do not directly scavenge reactive oxygen species, but rather protect photosynthetic membranes from damage and consequent denaturation. X. humilis was found to emit isoprene, a volatile isoprenoid that acts as a membrane strengthener in plants. Isoprene emission was stimulated by drought and peaked at 80% RWC. We surmise that isoprene and non-volatile isoprenoids cooperate in reducing membrane damage in X. humilis, isoprene being effective when desiccation is moderate while non-volatile isoprenoids operate when water deficit is more extreme.

The impact of root temperature on photosynthesis and isoprene emission in three different plant species.

Most of the perennial plant species, particularly trees, emit volatile organic compounds (BVOCs) such as isoprene and monoterpenes, which in several cases have been demonstrated to protect against thermal shock and more generally against oxidative stress. In this paper, we show the response of three strong isoprene emitter species, namely, Phragmites australis, Populus x euramericana, and Salix phylicifolia exposed to artificial or natural warming of the root system in different conditions. This aspect has not been investigated so far while it is well known that warming the air around a plant stimulates considerably isoprene emission, as also shown in this paper. In the green house experiments where the warming corresponded with high stress conditions, as confirmed by higher activities of the main antioxidant enzymes, we found that isoprene uncoupled from photosynthesis at a certain stage of the warming treatment and that even when photosynthesis approached to zero isoprene emission was still ongoing. In the field experiment, in a typical cold-limited environment, warming did not affect isoprene emission whereas it increased significantly CO2 assimilation. Our findings suggest that the increase of isoprene could be a good marker of heat stress, whereas the decrease of isoprene a good marker of accelerated foliar senescence, two hypotheses that should be better investigated in the future.

Species-specific efficiency in PM2.5 removal by urban trees: From leaf measurements to improved modeling estimates.

The growing population in cities is causing a deterioration of air quality due to the emission of pollutants, causing serious health impacts. Trees and urban forests can contribute through the interception and removal of air pollutants such as particulate matter (PM). The dry deposition of PM by vegetation depends on air pollutant concentration, meteorological conditions, and specific leaf traits. Several studies explored the ability of different plant species to accumulate PM on leaf structures leading to the development of models to quantify the PM removal. The i-Tree Eco is the most used model to evaluate ecosystem services provided by urban trees. However, fine particulate matter (PM2.5) removal is still calculated with a poorly evaluated function of deposition velocity (which depends on wind speed and leaf area) without differentiating between tree species. Therefore, we present an improvement of the standard model calculation introducing a leaf trait index to distinguish the species effect on PM net removal. We also compared model results with measurements of deposited leaf PM by vacuum filtration. The index includes the effect of morphological and functional leaf characteristics of tree species using four parameters: leaf water storage, deposition velocity, resuspension rate and leaf washing capacity. Leaves of 11 common urban tree species were sampled in representative areas of the city of Ferrara (Italy) and at different times of the year from 2018 to 2021. This includes four deciduous broadleaf trees (Tilia cordata, Platanus acerifolia, Acer platanoides, Celtis australis), three evergreen broadleaf trees (Quercus ilex, Magnolia grandiflora, Nerium oleander), and four conifers (Thuja orientalis, Cedrus libani, Pinus pinaster, Picea abies). The results provide significant advancement in assessing PM removal using decision support tools such as models to properly select tree species for future urban tree planting programs aimed at improving air quality.

Urban conditions affect soil characteristics and physiological performance of three evergreen woody species.

Physiological studies conducted mainly in metropolitan areas demonstrated that urban environments generate stressful conditions for plants. However, less attention has been paid to plant response to urban conditions in small cities. Here, we evaluated to what extent the health and physiological functions of some Mediterranean urban species [Quercus ilex L., Nerium oleander L. and Pittosporum tobira (Thunb.) W.T. Aiton] were impacted by urban and peri-urban conditions in Pisa (Italy), a small medieval city with narrow streets that impede efficient public transport causing oversized private transport. Experimental period spanned from late-summer to winter in concomitance with the sharp increase in air pollutants. Climate and air quality, soil physical and chemical properties, and plant physiological traits including leaf gas exchanges, chlorophyll fluorescence and leaf pigments were assessed. In soil, the organic carbon affected aggregates and water stability and the concentrations of some micro-elements decreased in winter. Air pollutants impaired leaf gas exchanges and photochemical processes at photosystem II, depending on species, season, and urban conditions. Shrubs were more susceptible than the tree species, highlighting that the latter adapted better to pollutants along an urban-peri-urban transect in Mediterranean environments. This study gives information on the physiological adaptability of some of the most frequent Mediterranean urban species to stressful conditions and demonstrated that, even in a small city, urban conditions influence the physiology and development of vegetation, affecting the plant health status and its ability to provide key ecosystem services.

Consequences of Grazing Cessation for Soil Environment and Vegetation in a Subalpine Grassland Ecosystem.

