Atmospheric particulate matter (PM) is a global health issue. Studies have focused on coarse and fine PM. Still, newer studies imply that the ultrafine PM fraction harms human health due to their small size and large specific surface area. It is widely accepted that vegetation is a green-based solution, promoting deposition and reducing atmospheric PM concentrations. Various factors, including atmospheric conditions and leaf morphology influence deposition on leaves. Lack of focus on UFPs has led to a gap in knowledge concerning different atmospheric condition effects, such as wind speed, on this particular fraction.The project examine how the deposition of UFPs on Abies nordmanniana (Normann fir) is dependent on wind speed using wind tunnel experiments. The four wind speeds are 1.6, 2.4, 4.5 and 5.4 m s−1. UFPs are measured before and after plants in the wind tunnel using one ultrafine particle counter alternating between positions. The experiments operated at two concentration levels: natural ambient concentrations at the test facility and increased concentrations generated by a smoker.Polynomial regression models were applied on the data. The difference between the models and knowledge of the empty chamber's net uptake, indicated a net uptake of PM by the plants. Simple linear regression was used to investigate the relationship between wind speed and particle net uptake rate. Simple linear regression was expanded to include normally distributed simulations of wind speeds and particle net uptake rates.Most simple linear regression analyses identified a significant relationship between wind speed and net particle uptake.

The extent to which plants thermoregulate to maintain relatively stable metabolic function in response to gradual and rapid temperature changes that jeopardize crop production is unclear. Maize thermoregulation was investigated based on leaf temperature (TL) measurements and its relationship with photochemistry and stomatal conductance (gs) under dry and wet soil scenarios. Seasonal climatology was simulated in a growth chamber according to Beijing’s climatology with extreme “hot days” based on historical maxima.Maize behaved as a limited homeotherm, an adaptive strategy to maintain photosynthesis around optimum temperatures (Topt). Plants on drier soil had lower thermoregulatory capacity, with reduced gs, photosynthesis and transpiration, which impacted final yields, despite acclimation with a higher Topt to sustained stress. On hot days thermoregulation was affected by heat stress and water availability, suggesting that strong and frequent heatwaves will reduce crop activity although increased temperatures could bring photosynthesis closer to Topt in the region.We propose a novel mechanism to explain thermoregulation from the contribution of heat dissipation via non-photochemical quenching (NPQ) to TL, supporting our hypothesis that NPQ acts as a negative feedback mechanism from photosynthesis by increasing TL in suboptimal conditions. These results could help to design adaptation strategies based on deficit irrigation.Highlight Maize was able to maintain leaf temperatures in narrower ranges than air temperatures by dissipating sunlight not used in photosynthesis as heat energy with a key role of transpiration cooling to sustain optimum photosynthesis temperature.### Competing Interest StatementThe authors have declared no competing interest.

Climate change is causing problems for agriculture, but the effect of combined abiotic stresses on crop nutritional quality is not clear. Here we studied the effect of 10 combinations of climatic conditions (temperature, CO 2 , O 3 and drought) under controlled growth chamber conditions on the grain yield, protein, and mineral content of 3 wheat varieties. Results show that wheat plants under O 3 exposure alone concentrated + 15 to + 31% more grain N, Fe, Mg, Mn P and Zn, reduced K by − 5%, and C did not change. Ozone in the presence of elevated CO 2 and higher temperature enhanced the content of Fe, Mn, P and Zn by 2–18%. Water-limited chronic O 3 exposure resulted in + 9 to + 46% higher concentrations of all the minerals, except K. The effect of climate abiotic factors could increase the ability of wheat to meet adult daily dietary requirements by + 6% to + 12% for protein, Zn and Fe, but decrease those of Mg, Mn and P by − 3% to − 6%, and K by − 62%. The role of wheat in future nutrition security is discussed.

