Ecological strategies of Al-accumulating and non-accumulating functional groups from the cerrado sensu stricto

The cerrado's flora comprises aluminum-(Al) accumulating and non-accumulating plants, which coexist on acidic and Al-rich soils with low fertility. Despite their existence, the ecological importance or biological strategies of these functional groups have been little explored. We evaluated the leaf flushing patterns of both groups throughout a year; leaf concentrations of N, P, K, Ca, Mg, S, Al, total flavonoids and polyphenols; as well as the specific leaf area (SLA) on young and mature leaves within and between the groups. In Al-accumulating plants, leaf flushed throughout the year, mainly in May and September; for non-accumulating plants, leaf flushing peaked at the dry-wet seasons transition. However, these behaviors could not be associated with strategies for building up concentrations of defense compounds in leaves of any functional groups. Al-accumulating plants showed low leaf nutrient concentrations, while non-accumulating plants accumulated more macronutrients and produced leaves with high SLA since the juvenile leaf phase. This demonstrates that the increase in SLA is slower in Al-accumulating plants that are likely to achieve SLA values comparable to the rest of the plant community only in the wet season, when sunlight capture is important for the growth of new branches.A flora do cerrado é composta por espécies acumuladoras e não acumuladoras de alumínio (Al), coexistentes em solos ácidos, ricos em Al e com baixa fertilidade. Apesar da coexistência desses grupos funcionais, sua importância ecológica e suas estratégias biológicas são pouco conhecidas. Nós estudamos os padrões fenológicos de brotação foliar de ambos os grupos ao longo do ano, as concentrações foliares de N, P, K, Ca, Mg, S, Al, flavonoides totais e polifenóis e a área foliar específica (AFE) em folhas jovens e maduras, dentro e entre os grupos. Para as espécies acumuladoras de Al as brotações foliares foram distribuídas ao longo do ano, com maior intensidade entre maio e setembro; para as espécies não acumuladoras de Al observamos um pico de brotação durante a transição das estações seca e chuvosa. No entanto, estes comportamentos não podem ser associados às estratégias ligadas ao acúmulo foliar de metabólitos secundários por estes grupos funcionais. As espécies acumuladoras de Al apresentaram menores concentrações de nutrientes foliares, enquanto que as não acumuladoras concentraram mais macronutrientes e produziram folhas com alta AFE desde a fase juvenil. Isso demonstra que o aumento de AFE é mais lento nas espécies acumuladoras de Al, que devem atingir valores de AFE comparáveis ao resto da comunidade apenas na estação úmida, quando a captação de luz é importante para o crescimento de novos ramos.Coordenação de Aperfei çoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Universidade Estadual Paulista Instituto de Biociências Departamento de BotânicaUniversidade de São Paulo Faculdade de Ciências Farmacêuticas de Ribeirão Preto Departamento de Ciências FarmacêuticasUniversidade Estadual Paulista Instituto de Química Departamento de Química OrgânicaUniversidade Estadual Paulista Instituto de Biociências Departamento de BotânicaUniversidade Estadual Paulista Instituto de Química Departamento de Química OrgânicaFAPESP: 2010/07809-1FAPESP: 2012/13762-3FAPESP: 2007/59779-6FAPESP-VALE: 2010/51307-

Depth of water uptake in woody plants relates to groundwater level and vegetation structure along a topographic gradient in a neotropical savanna

Vegetation structure of the savannas is variable across the landscape, ranging from open grassland to savanna woodland within topographic gradients of a few hundred meters in length. Here we investigated whether patterns of soil water extraction by the woody layer and vegetation structure changed in response to groundwater depth. We determined depth of plant water uptake, groundwater level and vegetation structure on five different locations along a topographic gradient in the highlands of Central Brazil. The elevation gradient of about 110. m covered all vegetation physiognomies generally associated with topographic gradients in savannas of Central Brazil. To estimate the depth of plant water uptake in the different slope positions we relied on comparisons of hydrogen and oxygen isotope ratios of plant stem water, water from different soil depths, from groundwater and from rainfall. We subsequently used a stable isotope mixing model to estimate vertical partitioning of soil water by woody plants along the elevation gradient. We were able to show that groundwater level affected plant water uptake patterns and soil water partitioning among savanna woody species. Vegetation at higher elevation extracted water from deeper unsaturated soils and had greater variability in water uptake strategies, which was coupled to a denser and more complex woody layer. Plants on these soils used stored water from both shallow (<0.6. m) and deep (0.6-2.00. m) soil layers. At lower elevation sites, however, the presence of a water table near the soil surface restricted water uptake to the shallower wet season unsaturated zone of the soil profile. The sparser woody vegetation is probably composed of species that only rely in superficial water uptake, or are plastic in relation to root characteristics. © 2011 Elsevier B.V

Leaf traits combinations may explain the occurrence of savanna herbaceous species along a gradient of tree encroachment

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Processo FAPESP: 2013/18049-6Processo FAPESP: 2014/15304-8CNPq: 301589/2015-1In savanna environments, plants have specific leaf traits to deal with high irradiance. These traits allow plants to show high carbon assimilation capacity. However, under encroachment, reduced light availability may act as a filter on traits of plants established under typical savanna conditions. Here we studied morpho-physiological traits of species exclusively found in typical and forested savanna conditions to evaluate how encroachment selects for specific leaf traits in such environments. We also evaluated if species occurring in distinct encroached situations would show plasticity to deal with light variations. We studied two species exclusively found in typical savanna (TS, open condition), two species exclusively found in forested savanna (FS, encroached condition) and two species growing along a gradient of tree encroachment (typical, dense and forested savanna). We measured specific leaf area (SLA), maximum photosynthetic rate in an area basis (Amax), stomatal conductance (gs), water use efficiency (WUE), leaf carbon (C) and nitrogen (N) concentrations. We found that herbaceous species exclusively found in TS possess higher Amax, gs, WUE and C in comparison with plants from forested savanna. Such strategies are necessary to thrive under environments with elevated irradiances. In turn, species from FS showed elevated SLA and foliar N concentration, strategies linked to capture diffuse light in forested environments. Species capable of thriving in sites with distinct degrees of encroachment changed their leaf traits according with light availability. We conclude that differences in leaf traits between typical and forested savanna species may explain the non-occurrence of typical savanna species when their environment become encroached. Only those species capable of showing a certain degree of plasticity may survive under such distinct encroached states