La ocurrencia del límite arbóreo es un fenómeno global que implica un cambio en la dominancia de ... more La ocurrencia del límite arbóreo es un fenómeno global que implica un cambio en la dominancia de formas de vida. La importancia de la temperatura como determinante de este límite ecológico ha sido reconocida, pero hasta ahora las respuestas de las plantas vinculadas a este fenómeno no se han identificado claramente. Aquí analizamos el efecto de las temperaturas extremas sobre la supervivencia del tejido foliar y la asimilación de CO 2 como determinantes del límite superior de distribución de Vaccinium meridionale, una especie leñosa característica del límite arbóreo en los Andes tropicales. El registro mínimo absoluto de temperatura ambiental fue de-2,8 °C, mientras que la temperatura de daño foliar fue de-10,5+0,7 °C. La asimilación de CO 2 promedio (6,0+0,5 µmol•m-2 s-1) fue invariable entre épocas, siendo comparable a la de otras especies leñosas de la alta montaña tropical. Tanto la temperatura óptima para la fotosíntesis (15,7+1,8°C) como el rango en el que ocurre el 80% de la asimilación de CO 2 (9,3+1,6-22,2+1,9°C) son similares al régimen de temperaturas ambientales diurnas. Nuestros resultados demuestran que las temperaturas extremas no limitan el desempeño fisiológico de V. meridionale a nivel de supervivencia del tejido foliar e intercambio de gases en su límite altitudinal actual.
Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding cond... more Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding conditions.
Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decu... more Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decumbens en monocultivo (MO) y asociada a L. leucocephala (AS), se realizaron evaluaciones de radiación fotosintéticamente activa (RFA), asimilación (A), conductancia estomática (Gs), transpiración (E), humedad relativa (HR), potencial hídrico de la hoja (Øh), diferencial de presión vapor (DPV) e índice de área foliar (IAF) en ambas condiciones (AS y MO), en una zona de bosque húmedo tropical; estas evaluaciones se hicieron a los 5, 10 y 22 días después del pastoreo en ambas condiciones. Los valores más positivos de Øh se encontraron en AS, al igual que los valores más bajos de RFA, con diferencias significativas (P<0,05) para ambos indicadores en las fechas evaluadas; mientras que no se observaron diferencias para las variables microclimáticas HR y DPV. Las variables de intercambio de gases (E, Gs y A) mostraron valores significativamente mayores (P<0,05) en MO en todas las fechas. Los valores más altos (P<0,05) para IAF se obtuvieron en MO a partir de los 10 y 22 días de evaluación. Debido a la limitación en la capacidad fotosintética que ejerce la disminución de la luz sobre la gramínea, se concluye que la RFA es la variable que más determina el crecimiento y desarrollo de B. decumbens en AS.
Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding cond... more Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding conditions.
Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decu... more Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decumbens en monocultivo (MO) y asociada a L. leucocephala (AS), se realizaron evaluaciones de radiación fotosintéticamente activa (RFA), asimilación (A), conductancia estomática (Gs), transpiración (E), humedad relativa (HR), potencial hídrico de la hoja (Øh), diferencial de presión vapor (DPV) e índice de área foliar (IAF) en ambas condiciones (AS y MO), en una zona de bosque húmedo tropical; estas evaluaciones se hicieron a los 5, 10 y 22 días después del pastoreo en ambas condiciones. Los valores más positivos de Øh se encontraron en AS, al igual que los valores más bajos de RFA, con diferencias significativas (P<0,05) para ambos indicadores en las fechas evaluadas; mientras que no se observaron diferencias para las variables microclimáticas HR y DPV. Las variables de intercambio de gases (E, Gs y A) mostraron valores significativamente mayores (P<0,05) en MO en todas las fechas. Los valores más altos (P<0,05) para IAF se obtuvieron en MO a partir de los 10 y 22 días de evaluación. Debido a la limitación en la capacidad fotosintética que ejerce la disminución de la luz sobre la gramínea, se concluye que la RFA es la variable que más determina el crecimiento y desarrollo de B. decumbens en AS.
... Supercooling has been found to be the principal avoidance mechanism in leaves of the caulesce... more ... Supercooling has been found to be the principal avoidance mechanism in leaves of the caulescent giant rosette genus Espeletia in the Andes. ... In the genus Espeletia, Goldstein et al. (1985) have shown that water content influences the supercooling capacity of the leaves. ...
