Demographic, clinical and antibody characteristics of patients with digital ulcers in systemic sclerosis: data from the DUO Registry

OBJECTIVES: The Digital Ulcers Outcome (DUO) Registry was designed to describe the clinical and antibody characteristics, disease course and outcomes of patients with digital ulcers associated with systemic sclerosis (SSc). METHODS: The DUO Registry is a European, prospective, multicentre, observational, registry of SSc patients with ongoing digital ulcer disease, irrespective of treatment regimen. Data collected included demographics, SSc duration, SSc subset, internal organ manifestations, autoantibodies, previous and ongoing interventions and complications related to digital ulcers. RESULTS: Up to 19 November 2010 a total of 2439 patients had enrolled into the registry. Most were classified as either limited cutaneous SSc (lcSSc; 52.2%) or diffuse cutaneous SSc (dcSSc; 36.9%). Digital ulcers developed earlier in patients with dcSSc compared with lcSSc. Almost all patients (95.7%) tested positive for antinuclear antibodies, 45.2% for anti-scleroderma-70 and 43.6% for anticentromere antibodies (ACA). The first digital ulcer in the anti-scleroderma-70-positive patient cohort occurred approximately 5 years earlier than the ACA-positive patient group. CONCLUSIONS: This study provides data from a large cohort of SSc patients with a history of digital ulcers. The early occurrence and high frequency of digital ulcer complications are especially seen in patients with dcSSc and/or anti-scleroderma-70 antibodies

Hydraulic lift in a Neotropical savanna: Experimental manipulation and model simulations

The objective of this study was to assess the magnitude of hydraulic lift in Brazilian savannas (Cerrado) and to test the hypothesis that hydraulic lift by herbaceous plants contributes substantially to slowing the decline of water potential and water storage in the upper soil layers during the dry season. To this effect, field observations of soil water content and water potentials, an experimental manipulation, and model simulations, were used. Savannas of central Brazil exhibit consistent changes in tree density along shallow topographic gradients, from open savannas with relatively few trees in the lower portions of the topographic gradients to woodlands with a relatively high density of trees in the upper portions of the gradient. Herbaceous plant abundance follows the opposite trend. The diel recovery of soil water storage was higher in sites with more abundant herbaceous vegetation. Experimental removal of the above ground portion of herbaceous plants in a site with low tree density, during the dry season, substantially enhanced diel recovery of water potentials in the upper soil layers, consistent with the release of hydraulically lifted water from their shallow roots. In a site with high tree density, the release of hydraulically lifted water by woody plants contributed only 2% to the partial daily recovery of soil water storage, whereas the herbaceous layer contributed the remaining 98%. Non saturated water flow in the same savanna type contributed 8% to the partial daily recovery of soil water potential at the beginning of the dry season, decreasing to near 0% after 20 days of drought. During a 70-day rainless period the soil water potential dropped to -2.0 MPa near the soil surface. The simulation model predicted that without hydraulic lift, water potential in the upper soil layers in relatively dense savannas would have dropped to -3.8 MPa. The maximum contribution of hydraulic lift to the upper 100 cm of soil was 0.7 mm day-1 near the middle of the dry season. During the peak of the dry season, hydraulic lift can replace 23% of the ecosystem evapotranspiration in a site with high tree density and consequently greatly influences the water economy and other ecosystem processes in the Cerrado.Fil: Scholz, Fabian Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad Nacional de la Patagonia. Facultad de Ciencias Naturales. Departamento de Biología; ArgentinaFil: Bucci, Sandra Janet. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad Nacional de la Patagonia. Facultad de Ciencias Naturales. Departamento de Biología; ArgentinaFil: Hoffmann, William A.. North Carolina State University; Estados UnidosFil: Meinzer, Frederick C.. United States Department of Agriculture; Estados UnidosFil: Goldstein, Guillermo Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución. Laboratorio de Ecología Funcional; Argentina. University of Miami; Estados Unido

Foliar water uptake in arid ecosystems: seasonal variability and ecophysiological consequences