Ecosystems integrity and services are threatened by anthropogenic global changes. Mitigating and adapting to these changes require knowledge of ecosystem functioning in the expected novel environments, informed in large part through experimentation and modelling. This paper describes 13 advanced controlled environment facilities for experimental ecosystem studies, herein termed ecotrons, open to the international community. Ecotrons enable simulation of a wide range of natural environmental conditions in replicated and independent experimental units while measuring various ecosystem processes. This capacity to realistically control ecosystem environments is used to emulate a variety of climatic scenarios and soil conditions, in natural sunlight or through broad‐spectrum lighting. The use of large ecosystem samples, intact or reconstructed, minimizes border effects and increases biological and physical complexity. Measurements of concentrations of greenhouse trace gases as well as their net exchange between the ecosystem and the atmosphere are performed in most ecotrons, often quasi continuously. The flow of matter is often tracked with the use of stable isotope tracers of carbon and other elements. Equipment is available for measurements of soil water status as well as root and canopy growth. The experiments ran so far emphasize the diversity of the hosted research. Half of them concern global changes, often with a manipulation of more than one driver. About a quarter deal with the impact of biodiversity loss on ecosystem functioning and one quarter with ecosystem or plant physiology. We discuss how the methodology for environmental simulation and process measurements, especially in soil, can be improved and stress the need to establish stronger links with modelling in future projects. These developments will enable further improvements in mechanistic understanding and predictive capacity of ecotron research which will play, in complementarity with field experimentation and monitoring, a crucial role in exploring the ecosystem consequences of environmental changes.

Ecosystems integrity and services are threatened by anthropogenic global changes. Mitigating and adapting to these changes require knowledge of ecosystem functioning in the expected novel environments, informed in large part through experimentation and modelling. This paper describes 13 advanced controlled environment facilities for experimental ecosystem studies, herein termed ecotrons, open to the international community. Ecotrons enable simulation of a wide range of natural environmental conditions in replicated and independent experimental units while measuring various ecosystem processes. This capacity to realistically control ecosystem environments is used to emulate a variety of climatic scenarios and soil conditions, in natural sunlight or through broad-spectrum lighting. The use of large ecosystem samples, intact or reconstructed, minimizes border effects and increases biological and physical complexity. Measurements of concentrations of greenhouse trace gases as well as their net exchange between the ecosystem and the atmosphere are performed in most ecotrons, often quasi continuously. The flow of matter is often tracked with the use of stable isotope tracers of carbon and other elements. Equipment is available for measurements of soil water status as well as root and canopy growth. The experiments ran so far emphasize the diversity of the hosted research. Half of them concern global changes, often with a manipulation of more than one driver. About a quarter deal with the impact of biodiversity loss on ecosystem functioning and one quarter with ecosystem or plant physiology. We discuss how the methodology for environmental simulation and process measurements, especially in soil, can be improved and stress the need to establish stronger links with modelling in future projects. These developments will enable further improvements in mechanistic understanding and predictive capacity of ecotron research which will play, in complementarity with field experimentation and monitoring, a crucial role in exploring the ecosystem consequences of environmental changes.

Background: This paper describes how environmentally relevant parameters affect titanium dioxide's photocatalytic properties (TiO2) to decompose ozone (O3). Methods: Thus, experiments have been carried out in a box chamber with TiO2 coated roofing membrane samples to determine the significance of light intensity, temperature, initial O3 concentration, and relative humidity. Furthermore, an outdoor experiment was conducted where the roofing membrane was subjected to natural sunlight. Results: The results show a significant photocatalytic effect of TiO2. The half-life of the O3 decay curve is 5.8 min in near-ambient UV-light exposure compared with 7.1 min in dark conditions. Experiments conducted at higher light intensity show a more extensive degradation of O3, where the value of the reactive uptake coefficient increases from 0.044 to 0.051. Also, the measurements carried out under natural sunlight show a photocatalytic effect where the uptake coefficient value is 0.046. A larger photocatalytic effect is detected for the experiments conducted at 283 K and 303 K temperatures compared with experiments under standard conditions. Conclusion: Experiments carried out with a very high initial concentration of O3 show that 28.1 μg of O3 is decomposed in ambient conditions, where 2.3 μg is destroyed. This demonstrates that light intensity, temperature, ozone concentration, and relative humidity significantly impact TiO2's degradation of O3.

