Leaf antioxidant fluctuations and growth responses in saplings of Caesalpinia echinata Lam. (brazilwood) under an urban stressing environment

Higher frequency of legitimate pollinators and fruit set of autotetraploid trees of Libidibia ferrea (Leguminosae) compared to diploids in a mixed tropical urban population

In mixed-ploidy populations, newly formed polyploids initially occur at low frequencies when compared to diploids. However, polyploidy may lead to morphological and phenological changes, which promote reproductive isolation and favor polyploid establishment and reproductive success. Additionally, previous studies have shown that polyploidy can confer some adaptive advantages to organisms in stressful environments. Here, we investigate variation in reproductive phenology, floral traits and reproductive success between diploid and autotetraploid trees of Libidibia ferrea (Mart. Ex Tul.) L.P. Queiroz (Leguminosae) in a mixed tropical urban population, a stressful environment. We assessed ploidy levels, flowering and fruiting phenology, flowering synchrony, floral and reproductive biology, pollination and fruit and seed set. We tested the hypothesis that autotetraploid individuals have a higher frequency of pollinators and higher fruit and seed set per inflorescence (as a proxy of reproductive success) than diploids in an urban green space. Libidibia ferrea is a good model to test our hypothesis because it is self-incompatible (i.e. relies on pollinators to set fruits). In the urban ecosystem studied, we found that diploids flowered for 6-7 months/year and autotetraploids for 3-5 months/year. Flowering synchrony was low between and within cytotypes and even though autotetraploids and diploids exhibited some overlap in flowering period, diploids flowered alone for 2-3 months. Autotetraploids had significantly more flowers per inflorescences, larger flowers and larger pollen grains (as expected for polyploids), but also a higher frequency of visits by legitimate pollinators including two exclusive ones, and higher fruit and seed set per inflorescence when compared to diploids, despite having a shorter flowering period. Our findings reveal some advantages for polyploids over their related diploids in a tropical urban green space. Also, our results highlight the need for more studies that seek to understand abiotic mechanisms affecting reproductive output of polyploids in urban ecosystems.

Trace metals at the tree-litter-soil- interface in Brazilian Atlantic Forest plots surrounded by sources of air pollution

Passive biomonitoring was applied in four Atlantic forest plots in southeast Brazil, affected by different levels of trace metal pollution (OP site located in Minas Gerais State and PEFI, PP and STG located in São Paulo State). Native tree species were selected as biomonitors according to their abundance in each plot and successional classification. Current trace metal concentrations in total suspended particles, leaves of non-pioneer (NPi) and pioneer (Pi) species, topsoil (0-20 cm) and litter and concentration ratios at the plant/soil interface were analyzed to verify the atmosphere-plant-soil interactions, basal concentrations, spatial variations and metal accumulation at the ecosystem level. Redundant analysis helped to identify similar characteristics of metal concentrations in PP and PEFI, which can be influenced by the high concentrations of elements related to anthropogenic inputs. Analysis of variance and multivariate statistics indicated that the trees of OP presented higher concentrations of Cr, Fe, Mn and Ni than those in the other sites. High enrichment of Cd, Fe, Ni in non-pioneer plants indicated that the PP forest (initially considered as the least polluted) has still been affected by metal pollution. Soil collected in STG was enriched by all elements, however these elements were low available for plant uptake. Metal deposited in leaves and litter was an important sink for soil cycling, nevertheless, these metals are not bioavailable in most cases. Non-pioneer tree species revealed to be more appropriate than pioneer species to indicate the current panorama of the contamination and bioavailability levels of trace metals in the tree community-litter-soil interface of the Atlantic forest remnants included in this study.

Woody-plant ecosystems under climate change and air pollution-response consistencies across zonobiomes?

Forests store the largest terrestrial pools of carbon (C), helping to stabilize the global climate system, yet are threatened by climate change (CC) and associated air pollution (AP, highlighting ozone (O3) and nitrogen oxides (NOx)). We adopt the perspective that CC-AP drivers and physiological impacts are universal, resulting in consistent stress responses of forest ecosystems across zonobiomes. Evidence supporting this viewpoint is presented from the literature on ecosystem gross/net primary productivity and water cycling. Responses to CC-AP are compared across evergreen/deciduous foliage types, discussing implications of nutrition and resource turnover at tree and ecosystem scales. The availability of data is extremely uneven across zonobiomes, yet unifying patterns of ecosystem response are discernable. Ecosystem warming results in trade-offs between respiration and biomass production, affecting high elevation forests more than in the lowland tropics and low-elevation temperate zone. Resilience to drought is modulated by tree size and species richness. Elevated O3 tends to counteract stimulation by elevated carbon dioxide (CO2). Biotic stress and genomic structure ultimately determine ecosystem responsiveness. Aggrading early- rather than mature late-successional communities respond to CO2 enhancement, whereas O3 affects North American and Eurasian tree species consistently under free-air fumigation. Insect herbivory is exacerbated by CC-AP in biome-specific ways. Rhizosphere responses reflect similar stand-level nutritional dynamics across zonobiomes, but are modulated by differences in tree-soil nutrient cycling between deciduous and evergreen systems, and natural versus anthropogenic nitrogen (N) oversupply. The hypothesis of consistency of forest responses to interacting CC-AP is supported by currently available data, establishing the precedent for a global network of long-term coordinated research sites across zonobiomes to simultaneously advance both bottom-up (e.g., mechanistic) and top-down (systems-level) understanding. This global, synthetic approach is needed because high biological plasticity and physiographic variation across individual ecosystems currently limit development of predictive models of forest responses to CC-AP. Integrated research on C and nutrient cycling, O3-vegetation interactions and water relations must target mechanisms' ecosystem responsiveness. Worldwide case studies must be subject to biostatistical exploration to elucidate overarching response patterns and synthesize the resulting empirical data through advanced modelling, in order to provide regionally coherent, yet globally integrated information in support of internationally coordinated decision-making and policy development.

