Revegetation of mining-impacted sites with a tropical native grass: Constraints of climate seasonality and trace-element accumulation.

The iron ore mining activity results in considerable waste production and impacts on surrounding ecosystems. Natural recovery of impacted areas is absent or occurs slowly, especially when associated with prolonged dry seasons in tropical regions. The objective of this work was to unveil the mechanisms of Paspalum densum (Poir.) grass to overcome the periods of seasonal drought and its metal accumulation in areas impacted by iron mining, a tailings storage facilities and surrounding ferruginous grassland in Brazil. Lower mortality was observed among individuals in the tailings storage facilities, with a 74.3% survival rate. In contrast, after the beginning of the dry season, all individuals died in the ferruginous grassland. The plants in the tailings deposits showed better nutrition, with a higher concentration of P, Cu, Fe, Zn, Mn and greater capacity to accumulate Pb and Cd over time. Pb was the element with highest bioconcetration factor (BCF) and bioaccumulation coefficient (BAC), while Mn was the one with the highest translocation factor (TF). The dry season resulted in reduced chlorophyll a, b and total and effective quantum yield of photosystem II (PSII) of P. densum individuals. However, the plants in the tailings storage facilities showed adjustments to overcome the effects of drought, with an increase in the concentration of proline in leaves and reduction of oxidative damage (MDA and H2O2) at the end of the dry season. The grass P. densum showed rapid acclimatization in the tailings storage facilities and resistance to drought through antioxidant and photosynthetic adjustments and was still able to bioaccumulate and translocate in plant tissues some metals present in the iron ore impacted sites.

Iron toxicity resistance strategies in tropical grasses: The role of apoplastic radicular barriers.

The revegetation of mined areas poses a great challenge to the iron ore mining industry. The initial recovery process in degraded areas might rely on the use of Fe-resistant grasses. Tropical grasses, such as Paspalum densum and Echinochloa crus-galli, show different resistance strategies to iron toxicity; however, these mechanisms are poorly understood. The Fe-resistance mechanisms and direct iron toxicity as a function of root apex removal were investigated. To achieve this purpose, both grass species were grown for up to 480 hr in a nutrient solution containing 0.019 or 7 mmol/L Fe-EDTA after the root apices had been removed or maintained. Cultivation in the presence of excess iron-induced leaf bronzing and the formation of iron plaque on the root surfaces of both grass species, but was more significant on those plants whose root apex had been removed. Iron accumulation was higher in the roots, but reached phytotoxic levels in the aerial parts as well. It did not hinder the biosynthesis of chloroplastidic pigments. No significant changes in gas exchange and chlorophyll a fluorescence occurred in either grass when their roots were kept intact; the contrary was true for plants with excised root apices. In both studied grasses, the root apoplastic barriers had an important function in the restriction of iron translocation from the root to the aerial plant parts, especially in E. crus-galli. Root apex removal negatively influenced the iron toxicity resistance mechanisms (tolerance in P. densum and avoidance in E. crus-galli).

Physiological traits and antioxidant metabolism of leaves of tropical woody species challenged with cement dust.

Tropical woody species occurring in limestone outcrops are frequently exposed to particulate material from cement factories. The effects of 60-day cement dust exposure on physiological traits and enzymatic antioxidant system of young plant leaves of Guazuma ulmifolia Lam., Myracrodruon urundeuva Allemão and Trichilia hirta L. were investigated. Cement dust (2.5 or 5mgcm-2) was applied to the leaf surface or soil or both (leaf plus soil) and plants were maintained at greenhouse. Cement dust barely affected the mineral nutrient levels, except for iron whose content was decreased in leaves/leaflets of all species studied. The incident light was partly blocked in cement dust-treated leaves, regardless of the plant species, causing a decrease in the photosynthetic pigments in M. urundeuva. The chlorophyll b content, however, increased in G. ulmifolia and T. hirta leaves upon cement dust treatment. The potential quantum yield of photosystem II in challenged leaves of G. ulmifolia was 3.8% lower than that of control plants, while such trait remained unaffected in the leaves of the other species. No changes in leaf stomatal conductance and antioxidant enzymes activities were observed, except for M. urundeuva, which experienced a 31% increment in the superoxide dismutase activity upon 5mgcm-2 cement dust (leaf plus soil treatment), when compared with control plants. Overall, the mild changes caused by cement dust in the in physiological and biochemical traits of the species studied indicate that such species might be eligible for further studies of revegetation in fields impacted by cement factories.

