Gas exchange, growth, and chemical parameters in a native Atlantic forest tree species in polluted areas of Cubatão, Brazil

Responses of tropical tree species to urban air pollutants: ROS/RNS formation and scavenging

Air pollution in an urban environment is the major stress factor for vegetation due to the direct generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). To quantify urban air pollution-induced ROS/RNS formation, damage and detoxification, nine different biochemical parameters related to free radical formation, scavenging and membrane damage were estimated in twelve tropical tree species. The experiment was performed in three different seasons at four distinct urban environments in Varanasi city located in the Indo-Gangetic plain of India. Redundancy analysis was performed to statistically assess the relationship between air pollutants (PM_2.5, NO₂, SO₂ and O₃) and temperature with ROS/RNS generation and their detoxification. Significant effects of air pollution exposure and temperature on ROS/RNS formation, scavenging and membrane damage were recorded with increasing pollution load in the city for all the tree species. The extent of variability (47-87%) in responses of different tree species was due to their intrinsic ability to scavenge free radicals which minimized the membrane damage. PM_2.5, NO₂ and O₃ were identified as major pollutants that influenced trees to different extents in regulating ROS/RNS. However, the response was maximum against NO₂ (34-72%) followed by PM_2.5 (16-64%) and O₃ (3-31%), indicating that under urban environment, trees are considerably sensitive to the combined effects of both particulate and gaseous pollutants. Reactive oxygen intermediate release, total free radical scavenging activity, NO scavenging activity and membrane stability index were identified as major parameters which showed distinct responses with increasing pollution load. Caesalpinia sappan, Ficus religiosa and Albizia lebbeck were identified as most tolerant tree species having higher ROS/RNS scavenging potential resulted in lower membrane damage. Thus responses of urban trees to air pollution are governed by their intrinsic defence mechanisms to scavenge ROS/RNS by maintaining the membrane integrity through integrated cross-talk between different antioxidative pathways.

Efficiency of biomonitoring methods applying tropical bioindicator plants for assessing the phytoxicity of the air pollutants in SE, Brazil

In the tropical region, the greatest challenge of the biomonitoring approach is to establish linear relationships between biomarkers measured in plants and pollutant concentrations, since the bioindicator responses can be intensified or restricted by climatic variations. In southeastern Brazil, there are two regions affected by air pollution, where the Atlantic Forest remains and should be preserved. Consequently, both areas have been monitored by biomonitoring procedures using standardized and tropical plants. The industrial complex settled in Cubatão is one of the world's most famous examples of environmental pollution and degradation, with consequent decline of the Atlantic Forest. An oil refinery is among the most polluting industries in the Cubatão region. The other region is located in the Metropolitan Region of Campinas (MRC). The MRC has been affected by high levels of air pollutants originated from road traffic and is responsible for over 80% of CO, NOx, and hydrocarbon emissions and develops industrial activities that emit about 70% of the particulate matter present in the region. Both regions are distinguished by the climate, despite the fact that they are only about 130 km far from each other. Several studies carried out by our group in these regions aimed to establish the best native tree species and respective potential biomarkers for future assessment of pollution effects on tropical Forests. We present a critical review about the efficiency of native species compared to standardized bioindicator plants considering antioxidant defense system, nutrient accumulation, and microscopic aspects when exposed to atmospheric pollutants and climate.

Impacts of particulate matter pollution on plants: Implications for environmental biomonitoring

Air pollution is one of the serious problems world is facing in recent Anthropocene era of rapid industrialization and urbanization. Specifically particulate matter (PM) pollution represents a threat to both the environment and human health. The changed ambient environment due to the PM pollutant in urban areas has exerted a profound influence on the morphological, biochemical and physiological status of plants and its responses. Taking into account the characteristics of the vegetation (wide distribution, greater contact area etc.) it turns out to be an effective indicator of the overall impact of PM pollution and harmful effects of PM pollution on vegetation have been reviewed in the present paper, covering an extensive span of 1960 to March 2016. The present review critically describes the impact of PM pollution and its constituents (e.g. heavy metals and poly-aromatic hydrocarbons) on the morphological attributes such as leaf area, leaf number, stomata structure, flowering, growth and reproduction as well as biochemical parameters such as pigment content, enzymes, ascorbic acid, protein, sugar and physiological aspect such as pH and Relative water content. Further, the paper provides a brief overview on the impact of PM on biodiversity and climate change. Moreover, the review emphasizes the genotoxic impacts of PM on plants. Finally, on the basis of such studies tolerant plants as potent biomonitors with high Air Pollution Tolerance Index (APTI) and Air Pollution Index (API) can be screened and may be recommended for green belt development.