Foliar water uptake (FWU) has been reported for different species across several ecosystems types. However, little attention has been given to arid ecosystems, where FWU during dew formation or small rain events could ameliorate water deficits. FWU and their effects on leaf water potential (ΨLeaf) were evaluated in grasses and shrubs exploring different soil water sources in a Patagonian steppe. Also, seasonal variability in FWU and the role of cell wall elasticity in determining the effectson ΨLeaf were assessed. Eleven small rain events (< 8 mm) and 45 days with dew formation were recorded during the study period. All species exhibited FWU after experimental wetting. There was a large variability in FWU across species, from 0.04 mmol m−2 s−1 in species with deep roots to 0.75 mmol m−2 s−1 in species with shallow roots. Species-specific mean FWU rates were positively correlated with mean transpiration rates. The increase in ΨLeaf after leaf wetting varied between0.65 MPa and 1.67 MPa across species and seasons. The effects of FWU on ΨLeaf were inversely correlated with cell wall elasticity. FWU integrated over both seasons varied between 28 mol m−2 in species with deep roots to 361 mol m−2 in species with shallow roots. Taking into account the percentage of coverage of each species, accumulated FWU represented 1.6% of the total annual transpiration of grasses and shrubs in this ecosystem. Despite this low FWU integrated over time compared to transpiration, wetting leaves surfaces can help to avoid larger water deficit during the dry season.Fil: Cavallaro, Agustin. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; ArgentinaFil: Carbonell Silleta, Luisina. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Pereyra, Daniel A.. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Goldstein, Guillermo Hernan. University of Miami; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Scholz, Fabian Gustavo. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentin

Water economy of Neotropical savanna trees: Six paradigms revisited

Biologists have long been puzzled by the striking morphological and anatomical characteristics of Neotropical savanna trees which have large scleromorphic leaves, allocate more than half of their total biomass to belowground structures and produce new leaves during the peak of the dry season. Based on results of ongoing interdisciplinary projects in the savannas of central Brazil (cerrado), we reassessed the validity of six paradigms to account for the water economy of savanna vegetation. (1) All savanna woody species are similar in their ability to take up water from deep soil layers where its availability is relatively constant throughout the year. (2) There is no substantial competition between grasses and trees for water resources during the dry season because grasses exclusively explore upper soil layers, whereas trees access water in deeper soil layers. (3) Tree species have access to abundant groundwater, their stomatal control is weak and they tend to transpire freely. (4) Savanna trees experience increased water deficits during the dry season despite their access to deep soil water. (5) Stomatal conductance of savanna species is low at night to prevent nocturnal transpiration, particularly during the dry season. (6) Savanna tree species can be classified into functional groups according to leaf phenology. We evaluated each paradigm and found differences in the patterns of water uptake between deciduous and evergreen tree species, as well as among evergreen tree species, that have implications for regulation of tree water balance. The absence of resource interactions between herbaceous and woody plants is refuted by our observation that herbaceous plants use water from deep soil layers that is released by deep-rooted trees into the upper soil layer. We obtained evidence of strong stomatal control of transpiration and show that most species exhibit homeostasis in maximum water deficit, with midday water potentials being almost identical in the wet and dry seasons. Although stomatal control is strong during the day, nocturnal transpiration is high during the dry season. Our comparative studies showed that the grouping of species into functional categories is somewhat arbitrary and that ranking species along continuous functional axes better represents the ecological complexity of adaptations of cerrado woody species to their seasonal environment.Fil: Goldstein, Guillermo Hernan. University of Miami; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; ArgentinaFil: Meinzer, Frederick C.. USDA Forest Service; Estados UnidosFil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Scholz, Fabian Gustavo. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Franco, Augusto C.. Universidade do Brasília; BrasilFil: Hoffmann, William A.. University of North Carolina; Estados Unido

Grazing increases evapotranspiration without the cost of lowering soil water storages in arid ecosystems

