Carmen Eugenia Rodríguez Ortíz

Photosynthetic parameters of two invasive tree species of the Brazilian Pantanal in response to seasonal flooding

The Pantanal is the largest wetland in the world with extremely high plant and animal diversity, but large areas have been invaded by Vochysia divergens Pohl (Vochysiaceae), a tree that is native to the Amazon Basin, and Curatella americana L. (Dilleniaceae), a tree that is native to the Brazilian savanna (cerrado). V. divergens is reportedly floodadapted, thus its ability to invade the Pantanal may not be surprising, but the invasion of C. americana is counterintuitive, because this species is adapted to the well-drained soils of the cerrado. Thus, we were interested in comparing the photosynthetic capacity, in terms of CO2 conductance, carboxylation, and electron transport of these species over a seasonal flooding cycle. Given that V. divergens is reportedly flood-adapted, we predicted that this species would have a higher photosynthetic capacity than C. americana, especially under flooding. To test this hypothesis we measured the photosynthetic CO2 response (PN/Cc) of V. divergens and C. americana within 1 year to determine, if photosynthetic capacity varied systematically over time and between species. Contrary to our hypothesis, V. divergens did not always have a higher photosynthetic capacity than C. americana. Rather, species differences were influenced by temporal variations in flooding and the leaf age. Leaf CO2 assimilation and photosynthetic capacity of both species were lower during the flood period, but the differences were not statistically significant. The physiological performance of both species was strongly related to leaf N and P concentrations, but P limitation appeared to be more important than N limitation for these species and ecosystem. Photosynthetic capacity was higher and more stable for V. divergens, but such an advantage did not result in a statistically significant increase in PN. Our results suggest that both species are tolerant to flooding even though they are adapted to very different hydrological conditions. Such physiological plasticity, especially for C. americana, might be a key feature for the ability to survive and persist in the seasonally flooded Pantanal.

The physiological light response of two tree species across a hydrologic gradient in Brazilian savanna (Cerrado)

Tropical savanna ecosystems are extremely diverse and important for global carbon storage. In the state of Mato Grosso, tropical savanna (locally known as the Cerrado), turns from well-drained, upland areas into seasonally flooded areas within the Pantanal; however, the Cerrado and the Pantanal share many common tree species, such as Vochysia divergens, a flood-adapted tree native to the Amazon Basin, and Curatella americana, a tree, adapted native to the welldrained the Cerrado. We measured the photosynthetic light response of these species in the the Cerrado and the Pantanal over a 1-year period to determine how these species physiologically adjust to these hydrologically distinct habitats. We hypothesized that neither species would experience a significant decline in maximum, light-saturated photosynthetic rate (Pmax) in their naturalized habitat. Physiological performance of each species was generally higher in the habitat that they were adapted to; however, our data indicated that both species have broad tolerance for seasonal variations in hydrology, allowing them to tolerate seasonal drought during the dry season in the Cerrado, and seasonal flooding during the wet season in the Pantanal. In V. divergens, flexible water-use efficiency, higher specific leaf area (SLA), and a greater ability to adjust mass-based Pmax (Pmax,m) to variations in leaf N and P concentration appeared to be key traits for withstanding prolonged drought in the Cerrado. In C. americana, increases in SLA and higher nutrient-use efficiency appeared to be important in maintaining high rates of Pmax,m in the seasonally flooded Pantanal. Flexibility in physiology and resource-use efficiency may allow these species to survive and persist in habitats with broadly differing hydrology.

Photosynthetic light and carbon dioxide response of the invasive tree, Vochysia divergens Pohl, to experimental flooding and shading

Vochysia divergens Pohl is considered to be a flood-adapted, light-demanding pioneer species that has been invading grasslands of the Brazilian Pantanal. In these areas, a successful invasion requires an ability to tolerate physiologically wide fluctuations in surface hydrology and shading induced by a dense cover of grasses and other vegetation. We evaluated how flooding and shading affected the photosynthetic performance of V. divergens saplings by measuring light-saturated gas exchange (net photosynthetic rate, PN; stomatal conductance, gs), and intercellular CO2 (PN/Ci) and photosynthetic photon flux density (PN/PPFD) response curves over a 61-d field experiment. Shading and flooding reduced significantly light-saturated PN and gs and affected multiple aspects of the leaf gas exchange response of V. divergens to variations in PPFD and CO2. Flooding influenced the physiology of this species more than shading. Given the success of V. divergens at invading and expanding in seasonally flooded areas of the Pantanal, the results were surprising and highlighted the physiological ability of this species to tolerate suboptimal conditions. However, the consistently higher light-saturated PN and gs under nonflooded conditions suggested that the invasive success of V. divergens might not be related to its physiological potential during flooding, but to situations, when flooding recedes during the dry season and soil water availability is adequate.

