Higo José Dalmagro

Variations in aboveground vegetation structure along a nutrient availability gradient in the Brazilian pantanal

Background and aimsForest expansion into seasonally flooded (hyperseasonal) savanna of the Brazilian Pantanal has been occurring for decades. Our goal was to evaluate how ecosystem physiognomy varied across a nutrient availability gradient and if hyperseasonal savanna had adequate nutrient stocks to support forest expansion.MethodsWe quantified soil properties, aboveground ecosystem structure, and nutrient stocks of three savanna and three forest stands in the Pantanal of Mato Grosso, Brazil, and used correlation analysis to assess how aboveground vegetation structure varied across a soil nutrient availability gradient.ResultsWood and foliage carbon storage and leaf area index were positively correlated with soil extractable phosphorus (P), calcium (Ca2+), and magnesium (Mg2+) concentrations but not soil organic matter or texture. Soil profiles indicated that vegetation enriched surface P and K+ availability but not Ca2+ and Mg2+. Savanna ecosystems had adequate K+, Ca2+, and Mg2+ to support gallery and riparian forests but not palm forest, while the savanna P stock was inadequate to support forest expansion.ConclusionsHyperseasonal savanna has adequate nutrients (except P) to support forest expansion. Forest trees likely invade P-deficient savanna by surviving in P-rich microsites. Over time, biotic enrichment of soil may accelerate forest expansion into P-poor savanna.

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.

Biochar from sugarcane filtercake reduces soil CO2 emissions relative to raw residue and improves water retention and nutrient availability in a highly-weathered tropical soil.

In Brazil, the degradation of nutrient-poor Ferralsols limits productivity and drives agricultural expansion into pristine areas. However, returning agricultural residues to the soil in a stabilized form may offer opportunities for maintaining or improving soil quality, even under conditions that typically promote carbon loss. We examined the use of biochar made from filtercake (a byproduct of sugarcane processing) on the physicochemical properties of a cultivated tropical soil. Filtercake was pyrolyzed at 575°C for 3 h yielding a biochar with increased surface area and porosity compared to the raw filtercake. Filtercake biochar was primarily composed of aromatic carbon, with some residual cellulose and hemicellulose. In a three-week laboratory incubation, CO2 effluxes from a highly weathered Ferralsol soil amended with 5% biochar (dry weight, d.w.) were roughly four-fold higher than the soil-only control, but 23-fold lower than CO2 effluxes from soil amended with 5% (d.w.) raw filtercake. We also applied vinasse, a carbon-rich liquid waste from bioethanol production typically utilized as a fertilizer on sugarcane soils, to filtercake- and biochar-amended soils. Total CO2 efflux from the biochar-amended soil in response to vinasse application was only 5% of the efflux when vinasse was applied to soil amended with raw filtercake. Furthermore, mixtures of 5 or 10% biochar (d.w.) in this highly weathered tropical soil significantly increased water retention within the plant-available range and also improved nutrient availability. Accordingly, application of sugarcane filtercake as biochar, with or without vinasse application, may better satisfy soil management objectives than filtercake applied to soils in its raw form, and may help to build soil carbon stocks in sugarcane-cultivating regions.

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.

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.

Soil CO2 concentrations and efflux dynamics of a tree island in the Pantanal wetland

The Pantanal is the largest tropical wetland on the planet and yet little information is available on the biomes carbon cycle. We used an automatic station to measure soil CO2 concentrations and oxidation-reduction potential over the 2014 and 2015 flood cycles of a tree island in the Pantanal that is immune to inundation during the wetlands annual flooding. The soil CO2 concentration profile was then used to estimate soil CO2 efflux over the two periods. In 2014, subsurface soil saturation at 0.30 m depth created conditions in that layer that led to CO2 buildup close to 200,000 ppm and soil oxidation-reduction potential below –300 mV, conditions that were not repeated in 2015 due to annual variability in soil saturation at the site. Mean CO2 efflux over the 2015 flood cycle was 0.023 ± 0.103 mg CO2-C m-2 s-1 representing a total annual efflux of 593 ± 2690 mg CO2-C m-2 y-1. Unlike a nearby tree island site that experiences full inundation during the wet season, here the soil dried quickly following repeated rain events throughout the year which led to the release of soil CO2 pulses from the soil. This study not only highlights the complexity and heterogeneity in the Pantanals carbon balance based on differences in topography, flood cycles and vegetation, but also the challenges of applying the gradient-method in the Pantanal due to deviations from steady-state 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.

