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.

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.

Gas exchange, antioxidants and foliar injuries in saplings of a tropical woody species exposed to ozone.

Ozone (O(3)) reaches phytotoxical concentrations in the tropics, but the sensitivity of tropical plant species to O(3) remains unknown. Visible foliar injuries, carbon assimilation (A(sat)), stomatal conductance, superoxide dismutase enzyme (SOD) activity and ascorbic acid concentration (AA) were evaluated in different-aged leaves of Psidium guajava 'Paluma' saplings. We hypothesized that the old leaves are less capable of combating the stress induced by O(3) and hence exhibit more severe leaf injuries. Three O(3) exposure experiments were performed with 'Paluma' saplings in sites with high O(3) concentration and also under filtered air conditions. The exposure experiments corresponding to the seasons spring/2006, summer and autumn/2007. The decrease of A(sat) was greater in old leaves of saplings exposed to O(3), except in the second experiment, when the AA concentrations were more pronounced than in the other experiments. In second experiment, O(3) uptake was similar to that of the first experiment, but the injuries were less severe, probably due to the high AA concentrations. It was not possible to identify a pattern of superoxide dismutase enzyme (SOD) activity due to the high variability in the results from O(3) exposed and reference saplings. O(3) uptake/A(sat) was higher in leaves exhibiting greater injury, suggesting that decrease in A(sat) may have been the main feature associated with the visible foliar symptons.

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).

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.

Ozone stomatal flux and O3 concentration-based metrics for Astronium graveolens Jacq., a Brazilian native forest tree species.

The current levels of surface ozone (O3) are high enough to negatively affect trees in large regions of São Paulo State, southeastern Brazil, where standards for the protection of vegetation against the adverse effects of O3 do not exist. We evaluated three O3 metrics - phytotoxic ozone dose (POD), accumulated ozone exposure over the threshold of 40 ppb h (AOT40), and the sum of all hourly average concentrations (SUM00) - for the Brazilian native tropical tree species Astronium graveolens Jacq. We used the DO3SE (Deposition of Ozone for Stomatal Exchange) model and calculated PODY for different thresholds (from 0 to 6 mmol O3 m(-2) PLA s(-1)), evaluating the model's performance through the relationship between measured and modelled conductance. The response parameters were: visible foliar injury, considered as incidence (% injured plants), severity (% injured leaves in relation to the number of leaves on injured plants), and leaf abscission. The model performance was suitable and significant (R(2) = 0.58; p < 0.001). POD0 was better correlated to incidence and leaf abscission, and SUM00 was better correlated to severity. The highest values of O3 concentration-based metrics (AOT40 and SUM00) did not coincide with those of POD0. Further investigation may improve the model and contribute to the proposition of a national standard for the protection of native species.

DO3SE model applicability and O3 flux performance compared to AOT40 for an O3-sensitive tropical tree species (Psidium guajava L. 'Paluma').

Phytotoxic ozone (O3) levels have been recorded in the Metropolitan Region of São Paulo (MRSP). Flux-based critical levels for O3 through stomata have been adopted for some northern hemisphere species, showing better accuracy than with accumulated ozone exposure above a threshold of 40 ppb (AOT40). In Brazil, critical levels for vegetation protection against O3 adverse effects do not exist. The study aimed to investigate the applicability of O3 deposition model (Deposition of Ozone for Stomatal Exchange (DO3SE)) to an O3-sensitive tropical tree species (Psidium guajava L. 'Paluma') under the MRSP environmental conditions, which are very unstable, and to assess the performance of O3 flux and AOT40 in relation to O3-induced leaf injuries. Stomatal conductance (g s) parameterization for 'Paluma' was carried out and used to calculate different rate thresholds (from 0 to 5 nmol O3 m(-2) projected leaf area (PLA) s(-1)) for the phytotoxic ozone dose (POD). The model performance was assessed through the relationship between the measured and modeled g sto. Leaf injuries were analyzed and associated with POD and AOT40. The model performance was satisfactory and significant (R (2) = 0.56; P < 0.0001; root-mean-square error (RMSE) = 116). As already expected, high AOT40 values did not result in high POD values. Although high POD values do not always account for more injuries, POD0 showed better performance than did AOT40 and other different rate thresholds for POD. Further investigation is necessary to improve our model and also to check if there is a critical level of ozone in which leaf injuries arise. The conclusion is that the DO3SE model for 'Paluma' is applicable in the MRSP as well as in temperate regions and may contribute to future directives.

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.