Areas covered by seminatural grasslands have been in constant decline for decades in Europe. This trend is particularly strong for mountain territories, where such traditional agricultural practices as cattle grazing are no longer economically feasible. This study was conducted in the subalpine pasture of Cinte Tesino (TN, Italy), where local farmers have applied the following different management strategies: shorter and longer grazing durations during the season and a complete abandonment for the last 15 years. We aimed to study how these different management strategies impact the functioning and diversity of vegetation and the chemical and biological characteristics of the soil. Species richness was higher in plots subjected to longer grazing with a prevalence of D. caespitosa in terms of biomass share. A decline in species richness in abandoned plots was accompanied by an increase in the share of other graminoids in collected biomass. A concomitant increase in leaf N concentration and light availability in grazed plots resulted in higher photosynthetic efficiency in some species, as revealed by the δ13C of plant tissues. Soils under grazing were characterised by a higher concentration of total and extractable N, almost doubled microbial biomass C and increased extracellular enzymes activity, evidencing nutrient cycling mobilization. While the microbial pool was characterised by lower mineralization rates, C was lost from the soil with 15 years of abandonment. The longer grazing season demonstrated to be the most beneficial, promoting species richness, C accumulation and better soil microbial functioning. A change in soil pH from strongly acidic to moderately acidic with longer grazing is likely one of the important factors adding to the success in the functioning of primary producers and decomposers in this site.

The relationship between isoprene emission, CO(2) assimilation and water use efficiency across a range of poplar genotypes.

Poplars (Populus sp.) are among the strongest isoprene (Iso)-emitting plants. Ten poplar genotypes belonging to four different species were grown under the same environmental conditions in a common garden experiment, to study the influence of the genetic variability on Iso emission and on the relationship between Iso and photosynthesis. Photosynthesis ranged from 13 to 20 µmol CO(2) m(-2) s(-1) , whereas Iso emission ranged from 18.2 to 45.2 nmol m(-2) s(-1) . There was no clear association between Iso emission and photosynthesis. In most genotypes, photosynthetic capacity developed earlier than Iso emission capacity. The emission of Iso was inversely correlated with the intercellular CO(2) concentration (C(i) ) and positively correlated with instantaneous water use efficiency. It is speculated that, by regulating C(i) , stomatal opening also indirectly controls Iso emission in poplars. A positive linear correlation between the fraction of recently assimilated carbon emitted as Iso and Iso emission rate was found. The slope of this relationship indicated that each nanomole of Iso emitted requires a fixed fraction of photosynthetic carbon regardless of the intra- and interspecific variability in the Populus genus, and of leaf ontogeny. A comparison with data from recent studies showed that the slope of this relationship increases in drought-stressed leaves. However, this might be explained by an increasing contribution of carbon sources for Iso biosynthesis from stored photosynthates. If this is true, then the amount of carbon directly shunted from photosynthesis into Iso is constant in all poplars and is not influenced by abiotic stresses.

Global climate change and tree nutrition: effects of elevated CO2 and temperature.

Although tree nutrition has not been the primary focus of large climate change experiments on trees, we are beginning to understand its links to elevated atmospheric CO2 and temperature changes. This review focuses on the major nutrients, namely N and P, and deals with the effects of climate change on the processes that alter their cycling and availability. Current knowledge regarding biotic and abiotic agents of weathering, mobilization and immobilization of these elements will be discussed. To date, controlled environment studies have identified possible effects of climate change on tree nutrition. Only some of these findings, however, were verified in ecosystem scale experiments. Moreover, to be able to predict future effects of climate change on tree nutrition at this scale, we need to progress from studying effects of single factors to analysing interactions between factors such as elevated CO2, temperature or water availability.

Innovative Characterization of Particulate Matter Deposited on Urban Vegetation Leaves through the Application of a Chemical Fractionation Procedure.

In this study, we have evaluated the efficiency of a chemical fractionation procedure for the characterization of both the water-soluble and the insoluble fraction of the main elemental components of particulate matter (PM) deposited on urban leaves. The proposed analytical approach is based on the chemical analysis of leaf washing solutions and membrane filters used for their filtration. The ionic concentration of leaf washing solutions was compared with their electrical conductivity, making it a valuable proxy for the quantification of the water-soluble and ionic fraction of leaf deposited PM. The chemical composition of both the water-soluble and the insoluble fraction of PM, resulting from this fractionation procedure, was compared with results obtained by scanning electron microscopy coupled with energy-dispersed X-Rays spectroscopy (SEM/EDX) and processed through chemometrics. Results obtained proved that the proposed approach is able to provide an estimation of total leaf deposited PM and it is highly reliable for the evaluation of the emission impact of different PM sources, being able to increase the selectivity of PM elemental components as specific source tracers; consequently providing useful information also for the assessment of human health risks.

Coppicing shifts CO2 stimulation of poplar productivity to above-ground pools: a synthesis of leaf to stand level results from the POP/EUROFACE experiment.

A poplar short rotation coppice (SRC) grown for the production of bioenergy can combine carbon (C) storage with fossil fuel substitution. Here, we summarize the responses of a poplar (Populus) plantation to 6 yr of free air CO(2) enrichment (POP/EUROFACE consisting of two rotation cycles). We show that a poplar plantation growing in nonlimiting light, nutrient and water conditions will significantly increase its productivity in elevated CO(2) concentrations ([CO(2)]). Increased biomass yield resulted from an early growth enhancement and photosynthesis did not acclimate to elevated [CO(2)]. Sufficient nutrient availability, increased nitrogen use efficiency (NUE) and the large sink capacity of poplars contributed to the sustained increase in C uptake over 6 yr. Additional C taken up in high [CO(2)] was mainly invested into woody biomass pools. Coppicing increased yield by 66% and partly shifted the extra C uptake in elevated [CO(2)] to above-ground pools, as fine root biomass declined and its [CO(2)] stimulation disappeared. Mineral soil C increased equally in ambient and elevated [CO(2)] during the 6 yr experiment. However, elevated [CO(2)] increased the stabilization of C in the mineral soil. Increased productivity of a poplar SRC in elevated [CO(2)] may allow shorter rotation cycles, enhancing the viability of SRC for biofuel production.