Radish (Raphanus sativus L.): a model for studying plant responses to air pollutants and other environmental stresses

The use of Raphanus sativus L. as a model crop for studies on plant response to environmental stresses is reviewed with emphasis on the effects of different atmospheric pollutants (O(3), SO(2), NO(2), acidic precipitation) and their combinations. Responses to temperature, light supply, water stress, and atmospheric CO(2) are also studied and discussed. In addition, the references reviewed are evaluated in terms of their experimental protocols on growth conditions and recommendations for optimal ranges of environmental and cultural variables, i.e. light, temperature, nutrient supply are given. Its distinct pattern of biomass partitioning, the small dimensions along with short and easy culture make radish an excellent experimental plant. The fleshy below-ground storage organ, formed by the hypocotyl and upper radicle, acts as the major sink during vegetative development. Abundant assimilate supply due to elevated levels of CO(2) along with high irradiation frequently promote hypocotyl growth more than shoot growth, whereas under conditions of stress shoot growth is maintained at the expense of the hypocotyl. This makes the hypocotyl: shoot ratio of radish a very sensitive and suitable indicator for various environmental stresses. Potential weaknesses and shortcomings of radish in its role as a model crop, particularly the high variability of injury and growth responses, are discussed along with possible solutions. Future research needs are derived from the summarized results presented and from some disparities among findings within the literature reviewed.     

A study of air pollutants and acute asthma exacerbations in urban areas: status report

A study to try to better understand the interactions between various air contaminants and acute asthma exacerbations is described. The study evaluates temporal associations between a panel of air contaminants and acute asthmatic exacerbations as measured by emergency room visits for asthma in communities in the Bronx and Manhattan in New York City (NYC). In addition, ambient levels of various air pollutants in two NYC communities are being compared. Almost 2 years of daily data have been collected for most of the air contaminants to be investigated. The air contaminants measured include gaseous compounds (ozone, sulfur dioxide, nitrogen oxides, aldehydes, nitrous acid, nitric acid, hydrochloric acid and ammonia), particulate matter components (metals, elemental and organic carbon, sulfate, hydrogen ion, pollen, mold spores and particle mass and number).     

Differences in airborne particle and gaseous concentrations in urban air between weekdays and weekends

Airborne particle number concentrations and size distributions as well as CO and NO_x concentrations monitored at a site within the central business district of Brisbane, Australia were correlated with the traffic flow rate on a nearby freeway with the aim of investigating differences between weekday and weekend pollutant characteristics. Observations over a 5-year monitoring period showed that the mean number particle concentration on weekdays was (8.8±0.1)×10³ cm⁻³ and on weekends (5.9±0.2)×10³ cm⁻³—a difference of 47%. The corresponding mean particle number median diameters during weekdays and weekends were 44.2±0.3 and 50.2±0.2 nm, respectively. The differences in mean particle number concentration and size between weekdays and weekends were found to be statistically significant at confidence levels of over 99%. During a 1-year period of observation, the mean traffic flow rate on the freeway was 14.2×10⁴ and 9.6×10⁴ vehicles per weekday and weekend day, respectively—a difference of 48%. The mean diurnal variations of the particle number and the gaseous concentrations closely followed the traffic flow rate on both weekdays and weekends (correlation coefficient of 0.86 for particles). The overall conclusion, as to the effect of traffic on concentration levels of pollutant concentration in the vicinity of a major road (about 100 m) carrying traffic of the order of 10⁵ vehicles per day, is that about a 50% increase in traffic flow rate results in similar increases of CO and NO_x concentrations and a higher increase of about 70% in particle number concentration.     

Predisposition of trees by air pollutants to low temperatures and moisture stress

Air pollution can have direct effects on trees. It can cause visible injury to foliage and a disruption of physiological processes, such as photosynthesis and carbon allocation, leading to losses in growth and productivity. This review suggests that of equal or greater importance is the potential of air pollutants to indirectly affect tree growth and vitality by predisposing them to injury from other abiotic and biotic stresses. Predisposition by air pollutants can be the result of a disruption in biochemical processes, such as enzyme activity or production, or physiological factors (e.g. stomatal closure, carbon allocation). Air pollutants such as SO(2), O(3) and acidic mists have been implicated as predisposing agents to two of the most important of these stresses: low temperature and soil moisture. Probable mechanisms, as well as implications of predicted changes in global climate will be discussed.     

