Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than~6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO2 assimilation than small trees. Stemspecific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance (Kleaf) than small trees and all tree sizes exhibited lower Kleaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits.

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The Cerrado Domain comprises one of the most diverse savannas in the world and is undergoing a rapid loss of habitats due to changes in fire regimes and intense conversion of native areas to agriculture. We reviewed data on the biogeochemical functioning of Cerrado ecosystems and evaluated the potential impacts of regional climate changes. Variation in temperature extremes and in total amount of rainfall and altitude throughout the Cerrado determines marked differences in the composition of species. Cerrado ecosystems are controlled by interactions between water and nutrient availability. In general, nutrient cycles (N, P and base cations) are very conservative, while litter, microbial and plant biomass are important stocks. In terms of C cycling, root systems and especially the soil organic matter are the most important stocks. Typical cerrado ecosystems function as C sinks on an annual basis, although they work as source of C to the atmosphere close to the end of the dry season. Fire is an important factor altering stocks and fluxes of C and nutrients. Predicted changes in temperature, amount and distribution of precipitation vary according to Cerrado sub-regions with more marked changes in the northeastern part of the domain. Higher temperatures, decreases in rainfall with increase in length of the dry season could shift net ecosystem exchanges from C sink to source of C and might intensify burning, reducing nutrient stocks. Interactions between the heterogeneity in the composition and abundance of biological communities throughout the Cerrado Domain and current and future changes in land use make it difficult to project the impacts of future climate scenarios at different temporal and spatial scales and new modeling approaches are needed.Keywords: Savanna, nutrient cycling, fire, land use, climate change, carbon. Os impactos potenciais das mudanças climáticas no funcionamento biogeoquímico dos ecossistemas de cerradoResumo O Domínio Cerrado é composto por uma das savanas mais diversas do mundo e está passando por uma rápida perda de habitats devido às mudanças nos regimes de fogo e intensa conversão de áreas nativas para a agricultura. Os dados sobre o funcionamento biogeoquímico do Cerrado foram revisados, avaliando-se os potenciais impactos das mudanças climáticas regionais. As variações na temperatura, na precipitação e altitude ao longo do Cerrado determinam diferenças marcantes na composição das espécies. Os ecossistemas de Cerrado são controlados por interações entre a água e a disponibilidade de nutrientes. Em geral, a ciclagem de nutrientes (N, P e cátions) são muito conservadores, enquanto a serapilheira, a biomassa microbiana e vegetal são importantes compartimentos de estoque. Em termos de ciclagem de C, o sistema radicular e, especialmente, a matéria orgânica do solo são os estoques mais importantes. Em bases anuais, o ecossistema de cerrado típico funciona como sumidouros de C embora o opere como fonte de C para a atmosfera ao final da estação seca. O fogo é um fator importante alterando...

RESUMO -(Características funcionais de folhas de sol e sombra de espécies arbóreas em uma mata de galeria no Distrito Federal, Brasil). As matas de galeria são formações fl orestais que ocupam cerca de 10% da área dos cerrados e representam 1/3 da diversidade de espécies arbóreas ali encontradas. Estudos recentes têm demonstrado a importância dessas fl orestas em regiões do Brasil central, mas pouco se sabe sobre a fi siologia e plasticidade de espécies de mata de galeria em relação a variantes ambientais, como a irradiação solar. No presente estudo, foram comparados in situ aspectos fi siológicos e nutricionais de folhas de sol e sombra, em dez espécies arbóreas comumente encontradas em matas de galeria. Folhas de sol apresentaram maiores valores de assimilação de CO 2 em base de área (A area ), condutância estomática (gs), rendimento quântico do fotossistema II (Φ FSII ) e uma maior fração de centros de reação abertos (qL), enquanto folhas de sombra apresentaram uma maior área foliar específi ca. Diferenças não foram encontradas para potencial hídrico foliar, assimilação de CO 2 em base de massa e para a concentração foliar de macronutrientes. Dos atributos foliares analisados, a abertura estomática e o rendimento quântico do fotossistema II foram os principais fatores atuantes na A area em folhas de sol, enquanto em folhas de sombra apenas Φ FSII foi infl uente. As diferenças encontradas demonstram que, assim como em outras formações fl orestais, em mata de galeria as espécies arbóreas possuem a capacidade de se aclimatarem às condições contrastantes de sombreamento que ocorrem neste tipo de ambiente. Palavras-chave: matas de galeria, fotossíntese, nitrogênio, fósforo, luz, fl uorescência, trocas gasosas ABSTRACT -(Leaf functional traits in sun and shade leaves of gallery forest trees in Distrito Federal, Brazil). Gallery forest is a forest formation that covers about 10% of the cerrado biome and represents about 1/3 of cerrado tree diversity in Brazil. Recent studies demonstrate the importance of gallery forest in central regions of Brazil, but little is known about the physiology and plasticity of gallery forest species in relation to environmental variability, particularly in terms of light availability. In this study we compared in situ physiological and nutritional aspects of shade and sun leaves, in ten tree species commonly found in gallery forests. Relative to shade leaves, sun leaves had higher values of CO 2 assimilation rates on an area basis (A area ), of stomatal conductance (gs), of quantum yield of Photosystem II (Φ PSII ); and a larger fraction of PSII centers in the open state (q L ), while shade leaves showed higher specifi c leaf area. However, shade and sun leaves did not differ in terms of leaf water potential, CO 2 assimilation on a mass basis and in leaf concentrations of macronutrients. Φ PSII and gs were the main factors that infl uenced A area in sun leaves, while only Φ PSII signifi cantly affected A area of shade leaves. The differences found here demonstrate that, like in other fo...