Grazing is the predominant land use practice in arid environments; however, there are relatively few studies of grazing effects on ecosystem functioning. We assessed the impact of grazing on soil moisture, evapotranspiration (ET), canopy conductance (Gc), and root water uptake in the Patagonian steppe. Studies were done in 3 sites along a gradient of grazing intensity. High grazing intensity increased the soil water storage by 24% and decreased the amount of water extracted from deep layers compared to the low grazing intensity. Grazing affected ET and its partitioning into transpiration (T) and evaporation. High shrub cover and Gc increased ET and T or ET partitioning in the heavily grazed site. Annual ET increased from 78% to 92% of the annual precipitation from the lowest to the highest grazing intensity, respectively. Total T was 21% higher in the highest intensity site compared to the lowest intensity site. Changes in Gc suggest that grazing modified the canopy architecture, and thus the response of vegetation to environmental factors. At the beginning of the growing season when moisture was high, Gc exhibited the highest value in the heavily grazed site, but a strong regulation of water losses was observed under drier conditions. This study emphasizes the need to assess simultaneously multiple factors for understanding regulatory mechanisms of grazing effects on hydrological processes. From a sustainable management point of view, we suggest that increasing the number of water sources, and thus spreading the sheep in a paddock, can enhance the stocking rate while maintaining soil water storage.Fil: Pereyra, Daniel A.. Universidad Nacional de la Patagonia "san Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; ArgentinaFil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "san Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; ArgentinaFil: Arias, Nadia Soledad. Universidad Nacional de la Patagonia "san Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; ArgentinaFil: Ciano, Nicolás. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; ArgentinaFil: Cristiano, Piedad María. Universidad de Buenos Aires; ArgentinaFil: Goldstein, Guillermo Hernan. University of Miami; Estados Unidos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Scholz, Fabian Gustavo. Universidad Nacional de la Patagonia "san Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; Argentin

Conformational plasticity of the intrinsically disordered protein ASR1 modulates its function as a drought stress-responsive gene.

Plants in arid zones are constantly exposed to drought stress. The ASR protein family (Abscisic, Stress, Ripening) -a subgroup of the late embryogenesis abundant superfamily- is involved in the water stress response and adaptation to dry environments. Tomato ASR1, as well as other members of this family, is an intrinsically disordered protein (IDP) that functions as a transcription factor and a chaperone. Here we employed different biophysical techniques to perform a deep in vitro characterization of ASR1 as an IDP and showed how both environmental factors and in vivo targets modulate its folding. We report that ASR1 adopts different conformations such as α-helix or polyproline type II in response to environmental changes. Low temperatures and low pH promote the polyproline type II conformation (PII). While NaCl increases PII content and slightly destabilizes α-helix conformation, PEG and glycerol have an important stabilizing effect of α-helix conformation. The binding of Zn2+in the low micromolar range promotes α-helix folding, while extra Zn2+ results in homo-dimerization. The ASR1-DNA binding is sequence specific and dependent on Zn2+. ASR1 chaperone activity does not change upon the structure induction triggered by the addition of Zn2+. Furthermore, trehalose, which has no effect on the ASR1 structure by itself, showed a synergistic effect on the ASR1-driven heat shock protection towards the reporter enzyme citrate synthase (CS). These observations prompted the development of a FRET reporter to sense ASR1 folding in vivo. Its performance was confirmed in Escherichia coli under saline and osmotic stress conditions, representing a promising probe to be used in plant cells. Overall, this work supports the notion that ASR1 plasticity is a key feature that facilitates its response to drought stress and its interaction with specific targets

Controls on stand transpiration and soil water utilization along a tree density gradient in a Neotropical savanna

Environmental controls of stand-level tree transpiration (E) and seasonal patterns of soil water utilization were studied in five central Brazilian savanna (Cerrado) sites differing in tree density. Tree density of Cerrado vegetation in the study area consistently changes along topographic gradients from ∼1000 trees ha-1 in open savannas (campo sujo) at the lower end of the topographic gradient to >3000 trees ha-1 in woodlands (cerradão) at the upper end of the gradient. Tree canopy resistance (rC) increased linearly with increasing daily mean air saturation deficit (D) at all sites, but cerradão and cerrado denso sites with higher tree density and higher tree leaf area index (LAI) had lower rC values at all values of D compared to physiognomies with lower tree density, suggesting that rC was less sensitive to changes in D in physiognomies with high tree density and LAI. During the peak of the dry season, mean soil water potential at 0.20 m depth was most negative in the sites with the lowest tree basal area and increased linearly with basal area across sites. In contrast, soil water storage in the 0.10-2.50 m layer decreased exponentially with increasing basal area, consistent with trees in higher density sites utilizing a larger proportion of available soil water at depth during the dry season. Maximum tree transpiration was highest in the cerradão and cerrado denso (∼0.81 mm day-1). Despite higher evaporative demand during the dry season, E was similar between the dry and wet seasons within each study site, which was associated with lower LAI and canopy conductance (gC) during the dry season compared to the wet season. Leaf area index was a good predictor of E and gC. For both dry and wet season data combined, E increased asymptotically with increasing LAI across all physiognomic types, allowing LAI to be used as a predictor of spatial variation of E. The lack of seasonality in E across the Cerrado physiognomies studied could not be explained by individual constraining variables such as D or soil water potential near the surface, but was consistent with the influence of multiple regulatory effects of D and soil water potential on seasonal changes in leaf area and gC.Fil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Scholz, Fabian Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Goldstein, Guillermo Hernan. University of Miami; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hoffmann, William A.. North Carolina State University; Estados UnidosFil: Meinzer, Frederick C.. USDA Forest Service; Estados UnidosFil: Franco, Augusto C.. Universidade do Brasília; BrasilFil: Giambelluca, Thomas. University of Hawaii at Manoa; Estados UnidosFil: Miralles-Wilhelm, Fernando. Florida International University; Estados Unido