Response of a grassland ecosystem to air pollutants. IV. The chemical climate: concentrations of relevant non-criteria pollutants (trace gases and aerosols)

The concentrations of sulphur dioxide, nitric acid, nitrous acid, hydrogen chloride, ammonia and sulphate, nitrate, chloride and ammonium in aerosols were measured continuously for two years at the rural site of Rotenkamp near Braunschweig in south-east Lower Saxony. The level of air pollution registered is typical for rural areas near industrial areas in Central Europe. Long-range transport of polluted air masses from Saxony-Anhalt and Saxony affects air quality when high-pressure areas over Eastern Europe result in easterly winds and reduced vertical exchange due to low inversion layers.     

PCBs and PAHs in U.K. urban air

As part of a long term air monitoring programme the ambient air in four UK urban areas was sampled throughout 1991. Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were sampled from the air in London, Cardiff, Manchester and Stevenage. Both vapour and particulate phases were collected at each site, and total concentrations are reported for 26 alternate weeks of the year.

Total PAH concentrations (sum of 15 compounds) varied between 11 and 735 ng/m³ for the four sites. For each site PAH levels were dominated by the lower molecular weight compounds of phenanthrene, fluorene and pyrene, which made up more than 75% of the ΣPAH. The contribution of individual compounds to the total was broadly similar at each site in both the winter and summer. Concentrations of the higher molecular weight compounds were greater by a factor of 2.5 in the winter months.

Eight PCB congeners (28, 52, 77, 101, 118, 138, 153 and 180) were measured at each site. London gave the highest recorded value of 3.85 ng ΣPCB/m³. Values at the four sites ranged between 0.19–3.85 ng/m³, this range being similar to levels reported in other European and American cities. Congeners 28 and 52 dominated the air mixture, comprising > 80% of the measured total. PCB concentrations in the summer were, on average, double those for the winter.     

Seasonal variation of the size distribution of urban particulate matter and associated organic pollutants in the ambient air

Size-segregated samples of urban particulate matter (<0.95, 0.95–1.5, 1.5–3.0, 3.0–7.5, >7.5 μm) were collected in Thessaloniki, northern Greece, during winter and summer of 2007–2008, in order to study the size distribution of organic compounds such as polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (AHs) including n-alkanes and the isoprenoids pristane and phytane, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). All organic compounds were accumulated in the particle size fraction <0.95 μm particularly in the cold season. Particulate matter displayed a bimodal normalized distribution in both seasons with a stable coarse mode located at 3.0–7.5 μm and a fine mode shifting from 0.95–1.5 μm in winter to <0.95 μm in summer. Unimodal normalized distributions, predominant at 0.95–1.5 μm size range, were found for most organic compounds in both seasons, suggesting gas-to-particle transformation after emission. A second minor mode at larger particles (3.0–7.5 μm) was observed for C₁₉ and certain OCPs suggesting redistribution due to volatilization and condensation.     

Roadside BTEX and other gaseous air pollutants in relation to emission sources

Hourly concentrations of benzene, toluene, ethylbenzene, m,p-xylenes, and o-xylene (BTEX) plus CO, NO_x, SO₂ were monitored at roadsides simultaneously with the traffic volume during the dry season of 2004, in Hanoi, Vietnam. The selected three streets included Truong Chinh (TC) with high traffic volume, Dien Bien Phu (DBP) with low traffic volume, and Nguyen Trai (NT) with high traffic volume running through an industrial estate. BTEX were sampled by SKC charcoal tubes and analyzed by GC–FID. Geometric means of hourly benzene, toluene, ethylbenzene, m,p-xylenes and o-xylene are, respectively, 65, 62, 15, 43, and 22 μg m⁻³ in TC street; 30, 38, 9, 26, and 13 μg m⁻³ in DBP street; and 123, 87, 24, 56, and 30 μg m⁻³ in NT street. Levels of other gaseous pollutants including CO, NO_x, and SO₂, measured by automatic instruments, were low and not exceeding the Vietnam national ambient air quality standards. BTEX levels were comparatively analyzed for different downwind distances (3–50 m) from the street, between peak hours and off-peak hours, as well as between weekdays and weekend. Results of principal component analysis suggest that the gaseous pollutants are associated with different vehicle types.     