Nitrogen oxides (NOx) in urban air close to ground have significant health implications. Restrictions in traffic, mandatory use of catalytic converters on vehicles, and novel photocatalytic coatings on surfaces contribute to reducing the level of NOx in cities. The aim of this study is to establish environmental profiles of NOx removal by a Three-Way Catalyst (TWC) car converter and by a photocatalytic surface coating (for asphalt and concrete pavements) for fostering technological development in reducing the levels of NOx in urban air. We assessed the environmental performance for the removal of 1 kg NOx by the two technologies with Life Cycle Assessment (LCA; EF.3 impact assessment method). In order to do so, we established Life-Cycle-Inventory (LCI) data representing production, operation and end-of-life of the two technologies based on data from literature and industry. The production of photocatalytic surface coatings, used on concrete and asphalt, has environmental loads two orders of magnitude lower than the environmental benefits of NOx reduction expressed as a reduction in Photochemical Ozone Formation (POF), Acidification (A), and Terrestrial Eutrophication (TE). The vehicle catalytic converter shows similar results except that the use of rare earth elements in the production constitutes a significant load to Freshwater Ecotoxicity (FET) and that additional use of fuel during operation induces a modest Climate Change (CC) impact. For both technologies, the environmental benefits of reducing NOx far exceed any adverse environmental aspects of the production of the technologies.

By this in vitro study addressing greenhouse gas (GHG) emissions from soil-plant mesocosms, we suggest a method to investigate the joint effects of environmental conditions, growth of plants, and agricultural soil management. Soils from two long-term agricultural trials in France were placed in climate chambers. The rotation trial was with or without grain legumes, and the tillage trial used plowing or reduced tillage. Environmental conditions consisted of two contrasting temperature regimes combined with ambient (400 ppm) or high (700 ppm) CO2 concentrations in climate chambers. The plant growth went from seeding to vegetative growth. Carbon dioxide gas exchange measurements were conducted in both soil types for a period representing initial plant growth. The CO2 exchange was influenced by the growing plants increasing the mesocosm respiration and gross ecosystem production. The environmental settings had no noticeable impact on the CO2 exchange in the soils from the legume trial. The CO2 exchange from the tillage trial soils exhibited variations induced by the environmental conditions depending on the tillage treatment. The N2O emission measurements in the legume trial soils showed little variability based on rotation, however, in soils with legumes, indications that higher temperatures will lead to more N2O emission were seen.

During water stress, crops undertake adjustments in functional, structural, and biochemical traits. Hyperspectral data and machine learning techniques (PLS-R) can be used to assess water stress responses in plant physiology. In this study, we investigated the potential of hyperspectral optical (VNIR) measurements supplemented with thermal remote sensing and canopy height (hc) to detect changes in leaf physiology of soybean (C3) and maize (C4) plants under three levels of soil moisture in controlled environmental conditions. We measured canopy evapotranspiration (ET), leaf transpiration (Tr), leaf stomatal conductance (gs), leaf photosynthesis (A), leaf chlorophyll content and morphological properties (hc and LAI), as well as vegetation cover reflectance and radiometric temperature (TL,Rad). Our results showed that water stress caused significant ET decreases in both crops. This reduction was linked to tighter stomatal control for soybean plants, whereas LAI changes were the primary control on maize ET. Spectral vegetation indices (VIs) and TL,Rad were able to track these different responses to drought, but only after controlling for confounding changes in phenology. PLS-R modeling of gs, Tr, and A using hyperspectral data was more accurate when pooling data from both crops together rather than individually. Nonetheless, separated PLS-R crop models are useful to identify the most relevant variables in each crop such as TL,Rad for soybean and hc for maize under our experimental conditions. Interestingly, the most important spectral bands sensitive to drought, derived from PLS-R analysis, were not exactly centered at the same wavelengths of the studied VIs sensitive to drought, highlighting the benefit of having contiguous narrow spectral bands to predict leaf physiology and suggesting different wavelength combinations based on crop type. Our results are only a first but a promising step towards larger scale remote sensing applications (e.g., airborne and satellite). PLS-R estimates of leaf physiology could help to parameterize canopy level GPP or ET models and to identify different photosynthetic paths or the degree of stomatal closure in response to drought.