Crown structural properties, wood density, and liana load: Influence on growth and mortality in subtropical forests

Wood density (WD) and other wood mechanical and structural properties may have a strong functional relationship with demographic patterns and allometry of trees. We analyzed the influence of WD, structural properties, architectural traits, and community-level attributes on growth rates (GRs) and mortality modes of canopy tree species in a subtropical forest of Argentina. Stem WD and the WD, strength, stiffness, toughness, and hardness of branches were measured in 10 canopy species. Architectural traits and liana load were also determined. Strength and hardness of branches were linearly correlated to branch WD, and GRs were linearly correlated to stem WD across species. At the individual level, trees with greater hardness and toughness in branches died mostly uprooted, and trees with greater branch stiffness and susceptibility to colonization by lianas were mostly broken. At the community level, the suppressed trees died mostly broken. The dominant trees with high local tree density died mostly broken, whereas more isolated trees died mostly uprooted. Mortality modes were determined not only by mechanical properties, but also by community properties such as liana load, crown canopy position, and number of neighboring trees. Other biophysical traits besides WD are important explanatory variables when dry wood is used to describe functional characteristics of trees.La densité du bois (DB) et d’autres propriétés mécaniques et structurales pourraient avoir une étroite relation fonctionnelle avec les patrons démographiques et l’allométrie des arbres. Nous avons analysé l’influence de la DB, des pro priétés structurales, des traits architecturaux et des attributs à l’échelle de la communauté sur le taux de croissance (TC) et la cause de mortalité des espèces arborescentes dominantes dans une forêt subtropicale en Argentine. La DB du tronc ainsi que la DB, la résistance, la rigidité, la ténacité et la dureté des branches ont été mesurées chez 10 espèces dominantes. De plus, les traits architecturaux et la charge de lianes ont été déterminés. La résistance et la dureté des branches étaient liné airement corrélées à la DB des branches et le TC était linéairement corrélé à la DB du tronc chez l’ensemble des espèces. À l’échelle individuelle, les arbres dont les branches avaient la plus grande dureté et la plus grande ténacité sont le plus sou vent morts renversés et ceux dont les branches avaient la plus grande rigidité et qui étaient les plus sujets à être colonisés par les lianes sont morts pour la plupart après avoir été cassés. À l’échelle de la communauté, les arbres supprimés sont morts pour la plupart après avoir été cassés. Les arbres dominants dont la densité était localement élevée sont surtout morts après avoir été cassés tandis que les arbres plus isolés son surtout morts après avoir été déracinés. La façon dont la mortalité est survenue était déterminée par les propriétés mécaniques mais aussi par les propriétés de la communauté, telles que la charge de lianes, la position de la cime dans le couvert et le nombre d’arbres avoisinants. D’autres traits bio physiques à part la DB sont d’importantes variables explicatives lorsque du bois sec est utilisé pour décrire les caractéris tiques fonctionnelles des arbres.Fil: Rodríguez, Sabrina A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; ArgentinaFil: Cristiano, Piedad María. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Lezcano, Oscar A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; ArgentinaFil: Suirezs, Teresa Maria. Universidad Nacional de Misiones; ArgentinaFil: Díaz Villa, M. Virginia E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biociencias de la Patagonia; ArgentinaFil: Goldstein, Guillermo Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. University of Miami; Estados UnidosFil: Campanello, Paula Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ingeniería - Sede Esquel. Centro de Estudios Ambientales Integrados; Argentin

Evapotranspiration and energy balance of Brazilian savannas with contrasting tree density

