The study investigates the effect of land-use change on nitrous oxide (N 2 O) and methane (CH 4) ... more The study investigates the effect of land-use change on nitrous oxide (N 2 O) and methane (CH 4) fluxes from soil, in savanna ecosystems of the Orinoco region (Venezuela). Gas fluxes were measured by closed static chambers, in the wet and dry season, in representative systems of land management of the region: a cultivated pasture, an herbaceous savanna, a tree savanna and a woodland (control site). Higher N 2 O emissions were observed in the cultivated pasture and in the herbaceous savanna compared with the tree savanna and the woodland, and differences were mainly related to fine soil particle content and soil volumetric water content measured in the studied sites. Overall N 2 O emissions were quite low in all sites (0-1.58 mg N 2 ON m À2 day À1). The cultivated pasture and the woodland savanna were on average weak CH 4 sinks (À0.05 AE 0.07 and À0.08 AE 0.05 mg CH 4 m À2 day À1 , respectively), whereas the herbaceous savanna and the tree savanna showed net CH 4 production (0.23 AE 0.05 and 0.19 AE 0.05 mg CH 4 m À2 day À1 , respectively). Variations of CH 4 fluxes were mainly driven by variation of soil waterfilled pore space (WFPS), and a shift from net CH 4 consumption to net CH 4 production was observed at around 30% WFPS. Overall, the data suggest that conversion of woodland savanna to managed landscape could alter both CH 4 and N 2 O fluxes; however, the magnitude of such variation depends on the soil characteristics and on the type of land management before conversion.
The seasonal changes in the energy balance after the substitution of a herbaceous savanna by a Br... more The seasonal changes in the energy balance after the substitution of a herbaceous savanna by a Brachiaria field located in the Orinoco lowlands were assessed over an entire year using the eddy covariance technique. Simultaneously, an herbaceous savanna was monitored as a control. This work provides evidence that the vegetation replacement lead to different patterns of energy and water balance. The seasonal trends of the latent heat flux (λE) to available energy (Ra) ratio tended to decrease as senescence increased due to seasonal influence of air humidity mole fraction deficit and soil water content on leaf area index (LAI) and surface conductance (gs). Therefore, the partitioning of the available energy depended on both climatological (i.e., solar radiation, volumetric soil water content and air humidity mole fraction deficit) and biological variables (i.e., conductance behavior and LAI) which were stress-induced. For the wet season, the seasonally averaged daily λE in the Brachia...
In the Orinoco lowlands, savannas have been often replaced by pastures composed of the C 4 grass,... more In the Orinoco lowlands, savannas have been often replaced by pastures composed of the C 4 grass, Brachiaria decumbens Stapf. We addressed following questions: (1) How does the replacement of the native vegetation affect CO 2 exchange on seasonal and annual scales? (2) How do biophysical constraints change when the landscape is transformed? To assess how these changes affect carbon exchange, we determined simultaneously the CO 2 fluxes by eddy covariance, and the soil CO 2 efflux by a chamber-based system in B. decumbens and herbaceous savanna stands. Measurements covered a one-year period from the beginning of the dry season (November 2008) to the end of the wet season (November 2009). During the wet season, the net ecosystem CO 2 exchange reached maximum values of 23 and 10 mol(CO 2) m-2 s-1 in the B. decumbens field and in the herbaceous savanna stand, respectively. The soil CO 2 efflux for both stands followed a temperature variation during the dry and wet seasons, when the soil water content (SWC) increased above 0.087 m 3 m-3 in the latter case. Bursts of CO 2 emissions were evident when the dry soil experienced rehydration. The carbon source/sink dynamics over the two canopies differed markedly. Annual measurements of the net ecosystem production indicated that the B. decumbens field constituted a strong carbon sink of 216 g(C) m-2 y-1. By contrast, the herbaceous savanna stand was found to be only a weak sink [36 g(C) m-2 y-1 ]. About 53% of the gross primary production was lost as the ecosystem respiration. Carbon uptake was limited by SWC in the herbaceous savanna stand as evident from the pattern of water-use efficiency (WUE). At the B. decumbens stand, WUE was relatively insensitive to SWC. Although these results were specific to the studied site, the effect of land use changes and the physiological response of the studied stands might be applicable to other savannas.