Biochars from local agricultural waste residues contribute to soil quality and plant growth in a Cerrado region (Brazil) Arenosol

Arenosols (sandy soils) in the Cerrado region of Mato Grosso, Brazil, are increasingly used for maize production, the second most important crop in the region after soybean. Yet, these soils are typically nutrient poor with low soil water retention, requiring high fertilizer inputs that are often lost in surface runoff or leached. The addition of biochar, a more recalcitrant organic amendment, may therefore be beneficial in Cerrado Arenosols, contributing to sustainable crop production in the region. To examine biochar contribution to soil nutrient levels and maize growth in a Cerrado Arenosol, we conducted a greenhouse experiment using biochars made from local agricultural waste feedstocks. These were cotton husks, swine manure, eucalyptus sawmill residue, and sugarcane filtercake, pyrolyzed at 400 °C, and applied to soil at five rates: 0%, 1%, 2%, 3%, and 4% by weight. Maize plants were grown under unstressed conditions (e.g., no nutrient or water limitations) to highlight any possible negative effects of the biochars. After 42 days, soils were analyzed for nutrient levels, and plant physical and physiological measurements were taken. Filtercake biochar had the highest plant biomass and physiological properties (e.g., photosynthesis, respiration, nitrogen use efficiency), while cotton biochar had the lowest. Importantly, maize biomass decreased with increasing application rates of cotton and swine manure biochars, while biomass did not vary in response to biochar application rate for filtercake and eucalyptus biochars. In this study, we found that while each biochar exhibited potential for improving chemical and physical properties of Cerrado Arenosols, filtercake biochar stood out as most promising. Biochar application rate was identified a key factor in ensuring crop productivity. Transforming these agricultural residues readily available in the region into more stable biochar can thus contribute to sustainable crop management and soil conservation, providing an alternative form of waste disposal for these residual materials.

Spatial patterns of DOC concentration and DOM optical properties in a Brazilian tropical river‐wetland system

The Cerrado (savanna) and Pantanal (wetland) biomes of central-western Brazil have experienced significant development activity in recent decades, including extensive land cover conversion from natural ecosystems to agriculture and urban expansion. The Cuiaba River transects the Cerrado biome prior to inundating large areas of the Pantanal, creating one of the largest biodiversity hotspots in the world. We measured dissolved organic carbon (DOC) and the optical absorbance and fluorescence properties of dissolved organic matter (DOM) from 40 sampling locations spanning Cerrado and Pantanal biomes during wet and dry seasons. In the upper, more agricultural region of the basin, DOC concentrations were highest in the rainy season with more aromatic and humified DOM. In contrast, DOC concentrations and DOM optical properties were more uniform for the more urbanized middle region of the basin between wet and dry seasons, as well as across sample locations. In the lower region of the basin, wet season connectivity between the river and the Pantanal floodplain led to high DOC concentrations, a four-fold increase in HIX (an indicator of DOM humification) and a 50% reduction in the spectral slope (SR). Basin-wide, wet season values for SR, HIX and FI (fluorescence index) indicated an increasing representation of terrestrially derived DOM that was more humified. Parallel factor analysis (PARAFAC) identified two terrestrially derived components (C1 and C2) representing 77% of total fluorescing DOM (fDOM). A third, protein-like fDOM component increased markedly during the wet season within the more urban-impacted region.

Transpiração pelo método da sonda de dissipação térmica em floresta de transição Amazônica-Cerrado

The objective of this study was to analyse the behavior of sap flow in a transition Amazon-Savannah forest species, to characterize the dependence of sap flow as a function of atmospheric vapor pressure deficit (VPD). The sap flow was measured using the technique proposed by Granier, using heat dissipation probes in five different species. The data were divided into four seasons. In the experimental period, the curves of seasonal variation of sap flow showed an occurrence of peaks in the wet season. This seasonal sap flow trend was evidenced by the relationship between daily values of transpiration and VPD. The threshold value of VPD at these stations ranged from 1 to 1.5 kPa. Considering sap flow as representative of plant transpiration, reduction of the flux in the dry season did not confirm the hypothesis of maintenance of evapotranspiration process. The sap flow in the studied species was influenced more by weather than soil water availability. This raises the possibility of water storage in the stem during drier periods, when leaf area decreases. However the transpiration rate is not significantly different from that of the rainy season.