Influência da escarificação e da temperatura sobre a germinação de sementes de Samanea tubulosa (Benth.) Barneby & J.W. Grimes (sete cascas)

Samanea tubulosa (Benth.) Barneby & J.W Grimes (sete cascas) e uma planta arborea nativa do Pantanal Matogrossense, cujas sementes possuem dormencia provavelmente causada pela impermeabilidade do tegumento a agua. O presente trabalho foi conduzido com o objetivo de comparar a eficiencia da escarificacao mecânica e quimica para superar a dormencia tegumentar e o efeito da temperatura sobre a germinacao de sementes de sete cascas. Foram empregados quatro diferentes procedimentos de escarificacao: testemunha (sem escarificacao); a escarificacao mecânica; a escarificacao com acido sulfurico durante cinco minutos e a escarificacao com acido sulfurico durante dez minutos. Os niveis de temperatura empregados foram de 20, 25, 30 e 35oC. A semeadura foi realizada em papel toalha germitest, na forma de rolo. O delineamento experimental adotado foi o inteiramente casualizado com os tratamentos em esquema fatorial 4x4. Para cada tratamento, foram utilizadas quatro repeticoes de 25 sementes. Foi avaliada a porcentagem de germinacao das sementes, utilizado como criterio emissao da raiz primaria com 2 mm de comprimento. Foi observado que a especie S. tubulosa possui dormencia tegumentar causada pela impermeabilidade do tegumento a agua. As escarificacoes quimica com acido sulfurico por cinco e dez minutos foram eficientes para superacao da dormencia e as combinacoes de escarificacao com temperatura que promoveram maiores porcentagens de germinacao para a especie foram a escarificacao com imersao em acido sulfurico durante cinco e dez minutos e as temperaturas de 25, 30 e 35oC.

Photosynthetic response of a wetland- and an upland-adapted tree species to seasonal variations in hydrology in the Brazilian Cerrado and Pantanal

Savanna (Cerrado) of the Brazilian Pantanal exhibits large variations in hydrology, ranging from well drained to intermittently flooded. Climate and land use change has led to the expansion of “super-dominant” tree species in both habitats, including Vochysia divergens, which is adapted to flooding, and Curatella americana, which is adapted to upland Cerrado. There is both theoretical and practical interest in evaluating the potential net photosynthesis rate of these species to help explain their success in invading new areas with widely differing hydrological regimes. We hypothesized that these species have physical or biochemical adjustments their photosynthetic characteristics that allow them to thrive in their native and invaded environments. To test these hypotheses, we measured chloroplast CO2 concentration response curves, leaf nitrogen and phosphorus concentrations, and specific leaf area of both species over a year in the Pantanal and Cerrado. Neither species displayed a significant decline in potential net photosynthesis in their invaded habitats compared to their native habitats. The relatively constant rate of leaf gas exchange may be important for their success at invading novel habitats, however, there were statistically significant interactions between species, ecosystem, and season that were due in part to complex interactions between biophysical, biochemical, and phenological variables. The specific leaf area (SLA) for both species was higher in their invaded habitats; however, V. divergens exhibited a significant decline in stomatal conductance and an increase in intrinsic water use efficiency in the Cerrado, especially during the dry season. High physiological flexibility, and the ability to maintain a relatively constant value of A, may allow these species to cope with large seasonal variations in soil hydrology and expand into habitats with completely different hydrological conditions.

Trocas gasosas de uma espécie lenhosa na floresta de transição amazônia - cerrado

As florestas de transicao parecem ter um balanco de CO2 nulo, porem as mudancas climaticas que tem ocorrido, como a seca prolongada, podem alterar esse equilibrio a longo prazo. Desta forma, o presente trabalho teve como objetivo estudar as variaveis fisiologicas: fotossintese, fotorrespiracao e respiracao, e entender como essas variaveis podem ser afetadas pelas variacoes sazonais e a posicao da folha na copa da arvore de uma especie vegetal caracteristica de floresta de transicao Amazonia-Cerrado, a Brosimum lactescens S Moore (Moraceae). Utilizando-se um sistema portatil LI-6400 (LI-COR, Inc., Lincoln, NE, USA), as medidas foram realizadas mensalmente. Verificou-se que na estacao seca, houve um incremento substancial na densidade de fluxo fotossinteticamente ativo, DFFA, elevando o deficit de pressao de vapor (DPV). Visando reduzir as perdas de agua, a planta tende a promover o fechamento dos estomatos, havendo uma diminuicao da condutância estomatica (gs), reduzindo assim tambem a concentracao de carbono interno (Ci). Como consequencia, verificou-se que a fotossintese comportou-se de maneira descendente. Contudo. Nesse contexto, como estrategia para dissipacao de energia em excesso, a fotorrespiracao (Rp) aumentou e de forma analoga a respiracao (Rd) tambem aumentou. Os resultados encontrados neste estudo sugerem que variacoes na distribuicao da precipitacao alteram significativamente as trocas gasosas da especie estudada.