Figure 1. Locations of Trachypogon savannas at the Orinoco Llanos (Venezuela). The scale = 1:4,00... more Figure 1. Locations of Trachypogon savannas at the Orinoco Llanos (Venezuela). The scale = 1:4,000,000. We analyzed the ecological factors affecting the oc-currence of termite mounds within and among physio-nomie types of Trachypogon savannas from the central and ...
... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effe... more ... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effects of chronic doses of ozone (03) and rates of nitrogen (N) fertilizer on N content of ladino clover (Trifoliurn r-epens L. cv. Tillman) and tall fescue (Festuca arunrlinacea Schreb. cv. ...
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007
The effect of land use changes on the woody cover and patchiness of the Orinoco lowlands was anal... more The effect of land use changes on the woody cover and patchiness of the Orinoco lowlands was analyzed from 1951 to 1997 by using a stretched exponential model in terms of the patch size distribution. We selected five production systems on the basis of the following components: policy option, technology and environment. They are: (a) high-input pasture in deep soil, (b) low-input cropping in deep soil, (c) high-input cropping in deep soil, (d) low-input cropping in shallow soil and (e) extensive cattle grazing in shallow soil. For comparison, stands with similar soil depth and woody density were selected at the protected Biological Reserve in the Calabozo region. Results indicate that the distribution of the patches was described by the stretched exponential distribution model with c as the exponent distribution. The magnitude of c reflected the effect of land use changes over time. Thus, the parameter c for human impacted stands was higher than that for the fallow stands. The stretched exponential model implies that the human impact had a multiscalar effect on the Orinoco mosaic, in terms of the multiplicative processes. There is a generic mechanism exhibiting an anomalous distribution of the patches such as has been proposed for physical systems. Therefore, the number of generation of the multiplicative processes (i.e. inverse of c) for impacted stands was lower than that in the fallow stands. As the time from fallow establishment proceeded, there was a tendency to patch re-organization by biotic effects.
Water relations were analysed in a semi-deciduous forest grove occurring in the oxisols of the Or... more Water relations were analysed in a semi-deciduous forest grove occurring in the oxisols of the Orinoco savannas. This grove has a shallow unconsolidated ironstone cuirass, which is overlaid by a sandy loam layer (0.0-0.5 m) that contains more than 90% of the grove forest root phytomass. Evapotranspiration and through drainage were calculated by using data from the soil profile as related to physical characteristics of the site root zone, hydraulic conductivity, volumetric water content and potential hydraulic gradient. Mean annual evapotranspiration was 783 mm year(-1) and annual through drainage below the root zone was 14% (162 mm year(-1)) of the gross rainfall. This drainage recharged the 42% of the annual saturation deficit of the water table. Similar mean annual evapotranspiration (770 mm year(-1)) was also calculated by using the water balance components. The mean daily coupling omega factor (Ω) between the grove canopy and the surrounding atmosphere indicated that a high degree of coupling (Ω=0.14±0.16) occurs in the grove and evapotranspiration was mainly controlled by surface conductance. As the dry season proceeded, the soil saturation deficit (δθ) increased rapidly resulting in a threshold surface conductance (0.030-0.005 m s(-1)) for δθ ranging from 0.05 to 0.10. Hypotheses to explain the omnipresence of perennial species in the wide range of physical conditions in neotropical savannas are discussed.
The strength of carbon sink and stock was assessed in a protected savanna of the Orinoco Llanos b... more The strength of carbon sink and stock was assessed in a protected savanna of the Orinoco Llanos by the harvesting plant phytomass and using allometric relationships between the dry mass and the censuses of plant height. Thus, changes in the carbon stock and the proportion in the treergrass proportion were evaluated throughout age states. Results indicate that the carbon stock in the vegetation increased from 207 to 9215 g C m y2 whereas in the soil, it varied 6680 to 12 196 g C m y2 . y2 Ž . The carbon stock accumulation was mainly related to increases in the woody layer from 36 to 9215 g C m 255-fold and y2 Ž . in the soil from 1341 to 12 196 g C m nine-fold , respectively. The estimated pool of carbon sequestered in the Orinoco Llanos by the restored forest in 51 years was 5.69 Pg C. The expansion and conservation of this carbon pool might remove CO from the atmosphere to help compensate for CO liberation associated with other land uses or industrial practices. 2 2 q 1998 Elsevier Science B.V.