Tropical savannas including those of central Brazil (Cerrado) serve as an important regulator of energy and mass exchange with the atmosphere. However, the effects of interactions between grasses and deeply rooted trees and shrubs on energy and water fluxes of savannas are not well understood. In this study, eddy-covariance measurements were used to observe and compare the energy balance and evapotranspiration at two adjacent Cerrado sites differing in woody plant density. Latent energy flux (LE) and evapotranspiration (ET) for Cerrado Denso (8-10-m trees with a cover density of approximately 50% and an understory of grass and shrubs) were generally similar to or greater than for Campo Cerrado (widely scattered 3-4-m trees with a cover density of about 5% and an understory of grasses, shrubs, and sedges), with the greatest difference between the sites occurring during the dry season. Mean annual ET was 823 and 689 mm yr-1, and LE averaged 63.9 ± 11.7 and 53.5 ± 14.3 W m-2 at Cerrado Denso and Campo Cerrado, respectively. At both sites, ET reached a minimum at near the end of the dry season, indicating that reduced water availability constrained dry season ET at both sites. The Bowen ratio at both sites increased as soil moisture decreased, but with a stronger dependency at the Campo Cerrado site, presumably due to the dominance of shallow-rooted plants and the larger contribution of soil evaporation there. Energy partitioning, as indicated by the Bowen ratio, was also strongly influenced by variations in leaf area index (LAI). The strong similarity in the Bowen ratio-LAI relationship for the two sites suggests that LAI can be used to explain much of the observed temporal and spatial ET variability across seasons and variations in woody plant density in the Cerrado.Fil: Giambelluca, Thomas W.. University of Hawaii at Manoa; Estados UnidosFil: Scholz, Fabian Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Bucci, Sandra Janet. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Meinzer, Frederick C.. Forestry Sciences Laboratory; Estados UnidosFil: Goldstein, Guillermo Hernan. University of Miami; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; ArgentinaFil: Hoffmann, William A.. University of North Carolina; Estados UnidosFil: Franco, Augusto C.. Universidade do Brasília; BrasilFil: Buchert, Martin P.. University of Hawaii at Manoa; Estados Unidos. H.W. Lochner, Inc.; Estados Unido

Stem and leaf hydraulics of congeneric tree species from adjacent tropical savanna and forest ecosystems

Leaf and stem functional traits related to plant water relations were studied for six congeneric species pairs, each composed of one tree species typical of savanna habitats and another typical of adjacent forest habitats, to determine whether there were intrinsic differences in plant hydraulics between these two functional types. Only individuals growing in savanna habitats were studied. Most stem traits, including wood density, the xylem water potential at 50% loss of hydraulic conductivity, sapwood area specific conductivity, and leaf area specific conductivity did not differ significantly between savanna and forest species. However, maximum leaf hydraulic conductance (Kleaf) and leaf capacitance tended to be higher in savanna species. Predawn leaf water potential and leaf mass per area were also higher in savanna species in all congeneric pairs. Hydraulic vulnerability curves of stems and leaves indicated that leaves were more vulnerable to drought-induced cavitation than terminal branches regardless of genus. The midday Kleaf values estimated from leaf vulnerability curves were very low implying that daily embolism repair may occur in leaves. An electric circuit analog model predicted that, compared to forest species, savanna species took longer for their leaf water potentials to drop from predawn values to values corresponding to 50% loss of Kleaf or to the turgor loss points, suggesting that savanna species were more buffered from changes in leaf water potential. The results of this study suggest that the relative success of savanna over forest species in savanna is related in part to their ability to cope with drought, which is determined more by leaf than by stem hydraulic traits. Variation among genera accounted for a large proportion of the total variance in most traits, which indicates that, despite different selective pressures in savanna and forest habitats, phylogeny has a stronger effect than habitat in determining most hydraulic traits.Fil: Hao, Guang-You. Chinese Academy of Sciences; República de ChinaFil: Hoffmann, William A.. North Carolina State University; Estados UnidosFil: Scholz, Fabian Gustavo. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Meinzer, Frederick C.. United States Department of Agriculture; ArgentinaFil: Franco, Augusto C.. Universidade do Brasília; BrasilFil: Cao, Kun-Fang. Chinese Academy of Sciences; República de ChinaFil: Goldstein, Guillermo Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. University of Miami; Estados Unidos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución. Laboratorio de Ecología Funcional; Argentin