Oxidative stress induced by HCH in Hydrilla verticillata (l.f.) Royle: modulation in uptake and toxicity due to Fe

The effect of hexachlorocyclohexane (HCH) singly and in combination with iron was studied on chlorophyll, malondialdehyde, cysteine, total -SH contents and potassium ion leakage in the plants of Hydrilla verticillata. The effect of HCH was also studied on glutathione (reduced and oxidised) content and superoxide dismutase activity. The results showed an increase in malondialdehyde content and potassium ion leakage with increase in HCH concentrations, however, the presence of Fe played a protective role. The chlorophyll content was decreased with increase in HCH concentrations and exposure period. However, the chlorophyll content at 2 and 5 microg ml(-1) was significantly higher in HCH-treated plants as compared to HCH + Fe after 168 h, showing protective role of Fe. The results showed significant increase up to 1 microg ml(-1) in cysteine content with increase in concentrations in both the treatments. The total -SH content was increased with increase in concentrations in both the treatments. In HCH-treated plants, non-significant change was noticed in reduced glutathione (GSH) content however, oxidised glutathione (GSSG) content was increased significantly after 168 h, indicative of oxidative stress. In addition, superoxide dismutase activity was increased non-significantly with increase in HCH concentrations. The accumulation of HCH singly and in presence of Fe was concentration- and duration-dependent. The accumulation of HCH was decreased in presence of Fe at higher concentrations. In contrast, the accumulation of Fe was increased in presence of HCH at higher concentrations. The results showed that malondialdehyde content and potassium ions leakage are the primary responses of toxicity.     

Response of a grassland ecosystem to air pollutants. VI. The chemical climate: concentrations and potential flux densities of relevant criteria pollutants

Of the so-called criteria air pollutants, ozone (O3) and sulfur dioxide (SO2) are relevant to agriculture due to their known toxic (O3, SO2) and fertilizing (SO2) potentials. A proper entity to describe pollutant doses in dose-response relationships is the cumulative flux density absorbed by the respective receptor systems. For nutrient budgets the whole ecosystem acts as receptor; for toxicological considerations, stomatal uptake has to be considered primarily. In Central Europe, the atmospheric inputs of oxidized S (SO2, SO3(2-) and SO4(2-)) have declined from the past, and at present are generally below the nutrient requirements of agroecosystems. In contrast, the phytotoxic potential of O3 has increased during the last decade. Pollutant absorbed doses and weighted concentrations were used to describe the risk potential. It could be shown that these two differ significantly.     

Modeling non-linear changes in an urban setting: From pro-environmental affordances to responses in behavior,emissions and air quality

Interactions in urban environment were investigated using a multidisciplinary model combination, with focus on traffic, emissions and atmospheric particles. An agent-based model was applied to simulate the evolution of unsustainable human behavior (usage of combustion-based personal vehicles) as a function of pro-environmental affordances (opportunities for sustainable choices). Scenarios regarding changes in multi-pollutant emissions were derived, and the non-linear implications to atmospheric particles were simulated with a box model. Based on the results for a Nordic city, increasing pro-environmental affordances by 10%, 50% or 100% leads to emission reductions of 15%, 30% and 40% within 2 years. To reduce ambient particle mass, emissions from traffic should decrease by > 15%, while the lung deposited surface area decreases in all scenarios (-23%, -32% and -36%, correspondingly). The presented case is representative of one season, but the approach is generic and applicable to simulating a full year, given meteorological and pollution data that reflects seasonal variation. This work emphasizes the necessity to consider feedback mechanisms and non-linearities in both human behavior and atmospheric processes, when predicting the outcomes of changes in an urban system.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-022-01827-8.     