Communications in Soil Science and Plant Analysis, 2007
Field measurements showed the nitrogen (N) inputs and output of a fertilized pineapple crop [Anan... more Field measurements showed the nitrogen (N) inputs and output of a fertilized pineapple crop [Ananas comosus (L.) Merr. c.v. Red Spanish] growing in the Orinoco llanos during consecutive seasonal courses. The process rate changed with growth life‐cycle stages and seasonal conditions. The N accumulated by pineapple over the growing period was 226 kg N ha. It depended on the available N in the soil and the timing of split application of N fertilizer. Detailed monitoring of plant N‐accumulation rate showed a maximum rate (3.20 kg N ha d) at the harvesting time. The N‐harvested ratio and N‐use efficiency were 0.27 and 138 g g, respectively. The calculated N‐mineralization rate of the soil was 167 kg N ha over the life cycle. The fate of fertilizer N applied to pineapple was determined in microplots using urea labelled with 9.634% atom excess N. Fertilizer N recovery accounted for 48% of the applied N. The corresponding fractions of N recovered in the soil were 0.16 for the 0.0‐ to 0.3‐m depth and 0.01 for the 0.3‐ to 0.7‐m depth. The unrecovered fertilizer N in this study (34%) was largely due to volatilization (20% of the fertilizer) and denitrification (1.2%). Volatilization was shown to be greatly influenced by the seasonal conditions, namely the volumetric soil water content. In the pineapple field, monitored N input exceeded N output by 134 kg N ha, which is likely to lead to maintenance of soil N. Furthermore, utilization of N from crop residues input (164 kg N ha) has repercussions for the sustainable use of the Savanna Oligotrophic soils.
... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effe... more ... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effects of chronic doses of ozone (03) and rates of nitrogen (N) fertilizer on N content of ladino clover (Trifoliurn r-epens L. cv. Tillman) and tall fescue (Festuca arunrlinacea Schreb. cv. ...
The HER2/neu oncogene product, p185 HER2/neu , is overexpressed on the surface of many human brea... more The HER2/neu oncogene product, p185 HER2/neu , is overexpressed on the surface of many human breast cancers. Strains of transgenic mice have been developed that express the rat neu oncogene in mammary epithelial cells and develop spontaneous mammary tumors that overexpress p185 neu . This model provides an ideal system for testing interventions to prevent tumor development. In this study, we immunized neu-transgenic mice with a vaccine consisting of the extracellular domain of p185 neu (NeuECD). Immunized mice developed Neu-speci®c humoral immune responses, as measured by circulating anti-Neu antibodies in their sera, and cellular immune responses, as measured by lymphocyte proliferation to NeuECD in vitro. In addition, the subsequent development of mammary tumors was signi®cantly lower in immunized mice than in controls and vaccine treatment was associated with a signi®cant increase in median survival.
... José San-José Æ Rubén Montes Æ Miguel Angel Mazorra Æ Ernesto Aguirre Ruiz Æ Nathaly Matute .... more ... José San-José Æ Rubén Montes Æ Miguel Angel Mazorra Æ Ernesto Aguirre Ruiz Æ Nathaly Matute ... histosols are important in the global carbon cycle, although covering little more than 1% of the world's land surface, they hold about 20% of global soil carbon (Brady and Weil ...