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.

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.

Response of Brazilian native trees to acute ozone dose

Ozone (O3) is a toxic secondary pollutant able to cause an intense oxidative stress that induces visual symptoms on sensitive plant species. Controlled fumigation experiment was conducted with the aim to verify the O3 sensibility of three tropical species: Piptadenia gonoachanta (Mart.) Macbr. (Fabaceae), Astronium graveolens Jacq. (Anacardiaceae), and Croton floribundus Spreng. (Euphorbiaceae). The microscopical features involved in the oxidative stress were recognized based on specific histochemical analysis. The three species showed visual symptoms, characterized as necrosis and stippling between the veins, mostly visible on the adaxial leaf surface. All the studied species presented hypersensitive-like response (HR-like), and peroxide hydrogen accumulation (H2O2) followed by cell death and proanthocyanidin oxidation in P. gonoachanta and A. graveolens. In P. gonoachanta, a decrease in chlorophyll autofluorescence occurred on symptomatic tissues, and in A. graveolens and C. floribundus, a polyphenol compound accumulation occurred. The responses of Brazilian native species were similar to those described for sensitive species from temperate climate, and microscopical markers may be useful for the detection of ozone symptoms in future studies in the field.

The genus Caesalpinia L. (Caesalpiniaceae): phytochemical and pharmacological characteristics

The genus Caesalpinia (Caesalpiniaceae) has more than 500 species, many of which have not yet been investigated for potential pharmacological activity. Several classes of chemical compounds, such as flavonoids, diterpenes, and steroids, have been isolated from various species of the genus Caesalpinia. It has been reported in the literature that these species exhibit a wide range of pharmacological properties, including antiulcer, anticancer, antidiabetic, anti-inflammatory, antimicrobial, and antirheumatic activities that have proven to be efficacious in ethnomedicinal practices. In this review we present chemical and pharmacological data from recent phytochemical studies on various plants of the genus Caesalpinia.

Critical analysis of the potential of Ipomoea nil'Scarlet O'Hara' for ozone biomonitoring in the sub-tropics

This study aimed to analyze critically the potential of Ipomoea nil'Scarlet O'Hara' for O(3) biomonitoring in the sub-tropics. Four field experiments (one in each season of 2006) were carried out in a location of the city of São Paulo mainly polluted by O(3). Each experiment started with 50 plants, and lasted 28 days. Sub-lots of five plants were taken at intervals between three or four days long. Groups of four plants were also exposed in closed chambers to filtered air or to 40, 50 or 80 ppb of O(3) for three consecutive hours a day for six days. The percentage of leaf injury (interveinal chloroses and necroses), the concentrations of ascorbic acid (AA) and the activity of superoxide dismutase (SOD) and peroxidases (POD) were determined in the 5th, 6th and 7th oldest leaves on the main stem of the plants taken in all experiments. Visible injury occurred in the plants from all experiments. Seasonality in the antioxidant responses observed in plants grown under field conditions was associated with meteorological variables and ozone concentrations five days before leaf analyses. The highest levels of antioxidants occurred during the spring. The percentage of leaf injury was explained (R(2) = 0.97, p < 0.01) by the reduction in the levels of AA and activity of POD five days before the leaf analyses and by the reduction in the levels of particulate matter, and enhancement of temperature and global radiation 10 days before this same day. Although I. nil may be employed for qualitative O(3) biomonitoring, its efficiency for quantitative biomonitoring in the sub-tropics may be compromised, depending on how intense the oxidative power of the environment is.

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.

The redox state of Ipomoea nil 'Scarlet O'Hara' growing under ozone in a subtropical area

The occurrence of visible leaf injury caused by ozone in Ipomoea nil 'Scarlet O'Hara' may be regulated by their redox state, affecting its bioindicator efficiency. Thus, this study aimed to determine whether the redox state of I. nil plants in a subtropical area (São Paulo, SE-Brazil) contaminated by ozone oscillates, and to identify the environmental factors behind these variations. We comparatively evaluated indicators of redox state (ascorbic acid, glutathione, superoxide dismutase, ascorbate peroxidase, glutathione reductase) and leaf injury during nine field experiments of 28 days each. The variations in the redox indicators were explained by the combined effects of chronic levels of ozone and meteorological variables (mainly global solar radiation and air temperature) 3-6 days prior to the sampling days. The ascorbic acid and glutathione were crucial for increasing plant tolerance to ozone. Weak visible injury was observed in all experiments and occurred in leaves with low levels of ascorbic and dehydroascorbic acids.

How the redox state of tobacco 'Bel-W3' is modified in response to ozone and other environmental factors in a sub-tropical area?

This study intended to determine whether the redox state in plants of Nicotiana tabacum 'Bel-W3' fluctuates in response to the environmental factors in a sub-tropical area contaminated by ozone (São Paulo, SE-Brazil) and which environmental factors are related to this fluctuation, discussing their biomonitoring efficiency. We comparatively evaluated the indicators of redox state (ascorbic acid, glutathione, superoxide dismutase, ascorbate peroxidase, and glutathione reductase) and leaf injury in 17 field experiments performed in 2008. The redox state was explained by the combined effects of chronic levels of O(3) and meteorological variables 4-6 days prior to the plant sampling. Moderate leaf injury was observed in most cases. The redox state of tobacco decreases few days after their placement in the sub-tropical environment, causing them to become susceptible to oxidative stress imposed by chronic doses of O(3). Its bioindicator efficiency would not be diminished in such levels of atmospheric contamination.