Assessing redox potential of a native tree from the Brazilian Atlantic Rainforest: a successful evaluation of oxidative stress associated to a new power generation source of an oil refinery

The antioxidant responses in saplings of Tibouchina pulchra (a native tree from the Brazilian Atlantic Rainforest) exposed around an oil refinery in the city of Cubatão (SE Brazil), varied during the exchange of its power generation source, from boilers fueled with oil to a thermoelectric fueled with natural gas. The redox potential changed in response to an interaction of air pollution and meteorological parameters, indicating that the pro-oxidant/antioxidant balance was not reached after the exchange of the power generation system. The gain in environmental quality in the region was not achieved as expected due the technological modernization, at least relative to oxidative stressors. These conclusions were based on results of analyses of enzymatic antioxidants: superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR); non-enzymatic antioxidants: reduced, oxidized and total ascorbic acid (AsA, DHA, totAA) and glutathione (GSH, GSSG, totG), their redox state (AsA/totAA and GSH/totG) and an indicator of lipid peroxidation (MDA). We also applied exploratory multivariate statistics in order to verify if the temporal sequence of changes in the plant redox capacity coincided with changes in the profile of air pollution, climatic conditions or with their interactions and if the environmental benefits that would supposedly be promoted by the mentioned exchange of power generation system were achieved in the region.

Responses of a tropical tree species to ozone: visible leaf injury, growth, and lipid peroxidation

The Brazilian native tree species Astronium graveolens was indicated as sensitive to ozone in a fumigation experiment. Thus, the objective of this study was to evaluate how sensitive A. graveolens is to ozone under realistic conditions in the field. Eighteen saplings were exposed to ozone in a contaminated area and in a greenhouse with filtered air during two exposure periods of approximately 63 days each (March-May 2012 and September-October 2012). Leaf injury was analyzed by means of its incidence and severity, the leaf injury index (LII) and the progression of leaf abscission. These variables were monitored weekly, whereas growth and lipid peroxidation were monitored monthly. Plants exposed to ozone showed significant growth decrease and visible leaf injury increase, but lipid peroxidation and leaf abscission remained unchanged. These results indicated that plants subjected to ozone possibly diverted energy from growth to the production of antioxidants necessary to cope with ozone-induced oxidative stress.

Leaf reflectance variation along a vertical crown gradient of two deciduous tree species in a Belgian industrial habitat

The reflectometry of leaf asymmetry is a novel approach in the bio-monitoring of tree health in urban or industrial habitats. Leaf asymmetry responds to the degree of environmental pollution and reflects structural changes in a leaf due to environmental pollution. This paper describes the boundary conditions to scale up from leaf to canopy level reflectance, by describing the variability of adaxial and abaxial leaf reflectance, hence leaf asymmetry, along the crown height gradients of two tree species. Our findings open a research pathway towards bio-monitoring based on the airborne remote sensing of tree canopies and their leaf asymmetric properties.

Study on the Adsorption Capacities for Airborne Particulates of Landscape Plants in Different Polluted Regions in Beijing (China)

Urban landscape plants are an important component of the urban ecosystem, playing a significant role in the adsorption of airborne particulates and air purification. In this study, six common landscape plants in Beijing were chosen as research subjects, and the adsorption capacities for each different plant leaf and the effects of the leaf structures for the adsorption capacities for particulates were determined. Preliminary results show that needle-leaved tree species adsorbed more airborne particulates than broad-leaved tree species for the same leaf area. Pinus tabuliformis exhibits the highest adsorption capacity, at 3.89 ± 0.026 μg·cm(-2), almost two times as much as that of Populus tomentosa (2.00 ± 0.118 μg·cm(-2)). The adsorption capacities for PM10 of the same tree species leaves, in different polluted regions had significant differences, and the adsorption capacities for PM10 of the tree species leaf beside the Fifth Ring Road were higher than those of the tree species leaves in the Botanical Garden, although the adsorption capacities for PM2.5 of the same tree species in different polluted regions had no significant differences. By determining the soluble ion concentrations of the airborne particulates in two regions, it is suggested that the soluble ion concentrations of PM10 in the atmosphere in the Botanical Garden and beside the Fifth Ring Road have significant differences, while those of PM2.5 in the atmosphere had no significant differences. In different polluted regions there are significant adaptive changes to the leaf structures, and when compared with slightly polluted region, in the seriously polluted region the epidermis cells of the plant leaves shrinked, the surface textures of the leaves became rougher, and the stomas' frequency and the pubescence length increased. Even though the plant leaves exposed to the seriously polluted region changed significantly, these plants can still grow normally and healthily.