Although most point sources of persistent organic pollutants (POPs), including polycyclic aromatic hydrocarbons (PAHs), are at lower latitudes, the Arctic region is contaminated. In particular, PAHs now dominate the POP body burden of the region’s marine biota at the lower trophic levels. Greenlandic Inuits have the most elevated levels of POPs in their blood compared to any other population, due to their consumption of seal meat and other marine mammals. PAHs, the by-products of the incomplete combustion of petroleum products, are known carcinogens and have been shown to affect the immune system, reproduction, endocrine functions, and the nervous system. With industrial activities and climate change set to increase local PAH emissions, it is paramount to document changes in atmospheric PAH deposition to further investigate PAH exposure in the region and attribute contaminations to their sources. As a measure of atmospheric pollution, we sampled bryophyte herbarium specimens of three common and widespread species collected in Greenland between the 1920s and 1970s after which time new collections were not available. They were analyzed for 19 PAHs using GC-MS (gas chromatography mass spectrometry). The presence of more low-molecular-weight PAHs than high-molecular-weight PAHs is evidence that the PAH contamination in Greenland is due to long-range transport rather than originating from local sources. The results show peaks in PAH atmospheric deposition in the first part of the 19th century followed by a trend of decrease, which mirror global trends in atmospheric pollution known from those periods. PAHs associated with wood and fossil-fuel combustion decrease in the 1970s coinciding with the disappearance of charcoal pits and foundries in Europe and North America, and a shift away from domestic heating with wood during the 19th century. The results highlight the value of bryophytes as bioindicators to measure PAH atmospheric pollution as well as the unrealized potential of herbaria as historical records of environmental change.

When assessing potentials for crop production under future climatic conditions, multiple environmental parameters need to be included. An increase in carbon dioxide [CO2], higher temperatures, and regional changes in tropospheric ozone [O-3] will influence the growth responses of existing crop species and varieties. Ozone is phytotoxic and a plant stressor at current concentrations, reducing yields worldwide, but possible interactions with changes in other abiotic factors have been considered very little. In this study, we have used eight combinations: two levels of temperature, two levels of [CO2], and three [O-3] exposure regimes to assess the impact of medium-to-high ozone concentrations (80-100 ppb) on wheat growth when other abiotic factors change. Two modern spring wheat varieties (KWS Bittern and Lennox) and a landrace variety (Lantvete) were grown to maturity in climate chambers. We examined plant performance during growth as development rate, rate of photosynthesis, stomatal conductance, water use, and at harvest as total aboveground dry matter and grain yield. All three varieties lost yield in all treatments compared to the ambient treatment that had the following settings: Lowest temperature, ambient [CO2], and very low [O-3]. For episodic ozone exposure in the ambient or high [CO2] and high-level temperature treatment, the yield losses were 18 and 25%, respectively, for KWS Bittern; 44 and 34% for Lennox; and 16 and 37% for Lantvete. The yields of the modern varieties are significantly higher than the landrace variety in two out of eight treatments, although they are higher by weight in seven of the eight treatments. The landrace variety's fraction loss from its highest grain yield in the ambient treatment to the high-[CO2]-and high-level-temperature-treatments was smaller than the modern varieties', showing a comparably higher degree of plasticity of performance. Current crop varieties might be more sensitive to ozone than older varieties, emphasizing the need of future breeding programs to expand the gene pool to provide more climate robust crops.