Effect of irrigation and ontogeny in estimating the leaf area of Hancornia speciosa Gómez (mangabeira)

Leaf area estimation by regression curves using the product of the length by the breadth of the leaf blade as an independent variable is commonly used in plant growth analysis. However, depending on the nature of the plant species and the farming conditions,it is possible to find variations which affect this allometric relationship, leading to non-universality of a single regression curve. Due to this problem, the present work aimed to evaluate the effect of irrigation and ontogeny in estimating the leaf area of Hancornia speciosa to test the hypothesis that the irrigation would affect such allometric relationship. It was found that the regression models obtained for the irrigated and the non-irrigated plants differed from each other, and there was the need to include specific leaf area into the model to estimate the leaf area for non-irrigated plants. The non inclusion of that variable in the regression model caused a difference on the estimative that increased with the reduction of the specific leaf area. Recently expanded leaves from irrigated and non-irrigated plants differed to each other in their specific leaf area due to dry matter differences but not due to tissue length.

Uso e conservação da negramina (Siparuna guianensis Aubl.) em Bom Sucesso, Várzea Grande-MT

Este trabalho teve como objetivo realizar um estudo da especie medicinal Siparuna guianensis (negramina), na comunidade ribeirinha de Bom Sucesso, localizada no municipio de Varzea Grande - MT. Foi usada a entrevista semiestruturada com questoes fechadas e/ou abertas e concluiu-se que sua principal forma de preparo e a decoccao das folhas, utilizada na forma de banho para alivio da gripe, febre e dores no corpo, e que este conhecimento nao esta sendo repassado as novas geracoes do local.This work aimed to achieve an study of medicinal specie Siparuna guianensis (negramina) in the riverside community of Bom Sucesso, located in Varzea Grande-MT city. Using the semi-structured interview with closed questions and / or open, and concluded that its main form of preparation is a decoction of the leaves, used as a bath to relieve flu, fever and pain in the body, and that this knowledge is not being passed to new generations of the site.

Physiological adjustments of an invasive tree species to extreme hydrological events in a tropical seasonal wetland

Key messageWe analyzed the response ofVochysia divergensPohl trees to hydrological variation over seasons in a Brazilian wetland-based 26 physiological parameters. Dryseason conditions had a greater effect on the photosynthetic function than those in the wet season.AbstractPlants in seasonal wetlands are subject to large hydrological fluctuations and the physiological trade-offs that occur during these variations are still poorly understood. Within the Brazilian Pantanal, the largest tropical seasonal wetland in the world, the abundance of Vochysia divergens Pohl (Vochysiaceae) has been increasing and it forms mono-specific stands. The physiological performance of V. divergens trees to withstand seasonal variations in flooding and drought was evaluated to understand how the hydrological regime affects the species habitat and encourages new areas to be occupied. Individuals were evaluated for changes in their physiological parameters by means of CO2 response curves, chlorophyll fluorescence, photosynthetic pigment and nitrogen (N) concentrations. Drought conditions caused reductions of 82, 64 and 80% of the maximum rate of CO2-saturated photosynthesis (Amax m), electron transport (Jmax m), and carboxylation (Vcmax m) per unit leaf mass, an increase in leaf fluorescence (F0: 27%) and non-photochemical quenching (ΦNPQ: 18%), and a decrease in photochemical quantum yield of photosystem II (ΦPSII in: 29%). The dry season also caused a significant reduction in leaf photosynthetic pigments and an increase in leaf N concentration, but most of the N was allocated away from carboxylation and electron transport proteins and toward leaf structure. Our data indicate that dry season drought caused a significant decline in biochemical properties associated with leaf gas exchange and an increase in allocation to leaf structure. The ability to rapidly shift to high photosynthesis as soon as water levels rise in the wet season may be critical for the growth and expansion of this species in the Pantanal.

Uso y conservación del negramina (Siparuna guianensis Aublet.) en Bom Sucesso, Várzea Grande-MT

Este trabalho teve como objetivo realizar um estudo da especie medicinal Siparuna guianensis (negramina), na comunidade ribeirinha de Bom Sucesso, localizada no municipio de Varzea Grande - MT. Foi usada a entrevista semiestruturada com questoes fechadas e/ou abertas e concluiu-se que sua principal forma de preparo e a decoccao das folhas, utilizada na forma de banho para alivio da gripe, febre e dores no corpo, e que este conhecimento nao esta sendo repassado as novas geracoes do local.This work aimed to achieve an study of medicinal specie Siparuna guianensis (negramina) in the riverside community of Bom Sucesso, located in Varzea Grande-MT city. Using the semi-structured interview with closed questions and / or open, and concluded that its main form of preparation is a decoction of the leaves, used as a bath to relieve flu, fever and pain in the body, and that this knowledge is not being passed to new generations of the site.