Eduardo Arcoverde de Mattos

Overnight rainfall inducing rapid changes in photosynthetic behaviour in a cerrado woody species during a dry spell amidst the rainy season

We examined the effects of a short rainfall during a dry spell amidst the rainy season on CO2 and H2O gas exchange and chlorophyll a fluorescence in leaves of Miconia albicans (Sw.) Tr. (Melastomataceae), a common shrub of the Brazilian cerrado. A strong midday depression of gas exchange was observed at the end of the dry spell. Nevertheless, during the day after a rainfall, net CO2 uptake (JCO2), stomatal conductance to water vapour (gs), transpiration rates (JH2O) and the actual photosystem II (PSII) efficiency (ΔF/F´m) increased, whereas the fraction of light absorbed in the PSII antennae that is dissipated directly within the antennae (1 – F´v/F´m) and the degree of PSII closure (1 – qP) decreased. Although CO2 and H2O gas exchange were very sensitive to the rain-free event in the wet season, the occurrence of a small rainfall was enough to elicit rapid changes in gs, JH2O and JCO2. We hypothesise that the strong effect of the dry spell during the wet season on gas exchange may be due to the highest leaf area available for transpiration at this time and a lower hydraulic limit for catastrophic embolism to occur.

Photosynthesis and carbon gain under contrasting light levels in seedlings of a pioneer and a climax tree from a Brazilian Semideciduous Tropical Forest

In this study we evaluated photosynthetic characteristics and patterns of biomass accumulation in seedlings of two tree species from a Semideciduous Tropical Forest of Brazil. Seedlings of Trema micrantha (L.) Blum. (pioneer) and Hymenaea courbaril (L.) var. stilbocarpa (Hayne) Lee & Langenh. (climax) were grown for 4 months under low light (LL) (5%-8% of sunlight) and high light (HL) (100% of sunlight). Under HL, T. micrantha showed higher CO2 assimilation rates (ACO2) and light saturation than H. courbaril. Under LL, ACO2 were higher in H. courbaril. Under LL, total chlorophyll and carotenoid contents per unit leaf area were higher in H. courbaril. Chlorophyll a/b ratio was higher in T. micrantha under both light regimes. ACO2 and Fv/Fm ratio at both pre-dawn and midday in H. coubaril were lower in HL indicating chronic photoinhibition. Thus, the climax species was more susceptible to photoinhibition than the pioneer. However, H. courbaril produced higher total biomass under both treatments showing high efficiency in the maintenance of a positive carbon balance. Thus, both species expressed characteristics that favor growth under conditions that resemble their natural microenvironments, but H. courbaril also grew under HL. The ecophysiological range of responses to contrasting light levels of this climax plant seems to be broader than generally observed for other rainforest climax species. We propose that this could be related to the particular spatio-temporal light regime of the semideciduous forests.

Expression of crassulacean acid metabolism in Clusia hilariana Schlechtendal in different stages of development in the field

Expression of crassulacean acid metabolism (CAM) in the obligate CAM-tree Clusia hilariana SCHLTDL. was studied in the restinga of Jurubatiba National Park, on the Atlantic coast of Rio de Janeiro state, Brazil, comparing plants at different developmental stages. Between young and mature plants there were trends of differences in six parameters, which are all related to CAM expression. From young to mature plants there were tendencies for a decrease of (1) the degree of succulence, (2) the degree of day/night changes of malic acid levels, (3) titratable acidity with nocturnal acid accumulation, (4) the degree of day/night changes of free hexoses with nocturnal break down, (5) effective quantum use efficiency of photosystem II at high photosynthetic photon flux density, and (6) protection from photoinhibition. These tendencies form a clear pattern which suggests that CAM was somewhat more pronounced in leaves of young plants than in leaves of mature plants. A developmental regulation may be involved. However, the observations are probably best explained by stress, since in the dry soils of the restinga young plants have no access to the ground water table while adult trees develop extensive root systems.

Comparison of the performance of three different ecophysiological life forms in a sandy coastal restinga ecosystem of SE-Brazil: a nodulated N2-fixing C3-shrub (Andira legalis (Vell.) Toledo), a CAM-shrub (Clusia hilariana Schltdl.) and a tap root C3-hemicryptophyte (Allagoptera arenaria (Gomes) O. Ktze.)