Se estudiaron las interrelaciones entre la vegetación y el relieve en dos topo-secuencias corresp... more Se estudiaron las interrelaciones entre la vegetación y el relieve en dos topo-secuencias correspondientes al Parque Nacional Aguaro-Guariquito, estado Guárico, Venezuela. La primera es un paisaje de altiplanicie de Mesa cubierta con una sabana bien drenada (sitio 1). En las aéreas disectadas de esta altiplanicie se presentan geofracturas con suelos permanentemente saturados donde se desarrollan los morichales (sitio 2). La otra toposecuencia corresponde a una planicie eólica con médanos, cuyos suelos provienen de materiales originados de la altiplanicie de Mesa y están cubiertos por sabanas húmedas (sitio 3), las cuales permanecen anegadas durante tres meses (junio -agosto) con una lámina de agua de 0.25 ± 0.10 m. Las zonas más deprimidas en esta topo-secuencia conducen a condiciones temporales de extremo anegamiento, donde se presenta el congrial (sitio 4), una comunidad dominada por Acosmium nitens y el saladillal (sitio 5), una vegetación caracterizada por la presencia de Caraipa llanorum. El congrial es anegado durante siete meses (junio -diciembre), con una lámina de agua de 1.02 ± 0.10 m. En contraste, el saladillal es inundado por seis meses (junio -noviembre) y la lámina de agua alcanza una altura de 0.80 ± 0.10 m. Las comunidades anegadas (sitios 2-5) se encuentran sobre suelos más ácidos (4.0 -4.6 unidades) que los característicos de la sabana bien drenada (sitio 1; 5.0 unidades). El pH estuvo asociado con la concentración de aluminio. El contenido de materia orgánica fue mayor en el sitio anegado (8.59 %) que en los estacionalmente inundables y en el bien drenado (0.7-1.0 %). El hábitat anegado es restrictivo de la biodiversidad. El congrial, el saladillal, la sabana húmeda y el morichal presentan 52, 52, 56 y 74 especies, respectivamente. En contraste, la sabana bien drenada presenta 114 especies. La similitud entre el congrial y el saladillal fue de 56 %. En relación con las otras comunidades, la similitud fue menor del 38 %. Los resultados indican que las formas de vidas Teroherbae y Teroculmi (e.g., especies
Page 1. Heterogeneity of the inland waterland palm ecotones (morichals) in the Orinoco lowlands,... more Page 1. Heterogeneity of the inland waterland palm ecotones (morichals) in the Orinoco lowlands, South America José San-José Rubén Montes Miguel Angel Mazorra Nathaly Matute Received: 8 May 2009 / Accepted: 13 ...
The study investigates the effect of land-use change on nitrous oxide (N 2 O) and methane (CH 4) ... more The study investigates the effect of land-use change on nitrous oxide (N 2 O) and methane (CH 4) fluxes from soil, in savanna ecosystems of the Orinoco region (Venezuela). Gas fluxes were measured by closed static chambers, in the wet and dry season, in representative systems of land management of the region: a cultivated pasture, an herbaceous savanna, a tree savanna and a woodland (control site). Higher N 2 O emissions were observed in the cultivated pasture and in the herbaceous savanna compared with the tree savanna and the woodland, and differences were mainly related to fine soil particle content and soil volumetric water content measured in the studied sites. Overall N 2 O emissions were quite low in all sites (0-1.58 mg N 2 ON m À2 day À1). The cultivated pasture and the woodland savanna were on average weak CH 4 sinks (À0.05 AE 0.07 and À0.08 AE 0.05 mg CH 4 m À2 day À1 , respectively), whereas the herbaceous savanna and the tree savanna showed net CH 4 production (0.23 AE 0.05 and 0.19 AE 0.05 mg CH 4 m À2 day À1 , respectively). Variations of CH 4 fluxes were mainly driven by variation of soil waterfilled pore space (WFPS), and a shift from net CH 4 consumption to net CH 4 production was observed at around 30% WFPS. Overall, the data suggest that conversion of woodland savanna to managed landscape could alter both CH 4 and N 2 O fluxes; however, the magnitude of such variation depends on the soil characteristics and on the type of land management before conversion.
The seasonal changes in the energy balance after the substitution of a herbaceous savanna by a Br... more The seasonal changes in the energy balance after the substitution of a herbaceous savanna by a Brachiaria field located in the Orinoco lowlands were assessed over an entire year using the eddy covariance technique. Simultaneously, an herbaceous savanna was monitored as a control. This work provides evidence that the vegetation replacement lead to different patterns of energy and water balance. The seasonal trends of the latent heat flux (λE) to available energy (Ra) ratio tended to decrease as senescence increased due to seasonal influence of air humidity mole fraction deficit and soil water content on leaf area index (LAI) and surface conductance (gs). Therefore, the partitioning of the available energy depended on both climatological (i.e., solar radiation, volumetric soil water content and air humidity mole fraction deficit) and biological variables (i.e., conductance behavior and LAI) which were stress-induced. For the wet season, the seasonally averaged daily λE in the Brachia...