Tree stems from wetland, floodplain and upland forests can produce and emit methane (CH4). Tree CH4 stem emissions have high spatial and temporal variability, but there is no consensus on the biophysical mechanisms that drive stem CH4 production and emissions. Here, we summarize up to 30 opportunities and challenges for stem CH4 emissions research, which, when addressed, will improve estimates of the magnitudes, patterns and drivers of CH4 emissions and trace their potential origin. We identified the need: (1) for both long-term, high-frequency measurements of stem CH4 emissions to understand the fine-scale processes, alongside rapid large-scale measurements designed to understand the variability across individuals, species and ecosystems; (2) to identify microorganisms and biogeochemical pathways associated with CH4 production; and (3) to develop a mechanistic model including passive and active transport of CH4 from the soil-tree-atmosphere continuum. Addressing these challenges will help to constrain the magnitudes and patterns of CH4 emissions, and allow for the integration of pathways and mechanisms of CH4 production and emissions into process-based models. These advances will facilitate the upscaling of stem CH4 emissions to the ecosystem level and quantify the role of stem CH4 emissions for the local to global CH4 budget.

It has been suggested that plant carbon (C) use by symbiotic arbuscular mycorrhizal fungi (AMF) may be compensated by higher photosynthetic rates because fungal metabolism creates a strong C sink that prevents photosynthate accumulation and downregulation of photosynthesis. This mechanism remains largely unexplored and lacks experimental evidence. We report here two experiments showing that the experimental manipulation of the mycorrhizal C sink significantly affected the photosynthetic rates of cucumber host plants. We expected that a sudden reduction in sink strength would cause a significant reduction in photosynthetic rates, at least temporarily. Excision of part of the extraradical mycorrhizal mycelium from roots, and causing no disturbance to the plant, induced a sustained (10-40%) decline in photosynthetic rates that lasted from 30 min to several hours in plants that were well-nourished and hydrated, and in the absence of growth or photosynthesis promotion by mycorrhizal inoculation. This effect was though minor in plants growing at high (700 ppm) atmospheric CO2 . This is the first direct experimental evidence for the C sink strength effects exerted by arbuscular mycorrhizal symbionts on plant photosynthesis. It encourages further experimentation on mycorrhizal source-sink relations, and may have strong implications in large-scale assessments and modelling of plant photosynthesis.

Abiotic environmental stresses have a negative impact on the yield and quality of crops. Understanding these stresses is an essential enabler for mitigating breeding strategies and it becomes more important as the frequency of extreme weather conditions increases due to climate change. This study analyses the response of barley (Hordeum vulgare L.) to a heat wave during grain filling in three distinct stages: the heat wave itself, the return to a normal temperature regime, and the process of maturation and desiccation. The properties and structure of the starch produced were followed throughout the maturational stages. Furthermore, the key enzymes involved in the carbohydrate supply to the grain were monitored. We observed differences in starch structure with well-separated effects because of heat stress and during senescence. Heat stress produced marked effects on sucrolytic enzymes in source and sink tissues. Early cessation of plant development as an indirect consequence of the heat wave was identified as the major contributor to final yield loss from the stress, highlighting the importance for functional stay-green traits for the development of heat-resistant cereals.