Tropical high andean ecosystems, known as paramos, are unique because they are highly diverse, ha... more Tropical high andean ecosystems, known as paramos, are unique because they are highly diverse, have a high number of endemic species, and play an essential role in different ecosystem services, but are especially susceptible to climate change. Most of the giant rosettes, a dominant growth-form in the paramos, depend on unique features like stems protected by marcescent leaves, voluminous stem pith, and leaf pubescence. However, Ruilopezia atropurpurea lacks these characteristics and must respond differently to endure the paramo extreme conditions. Additionally, unlike other rosettes, this species is found under contrasting exposed and understory microenvironments so that intraspecific plasticity is also expected. We evaluated the responses of R. atropurpurea in terms of leaf water relations, gas exchange, and morphological characteristics in temporal (seasonal and daily variations) and spatial (microsite differences) scales in a Venezuelan paramo. R. atropurpurea displayed lower leaf water potentials (minimum leaf water potentials of-1.5 MPa and-1.8 MPa at the turgor loss point), higher leaf conductance (620 mmol m-2 s-1), transpiration (5 molm-2 s-1), and CO 2 assimilation (13 mmol m-2 s-1) rates compared to other paramo giant rosettes. A reduction in leaf area and specific leaf area occurred from understory to exposed sites. R. atropurpurea diverges from the typical responses of most paramo giant rosettes to the extreme environmental conditions. This species' morphological and physiological plasticity permits it inhabit under variable microclimatic conditions, but despite its confirmed plasticity, it is not able to reach higher elevations as other giant rosettes successfully have.
In a scenario of world population increase and climate change, an efficient use of water is key f... more In a scenario of world population increase and climate change, an efficient use of water is key for agricultural production. Onion is one of the most profitable crops and can adapt to particular conditions of water stress. The objective of this research was to determine growing degree-days and accumulated radiation under non-stress conditions and yield of an F1 2000 hybrid of onion (Allium cepa L.) under water deficit (WD) and biofertilization in a semi-arid environment. An established nutrient requirement of 247 kg N, 240 kg P2O5(105 kg P), 240 kg K2O (199 kg K), and two irrigation factors were applied: normal irrigation with a daily and WD with a 3 d interval irrigation frequencies. The effect of biofertilization was evaluated through the inoculation of a microbial consortium (MC) in combination with four NPK fertilizer treatments. The crop accumulated 1334 degree-days and 1188 MJ m−2·d−1at the time of harvest at 71 d after transplanting. The yield was 36 t·ha−1, similar under bot...
Revista de la Facultad de Agronomía, Universidad del Zulia, 2021
The practice of producing more vigorous seedlings represents a competitive advantage at the time ... more The practice of producing more vigorous seedlings represents a competitive advantage at the time of transplanting a crop, and the use of combined biofertilizers are a sustainable ecological alternative. The objective of this research was to select a microbial consortium for the production of F1 2000 hybrid onion seedbeds under shade-house conditions. Five rhizobacterial strains of the genera Rhizobium (ME01 strain), Bradyrhizobium (Leu2A and YE1 strains), Ochrobactrum (ES1 strain) and Pseudomonas (Alf strain), which have shown favorable effects on pepper and lettuce seedlings. These rhizobacteria were inoculated in a mixed manner (microbial consortium) in onion as follows: Alf+ES1, ME01+ES1, ES1+Leu2A, Alf+Leu2A, YE1+ES1, ME01+Alf, YE1+Alf, ME01+YE1, YE1+Leu2A, ME01+Leu2A, using a soil from San Juan de Lagunillas-Mérida, Venezuela under shade-house conditions for 60 days. The following variables were determined: number of leaves, pseudostem base diameter, aerial and root length, aer...
Background: Stomatal response functions of dominant plant species can provide insights into the b... more Background: Stomatal response functions of dominant plant species can provide insights into the behaviour of ecosystems under environmental stress, and provide tools for modelling their response to climate change. However, they remain little studied in tropical Alpine ecosystems. Aims: Our objective was to formulate and compare stomatal response functions for two dominant páramo species with different adaptive strategies to drought, the stress tolerant shrub Hypericum laricifolium, and the stress avoiding giant rosette Espeletia schultzii and thus enable making projections as to their future fitness in a changing climate. Methods: A reanalysis of data found in the literature and new ecophysiological and micrometeorological measurements were used to fit and test new stomatal response functions to environmental variables for these two species. Results: The response functions of vapour pressure differences between leaf and air showed an exponential decrease for both species, while for photosynthetically active radiation (PAR), peak-form response functions provided the best fit. The response function for leaf water potential was linear for the drought-tolerant shrub and decreased exponentially for the stress avoiding giant rosette. Several thresholds prior to stomatal closure were also included in the functions. Conclusions: Although stress-avoiding and stress-tolerant strategies are both successful in the Andean páramo, the response functions suggest that the tolerant shrub could be more resistant to more intense drought.
