Atributos e tipos funcionais de espécies lenhosas no cerrado

Tese (doutorado)—Universidade de Brasília, Instituto de Ciências Biológicas, Departamento de Ecologia, Programa de Pós-Graduação em Ecologia, 2010.A marcante sazonalidade das chuvas representa um importante filtro ambiental ao estabelecimento e crescimento da vegetação savânica do cerrado. Outra característica importante deste ambiente é a grande heterogeneidade da configuração do dossel arbóreo. Em distâncias da ordem de dezenas de metros, podemos encontrar savanas com graus contrastantes de adensamento de árvores. Desta forma, ao logo da paisagem são encontradas áreas em que a luz pode ser escassa, se tornando um fator limitante ao crescimento arbóreo, enquanto em outras áreas, a presença de luz em intensidades elevadas pode ocasionar danos por excesso de energia absorvida ou alterar o metabolismo fotossintético em função do aumento da temperatura foliar. Apesar da predominância de savanas na região do cerrado, estão presentes áreas com vegetação florestal, com fronteiras bem delimitadas entre estas duas fitofisionomias. As florestas apresentam diferenças marcantes em relação às savanas na disponibilidade de luz e água. Contudo, indivíduos de algumas espécies típicas de floresta conseguem estabelecer-se em áreas savânicas. No primeiro capítulo, elaboramos modelos estatísticos para a descrição de aspectos ecofisiológicos de árvores estabelecidas na savana, investigando a influência da sazonalidade climática e possíveis diferenças entre plantas de espécies típicas da savana e típicas de floresta. Para tanto, selecionamos 12 pares congenéricos, compostos de uma espécie típica da savana e uma típica de floresta. Realizamos as medições na estação seca e chuvosa, estimando a taxa fotossintética, condutância estomática, curvas de resposta à luz, CO2 e temperatura, fluorescência da clorofila a (partição de energia no fotossistema II) e potencial hídrico foliar mínimo. Contrariando nossas expectativas, os dois grupos de espécies (savânicas e florestais) não demonstraram diferenças em nenhum dos atributos avaliados. As medições de trocas gasosas e potencial hídrico revelaram mudanças fisiológicas entre estações do ano, porém, ambos os grupos responderam vii de maneira similar. Com isto, apesar das plantas típicas de floresta terem evoluído em ambientes marcantemente diferentes das savanas, em termos de luminosidade e disponibilidade hídrica, os indivíduos deste grupo que crescem nas savanas apresentaram características similares às plantas típicas deste ambiente. No segundo capítulo, avaliamos as respostas das trocas gasosas de três espécies arbóreas ao aumento da disponibilidade de água no solo e da umidade do ar (que resulta na diminuição da demanda evaporativa) durante a estação seca. Para isto, realizamos curvas de resposta ao déficit de pressão de vapor folhaatmosfera em indivíduos estabelecidos naturalmente na savana, em áreas irrigadas e não irrigadas. A fotossíntese e condutância estomática foram fortemente reguladas pela disponibilidade de água no solo e pela demanda evaporativa. Deste modo, a restrição da assimilação de carbono imposta pela estação seca só seria evitada em situações que propiciassem a elevação da disponibilidade de água no solo acompanhadas de condições microclimáticas que diminuíssem a demanda evaporativa. No terceiro capítulo, agrupamos as espécies arbóreas mais comuns na região savânica analisada em sete tipos funcionais relacionados a características dos ambientes em que estas ocorrem (abertura do dossel, altura e área basal das árvores, biomassa de gramíneas e de serapilheira) levando em conta o grau de similaridade de atributos das espécies. Analisando os estados dos atributos ao longo da variação do ambiente, constatamos a existência tanto de padrões de convergência de caracteres quanto padrões de divergência de caracteres na comunidade arbórea. Isto evidencia que, mesmo em escalas espaciais finas (compreendendo poucos quilômetros de distância), os filtros ambientais selecionaram espécies com atributos semelhantes, enquanto a competição inter-específica favoreceu a diferenciação dos atributos de espécies que coexistem. _________________________________________________________________________________ ABSTRACTThe strong rainfall seasonality represents an important environmental filter on the establishment and growth of the cerrado savanna-like vegetation. Another important feature of this environment is the great heterogeneity of the tree canopy configuration. At distances in the order of tens of meters, we can find savannas with contrasting degrees of tree density. Thus, across the landscape, there are areas where light availability can be scarce, becoming a limiting factor for tree growth, although in other areas, high light intensities can cause damages by excess of absorbed energy or imbalance of the photosynthetic metabolism due to increased leaf temperature. Despite the predominance of savannas in the cerrado, there are areas with forest vegetation, forming well-defined boundaries between these two vegetation types. Forests have significant differences in relation to the savannas concerning light and water availability. However, some typical forest species have established individuals in savannic areas. In the first chapter, we developed statistical models to describe the ecophysiological aspects of established trees growing in the savannas investigating the influence of climatic seasonality and possible differences among plants of species typical of savanna and typical of forest. To this end, we selected 12 congeneric species pairs, consisting each one of a typical savanna species and a typical forest species, for measurements in dry and rainy seasons. We estimated the photosynthetic rate, stomatal conductance, light, CO2 and temperature response curves, chlorophyll a fluorescence (energy partitioning in photosystem II) and minimum leaf water potential. Contrary to ours expectations, both groups of species (savanna and forest) showed no differences in any of the studied traits. Measurements of gas exchange and water potential showed physiological changes among the seasons, although both groups responded similarly. Therefore, despite typical forest species have evolved in an environment markedly different from the savanna in terms of light and water availability, ix individuals of this group established in the savannas exhibited similar characteristics to typical savanna specie. In the second chapter, we evaluated the gas exchange responses of three tree species to increased soil water availability and air humidity (resulting in decreasing evaporative demand) during the dry season. For this, we conducted response curves of leaf-toair vapor pressure deficit on naturally established individuals in the savanna, in irrigated and non irrigated areas during the dry season. The photosynthesis and stomatal conductance were strongly regulated by soil water availability and evaporative demand. Therefore, the restrictions on carbon assimilation imposed by the dry season would only be avoided in situations that could provide higher availability of soil water accompanied by microclimatic conditions that adversely affect the evaporative demand. In the third chapter, we grouped the most common savanna tree species of the area in seven different functional types related to the environmental conditions which they occur (canopy openness, height and basal area of trees, biomass of grass and litter) taking into account the similarity degree of traits among species. Evaluating the condition of the traits along the environment variation, we note the existence of both trait-convergence and trait-divergence patterns on tree community. Therefore, even in fine spatial scale (including a few kilometers away), the environmental filters selected species with similar traits, while interspecific competition favored the differentiation of the coexistent species traits

