ABSTRACT
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.
Subject(s)
Air Pollutants/toxicity , Antioxidants/metabolism , Construction Materials/toxicity , Dust/analysis , Magnoliopsida/physiology , Plant Leaves/metabolism , Air Pollutants/analysis , Construction Materials/analysis , Iron/metabolism , Photosynthesis/drug effects , Photosystem II Protein Complex/metabolism , Plant Leaves/drug effects , Soil/chemistry , Species Specificity , Tropical ClimateABSTRACT
BACKGROUND AND AIMS: The relative role of Pleistocene climate changes in driving the geographic distribution and genetic diversity of South American species is not well known, especially from open biomes such as the Cerrado, the most diverse tropical savanna, encompassing high levels of endemism. Here the effects of Quaternary climatic changes on demographic history, distribution dynamics and genetic diversity of Dimorphandra mollis, an endemic tree species widely distributed in the Cerrado, were investigated. METHODS: A total of 38 populations covering most of the distribution of D. mollis were analysed using internal transcribed spacer (ITS) sequences and nuclear microsatellite variation [simple sequence repeats (SSRs)]. The framework incorporated statistical phylogeography, coalescent analyses and ecological niche modelling (ENM). KEY RESULTS: Different signatures of Quaternary climatic changes were found for ITS sequences and SSRs corresponding to different time slices. Coalescent analyses revealed large and constant effective population sizes, with high historical connectivity among the populations for ITS sequences and low effective population sizes and gene flow with recent population retraction for SSRs. ENMs indicated a slight geographical range retraction during the Last Glacial Maximum. A large historical refugium across central Brazil was predicted. Spatially explicit analyses showed a spatial cline pattern in genetic diversity related to the paleodistribution of D. mollis and to the centre of its historical refugium. CONCLUSIONS: The complex genetic patterns found in D. mollis are the result of a slight geographical range retraction during the Last Glacial Maximum followed by population expansion to the east and south from a large refugium in the central part of the Cerrado. This historical refugium is coincident with an area predicted to be climatically stable under future climate scenarios. The identified refugium should be given high priority in conservation polices to safeguard the evolutionary potential of the species under predicted future climatic changes.
Subject(s)
Genetic Variation/genetics , Refugium , Trees/genetics , Biological Evolution , Grassland , Phylogeny , Trees/classificationABSTRACT
O fogo exerce um papel importante como modelador dos ecossistemas de diversas formações vegetais, especialmente o Cerrado. Sua ação induz a brotação em diversas espécies, muitas vezes formando folhas mais vigorosas e fisiologicamente mais ativas. Nesse contexto, o presente trabalho investigou o desempenho fotossintético de folhas jovens e maduras de Vochysia cinnamomea Pohl (Vochysiaceae) em resposta à ação do fogo natural sobre uma área de cerrado rupestre da Serra da Canastra, Minas Gerais, comparando-se; (1) folhas jovens de área queimada e não queimada e (2) folhas jovens e maduras de um mesmo indivíduo. Foram analisadas folhas maduras de indivíduos de área não queimada cuja brotação ocorreu anterior à queimada, e folhas jovens de indivíduos de áreas queimadas e não queimadas cuja brotação ocorreu após a passagem do fogo. Foram coletados e analisados dados relativos às taxas fotossintéticas, rendimento quântico potencial e efetivo, taxa relativa de transporte de elétrons, assimilação líquida de CO2, condutância estomática, transpiração e teores de clorofila. Não houve diferenças significativas entre as folhas jovens da área queimada e da área não queimada em relação aos processos fisiológicos testados. Desta forma não há nenhum tipo de resposta rápida em relação à passagem do fogo. Entretanto, foram encontradas diferenças significativas quando comparadas folhas jovens e maduras. É fato que folhas jovens de V. cinnamomea são estruturalmente distintas de folhas maduras, são mais suculentas e pilosas enquanto as folhas maduras são mais coriáceas, glabras e com cutícula evidente. Estas diferenças estruturais e os estágios fisiológicos de maturação distintos se refletem nas características fisiológicas estudadas nestas folhas que, quando maduras apresentam-se com menor grau de fotoinibição, maior teor de clorofilas e maior assimilação líquida de CO2.