Establishing the redox potential of Tibouchina pulchra (Cham.) Cogn., a native tree species from the Atlantic Rain Forest, in the vicinity of an oil refinery in SE Brazil

The present study aimed to establish the seasonal variations in the redox potential ranges of young Tibouchina pulchra plants growing in the Cubatão region (SE Brazil) under varying levels of oxidative stress caused by air pollutants. The plants were exposed to filtered air (FA) and non-filtered air (NFA) in open-top chambers installed next to an oil refinery in Cubatão during six exposure periods of 90 days each, which included the winter and summer seasons. After exposure, several analyses were performed, including the foliar concentrations of ascorbic acid and glutathione in its reduced (AsA and GSH), total (totAA and totG) and oxidized forms (DHA and GSSG); their ratios (AsA/totAA and GSH/totG); the enzymatic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR); and the content of malondialdehyde (MDA). The range of antioxidant responses in T. pulchra plants varied seasonally and was stimulated by high or low air pollutant concentrations and/or air temperatures. Glutathione and APX were primarily responsible for increasing plant tolerance to oxidative stress originating from air pollution in the region. The high or low air temperatures mainly affected enzymatic activity. The content of MDA increased in response to increasing ozone concentration, thus indicating that the pro-oxidant/antioxidant balance may not have been reached.

The guava tree as bioindicator during the process of fuel replacement of an oil refinery

This study was performed to verify whether the exchange of the fuel used in the boilers of a crude oil refinery located in Cubatão (SE Brazil) would result in alterations on gas exchange, growth and leaf injuries in saplings of Psidium guajava 'Paluma'. The purpose of the refinery was to reduce the SO2 emission, but using natural gas as fuel could increase the concentrations of O3 precursors in the atmosphere. Thus a biomonitoring was performed with a native species sensitive to O3. The plants were exposed in five areas (CM1, CM5, CEPEMA, Centro, and RP) at different distances to the refinery, both before and after the fuel exchange. We performed six exposures under environmental conditions, with length of ca. 90 days each. With the utilization of natural gas, the saplings presented reductions in carbon assimilation rate under saturating light conditions (Asat, μmolCO2m(-2)s(-1)) and the stomatal conductance (gs, molH2Om(-2)s(-1)), and increase in height, number of leaves, and dry mass of leaves and shoots. There were also reductions in root dry mass and in the root/shoot ratio. The saplings also presented O3-induced leaf injuries. The responses of P. guajava 'Paluma' were altered after the fuel exchange as a result of a new combination of pollutants in the atmosphere. The fuel exchange has not resulted in environmental benefit to the surrounding forest; it has only altered the contamination profile of the region.

Physiological responses of the tropical tree Tibouchina pulchra Cogn under the influence of combustion of crude oil and natural gas at an oil refinery

A refinery located on the slopes of a mountain range in the city of Cubatão (SE-Brazil) is the main source of sulfur dioxide (SO(2)) in the region. For this reason, the refinery replaced a system in which energy was produced from crude oil combustion in boilers with a system of energy and vapor co-generation in a thermoelectric power plant fueled by natural gas. The aim of this study was to investigate the responses of Tibouchina pulchra to the fuel switching. Saplings planted in pots were distributed throughout monitoring sites around the polluting source (sites I, II, III and IV) and in a site (V) far from emissions. Changes on the plants responses occur along the three fuel switching phases. During the last phase, increased carbon assimilation (Asat) and decreased stomatal conductance (gs) were observed in plants growing in sites II and III; as a consequence, intrinsic water use efficiency (iWUE) increased. However, the increase in Asat did not promote growth increase suggesting that changes at the refinery did not result in better air quality, but only in a change in the main contaminants.

A study of air pollution with heavy metals in Athens city and Attica basin using evergreen trees as biological indicators

Concentrations of five metals (cadmium, chromium, copper, nickel and lead) were determined in tree leaves collected from 13 areas of the Attica basin and Athens city, Greece. Geographical distribution patterns were investigated, and factors affecting toxic element accumulation in trees were discussed. The mean heavy metal content in the tree leaves is described in the descending order of copper>lead>nickel>chromium>cadmium. Generally, the most damaged areas have been proved to be those near the city center and in the vicinity of the Attica highway. The geomorphological relief of the area plays an important role in the dispersion of airborne particles from pollution sources to the surrounding area. Areas on the NE region are also polluted mainly due to wind directions. In Citrus aurantium leaves, with relatively impermeable cuticle, high chromium, copper and nickel concentration would be possibly caused only by significant stomatal uptake. The conifer tree Pinus brutia providing a rough leaf surface also showed elevated concentrations, especially of cadmium and lead. The thick waxy cuticle of the sclerophyllous broad-leaved Olea europaea forms a smooth sheet increasing the barrier properties of the leaf epidermis and causing a reduction in leaf permeability. The dense trichomes of the abaxial epidermis of Olea europaea also act as a pollution screen keeping away the air particles from the epidermis stomata. The presence of a certain metal within the leaf cells could reduce the uptake or toxicity of some others.