Sugarcane (Saccharum spp.) is the world most productive sugar producing crop, making an understanding of its stress physiology key to increasing both sugar and ethanol production. To understand the behavior and salt tolerance mechanisms of sugarcane, two cultivars commonly used in Brazilian agriculture, RB867515 and RB855536, were submitted to salt stress for 48 days. Physiological parameters including net photosynthesis, water potential, dry root and shoot mass and malondialdehyde (MDA) content of leaves were determined. Control plants of the two cultivars showed similar values for most traits apart from higher root dry mass in RB867515. Both cultivars behaved similarly during salt stress, except for MDA levels for which there was a delay in the response for cultivar RB867515. Analysis of leaf macro- and micronutrients concentrations was performed and the concentration of Mn2+ increased on day 48 for both cultivars. In parallel, to observe the effects of salt stress on protein levels in leaves of the RB867515 cultivar, two-dimensional gel electrophoresis followed by MS analysis was performed. Four proteins were differentially expressed between control and salt-treated plants. Fructose 1,6-bisphosphate aldolase was down-regulated, a germin-like protein and glyceraldehyde 3-phosphate dehydrogenase showed increased expression levels under salt stress, and heat-shock protein 70 was expressed only in salt-treated plants. These proteins are involved in energy metabolism and defense-related responses and we suggest that they may be involved in protection mechanisms against salt stress in sugarcane.

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The present study investigated the dynamic on a short-time scale in the vegetation in moist grassland of the Sete Cidades National Park, Piauí. Herb-subshrub layer samples was carried out in July 2007July , 2009July and 2011. Changes in structural, floristic and functional traits in the community were assessed by species richness, diversity and similarity indices between those periods, as well as by hierarchical classification and ordination. Cluster and Principal Component Analyses identified functional groups according to 23 species trait state. To distinguish the contribution of space and time configuration in the community structure, we used the variance partition technique. The functional groups of chamaephytes and therophytes II were associated with wetter sites, while the groups of non-tussock hemicriptophytes I, tussock hemicriptophytes (FG4), and geophytes (FG5) were associated to the drier ones. We found a non-accelerated dynamics, at least on a short-time scale, represented by some descriptors in the community, such as the close similarity between the inventories and ordering of sampling transects in moist grassland. Therefore, besides considering the partition of the temporal niche as a mechanism for the co-existence of species, the heterogeneity of space dictated by environmental filters seems to determine the stability of the this grassland communities over time.Keywords: herbaceous and subshrub layer, line intersection method, spatial patterns, temporal patterns, plant functional traits. Mudança temporal nas espécies e atributos funcionais de plantas em campo limpo úmido de Cerrado no Parque Nacional de Sete Cidades, Piauí, BrasilResumo O presente estudo investigou a dinâmica em uma curta escala de tempo na vegetação de campo limpo úmido do Parque Nacional Sete Cidades Park, Piauí. Amostragens da camada herbáceo-subarbustiva foram realizadas em julho de 2007, 2009 e 2011. Mudanças estruturais, florísticas e de atributos funcionais da comunidade foram avaliadas por índices de riqueza de espécies, diversidade e similaridade entre esses períodos, bem como por classificação hierárquica e ordenação. Análise de Componentes Principais e de Cluster identificaram grupos funcionais de acordo com 23 atributos das espécies. Para distinguir a contribuição do espaço e do tempo nas análises, usamos técnicas de partição de variância. Os grupos funcionais das caméfitas e terófitas II foram associados com os locais mais úmidos, enquanto os grupos de hemicriptófitas I não entouceiradas, hemicriptófitos entouceiradas e das geófitas (GF5) foram associados aos mais secos. Nós encontramos uma dinâmica não-acelerada, pelo menos em uma escala de curta duração, representada por alguns descritores da comunidade, tais como a similaridade entre os inventários e a ordenação dos transectos no campo limpo úmido. Assim, além de considerar a partição do nicho temporal como um mecanismo para a coexistência de espécies, a heterogeneidade do espaço ditada por filtros ambientais parece determinar a estabilidade destas comun...

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