Post-fire effect plays an important role as a modulator of plant ecosystems, especially of the Cerrado. It induces leaf sprouting in several species, often forming vigorous and more physiologically active leaves. In the present study it was investigated the photosynthetic performance of young and mature leaves of Vochysia cinnamomea Pohl (Vochysiaceae) in response to the fire action in a "cerrado rupestre" area of Serra da Canasta, Minas Gerais, comparing; (1) young leaves from fired and intact area, and (2) young and mature leaves from the same plant. Mature leaves from intact area plants which leaf sprouting occurred before fire action in the adjacent area, and young leaves from intact and fired area which leaf sprouting occurred after fire action were analyzed. Data were collected and analyzed on photosynthetic rates, potential and effective quantum yield, electron transport rate, CO2 assimilation, stomatal conductance, transpiration and chlorophyll contents. There were no significant differences between the young leaves of the burned and unburned area in relation to physiological parameters tested. Thus there is no kind of quick response in relation to fire effects. However, significant differences between young and mature leaves were found. Young leaves are structurally distinct of the mature leaves, been more succulent and pilous while mature leaves are more coriaceous, glabrous and with thicked cuticle. The structural differences between young and mature leaves are reflected in distinct physiological performance. Mature leaves present lower degree of photoinhibition, higher pigment content and CO2 assimilation.
Subject(s)
Photosynthesis , Chlorophyll , Plant Leaves , Grassland , Electron Transport , Fires , EcosystemABSTRACT
Physiological changes that increase plant performance during exposure to high temperatures may play an inverse role during exposure to low temperatures. The objective of this study was to test variations in photosystem II response to heat and cold stress in the leaves of a bromeliad with crassulacean acid metabolism submitted to high or low temperatures. Leaves were maintained under constant temperatures of 10 and 35°C and used to examine possible relationships among physiological responses to high and low temperatures and organic acid accumulation. We also tested if distinct parts of bromeliad leaves show differences in photosynthetic thermotolerance. The samples from leaves maintained at 35°C showed greater heat tolerance values, while those from leaves maintained at 10°C showed lower cold tolerance values. Our results identified a strong negative relationship between the organic acid accumulation and thermal tolerance of bromeliad leaves that largely explained the differences in thermal tolerance among groups. One of these differences occurred among regions of a single leaf, with the base showing critical heat values of up to 8°C higher than the top region, suggesting a possible partitioning of leaf response among its regions. Differences in thermal tolerance were also observed between sampling times, with higher values observed in the morning.
Subject(s)
Acids/metabolism , Bromeliaceae/physiology , Plant Leaves/metabolism , Temperature , Bromeliaceae/metabolism , Photosynthesis , Stress, PhysiologicalABSTRACT
Objetivou-se com esse estudo foi avaliar a influência da fertilização nitrogenada e do sombreamento artificial sobre a produtividade e variáveis bromatológicas da Brachiaria brizantha cv. Marandu. A pastagem foi submetida a quatro doses de adubação (0, 50, 70 e 100 kg de N por aplicação) e a quatro percentuais de sombreamento (0, 47, 53 e 66%) por meio de tela de náilon. A produção de matéria seca teve resposta linear para o sombreamento e a fertilização nitrogenada, onde reduziu com o sombreamento e aumentou com as doses de N. Os valores médios do índice de área foliar e a interceptação luminosa foram superiores ao preconizado no manejo de pastagens. O sombreamento não alterou a altura do dossel e o teor de FDN. Os maiores teores de FDN foram com 100 kg de N e os menores de FDA com 47,5% de sombreamento. O teor de PB decresceu linearmente em função do aumento sombreamento e das doses de N. A produção do capim-marandu responde positivamente ao aumento do N e negativamente ao sombreamento, enquanto que a quantidade e a qualidade da proteína decrescem pela ação de ambos os fatores.
The objective of this study was to evaluate the influence of nitrogen fertilization and artificial shading on yield and nutritive value of variables Brachiaria brizantha. Marandu. The pasture was subjected to four fertilizer levels (0, 50, 70 and 100 kg N per application) and four percentage shading (0, 47, 53 and 66%) through nylon screen. The dry matter production had linear response to nitrogen fertilization and shading, where shading and decreased with increased with doses of N. The mean values of leaf area index and light interception were higher than recommended in pasture management. Shading did not affect canopy height and NDF. The highest NDF were with 100 kg N and under ADF with 47.5% shading. The CP decreased linearly with the increase shading and levels of N. The production of Marandu palisadegrass responds positively to increased N and negatively to shading, while the quantity and quality of the protein decreases the action of both factors.
