José de Souza Nogueira

Patterns of water and heat flux across a biome gradient from tropical forest to savanna in Brazil

[1] We investigated the seasonal patterns of water vapor and sensible heat flux along a tropical biome gradient from forest to savanna. We analyzed data from a network of flux towers in Brazil that were operated within the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). These tower sites included tropical humid and semideciduous forest, transitional forest, floodplain (with physiognomies of cerrado), and cerrado sensu stricto. The mean annual sensible heat flux at all sites ranged from 20 to 38 Wm 2 , and was generally reduced in the wet season and increased in the late dry season, coincident with seasonal variations of net radiation and soil moisture. The sites were easily divisible into two functional groups based on the seasonality of evaporation: tropical forest and savanna. At sites with an annual precipitation above 1900 mm and a dry season length less than 4 months (Manaus, Santarem and Rondonia), evaporation rates increased in the dry season, coincident with increased radiation. Evaporation rates were as high as 4.0 mm d 1 in these evergreen or semidecidous forests. In contrast, ecosystems with precipitation less than 1700 mm and a longer dry season (Mato Grosso, Tocantins

EFFECTS OF METEOROLOGICAL VARIATIONS ON THE CO2 EXCHANGE OF A BRAZILIAN TRANSITIONAL TROPICAL FOREST

The net ecosystem CO2 exchange (NEE) of a 28-30 m tall transitional (eco- tonal) tropical forest of the Brazilian Amazon was quantified using tower-based eddy co- variance. Measurements were made between August 1999 and July 2001 and were used to develop nonlinear statistical models to assess daily variations in ecophysiological param- eters and provide annual estimates of NEE, gross ecosystem CO2 exchange (GEE), and respiration (Re). Diurnal trends in NEE were correlated with variations in photosynthetic photon flux density ( Q), vapor pressure deficit (V ), and temperature. Seasonal trends in the CO2-flux components estimated from nonlinear regression ( Amax and R0) were highly cor- related with soil water availability and canopy structural properties (LAI and litter pro- duction). These results suggest that variations in soil water content can affect rates of canopy photosynthesis and whole forest respiration by altering both physiological processes and canopy structural properties. Estimates of the annual NEE suggest that the forest was in balance with respect to CO2 during the study period, which, in terms of rainfall, was a relatively typical period compared to the 30-yr average rainfall regime. Our results also suggest that the warmer and dryer microclimate and decline in LAI that accompany land- cover change will cause transitional forests to be sources of CO 2 to the atmosphere.

The Sensitivity of Diel CO2 and H2O Vapor Exchange of a Tropical Transitional Forest to Seasonal Variation in Meteorology and Water Availability

Abstract Measurements of ecosystem gas exchange, meteorology, and hydrology (rainfall and soil moisture) were used to assess the seasonal patterns of, and controls on, average diel (24 h) net ecosystem CO2 exchange (NEE), evapotranspiration (E), and bulk canopy water vapor conductance (Gc) of a tropical transitional (ecotonal) forest in the Brazilian Amazon. Diel trends in E and NEE were almost completely explained by the diel variation in photosynthetic photon flux density (QPPFD), and while the QPPFD response of E varied little over the annual cycle, the QPPFD response of NEE declined substantially during the dry season, and the magnitude of hysteresis in the NEE–QPPFD response increased as well. The magnitude of the residuals for the QPPFD versus NEE response was significantly negatively correlated with total monthly rainfall and surface soil moisture and positively correlated with the maximum daily temperature and atmospheric vapor pressure deficit (V). Average daily Gc was also significantly correlat...

Seasonal Patterns of Evapotranspiration for a Vochysia divergens Forest in the Brazilian Pantanal

The recent and widespread expansion of the pioneer tree species Vochysia divergens Pohl into western Brazil has the potential to significantly alter the structure and function of the Pantanal—a UNESCO World Heritage Site and the World’s largest tropical wetland. Here we assess the seasonal pattern of evapotranspiration (ET) and micrometeorological variables of V. divergens (locally known as cambarazal), located in the Northeast of the Brazilian Pantanal. ET was calculated from a number of micrometeorological measurements recorded between January 2007 and January 2008. The results indicate that ET was the dominant sink for net radiation (Rn) during the wet and dry seasons, primarily because the forest was either flooded (December–May) or retained a high level of soil moisture. ET decreased during the dry season due to a decline in Rn and surface water availability, and an increase in atmospheric vapor pressure deficit. Based on this analysis we conclude that the spread of V. divergens into the Pantanal and the associated high rates of ET are due in part to high water availability, even during the dry season, and the consistently high leaf area index that increases the transpiration surface area when the water table is below the soil surface.

A molecular dynamic study of the starch obtained from the Mangifera indica Cv. Bourbon and Espada seeds by 13C solid state NMR

Abstract The molecular mobility of the starch obtained from Mangifera indica Cv. Bourboun and Espada , has been characterised by 13 C solid state nuclear magnetic resonance, using techniques, such as magic angle spinning (MAS) and cross polarisation magic angle spinning (CPMAS) NMR and by proton spin-lattice relaxation time in the rotating frame ( T 1 H ρ ). The CPMAS 13 C NMR spectra of these seeds showed three signals for Bourboun and two very broad signals for Espada . The seeds of the Mangifera indica Cv. Bourboun and Espada are heterogeneous amorphous polysaccharides that present, at least, two domains with distinct molecular mobility. These domains differ in size and chain packing. The variable contact time decay confirms that these starches are amorphous and present one predominant rigid domain. Mango fruits were also analysed by delayed contact time experiments, and the 13 C decays showed that the polysaccharides are heterogeneous and contain one rigid domain that controls the relaxation parameter.