The response of ozone (O 3 ) dry deposition to ecosystem‐atmosphere interactions is poorly understood but is central to determining the potential for extreme pollution events under current and future climate conditions. Using observations and an interactive dry deposition scheme within two dynamic vegetation land models (Geophysical Fluid Dynamics Laboratory LM3.0/LM4.0) driven by observation‐based meteorological forcings over 1948–2014, we investigate the factors controlling seasonal and interannual variability (IAV) in O 3 deposition velocities ( V d,O3 ). Stomatal activity in this scheme is determined mechanistically, depending on phenology, soil moisture, vapor pressure deficit, and CO 2 concentration. Soil moisture plays a key role in modulating the observed and simulated V d,O3 seasonal changes over evergreen forests in Mediterranean Europe, South Asia, and the Amazon. Analysis of multiyear observations at forest sites in Europe and North America reveals drought stress to reduce V d,O3 by ~50%. Both LM3.0 and LM4.0 capture the observed V d,O3 decreases due to drought; however, IAV is weaker by a factor of 2 in LM3.0 coupled to atmospheric models, particularly in regions with large precipitation biases. IAV in summertime V d,O3 to forests, driven primarily by the stomatal pathway, is largest (15–35%) in semiarid regions of western Europe, eastern North America, and northeastern China. Monthly mean V d,O3 for the highest year is 2 to 4 times that of the lowest, with significant implications for surface O 3 variability and extreme events. Using V d,O3 from LM4.0 in an atmospheric chemistry model improves the simulation of surface O 3 abundance and spatial variability (reduces mean biases by ~10 ppb) relative to the widely used Wesely scheme.

Heatwaves pose a threat to crop production and are predicted to increase in frequency, length and intensity as a consequence of global warming. Future heatwaves will occur in addition to the ongoing increase of mean temperature and CO2. To test effects of heatwaves superimposed to future climate scenarios, 22 barley accessions were cultivated with elevated temperature (+ 5 degrees C) and CO2 (700 ppm) as single factors and in combination. The control treatment mimicked ambient Scandinavian early summer conditions (19/12 degrees C, day/night; 400 ppm CO2). Around flowering a 10-day heatwave of 33/28 degrees C (day/night) was superimposed to all treatments. The lowest average grain yield was observed when the heatwave was superimposed onto the combined elevated temperature and CO2 treatment. Here the yield decreased by 42% compared to no heatwave and 52% compared to ambient conditions. When the heatwave was superimposed onto ambient conditions the average grain yield decreased by 37% compared to no heatwave. There was no significant difference between the relative grain yield decrease caused by the heatwave in the ambient and future climate scenarios. In contrast, the vegetative aboveground biomass increased upon heatwave exposure, leading to a strong decline in the harvest index. Our results strongly emphasize the need to produce heatwave resilient cultivars.

The Arctic is considered a pristine environment, where pollution mainly originates from global sources. The present study examines particle number concentrations (PNCs) and the main sources of airborne ultrafine particles (UFPs, d < 100 nm) in the town Sisimiut and two nearby settlements, Sarfannguit and Itilleq, in West Greenland. Measurements were carried out during three weeks in April and May 2016. Air temperatures during the measurements ranged from -4.4 to + 8.7 degrees C. A portable condensation particle counter (P-Trak) was used for the measurements. Results showed that the lowest concentrations were found during days with high wind speeds, with the lowest PNC average of 72 +/- 11 cm(-3) (n = 9) (12 m/s). Background concentrations were usually low compared to more densely populated countries, with a couple of exceptions, where there was no clear cause for elevated PNCs in a background area East of Sisimiut. Measured PNCs in the flue gas in the waste incineration plant in Sisimiut showed up to 334,976 cm(-3) and are expected to be higher in the gas after it is released through the chimney. Average PNCs up to 77,009 +/- 43,880 cm(-3) (n = 26) were measured by a road located by the harbor in Sisimiut, while subsequent measurements at the same location showed much lower PNCs. The presence of heavy machinery elevated PNCs highly during two measurement events, giving PNCs up to 270,993 cm(-3) but dropping to 1180 cm(-3) 10 min later, after the vehicle had passed by. A measurement event in Sisimiut Airport while an aircraft landed and departed showed an average PNC of 44,741 +/- 85,094 cm(-3 )(n = 21). Two 24-h measurements resulted in average PNCs of 2960 +/- 5704 cm(-3) and 3935 +/- 10,016 cm(-3) respectively.