Efecto del nitrógeno en los parámetros fotosintéticos y de producción del cultivo de la gerbera (... more Efecto del nitrógeno en los parámetros fotosintéticos y de producción del cultivo de la gerbera (Gerbera jamesonii H. Bolus ex Hook. f.) Effect of nitrogen on photosynthetic parameters and yield of gerbera crop (Gerbera jamesonii Bolus ex Hook. f.
Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding cond... more Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding conditions.
In order to study the ecophysiological relations that affect the growth of B. decumbens in monocr... more In order to study the ecophysiological relations that affect the growth of B. decumbens in monocrop (MO) and associated with L. leucocephala (AS), evaluations of photosynthetic active radiation (PAR), assimilation (A) stomatic conductance (Gs), transpiration (E), ...
Acta Oecologica-international Journal of Ecology, Aug 1, 2021
Abstract The paramo, a high tropical Andean ecosystem, presents very distinct climatic, floristic... more Abstract The paramo, a high tropical Andean ecosystem, presents very distinct climatic, floristic and ecological features. Paramo plants have adapted to pronounced daily temperature fluctuations, freezing temperatures any night of the year, high incoming radiation and seasonal unfavorable water availability conditions. Long fallow agricultural systems are common in the paramo, permitting partial recuperation of the vegetation through a secondary succession. Different hypothesis related to plant traits (water relations and gas exchange characteristics or biomass allocation patterns) during succession have been proposed. Particular traits have been associated to the stages along successional gradients from early species (traits related to high resource acquisition abilities) to late species (traits linked to internal conservation of resources). Our purpose was to study plant functional responses of different herbaceous species in an old-field succession in the high tropical Andes. Plant traits (specific leaf area (SLA), maximum CO2 assimilation rates (Amax), leaf nitrogen content (Nleaf), leaf water relations and biomass allocation) were studied in grasses and forbs along different successional stages. Clear trends in SLA, Amax on a mass basis, Nleaf and aboveground/belowground biomass allocation were found along the successional gradient for grasses, while patterns were not as well-defined for forbs in the latter two traits. No patterns in leaf water relations characteristics were observed for either plant-growth forms. Strategies associated to plant traits significantly influence plant species dominance and community assembly during secondary succession in tropical alpine open environments like the paramos. Plant traits linked to rapid growth (SLA, Amax and Nleaf) dominate during early succession. In contrast to previous studies, drought resistance traits were not found to dominate in late succession stages for either grasses or forbs.
Temperature determines plant formations and species distribution along altitudinal gradients. Pla... more Temperature determines plant formations and species distribution along altitudinal gradients. Plants in the tropical high Andes, through different physiological and morphological characteristics, respond to freezing night temperatures and high daytime energy inputs which occur anytime of the year. The main objective of this study was to characterize day and night temperature related responses of two Lupinus species with different altitudinal ranges (L. meridanus, 1,800-3,600 and L. eromonomos, 3,700-4,300 m of altitude). Are there differences in night low temperature resistance mechanisms between the species along the gradient? How do these species respond, in terms of optimum temperature for photosynthesis, to increasing altitude? Lupinus meridanus shows frost avoidance, in contrast to L. eromonomos, which tolerates freezing at higher altitudes. Optimum temperature for photosynthesis decreases along the gradient for both species. Maximum CO 2 assimilation rates were higher in L. meridanus, while L. eromonomos showed decreasing CO 2 assimilation rates at the higher altitude. In most cases, measured daily leaf temperature is always within the 80 % of optimum for photosynthesis. L. meridanus' upper distribution limit seems to be restricted by cold resistance mechanisms, while L. eromonomos' to a combination of both cold resistance and to CO 2 assimilation responses at higher altitudes.
Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-li... more Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-line formation at a global scale. We studied gas exchange and water relations of Polylepis tarapacana in the field, considering the possible effects of water stress limitations imposed on net photosynthetic rate (P N). Daily courses of microclimatic variables, gas exchange, and leaf water potential were measured in both dry-cold and wet-warm seasons at an altitude of 4 300 m. Marked differences in environmental conditions between seasons resulted in differences for the dry-cold and wet-warm seasons in mean leaf water potentials (-1.67 and-1.02 MPa, respectively) and mean leaf conductances (33.5 and 58.9 mmol m-2 s-1 , respectively), while differences in mean P N (2.5 and 2.8 µmol m-2 s-1 , respectively) were not as evident. This may be related to limitations imposed by water deficit and lower photon flux densities during dry and wet seasons, respectively. Hence P. tarapacana has coupled its gas exchange characteristics to the extreme daily and seasonal variations in temperature and water availability of high elevations.
La ocurrencia del límite arbóreo es un fenómeno global que implica un cambio en la dominancia de ... more La ocurrencia del límite arbóreo es un fenómeno global que implica un cambio en la dominancia de formas de vida. La importancia de la temperatura como determinante de este límite ecológico ha sido reconocida, pero hasta ahora las respuestas de las plantas vinculadas a este fenómeno no se han identificado claramente. Aquí analizamos el efecto de las temperaturas extremas sobre la supervivencia del tejido foliar y la asimilación de CO 2 como determinantes del límite superior de distribución de Vaccinium meridionale, una especie leñosa característica del límite arbóreo en los Andes tropicales. El registro mínimo absoluto de temperatura ambiental fue de-2,8 °C, mientras que la temperatura de daño foliar fue de-10,5+0,7 °C. La asimilación de CO 2 promedio (6,0+0,5 µmol•m-2 s-1) fue invariable entre épocas, siendo comparable a la de otras especies leñosas de la alta montaña tropical. Tanto la temperatura óptima para la fotosíntesis (15,7+1,8°C) como el rango en el que ocurre el 80% de la asimilación de CO 2 (9,3+1,6-22,2+1,9°C) son similares al régimen de temperaturas ambientales diurnas. Nuestros resultados demuestran que las temperaturas extremas no limitan el desempeño fisiológico de V. meridionale a nivel de supervivencia del tejido foliar e intercambio de gases en su límite altitudinal actual.
Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding cond... more Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding conditions.
Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decu... more Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decumbens en monocultivo (MO) y asociada a L. leucocephala (AS), se realizaron evaluaciones de radiación fotosintéticamente activa (RFA), asimilación (A), conductancia estomática (Gs), transpiración (E), humedad relativa (HR), potencial hídrico de la hoja (Øh), diferencial de presión vapor (DPV) e índice de área foliar (IAF) en ambas condiciones (AS y MO), en una zona de bosque húmedo tropical; estas evaluaciones se hicieron a los 5, 10 y 22 días después del pastoreo en ambas condiciones. Los valores más positivos de Øh se encontraron en AS, al igual que los valores más bajos de RFA, con diferencias significativas (P<0,05) para ambos indicadores en las fechas evaluadas; mientras que no se observaron diferencias para las variables microclimáticas HR y DPV. Las variables de intercambio de gases (E, Gs y A) mostraron valores significativamente mayores (P<0,05) en MO en todas las fechas. Los valores más altos (P<0,05) para IAF se obtuvieron en MO a partir de los 10 y 22 días de evaluación. Debido a la limitación en la capacidad fotosintética que ejerce la disminución de la luz sobre la gramínea, se concluye que la RFA es la variable que más determina el crecimiento y desarrollo de B. decumbens en AS.
Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding cond... more Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding conditions.
Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decu... more Con el objeto de estudiar las relaciones ecofisiológicas que determinan el crecimiento de B. decumbens en monocultivo (MO) y asociada a L. leucocephala (AS), se realizaron evaluaciones de radiación fotosintéticamente activa (RFA), asimilación (A), conductancia estomática (Gs), transpiración (E), humedad relativa (HR), potencial hídrico de la hoja (Øh), diferencial de presión vapor (DPV) e índice de área foliar (IAF) en ambas condiciones (AS y MO), en una zona de bosque húmedo tropical; estas evaluaciones se hicieron a los 5, 10 y 22 días después del pastoreo en ambas condiciones. Los valores más positivos de Øh se encontraron en AS, al igual que los valores más bajos de RFA, con diferencias significativas (P<0,05) para ambos indicadores en las fechas evaluadas; mientras que no se observaron diferencias para las variables microclimáticas HR y DPV. Las variables de intercambio de gases (E, Gs y A) mostraron valores significativamente mayores (P<0,05) en MO en todas las fechas. Los valores más altos (P<0,05) para IAF se obtuvieron en MO a partir de los 10 y 22 días de evaluación. Debido a la limitación en la capacidad fotosintética que ejerce la disminución de la luz sobre la gramínea, se concluye que la RFA es la variable que más determina el crecimiento y desarrollo de B. decumbens en AS.