In the Orinoco lowlands, savannas have been often replaced by pastures composed of the C 4 grass,... more In the Orinoco lowlands, savannas have been often replaced by pastures composed of the C 4 grass, Brachiaria decumbens Stapf. We addressed following questions: (1) How does the replacement of the native vegetation affect CO 2 exchange on seasonal and annual scales? (2) How do biophysical constraints change when the landscape is transformed? To assess how these changes affect carbon exchange, we determined simultaneously the CO 2 fluxes by eddy covariance, and the soil CO 2 efflux by a chamber-based system in B. decumbens and herbaceous savanna stands. Measurements covered a one-year period from the beginning of the dry season (November 2008) to the end of the wet season (November 2009). During the wet season, the net ecosystem CO 2 exchange reached maximum values of 23 and 10 mol(CO 2) m-2 s-1 in the B. decumbens field and in the herbaceous savanna stand, respectively. The soil CO 2 efflux for both stands followed a temperature variation during the dry and wet seasons, when the soil water content (SWC) increased above 0.087 m 3 m-3 in the latter case. Bursts of CO 2 emissions were evident when the dry soil experienced rehydration. The carbon source/sink dynamics over the two canopies differed markedly. Annual measurements of the net ecosystem production indicated that the B. decumbens field constituted a strong carbon sink of 216 g(C) m-2 y-1. By contrast, the herbaceous savanna stand was found to be only a weak sink [36 g(C) m-2 y-1 ]. About 53% of the gross primary production was lost as the ecosystem respiration. Carbon uptake was limited by SWC in the herbaceous savanna stand as evident from the pattern of water-use efficiency (WUE). At the B. decumbens stand, WUE was relatively insensitive to SWC. Although these results were specific to the studied site, the effect of land use changes and the physiological response of the studied stands might be applicable to other savannas.
Figure 1. Locations of Trachypogon savannas at the Orinoco Llanos (Venezuela). The scale = 1:4,00... more Figure 1. Locations of Trachypogon savannas at the Orinoco Llanos (Venezuela). The scale = 1:4,000,000. We analyzed the ecological factors affecting the oc-currence of termite mounds within and among physio-nomie types of Trachypogon savannas from the central and ...
... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effe... more ... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effects of chronic doses of ozone (03) and rates of nitrogen (N) fertilizer on N content of ladino clover (Trifoliurn r-epens L. cv. Tillman) and tall fescue (Festuca arunrlinacea Schreb. cv. ...
2007 IEEE International Geoscience and Remote Sensing Symposium, 2007
The effect of land use changes on the woody cover and patchiness of the Orinoco lowlands was anal... more The effect of land use changes on the woody cover and patchiness of the Orinoco lowlands was analyzed from 1951 to 1997 by using a stretched exponential model in terms of the patch size distribution. We selected five production systems on the basis of the following components: policy option, technology and environment. They are: (a) high-input pasture in deep soil, (b) low-input cropping in deep soil, (c) high-input cropping in deep soil, (d) low-input cropping in shallow soil and (e) extensive cattle grazing in shallow soil. For comparison, stands with similar soil depth and woody density were selected at the protected Biological Reserve in the Calabozo region. Results indicate that the distribution of the patches was described by the stretched exponential distribution model with c as the exponent distribution. The magnitude of c reflected the effect of land use changes over time. Thus, the parameter c for human impacted stands was higher than that for the fallow stands. The stretched exponential model implies that the human impact had a multiscalar effect on the Orinoco mosaic, in terms of the multiplicative processes. There is a generic mechanism exhibiting an anomalous distribution of the patches such as has been proposed for physical systems. Therefore, the number of generation of the multiplicative processes (i.e. inverse of c) for impacted stands was lower than that in the fallow stands. As the time from fallow establishment proceeded, there was a tendency to patch re-organization by biotic effects.
