Impacts of ground-level ozone on sugarcane production.

Sugarcane is a vital commodity crop often grown in (sub)tropical regions which have been experiencing a recent deterioration in air quality. Unlike for other commodity crops, the risk of air pollution, specifically ozone (O3), to this C4 crop has not yet been quantified. Yet, recent work has highlighted both the potential risks of O3 to C4 bioenergy crops, and the emergence of O3 exposure across the tropics as a vital factor determining global food security. Given the large extent, and planned expansion of sugarcane production in places like Brazil to meet global demand for biofuels, there is a pressing need to characterize the risk of O3 to the industry. In this study, we sought to a) derive sugarcane O3 dose-response functions across a range of realistic O3 exposure and b) model the implications of this across a globally important production area. We found a significant impact of O3 on biomass allocation (especially to leaves) and production across a range of sugarcane genotypes, including two commercially relevant varieties (e.g. CTC4, Q240). Using these data, we calculated dose-response functions for sugarcane and combined them with hourly O3 exposure across south-central Brazil derived from the UK Earth System Model (UKESM1) to simulate the current regional impact of O3 on sugarcane production using a dynamic global vegetation model (JULES vn 5.6). We found that between 5.6 % and 18.3 % of total crop productivity is likely lost across the region due to the direct impacts of current O3 exposure. However, impacts depended critically on the substantial differences in O3 susceptibility observed among sugarcane genotypes and how these were implemented in the model. Our work highlights not only the urgent need to fully elucidate the impacts of O3 in this important bioenergetic crop, but the potential implications air quality may have upon tropical food production more generally.

S-nitrosoglutathione spraying improves stomatal conductance, Rubisco activity and antioxidant defense in both leaves and roots of sugarcane plants under water deficit.

Water deficit is a major environmental constraint on crop productivity and performance and nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. This study aims to test the hypothesis that leaf spraying of S-nitrosoglutathione (GSNO), an NO donor, improves the antioxidant defense in both roots and leaves of sugarcane plants under water deficit, with positive consequences for photosynthesis. In addition, the roles of key photosynthetic enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) in maintaining CO2 assimilation of GSNO-sprayed plants under water deficit were evaluated. Sugarcane plants were sprayed with water or GSNO 100 µM and subjected to water deficit, by adding polyethylene glycol (PEG-8000) to the nutrient solution. Sugarcane plants supplied with GSNO presented increases in the activity of antioxidant enzymes such as superoxide dismutase in leaves and catalase in roots, indicating higher antioxidant capacity under water deficit. Such adjustments induced by GSNO were sufficient to prevent oxidative damage in both organs and were associated with better leaf water status. As a consequence, GSNO spraying alleviated the negative impact of water deficit on stomatal conductance and photosynthetic rates, with plants also showing increases in Rubisco activity under water deficit.

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.

Searching for native tree species and respective potential biomarkers for future assessment of pollution effects on the highly diverse Atlantic Forest in SE-Brazil.

This study summarizes the first effort to search for bioindicator tree species and respective potential biomarkers for future assessment of potential mixed pollution effects on the highly diverse Atlantic Forest in SE-Brazil. Leaves of the three most abundant species inventoried in a phytosociological survey (Croton floribundus, Piptadenia gonoacantha and Astronium graveolens) were collected in four forest remnants during winter and summer (2012). Their potential bioindicator attributes were highlighted using a screening of morphological, chemical and biochemical markers. The leaf surface structure and/or epicuticular wax composition pointed the accumulator properties of C. floribundus and P. gonoacantha. C. floribundus is a candidate for assessing potential accumulation of Cu, Cd, Mn, Ni, S and Zn. P. gonoacantha is a candidate to monitor polycyclic aromatic hydrocarbons. Increased levels of secondary metabolites and decreased antioxidant capacity in leaves of A. graveolens may support its value as a bioindicator for oxidative pollutants by visible dark stipplings.

Climatic factors influence leaf structure and thereby affect the ozone sensitivity of Ipomoea nil 'Scarlet O'Hara'.

Phenotypic plasticity of the leaves can interfere with the plant sensitivity to ozone (O3) toxic effect. This study aimed to assess whether the leaf structure of Ipomoea nil changes due to climatic variations and whether these changes affect the species' sensitivity. Field exposures, in different seasons (winter and spring) were made. The leaves that developed during the winter were thinner, with a lower proportion of photosynthetic tissues, higher proportion of intercellular spaces and lower density and stomatal index compared to those developed during the spring. The temperature and relative humidity positively influenced the leaf thickness and stomatal index. The visible injuries during winter were positively correlated with the palisade parenchyma thickness and negatively correlated with the percentage of spongy parenchyma; during the spring, the symptoms were positively correlated with the stomatal density. In conclusion, the leaf structure of I. nil varied among the seasons, interfering in its sensitivity to O3.

Ozone phytotoxic potential with regard to fragments of the Atlantic Semi-deciduous Forest downwind of Sao Paulo, Brazil.

In the Metropolitan Region of Campinas (MRC), Brazil, high levels of primary pollutants contribute to ozone (O3) formation. However, little is known regarding the O3 effects in the tropics. Objectives in this study were to characterize the present levels of O3 pollution and to evaluate the relevance of current concentration-based indices for assessing the phytotoxic potential of O3. Changes in O3 concentrations and precursors at 5 monitoring stations within towns of MRC were analyzed. The daily O3 profile was typical for urban sites and showed little yearly variation. Given the permanently foliated forest canopy, yearly rather than seasonal O3 indices were thus more appropriate for estimating the effective ozone dose. With yearly SUM00, SUM60 and AOT40 of 156, 16 and 14 ppm h and confirmed by evidence of O3 injury in foliage, oxidative stress in the MRC has reached levels high enough to affect trees from the Atlantic Semi-deciduous Forest.

The efficiency of tobacco Bel-W3 and native species for ozone biomonitoring in subtropical climate, as revealed by histo-cytochemical techniques.

We aimed to verify whether hydrogen peroxide (H(2)O(2)) accumulation and cell death are detected early in three bioindicators of ozone (O(3)), Nicotiana tabacum 'Bel-W3', Ipomoea nil 'Scarlet O'Hara' and Psidium guajava 'Paluma', and whether environmental factors also affect those microscopic markers. The three species were exposed to chronic levels of O(3) in a subtropical area and a histo-cytochemical technique that combines 3,3'-diaminobenzidine (DAB) with Evans blue staining was used in the assessments. The three species accumulated H(2)O(2), but a positive correlation with O(3) concentration was only observed in N. tabacum. A positive correlation between O(3) and cellular death was also observed in N. tabacum. In I. nil and P. guajava, environmental factors were responsible for symptoms at the microscopic level, especially in P. guajava. We conclude that the most appropriate and least appropriate bioindicator plant for O(3) monitoring in the subtropics are N. tabacum 'Bel-W3' and P. guajava 'Paluma', respectively.