Physiological and proteomic analyses of Saccharum spp. grown under salt stress

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

Mudança temporal nas espécies e atributos funcionais de plantas em campo limpo úmido de Cerrado no Parque Nacional de Sete Cidades, Piauí, Brasil

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 comunidades campestres ao longo do tempo.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 2007, 2009 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

Effects of nutrient additions on plant biomass and diversity of the herbaceous-subshrub layer of a Brazilian savanna (Cerrado).

The Brazilian Cerrado is a diversity hotspot due to its high level of endemism and rapid loss of habitats. It is estimated that the number of herbaceous species is four times higher than that of woody species. Increasing levels of nitrogen additions to natural ecosystems have been indicated as a determinant of biodiversity loss. We investigated the effects of nutrient additions on the productivity (aboveground and belowground) and on diversity of the herbaceoussubshrub layer of a Brazilian savanna (cerrado stricto sensu). The experiment was carried out in the IBGE Ecological Reserve, near Bras??lia, Brazil. Between 1998 and 2006, N, P, N plus P, or Ca were applied to sixteen 225 m2 plots, arranged in a completely randomized design. Aboveground biomass was compared 1 year after the first fertilization and 10 years later. Floristic diversity was significantly different (P\0.01) between the treatments. The highest and lowest species richness were presented in control and NP, respectively. The addition of P alone or in combination with N induced invasion by Melinis minutiflora (exotic C4 grass). The aboveground biomass of this species was higher in NP and P plots. In the N treatment, Echinolaena inflexa (native C3 grass) presented elevated cover and biomass but M. minutiflora was absent. The invasion by alien species resulted in negative impacts on native grass species. Besides changes in aboveground biomass, addition of N and P also led, although to a lesser extent, to changes in the root morphology and biomass, but these responses were modulated by seasonal variation in soil moisture. The results suggest that environmental changes in nutrient availability can lead to important consequences for diversity and functioning of this savanna where the numerous rare species have more chance to persist under dystrophic conditions as some species that tend to be dominant would be less competitive

Two-dimensional gel electrophoresis patterns of proteins extracted from sugarcane leaves of the RB867515 cultivar watered (A) with distilled water and (B) after being subjected to 100 mM NaCl for 48 days.

<p>The strips used were 13-linear pH gradient of 3-11, stained with Coomassie G-250. The proteins indicated by numbers (1-4) correspond to those showing at least 1.5-fold difference in expression levels between the two different treatments; proteins indicated with letters (a-h) represent proteins with no difference in expression profile.</p

Net CO₂-exchange (µmol.m⁻²s⁻¹) for (A) cultivar RB855536 and (B) cultivar RB867515 over time.

<p>Leaf water potential (MPa) in sugarcane leaves during 48 days of salt treatment for (C) cultivar RB855536; and (D) cultivar RB867515. Values are presented as mean ± SD (n = 6). "•" are control plants and "▪" are salt-treated plants. *Significant at p≤0.05.</p

Cultivar RB867515 sugarcane leaf proteins differentially expressed between water-treated and salt-treated plants.

<p>Proteins were trypsin digested and identified by MALDI-ToF/ToF MS. “1-4” are differentially expressed proteins and “a-h” are proteins with no difference in protein expression.</p

Shoot dry mass for cultivars(A) RB855536 and (B) RB867515; and root dry mass for cultivars (C) RB855536 and (D) RB867515 after being subjected to 48 days of salt stress (100 mM NaCl).

<p>Lipid peroxidation levels (MDA) in sugarcane leaves during 48 days of salt stress (100 mM NaCl) for (E) cultivar RB855536 and (F) RB867515. Values are presented as mean ± SD (n = 6 plants). "•" are control plants and "▪" are salt-treated plants. *Significant at p≤0.05.</p