Estimativa do balanço de energia em cambarazal e pastagem no norte do Pantanal pelo método da razão de Bowen

O estudo do balanco de energia de uma superficie vegetada e a atmosfera e importante para caracterizar o microclima local, identificar interacoes entre variaveis ambientais e a vegetacao, e identificar efeitos das atividades antropogenicas. O objetivo deste trabalho foi estimar a variacao sazonal do balanco de energia pelo metodo da razao de Bowen em uma area de vegetacao monodominante de Cambara na RPPN SESC-Pantanal e uma area de pastagem na Fazenda Experimental da UFMT. Os componentes do balanco de energia apresentaram sazonalidade, com maiores medias na estacao chuvosa nas duas areas de estudo. No cambarazal houve maior variacao do fluxo de calor latente da estacao seca para a chuvosa que na pastagem. Entretanto, a variacao sazonal do fluxo de calor sensivel foi menor no cambarazal que na pastagem, devido ao efeito termo-regulador do cambarazal, em funcao da maior biomassa. A energia disponivel aos dois sitios foi destinada prioritariamente em fluxo de calor latente, 80,0% no cambarazal e 56,6% na pastagem, seguido pelo fluxo de calor sensivel, 19,1 e 42,9%, e pelo fluxo de calor no solo, 0,3 e 7,2%.

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.

Modelling gross primary production of a tropical semi-deciduous forest in the southern Amazon Basin

Semi-deciduous forest in the Amazon Basin is sensitive to temporal variation in surface water availability that can limit seasonal rates of leaf and canopy gas exchange. We estimated the seasonal dynamics of gross primary production (GPP) over 3 years (2005–2008) using eddy covariance and assessed canopy spectral reflectance using MODIS imagery for a mature tropical semi-deciduous forest located near Sinop, Mato Grosso, Brazil. A light-use efficiency model, known as the Vegetation Photosynthesis Model (VPM), was used to estimate seasonal and inter-annual variations in GPP as a function of the enhanced vegetation index (EVI), the land surface water index (LSWI), and local meteorology. Our results indicate that the standard VPM was incapable of reproducing the seasonal variation in GPP, primarily because the model overestimated dry-season GPP. In the standard model, the scalar function that alters light-use efficiency (εg) as a function of water availability (Wscalar) is calculated as a linear function of the LSWI derived from MODIS; however, the LSWI is negatively correlated with several measures of water availability including precipitation, soil water content, and relative humidity (RH). Thus, during the dry season, when rainfall, soil water content, and RH are low, LSWI, and therefore, Wscalar, are at a seasonal maximum. Using previous research, we derived new functions for Wscalar based on time series of RH and photosynthetic photon flux density (PPFD) that significantly improved the performance of the VPM. Whether these new functions perform equally well in water stressed and unstressed tropical forests needs to be determined, but presumably unstressed ecosystems would have high cloud cover and humidity, which would minimize variations in Wscalar and GPP to spatial and/or temporal variation in water availability.

Net radiation estimated by remote sensing in Cerrado areas in the Upper Paraguay River Basin

Abstract The Cerrado is a heterogeneous landscape which is shrinking due to deforestation, giving rise to managed ecosystems. The land cover changes alter net radiation (Rn), which determines the quantity of available energy to the energy balance partition. The objectives of this study were (1) to determine the spatial pattern of the vegetation indices, albedo, and land surface temperature (LST) and (2) to evaluate the Rn estimated by Landsat 5 Thematic Mapper (TM) images over Cerrado areas in the Upper Paraguay River Basin. We estimated the vegetation indices, albedo, LST, and Rn of five selected vegetation types. The values estimated by Landsat 5 TM images had seasonal variations with higher values of the vegetation indices and lower values of the albedo and the LST during the wet season. The riparian and Cerrado strictu sensu had higher values of vegetation indices and lower albedo and LST than grasslands. The Rn estimated by Landsat 5 TM images was highly correlated with the measured Rn. The Rn had a seasonal pattern, following the solar radiation, with higher values during the wet season and varied spatially with higher values in the riparian forest and Cerrado strictu sensu and lower in the grasslands. This study showed the applicability of the Landsat 5 TM images to estimate Rn, which can help to understand the heterogeneity in the study area.

Temporal Patterns of Energy Balance for a Brazilian Tropical Savanna under Contrasting Seasonal Conditions

The savanna of Central Brazil (locally known as cerrado) has a long history of land cover change due to human activity. These changes have led to the degradation of cerrado forests and woodlands, leading to the expansion of grass-dominated cerrados and pastures. Thus, the aim of this study was to evaluate the temporal variation in energy flux in areas of degraded, grass-dominated cerrado (locally known as campo sujo) in Central Brazil. The amount of partitioned into H declined as monthly rainfall increased and reached a level of approximately 30% during the wet season, while the amount of partitioned into increased as monthly rainfall increased and reached a level of approximately 60% during the wet season. As a result, H was significantly higher than during the dry season, resulting in a Bowen ratio (β = H/) of 3-5, while Le was higher than H during the wet season, resulting in a . These data indicate that the energy partitioning of grass-dominated cerrado is relatively more sensitive to water availability than cerrado woodlands and forests, and have important implications for local and regional energy balance.