Fluxes of carbon, water and energy over Brazilian cerrado: an analysis using eddy covariance and stable isotopes

Abstract

We present the energy and mass balance of cerrado sensu stricto (a Brazilian form of savanna), in which a mixture of shrubs, trees and grasses forms a vegetation with a leaf area index of 1-0 in the wet season and 0-4 in the dry season. In the wet season the available energy was equally dissipated between sensible heat and evaporation, but in the dry season at high irradiance the sensible heat greatly exceeded evaporation. Ecosystem surface conductance gî n the wet season rose abruptly to 0-3 mol m"^ s"^ and fell gradually as the day progressed. Much of the total variation in gs was associated with variation in the leaf-to-air vapour pressure deficit of water and the solar irradiance. In the dry season the maximal g^ values were only 0-1 mol m"^ s~\ Maximal net ecosystem fluxes of CO2 in the wet and dry season were -10 and -15 /Jmol CO2 m'^ s~', respectively (sign convention: negative denotes fluxes from atmosphere to vegetation). The canopy was well coupled to the atmosphere, and there was rarely a significant build-up of respiratory CO2 during the night. For observations in the wet season, the vegetation was a carbon dioxide sink, of maximal strength 0*15 mol m"^ d~\ However, it was a source of carbon dioxide for a brief period at the height of the dry season. Leaf carbon isotopic composition showed all the grasses except for one species to be C4, and all the palms and woody plants to be C3. The CO2 coming from the soil had an isotopic composition that suggested 40% of it was of C4 origin.

Measurements of CO2 exchange over a woodland savanna (Cerrado Sensu stricto) in southeast Brasil

“…Several experimental studies have adressed the carbon exchange using automatic monitoring in the Amazon rain forests as part of the LBA Project (LBA 1996;Grace et al 1996, Malhi et al 1998. Pioneer studies in Brazillian savanna were reported by Miranda et al (1997) in a Cerrado Sensu stricto in the central region, and by Vourlitis et al (2001) in a Cerradão vegetation at the ecotone between tropical savanna and rain forest in Central Brasil. Related investigations in South America about water cycle and carbon stocks in tropical savanna were developed in Venezuela (San Jose et al 2001;Szarzynsky and Anhuf et al 1999).…”

How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland

“…Since trees and grass canopies differ in their ability to intercept and absorb photons and transpire (Kelliher et al, 1993;Miranda, 1997), their relative composition can have a profound effect on the surface energy balance of a landscape, which in turn, can have a modifying feedback on the regional climate (Zeng and Neelin, 2000) and its water balance (Joffre and Rambal, 1993;Rodriguez-Iturbe et al, 1999a).…”

Spatial and temporal variability of canopy cover and understory light in a Cerrado of Southern Brazil

“…However, the obtained LAI values were not so different from the values described by Asner (1998) for 30 common species of Cerrado, these ranging from 3.1 to 5.9. Even when subtracting the highest stem area index (SAI) value of 0.7 for Cerrado trees (Asner, 1998), obtained values remained higher than those described by Miranda et al (1997). In another study in five Cerrado sites, Hoffmann et al (2005) found that LAI values ranged from 2.48 in the "cerradão" to 0.28 in the "campo sujo".…”

“…For a Eucalypt savanna in Australia, stated that LAI values were typically 1.0 in the wet season and 0.65 in the dry. Even for a Cerrado in central Brazil, Miranda et al (1997) obtained LAI values of 1.0 in the wet and 0.4 in the dry seasons, when considering only a mixture of leaves from shrubs, trees and grass. Values recorded in the Serra do Cipó National Park are may be a little high, because indirectly estimated LAI based on gap-fraction analysis included the projected stem and branch area.…”

“…O`Grady et al (2000) described seasonal variation in overstory LAI due to the greater contribution of deciduous and semi-deciduous species of Eucalypt in the Australian open-forest savanna. In the Brazilian Cerrado, Miranda et al (1997) also described seasonal changes in LAI and pointed out a reduction of about 35% in ecosystem photosynthetic rates simply due to the lower LAI in the dry season. In a recent study, Bucci et al (2008) showed that transpiration increases with LAI in all Cerrado studied physiognomies in both the dry and wet seasons.…”