... Supercooling has been found to be the principal avoidance mechanism in leaves of the caulesce... more ... Supercooling has been found to be the principal avoidance mechanism in leaves of the caulescent giant rosette genus Espeletia in the Andes. ... In the genus Espeletia, Goldstein et al. (1985) have shown that water content influences the supercooling capacity of the leaves. ...
Tropical high andean ecosystems, known as paramos, are unique because they are highly diverse, ha... more Tropical high andean ecosystems, known as paramos, are unique because they are highly diverse, have a high number of endemic species, and play an essential role in different ecosystem services, but are especially susceptible to climate change. Most of the giant rosettes, a dominant growth-form in the paramos, depend on unique features like stems protected by marcescent leaves, voluminous stem pith, and leaf pubescence. However, Ruilopezia atropurpurea lacks these characteristics and must respond differently to endure the paramo extreme conditions. Additionally, unlike other rosettes, this species is found under contrasting exposed and understory microenvironments so that intraspecific plasticity is also expected. We evaluated the responses of R. atropurpurea in terms of leaf water relations, gas exchange, and morphological characteristics in temporal (seasonal and daily variations) and spatial (microsite differences) scales in a Venezuelan paramo. R. atropurpurea displayed lower leaf water potentials (minimum leaf water potentials of-1.5 MPa and-1.8 MPa at the turgor loss point), higher leaf conductance (620 mmol m-2 s-1), transpiration (5 molm-2 s-1), and CO 2 assimilation (13 mmol m-2 s-1) rates compared to other paramo giant rosettes. A reduction in leaf area and specific leaf area occurred from understory to exposed sites. R. atropurpurea diverges from the typical responses of most paramo giant rosettes to the extreme environmental conditions. This species' morphological and physiological plasticity permits it inhabit under variable microclimatic conditions, but despite its confirmed plasticity, it is not able to reach higher elevations as other giant rosettes successfully have.
In a scenario of world population increase and climate change, an efficient use of water is key f... more In a scenario of world population increase and climate change, an efficient use of water is key for agricultural production. Onion is one of the most profitable crops and can adapt to particular conditions of water stress. The objective of this research was to determine growing degree-days and accumulated radiation under non-stress conditions and yield of an F1 2000 hybrid of onion (Allium cepa L.) under water deficit (WD) and biofertilization in a semi-arid environment. An established nutrient requirement of 247 kg N, 240 kg P2O5(105 kg P), 240 kg K2O (199 kg K), and two irrigation factors were applied: normal irrigation with a daily and WD with a 3 d interval irrigation frequencies. The effect of biofertilization was evaluated through the inoculation of a microbial consortium (MC) in combination with four NPK fertilizer treatments. The crop accumulated 1334 degree-days and 1188 MJ m−2·d−1at the time of harvest at 71 d after transplanting. The yield was 36 t·ha−1, similar under bot...
Revista de la Facultad de Agronomía, Universidad del Zulia, 2021
The practice of producing more vigorous seedlings represents a competitive advantage at the time ... more The practice of producing more vigorous seedlings represents a competitive advantage at the time of transplanting a crop, and the use of combined biofertilizers are a sustainable ecological alternative. The objective of this research was to select a microbial consortium for the production of F1 2000 hybrid onion seedbeds under shade-house conditions. Five rhizobacterial strains of the genera Rhizobium (ME01 strain), Bradyrhizobium (Leu2A and YE1 strains), Ochrobactrum (ES1 strain) and Pseudomonas (Alf strain), which have shown favorable effects on pepper and lettuce seedlings. These rhizobacteria were inoculated in a mixed manner (microbial consortium) in onion as follows: Alf+ES1, ME01+ES1, ES1+Leu2A, Alf+Leu2A, YE1+ES1, ME01+Alf, YE1+Alf, ME01+YE1, YE1+Leu2A, ME01+Leu2A, using a soil from San Juan de Lagunillas-Mérida, Venezuela under shade-house conditions for 60 days. The following variables were determined: number of leaves, pseudostem base diameter, aerial and root length, aer...