Trees as bioindicator of heavy metal pollution in three European cities

Concentrations of four heavy metals were determined in tree leaves and bark collected from polluted and non-polluted areas of three European cities (Salzburg, Belgrade and Thessaloniki) for a comparative study. Platanus orientalis L. and Pinus nigra Arn., widespread in urban northern and southern Europe, were tested for their suitability for air quality biomonitoring. Leaves and barks were collected uniformly of an initial quantity of about 30 g of each sample. Analysis was accomplished by electrothermal atomic absorption spectrometry after total digestion. Site-dependent variations were found with the highest concentration level measured in Belgrade, followed by Thessaloniki and Salzburg. A higher accumulation of heavy metals was found in bark compared to leaves. Pine tree bark, accumulating higher concentrations of trace metals compared to plane tree bark, shows a higher efficiency as bioindicator for urban pollution. Both indicator species are suitable for comparative studies on bioindication of urban air pollution.

Tibouchina pulchra (Cham.) Cogn., a native Atlantic Forest species, as a bio-indicator of ozone: visible injury

Tibouchina pulchra saplings were exposed to carbon filtered air (CF), ambient non-filtered air (NF) and ambient non-filtered air+40 ppb ozone (NF+O3) 8 h per day during two months. The AOT40 values at the end of the experiment were 48, 910 and 12,895 ppb h(-1), respectively, for the three treatments. After 25 days of exposure (AOT40=3871 ppb h(-1)), interveinal red stippling appeared in plants in the NF+O3 chamber. In the NF chamber, symptoms were observed only after 60 days of exposure (AOT40=910 ppb h(-1)). After 60 days, injured leaves per plant corresponded to 19% in NF+O3 and 1% in the NF treatment; and the average leaf area injured was 7% within the NF+O3 and 0.2% within the NF treatment. The extent of leaf area injured (leaf injury index) was mostly explained by the accumulated exposure of ozone (r2=0.89; p<0.05).

Effects of fluoride emissions on two tropical grasses: Chloris gayana and Panicum maximum cv. Colonião

In order to detect early effects of plant contamination by fluoride emission on two tropical grasses, Chloris gayana and Panicum maximum, previously cultivated under greenhouse conditions, were exposed to a single source of fluoride emission at a station at 1.1 km from an aluminum smelter in Ouro Preto, MG, Brazil. Controls were placed at a reference station 78km from the fluoride source. During an 8-day period of exposure leaf injury, ionic permeability, photosynthetic rates, stomatal conductance, transpiration, chlorophyll a fluorescence and chlorophyll, soluble carbohydrates and fluoride contents were evaluated. Plants at the Ouro Preto station showed an increase in fluoride content, leaf injury and ionic permeability. Symptoms of injury by fluoride exposure were visible after 3-4 days in both species. High electrolyte leakage and correlation coefficients between the total ionic permeability and the fluoride content in leaves indicate a fluoride effect on the structural and/or functional integrity of the cellular membranes. Leaf fluoride injuries were quite different in the two species. In C. gayana necroses were limited to the leaf tips, while in P. maximum damages were observed in the whole leaf, suggesting a higher susceptibility of this latter species to fluoride. Nonetheless, neither grass showed statistical differences with respect to photosynthetic rates, stomatal conductance, transpiration, chlorophyll a fluorescence and chlorophyll content in leaves without any apparent fluoride injury. Plants at the Ouro Preto station showed a significant decrease in reducing sugar content between 3 and 5 days of exposure to fluoride, but thereafter reducing sugar content increased reaching the content of control plants. Fluoride exposed plants also showed a remarkable starch content reduction, remaining always much lower than those at the reference station.