Responses of spring wheat (Triticum aestivum L.) to ozone produced by either electric discharge and dry air or by UV-lamps and ambient air

The aim of the present study was to examine if ozone produced similar effects on spring wheat growth with and without small amounts of nitrogen oxides. Two methods were used to produce ozone: the first method consisted of dry pressurized air fed to an electric discharge generator generating the byproducts, N2O5 and N2O, the second method consisted of ambient air fed to UV-lamps. Two spring wheat cultivars (Triticum aestivum L. cvs Minaret and Eridano) were exposed in small open-top chambers to charcoal-filtered air, non-filtered ambient air, and non-filtered ambient air with the addition of ozone for 8 h (0900 to 1700 h) daily, for five weeks. Plants were harvested every week. The growth of Minaret was shown to be more sensitive to O3 than that of Eridano. Leaf senescence increased with increasing ozone level in both cultivars. The total above-ground biomass dry weight decreased with increasing ozone concentration in Minaret, but not in Eridano. The Minaret plants reacted with more damaged leaf dry weight and inhibition of growth when O3 was produced by UV-lamps than when O3 was produced by air fed to an electric discharge generator. This could be explained by more nitrogen content per plant but not by increased nitrogen concentration in plant tissue in plants exposed to increased O3 and small amounts of incidental nitrogen oxides.     

Field controlled experiments on the physiological responses of maize (Zea mays L.) leaves to low-level air and soil mercury exposures

Thousands of tons of mercury (Hg) are released from anthropogenic and natural sources to the atmosphere in a gaseous elemental form per year, yet little is known regarding the influence of airborne Hg on the physiological activities of plant leaves. In the present study, the effects of low-level air and soil Hg exposures on the gas exchange parameters of maize (Zea mays L.) leaves and their accumulation of Hg, proline, and malondialdehyde (MDA) were examined via field open-top chamber and Hg-enriched soil experiments, respectively. Low-level air Hg exposures (<50 ng m^?3) had little effects on the gas exchange parameters of maize leaves during most of the daytime (p?>?0.05). However, both the net photosynthesis rate and carboxylation efficiency of maize leaves exposed to 50 ng m^?3 air Hg were significantly lower than those exposed to 2 ng m^?3 air Hg in late morning (p?<?0.05). Additionally, the Hg, proline, and MDA concentrations in maize leaves exposed to 20 and 50 ng m^?3 air Hg were significantly higher than those exposed to 2 ng m^?3 air Hg (p?<?0.05). These results indicated that the increase in airborne Hg potentially damaged functional photosynthetic apparatus in plant leaves, inducing free proline accumulation and membrane lipid peroxidation. Due to minor translocation of soil Hg to the leaves, low-level soil Hg exposures (<1,000 ng g^?1) had no significant influences on the gas exchange parameters, or the Hg, proline, and MDA concentrations in maize leaves (p?>?0.05). Compared to soil Hg, airborne Hg easily caused physiological stress to plant leaves. The effects of increasing atmospheric Hg concentration on plant physiology should be of concern.     

Arsenic accumulation and translocation in the submerged macrophyte Hydrilla verticillata (L.f.) Royle