Water relations were analysed in a semi-deciduous forest grove occurring in the oxisols of the Or... more Water relations were analysed in a semi-deciduous forest grove occurring in the oxisols of the Orinoco savannas. This grove has a shallow unconsolidated ironstone cuirass, which is overlaid by a sandy loam layer (0.0-0.5 m) that contains more than 90% of the grove forest root phytomass. Evapotranspiration and through drainage were calculated by using data from the soil profile as related to physical characteristics of the site root zone, hydraulic conductivity, volumetric water content and potential hydraulic gradient. Mean annual evapotranspiration was 783 mm year(-1) and annual through drainage below the root zone was 14% (162 mm year(-1)) of the gross rainfall. This drainage recharged the 42% of the annual saturation deficit of the water table. Similar mean annual evapotranspiration (770 mm year(-1)) was also calculated by using the water balance components. The mean daily coupling omega factor (Ω) between the grove canopy and the surrounding atmosphere indicated that a high degree of coupling (Ω=0.14±0.16) occurs in the grove and evapotranspiration was mainly controlled by surface conductance. As the dry season proceeded, the soil saturation deficit (δθ) increased rapidly resulting in a threshold surface conductance (0.030-0.005 m s(-1)) for δθ ranging from 0.05 to 0.10. Hypotheses to explain the omnipresence of perennial species in the wide range of physical conditions in neotropical savannas are discussed.
The strength of carbon sink and stock was assessed in a protected savanna of the Orinoco Llanos b... more The strength of carbon sink and stock was assessed in a protected savanna of the Orinoco Llanos by the harvesting plant phytomass and using allometric relationships between the dry mass and the censuses of plant height. Thus, changes in the carbon stock and the proportion in the treergrass proportion were evaluated throughout age states. Results indicate that the carbon stock in the vegetation increased from 207 to 9215 g C m y2 whereas in the soil, it varied 6680 to 12 196 g C m y2 . y2 Ž . The carbon stock accumulation was mainly related to increases in the woody layer from 36 to 9215 g C m 255-fold and y2 Ž . in the soil from 1341 to 12 196 g C m nine-fold , respectively. The estimated pool of carbon sequestered in the Orinoco Llanos by the restored forest in 51 years was 5.69 Pg C. The expansion and conservation of this carbon pool might remove CO from the atmosphere to help compensate for CO liberation associated with other land uses or industrial practices. 2 2 q 1998 Elsevier Science B.V.
Communications in Soil Science and Plant Analysis, 2007
Field measurements showed the nitrogen (N) inputs and output of a fertilized pineapple crop [Anan... more Field measurements showed the nitrogen (N) inputs and output of a fertilized pineapple crop [Ananas comosus (L.) Merr. c.v. Red Spanish] growing in the Orinoco llanos during consecutive seasonal courses. The process rate changed with growth life‐cycle stages and seasonal conditions. The N accumulated by pineapple over the growing period was 226 kg N ha. It depended on the available N in the soil and the timing of split application of N fertilizer. Detailed monitoring of plant N‐accumulation rate showed a maximum rate (3.20 kg N ha d) at the harvesting time. The N‐harvested ratio and N‐use efficiency were 0.27 and 138 g g, respectively. The calculated N‐mineralization rate of the soil was 167 kg N ha over the life cycle. The fate of fertilizer N applied to pineapple was determined in microplots using urea labelled with 9.634% atom excess N. Fertilizer N recovery accounted for 48% of the applied N. The corresponding fractions of N recovered in the soil were 0.16 for the 0.0‐ to 0.3‐m depth and 0.01 for the 0.3‐ to 0.7‐m depth. The unrecovered fertilizer N in this study (34%) was largely due to volatilization (20% of the fertilizer) and denitrification (1.2%). Volatilization was shown to be greatly influenced by the seasonal conditions, namely the volumetric soil water content. In the pineapple field, monitored N input exceeded N output by 134 kg N ha, which is likely to lead to maintenance of soil N. Furthermore, utilization of N from crop residues input (164 kg N ha) has repercussions for the sustainable use of the Savanna Oligotrophic soils.
... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effe... more ... 11. Nitrogen content and nitrogen RUBEN A. MONTES? ... Can. J. Bot. 61: 2 159-2 168. The effects of chronic doses of ozone (03) and rates of nitrogen (N) fertilizer on N content of ladino clover (Trifoliurn r-epens L. cv. Tillman) and tall fescue (Festuca arunrlinacea Schreb. cv. ...