Effects of initial climatic conditions on growth and accumulation of fluoride and nitrogen in leaves of two tropical tree species exposed to industrial air pollution

Saplings of Tibouchina pulchra and Psidium guajava, cultivated under standardized soil conditions, were placed in two sites at Cubatão (state of São Paulo, southeast Brazil) to study the effects of air pollution on growth, biomass allocation and foliar nitrogen and fluoride concentrations. Thirty-six potted plants were maintained over two periods of one year (Jul/00 to Jun/01; Dec/00 to Nov/01) at each of two experimental sites with distinct levels of air pollution: Pilões River Valley (PV) with vegetation virtually unaffected by air pollution; and Mogi River Valley (MV) severely affected by pollutants released mainly by chemical, fertilizer, iron and steel industries. For both species, saplings growing at MV showed alterations of growth and biomass allocation, as well as increased leaf concentrations of nitrogen and fluoride. Comparing both experimental periods, the one starting in winter (the driest season in Southeastern Brazil) seemed to affect the saplings more severely, the differences of the measured parameters between MV and PV being higher than in the second period. Multivariate analysis revealed two groups of data: one representing the MV and the other the PV saplings. For both species, saplings growing at MV showed differences in chemical composition, growth and biomass allocation, compared with the PV saplings. The results suggested that seasonal conditions of the first months of sapling exposure (summer or winter) modulate the intensity of responses to pollution stress.

Physiological responses of saplings of Caesalpinia echinata Lam., a Brazilian tree species, under ozone fumigation

The effects induced by long-term (30 day) and short-term (6h) exposures to ozone on the physiological parameters in young plants of Caesalpinia echinata Lam., a Brazilian tree species, were determined. Potted plants were maintained in open-top chambers in Valencia, Spain, under charcoal filtered air (mean O3 level: 29 microg m3), nonfiltered air (NF; 43 microg m3), and nonfiltered air plus O3 (NF + O3; 68 microg m3), simulating prevailing concentrations observed in the city of São Paulo, Brazil, during spring months (50 microg m3 in 2002). In the plants kept in NF + O3 for 30 days, although no foliar visible injuries were observed, the net carbon assimilation rate was reduced to 50%, stomatal conductance 42%, and transpiration 40%, when compared to the results for the NF plants. No changes in antioxidants, in leaf, stem, and root biomass, and in the root/shoot ratio were observed. Significant reductions were observed in gas exchange and in PSII photochemical efficiency (Fv/Fm) after 6 h of exposure to an O3 peak. The species was shown to be sensitive to ambient O3 concentrations measured in São Paulo.

White poplar (Populus alba) as a biomonitor of trace elements in contaminated riparian forests

Trees can be used to monitor the level of pollution of trace elements in the soil and atmosphere. In this paper, we surveyed the content of eight trace elements (As, Cd, Cu, Fe, Mn, Ni, Pb and Zn) in leaves and stems of white poplar (Populus alba) trees. We selected 25 trees in the riparian forest of the Guadiamar River (S. Spain), one year after this area was contaminated by a mine spill, and 10 trees in non-affected sites. The spill-affected soils had significantly higher levels of available cadmium (mean of 1.25 mg kg(-1)), zinc (117 mg kg(-1)), lead (63.3 mg kg(-1)), copper (58.0 mg kg(-1)) and arsenic (1.70 mg kg(-1)), than non-affected sites. The concentration of trace element in poplar leaves was positively and significantly correlated with the soil availability for cadmium and zinc, and to a lesser extent for arsenic (log-log relationship). Thus, poplar leaves could be used as biomonitors for soil pollution of Cd and Zn, and moderately for As.

Fingerprinting the impacts of global change on tropical forests

Recent observations of widespread changes in mature tropical forests such as increasing tree growth, recruitment and mortality rates and increasing above-ground biomass suggest that 'global change' agents may be causing predictable changes in tropical forests. However, consensus over both the robustness of these changes and the environmental drivers that may be causing them is yet to emerge. This paper focuses on the second part of this debate. We review (i) the evidence that the physical, chemical and biological environment that tropical trees grow in has been altered over recent decades across large areas of the tropics, and (ii) the theoretical, experimental and observational evidence regarding the most likely effects of each of these changes on tropical forests. Ten potential widespread drivers of environmental change were identified: temperature, precipitation, solar radiation, climatic extremes (including El Niño-Southern Oscillation events), atmospheric CO2 concentrations, nutrient deposition, O3/acid depositions, hunting, land-use change and increasing liana numbers. We note that each of these environmental changes is expected to leave a unique 'fingerprint' in tropical forests, as drivers directly force different processes, have different distributions in space and time and may affect some forests more than others (e.g. depending on soil fertility). Thus, in the third part of the paper we present testable a priori predictions of forest responses to assist ecologists in attributing particular changes in forests to particular causes across multiple datasets. Finally, we discuss how these drivers may change in the future and the possible consequences for tropical forests.