Worldwide contamination of arsenic in aquatic systems requires the development of a cost-effective, in situ phytoremediation technology. Hydrilla verticillata (L.f.) Royle, a submerged macrophyte widely distributed throughout the world, has the potential to effectively remove heavy metals from water. In order to understand the potential of H. verticillata for As phytofiltration and its impacts on As cycling in the water system, we investigated As accumulation, speciation and translocation in H. verticillata plants. Plant shoots showed a significant accumulation of As, with a maximum of >700 μg g⁻¹ dry weight (DW) after exposure to 20 μM arsenate [As(V)] or arsenite [As(III)] for 4 d, with no significant differences between the As(V) and As(III) treatments (P > 0.05). In addition, results of an in planta transport experiment showed that, after exposure of root and shoot to 2 μM As(V) and As(III) for 4 d, the bioconcentration factor (BCF) in roots for As(V) was almost twofold than that of As(III). Higher As BCFs in roots compared to shoots was also observed. Arsenic accumulated primarily in the cell walls of root cells (>73% of the total As in roots) and in the soluble parts of leaves (>60% of the total As in leaves). Regardless of the form of As supplied [As(III) or As(V)], As(V) was the dominant form in roots and As(III) was the dominant form in leaves. Further, basipetal translocation of As in this plant (?17%) was markedly higher than acropetal translocation (?3%). Because of accumulation of As in the shoot and immobilization of As below ground in roots, H. verticillata is a potential As phytofiltrator for bioremediation.     

Ecocytological and toxicological responses to copper in Perna viridis (L.) (Bivalvia: Mytilidae) haemocyte lysosomal membranes.

Bivalve lysosomes are sites of intense intracellular digestion. Lysosomes accumulate many pollutants to high concentrations resulting in membrane destabilisation. Consequently, the elucidation of lysosomal membrane integrity utilising the neutral red assay has been used to good effect in pollution monitoring. Naturally occurring environmental stressors also have the potential to destabilise the membrane. Exposure to elevated copper concentrations and extremes of temperature, salinity, hypoxia, emersion and inadequate ration were investigated in haemocyte lysosomes from the tropical bivalve, Perna viridis. Elevated copper concentrations destabilised the membrane although responses were not entirely related to the exposure-concentration. Environmental stressors induced through higher thermal regimes (29 degrees C and 35 degrees C), hyposalinity (10-25/1000) and prolonged emersion elicited significant lysosomal membrane destabilisation. Hypoxia and inadequate ration did not significantly effect membrane stability. The haemocyte lysosomal membranes were generally resistant to exogenous alterations within normal ranges and only showed significant labilisation at environmental extremes. P. viridis haemocyte lysosomal membrane biomarkers should, therefore, prove robust to natural stressors when deployed in marine monitoring programmes and thus prove a valuable, rapid, cost-effective cytological marker of pollution.     

Copper uptake and translocation in a submerged aquatic plant Hydrilla verticillata (L.f.) Royle

A comprehensive understanding of the uptake, tolerance and transport of heavy metals in the wetland system through aquatic plants will be essential for the development of phytoremediation technologies. Copper accumulation and translocation of a submersed macrophyte Hydrilla verticillata (L.f.) Royle were investigated. Plant shoots showed a significant accumulation of Cu with a maximum of 30830 mg Cu kg?1 dry weight after exposed to 4000 μg L?1 Cu for 4d. Both roots and shoots can directly take up Cu from solution and Cu mainly accumulated in cell wall fractions. Moreover, H. verticillata predominantly accumulated Cu through shoots from the aqueous solutions because of the higher weights and bioaccumulation factors of shoots than those of roots. Acropetal translocation of Cu in the plant is higher than the basipetal translocation, which implies that upward translocation of Cu is mainly via the xylem and downward translocation is mainly through the phloem. These findings contribute to the application of submerged aquatic plants to copper removal from moderately contaminated waters.     

Dissolved sulphur dioxide and sulphate in urban and rural precipitation (Norfolk,U.K.)

Sulphur dioxide washout and total sulphate scavenging by precipitation at a rural and urban site have been measured in Norfolk (easternmost part of U.K.) over a period of one year. The basic sampling period was one day although, on occasions, more intensive sampling was undertaken. Estimates have been made of the role of sulphur dioxide washout in the total sulphur removal process. Because the “same” rainfall was collected in the urban and rural locations, attempts have been made to compare city and rural sulphur dioxide washout and sulphate scavenging rates in relation to precipitation amount, intensity, atmospheric sulphur dioxide, rainfall pH and weather-type. There is a greater difference between urban and rural sulphur dioxide washout levels than between the respective precipitation sulphate levels. The field measurements of sulphur dioxide solubilities agree reasonably well with some previous theoretical work.