Iron plaque formation and morphoanatomy of roots from species of restinga subjected to excess iron.

The restingas, a sandy coastal plain ecosystem of Brazil, have received an additional amount of iron due to the activity of mining industries. The present study aims to characterize morphoanatomically and histochemically the iron plaque formation on roots of Ipomoea pes-caprae L. and Canavalia rosea DC, cultivated in hydroponic solution with and without excess iron. The iron plaque formation as well as changes in the external morphology of the lateral roots of both species were observed after the subjection to excess iron. Changes in the nutrient uptake, and in the organization and form of the pericycle and cortex cells were observed for both species. Scanning electron microscopy showed evident iron plaques on the whole surface of the root. The iron was histolocalized in all root tissues of both species. The species of restinga studied here formed iron plaque in their roots when exposed to excess of this element, which may compromise their development in environments polluted by particulated iron.

How does drought affect native grasses' photosynthesis on the revegetation of iron ore tailings?

The revegetation of areas degraded by iron ore mining is a difficult challenge mainly due to water availability and impoverished metal-rich substrates. We sought to understand the photosynthetic responses to drought of native tropical grasses Paspalum densum (Poir.) and Setaria parviflora (Poir.) grown in iron ore tailing. The grass P. densum presented better photosynthetic adjustments when grown in the iron ore tailing and S. paviflora in response to water stress. Both species accumulated iron above the phytotoxic threshold when grown in an iron ore tailing. The net photosynthesis, stomatal conductance, transpiration, and water use efficiency decreased followed by a reduction in leaf relative water content in response to water stress for both species. The photochemical efficiency of photosystem II only decreased at the point of maximum drought. At this point, the water-stressed grass grown in the iron ore tailing presented higher H2O2 concentrations, particularly S. parviflora. After rehydration, full recovery of photosynthetic variables was achieved with decreased malondialdehyde concentrations, increased catalase activity, and, consequently, decreased H2O2 concentrations in leaves for both species. The fast recovery of the native grasses P. densum and S. parviflora to drought in the iron ore tailing substrate is indicative of their resistance and potential use in the revegetation of impoverished mined areas with high iron content and seasonal water deficit.

Clusia hilariana and Eugenia uniflora as bioindicators of atmospheric pollutants emitted by an iron pelletizing factory in Brazil.

The objectives of this work were to evaluate if the pollution emitted by the pelletizing factory causes visual symptoms and/or anatomical changes in exposed Eugenia uniflora and Clusia hilariana, in active biomonitoring, at different distances from a pelletizing factory. We characterize the symptomatology, anatomical, and histochemistry alterations induced in the two species. There was no difference in the symptomatology in relation to the different distances of the emitting source. The foliar symptoms found in C. hilariana were chlorosis, necrosis, and foliar abscission and, in E. uniflora, were observed necrosis punctuais, purple spots in the leaves, and increase in the emission of new leaves completely purplish. The two species presented formation of a cicatrization tissue. E. uniflora presented reduction in the thickness of leaf. In C. hilariana, it was visualized hyperplasia of the cells and the adaxial epidermis did not appear collapsed due to thick cuticle and cuticular flanges. Leaves of C. hilariana showed positive staining for iron, protein, starch, and phenolic compounds. E. uniflora showed positive staining for total phenolic compounds and starch. Micromorphologically, there was accumulation of particulate matter on the leaf surface, obstruction of the stomata, and scaling of the epicuticular wax in both species. It was concluded that the visual and anatomical symptoms were efficient in the diagnosis of the stress factor. C. hilariana and E. uniflora showed to be good bioindicators of the atmospheric pollutants emitted by the pelletizing factory.

Leaf structural traits of tropical woody species resistant to cement dust.