In a sandy coastal restinga ecosystem NE of Rio de Janeiro, Brazil, subject to environmental stress due to high irradiance, high temperature and low water supply, a comparative ecophysiological study of three species of different morphotypes and physiotypes was conducted during the dry season. The morphotypes were two shrubs, Clusia hilariana Schltdl. and Andira legalis (Vell.) Toledo, and the taproot hemicryptophyte Allagoptera arenaria (Gomes) O. Ktze. The physiotype differences were that C. hilariana was performing crassulacean acid metabolism (CAM), A. legalis was a nodulated N2 fixing legume and A. arenaria had ample access to water by ground water tapping roots. All three species were light stressed and showed photoinhibition and high maximum values of non-photochemical quenching of chlorophyll fluorescence. δ13C values of bulk leaf organic matter (which integrate over the life span of the leaf) and instantaneous gas exchange patterns demonstrated that C. hilariana was performing CAM and the other two species C3-photosynthesis. A. arenaria performed generous and A. legalis conserving use of water. Based on the CO2 concentrating mechanism of CAM C. hilariana had the highest maximum rates of apparent photosynthetic electron transport, ETRmax. Uptake of atmospheric CO2 in the afternoon (phase IV of CAM) was expressed weakly showing that the plants were under some but not severe water stress. A. legalis showed the highest levels of total N and soluble non-protein N-compounds in its organs due to N2 fixation which, however, did not confer a higher photosynthetic capacity that must have been limited by factors other than nitrogen supply. Accumulation of amino compounds like proline and γ-aminobutyric acid in leaves of A. legalis which are known to act as osmoprotectants is likely to indicate drought stress in the dry season. Maximum net CO2 uptake of photosynthesis was higher in the water spending A. arenaria than in A. legalis. The comparative analysis of physiological traits characterised either instantaneously or integrated over the longer term shows that in addition to morphotypic characteristics physiotypic characteristics are important for space occupation and niche acquisition of the plants in the restinga.

Variação temporal de características morfológicas de folhas em dez espécies do Parque Nacional da Restinga de Jurubatiba, Macaé, RJ, Brasil

Ranking species in relation to a continuum of leaf-trait variation can be useful to infer community susceptibility to changes in resource availability and/or environmental conditions over time. Leaves of ten woody restinga species were sampled in February, April and August over a period of 3 years to characterize temporal variability of leaf mass per area (LMA), succulence (SUC), thickness (THI) and density (DEN). The species showed a trend toward higher leaf-trait values in dry months during the three-year study. Based on seasonal and interannual comparison of LMA, SUC, THI and DEN we suggest that plant responses to temporal heterogeneity in water availability were convergent, independent of leaf phenological patterns and phylogeny. Thus, the similarity observed among species in temporal dynamics of leaf traits points to water availability as a limiting factor for the success of sandy-coastal-plain occupation in northeastern Rio de Janeiro.

Are leaf physiological traits related to leaf water isotopic enrichment in restinga woody species

During plant-transpiration, water molecules having the lighter stable isotopes of oxygen and hydrogen evaporate and diffuse at a faster rate through the stomata than molecules having the heavier isotopes, which cause isotopic enrichment of leaf water. Although previous models have assumed that leaf water is well-mixed and isotopically uniform, non-uniform stomatal closure, promoting different enrichments between cells, and different pools of water within leaves, due to morpho-physiological traits, might lead to inaccuracies in isotopic models predicting leaf water enrichment. We evaluate the role of leaf morpho-physiological traits on leaf water isotopic enrichment in woody species occurring in a coastal vegetation of Brazil known as restinga. Hydrogen and oxygen stable isotope values of soil, plant stem and leaf water and leaf traits were measured in six species from restinga vegetation during a drought and a wet period. Leaf water isotopic enrichment relative to stem water was more homogeneous among species during the drought in contrast to the wet period suggesting convergent responses to deal to temporal heterogeneity in water availability. Average leaf water isotopic enrichment relative to stem water during the drought period was highly correlated with relative apoplastic water content. We discuss this observation in the context of current models of leaf water isotopic enrichment as a function of the Péclet effect. We suggest that future studies should include relative apoplastic water content in isotopic models.

Caracteres das sementes, plântulas e plantas jovens de Ormosia arborea (Vell.) Harms E Ormosia fastigiata Tul. (Leg-papilionoideae)