The HER2/neu oncogene product, p185 HER2/neu , is overexpressed on the surface of many human brea... more The HER2/neu oncogene product, p185 HER2/neu , is overexpressed on the surface of many human breast cancers. Strains of transgenic mice have been developed that express the rat neu oncogene in mammary epithelial cells and develop spontaneous mammary tumors that overexpress p185 neu . This model provides an ideal system for testing interventions to prevent tumor development. In this study, we immunized neu-transgenic mice with a vaccine consisting of the extracellular domain of p185 neu (NeuECD). Immunized mice developed Neu-speci®c humoral immune responses, as measured by circulating anti-Neu antibodies in their sera, and cellular immune responses, as measured by lymphocyte proliferation to NeuECD in vitro. In addition, the subsequent development of mammary tumors was signi®cantly lower in immunized mice than in controls and vaccine treatment was associated with a signi®cant increase in median survival.
... José San-José Æ Rubén Montes Æ Miguel Angel Mazorra Æ Ernesto Aguirre Ruiz Æ Nathaly Matute .... more ... José San-José Æ Rubén Montes Æ Miguel Angel Mazorra Æ Ernesto Aguirre Ruiz Æ Nathaly Matute ... histosols are important in the global carbon cycle, although covering little more than 1% of the world's land surface, they hold about 20% of global soil carbon (Brady and Weil ...
Se estudiaron las interrelaciones entre la vegetación y el relieve en dos topo-secuencias corresp... more Se estudiaron las interrelaciones entre la vegetación y el relieve en dos topo-secuencias correspondientes al Parque Nacional Aguaro-Guariquito, estado Guárico, Venezuela. La primera es un paisaje de altiplanicie de Mesa cubierta con una sabana bien drenada (sitio 1). En las aéreas disectadas de esta altiplanicie se presentan geofracturas con suelos permanentemente saturados donde se desarrollan los morichales (sitio 2). La otra toposecuencia corresponde a una planicie eólica con médanos, cuyos suelos provienen de materiales originados de la altiplanicie de Mesa y están cubiertos por sabanas húmedas (sitio 3), las cuales permanecen anegadas durante tres meses (junio -agosto) con una lámina de agua de 0.25 ± 0.10 m. Las zonas más deprimidas en esta topo-secuencia conducen a condiciones temporales de extremo anegamiento, donde se presenta el congrial (sitio 4), una comunidad dominada por Acosmium nitens y el saladillal (sitio 5), una vegetación caracterizada por la presencia de Caraipa llanorum. El congrial es anegado durante siete meses (junio -diciembre), con una lámina de agua de 1.02 ± 0.10 m. En contraste, el saladillal es inundado por seis meses (junio -noviembre) y la lámina de agua alcanza una altura de 0.80 ± 0.10 m. Las comunidades anegadas (sitios 2-5) se encuentran sobre suelos más ácidos (4.0 -4.6 unidades) que los característicos de la sabana bien drenada (sitio 1; 5.0 unidades). El pH estuvo asociado con la concentración de aluminio. El contenido de materia orgánica fue mayor en el sitio anegado (8.59 %) que en los estacionalmente inundables y en el bien drenado (0.7-1.0 %). El hábitat anegado es restrictivo de la biodiversidad. El congrial, el saladillal, la sabana húmeda y el morichal presentan 52, 52, 56 y 74 especies, respectivamente. En contraste, la sabana bien drenada presenta 114 especies. La similitud entre el congrial y el saladillal fue de 56 %. En relación con las otras comunidades, la similitud fue menor del 38 %. Los resultados indican que las formas de vidas Teroherbae y Teroculmi (e.g., especies
Page 1. Heterogeneity of the inland waterland palm ecotones (morichals) in the Orinoco lowlands,... more Page 1. Heterogeneity of the inland waterland palm ecotones (morichals) in the Orinoco lowlands, South America José San-José Rubén Montes Miguel Angel Mazorra Nathaly Matute Received: 8 May 2009 / Accepted: 13 ...
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