Cement industries located nearby limestone outcrops in Brazil have contributed to the coating of cement dust over native plant species. However, little is known about the extent of the response of tropical woody plants to such environmental pollutant particularly during the first stages of plant development and establishment. This work focused on the investigation of possible alterations in leaf structural and ultrastructural traits of 5-month-old Guazuma ulmifolia Lam. (Malvaceae), 6-month-old Myracrodruon urundeuva Allemão (Anacardiaceae), and 9-month-old Trichilia hirta L. (Meliaceae) challenged superficially with cement dust during new leaf development. Leaf surface of plants, the soil or both (leaf plus soil), were treated (or not) for 60 days, under controlled conditions, with cement dust at 2.5 or 5.0 mg cm(-2). After exposure, no significant structural changes were observed in plant leaves. Also, no plant death was recorded by the end of the experiment. There was also some evidence of localized leaf necrosis in G. ulmifolia and T. hirta, leaf curling in M. urundeuva and T. hirta, and bulges formation on epidermal surface of T. hirta, after cement dust contact with plant shoots. All species studied exhibited stomata obliteration while T. hirta, in particular, presented early leaf abscission, changes in cellular relief, and organization and content of midrib cells. No significant ultrastructural alterations were detected under the experimental conditions studied. Indeed, mesophyll cells presented plastids with intact membrane systems. The high plant survival rates, together with mild morphoanatomic traits alterations in leaves, indicate that G. ulmifolia is more resistant to cement dust pollutant, followed by M. urundeuva and T. hirta. Thus, the three plant species are promising for being used to revegetate areas impacted by cement industries activities.

Impact of cement dust pollution on Cedrela fissilis Vell. (Meliaceae): A potential bioindicator species.

Considering the impacts caused to vegetation in the vicinity of cement factories, the aim of this study was to evaluate the impacts of cement dust on the structural organization and physiological/biochemical traits of Cedrela fissilis leaflets, a woody species native to tropical America. Plants were exposed to 2.5 or 5 mg cm-2 cement dust applied to the leaf surface, to the soil or simultaneously to the leaf surface and the soil.. Leaves of shoot-treated plants exhibited chlorosis, marginal and inter veins necrosis, diminished thickness, epidermal cells less turgid, cellular collapse, obstructed stomata, senescence, rolling and some abscission. In few cases, individual death was recorded. Cement dust-treated plants also presented decreased amount of photosynthetic pigments and iron (Fe) and increase in calcium (Ca) levels. The cement crust formed in leaves surface blocked from 30 to 50% of the incoming light and reduced the stomatal conductance and the potential quantum yield of photosystem II. Control or soil-treated plants did not exhibit morphophysiological changes throughout the experiment. The activity of superoxide dismutase, catalase and ascorbate peroxidase increased in leaves of plants upon treatment with 2.5 mg cm(-2) cement dust, independent of the site application. Overall, these results indicate that C. fissilis is highly sensitive to cement dust at the initial stage of development.

Anatomical and histochemical characterization of Dipteryx odorata and Taralea oppositifolia, two native Amazonian species

Abstract Dipteryx odorata (Aubl.) Willd. and Taralea oppositifolia Aubl., Fabaceae: Dipterygeae, are two Amazonian species of great economic and pharmacological potential. The anatomy of these species, however, remains poorly studied. The aim of this work was to inventory leaf anatomical characteristics of D. odorata and T. oppositifolia and to locate and identify secretory structures and determine the main classes of metabolites they store. Vegetative branches were collected in Parque Ecológico de Gunma, Belém, state of Pará, Brazil. Some of the branches were destined for herborization while the remainder was submitted to standard protocols for anatomical analysis and histochemical tests. Both species were found to possess an unstratified epidermis, with D. odorata being amphistomatic and T. oppositifolia being hypostomatic, and dorsiventral mesophyll with spongy parenchyma and wide cellular space. The two species were also found to possess idioblasts and secretory cavities that produce a heterogeneous exudate consisting of polysaccharides, lipids, alkaloids and phenolic compounds. The species presented differences in leaf anatomy and chemical composition of the secretory structures, which may be useful in their differentiation.