RESUMO – Ormosia arborea (Vell.) Harms e Ormosia fastigiata Tul. sao especies similares em muitos caracteres morfologicos, o que resulta em dificuldade na sua identificacao, tanto em campo quanto em material herborizado. Neste estudo foram descritas as caracteristicas morfologicas das sementes e morfoanatomicas das plântulas e plantas jovens de O. arborea e O. fastigiata, coletadas em restinga e em mata ciliar, respectivamente. Sementes e plântulas foram processadas segundo tecnicas usuais. As sementes de O. arborea sao mais pesadas e tem germinacao hipogea criptocotiledonar. O caule contem tricomas tectores esparsos e grande quantidade de lenticelas e, na raiz, nodulacoes. A folha apresenta parenquima palicadico de celulas mais curtas, com base mais larga e presenca de pigmentos vacuolares, espacos intercelulares conspicuos no parenquima esponjoso, tricomas tectores restritos a nervura principal e celulas epidermicas da face adaxial maiores que as da face abaxial. A germinacao de O. fastigiata e fanerocotiledonar, e a plântula possui muitos tricomas ao longo do caule e lenticelas restritas a regiao basal deste. As folhas apresentam tricomas tectores em todas as nervuras, com parenquima palicadico de celulas tipicamente alongadas e parenquima esponjoso com espacos intercelulares reduzidos. Tais caracteristicas sao consistentes para separar as plântulas e sementes dessas especies, que tem a mesma denominacao popular e contribuem com informacoes uteis para o meio produtivo. Palavras-chave: Morfologia da semente, Mata ciliar e Restinga. CHARACTERS OF SEEDS, SEEDLINGS AND YOUNG PLANTS OF Ormosia arborea (Vell.) Harms AND Ormosia fastigiata Tul. (LEG-PAPILIONOIDEAE)

Carbon Sequestration: what really matters? - A reply to Buckeridge & Aidar

This is a reply to Buckeridge & Aidars (2002) Point of View on the possible usefulness of GMOs (genetically modified organisms) built to increase carbon sequestration, and Plant Gene Therapy (PGT), particularly in rain forests, as future tools to reduce excessive atmospheric CO2. We argue that the alternatives to carbon sequestration they presented should not be treated as scientific or political priority, since their arguments have major ecological and socio-political flaws, such as ecological unpredictability, the existence of an already high potential for carbon sequestration by native non-manipulated plants, and the relevance of scientific and political sovereignty in regard to the global change issue.

On the relative importance of CSR ecological strategies and integrative traits to explain species dominance at local scales

Summary Identifying ecological strategies based on functional traits has been one of the main focuses of studies on plant community assembly. Recently, an important and timely tool, “StrateFy”, has been proposed for detecting plant strategies across the globe according to the CSR scheme. The CSR scheme is undeniably efficient across scales, and distinct CSR strategies among species have been proposed to explain differing degrees of dominance among species. However, in a previous study we showed that dominance ranking of woody species in a resource-poor habitat (coastal sandy plain) was not explained by morphological traits commonly measured in functional approaches (such as those used to estimate CSR strategies), but by integrative traits (i.e. traits that are the result of different combinations of functional traits) more related to plant performance. Here, we used CSR analysis and StrateFy on a dataset collected on a coastal sandy plain to test the hypothesis that the dominance ranking would be compatible with the CSR strategies; i.e., that dominant species would show a greater proportion of the stress-tolerance (S%) strategy than subordinate species. Contrary to our hypothesis, all species exhibited an S/CS strategy, and the most-dominant species had neither similar values nor the highest S%. The inability of CSR analysis (as applied using StrateFy) to predict dominance ranking suggests that it can explain relative dominance when different strategies co-occur, but not in cases where dominant and subordinate plants share the same strategy. We argue that the relative importance of CSR and integrative traits for describing dominance ranking may depend on how CSR strategies are filtered in each environment. In environments where only a narrow range of strategy classes are viable, integrative traits may be more important for explaining variation in degrees of dominance. Thus, the ability of a given species to achieve dominance may depend on integrative traits resulting from multiple trait arrays, not necessarily captured by the SLA, LDMC and LA measurements that are used to calculate the relative proportions of strategies in StrateFy. This article is protected by copyright. All rights reserved.

Soil seed bank in a patchy vegetation of coastal sandy plains in southeastern Brazil

Large seed banks have been found in tropical dry forests and also in habitats with high seasonality in rainfall. However, patchily structured vegetation could induce great spatial variation in the seed bank. We characterized the seed bank in a patchy vegetation of restinga, a common type of coastal vegetation found in the Atlantic forest biome. We also evaluated whether there is any spatial variation between the litter and soil layer, bare sand, and the edge and center of vegetation patches with distinct species dominance. We found 104 seeds/m2 in the seed bank using a 5-cm-depth sampling. Seven out of 16 species found in the restinga seed bank germinated; two of these were found in the early stages of vegetation patches. We found a higher number of seeds at the edge than in the center of vegetation patches. However, there were no significant differences in the number of seeds in the seed bank between the litter and soil layer, and between vegetation patches with distinct species dominance. Bare sandy soils had lower seed bank densities than vegetation patches. A small seed bank size might be explained by the low proportion of seeds from herbaceous and woody species, which are pioneers in the Atlantic forest. However, seed bank might play an important role in the early stages of the successional process, due to the occurrence of the few species that are able to colonize new young vegetation patches.