Background: Stomatal response functions of dominant plant species can provide insights into the b... more Background: Stomatal response functions of dominant plant species can provide insights into the behaviour of ecosystems under environmental stress, and provide tools for modelling their response to climate change. However, they remain little studied in tropical Alpine ecosystems. Aims: Our objective was to formulate and compare stomatal response functions for two dominant páramo species with different adaptive strategies to drought, the stress tolerant shrub Hypericum laricifolium, and the stress avoiding giant rosette Espeletia schultzii and thus enable making projections as to their future fitness in a changing climate. Methods: A reanalysis of data found in the literature and new ecophysiological and micrometeorological measurements were used to fit and test new stomatal response functions to environmental variables for these two species. Results: The response functions of vapour pressure differences between leaf and air showed an exponential decrease for both species, while for photosynthetically active radiation (PAR), peak-form response functions provided the best fit. The response function for leaf water potential was linear for the drought-tolerant shrub and decreased exponentially for the stress avoiding giant rosette. Several thresholds prior to stomatal closure were also included in the functions. Conclusions: Although stress-avoiding and stress-tolerant strategies are both successful in the Andean páramo, the response functions suggest that the tolerant shrub could be more resistant to more intense drought.
Efecto del nitrógeno en los parámetros fotosintéticos y de producción del cultivo de la gerbera (... more Efecto del nitrógeno en los parámetros fotosintéticos y de producción del cultivo de la gerbera (Gerbera jamesonii H. Bolus ex Hook. f.) Effect of nitrogen on photosynthetic parameters and yield of gerbera crop (Gerbera jamesonii Bolus ex Hook. f.
Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding cond... more Growth and development of apamate (Tabebuia rosea (Bertol.) A. DC.) juveniles under flooding conditions.
In order to study the ecophysiological relations that affect the growth of B. decumbens in monocr... more In order to study the ecophysiological relations that affect the growth of B. decumbens in monocrop (MO) and associated with L. leucocephala (AS), evaluations of photosynthetic active radiation (PAR), assimilation (A) stomatic conductance (Gs), transpiration (E), ...
Acta Oecologica-international Journal of Ecology, Aug 1, 2021
Abstract The paramo, a high tropical Andean ecosystem, presents very distinct climatic, floristic... more Abstract The paramo, a high tropical Andean ecosystem, presents very distinct climatic, floristic and ecological features. Paramo plants have adapted to pronounced daily temperature fluctuations, freezing temperatures any night of the year, high incoming radiation and seasonal unfavorable water availability conditions. Long fallow agricultural systems are common in the paramo, permitting partial recuperation of the vegetation through a secondary succession. Different hypothesis related to plant traits (water relations and gas exchange characteristics or biomass allocation patterns) during succession have been proposed. Particular traits have been associated to the stages along successional gradients from early species (traits related to high resource acquisition abilities) to late species (traits linked to internal conservation of resources). Our purpose was to study plant functional responses of different herbaceous species in an old-field succession in the high tropical Andes. Plant traits (specific leaf area (SLA), maximum CO2 assimilation rates (Amax), leaf nitrogen content (Nleaf), leaf water relations and biomass allocation) were studied in grasses and forbs along different successional stages. Clear trends in SLA, Amax on a mass basis, Nleaf and aboveground/belowground biomass allocation were found along the successional gradient for grasses, while patterns were not as well-defined for forbs in the latter two traits. No patterns in leaf water relations characteristics were observed for either plant-growth forms. Strategies associated to plant traits significantly influence plant species dominance and community assembly during secondary succession in tropical alpine open environments like the paramos. Plant traits linked to rapid growth (SLA, Amax and Nleaf) dominate during early succession. In contrast to previous studies, drought resistance traits were not found to dominate in late succession stages for either grasses or forbs.
Temperature determines plant formations and species distribution along altitudinal gradients. Pla... more Temperature determines plant formations and species distribution along altitudinal gradients. Plants in the tropical high Andes, through different physiological and morphological characteristics, respond to freezing night temperatures and high daytime energy inputs which occur anytime of the year. The main objective of this study was to characterize day and night temperature related responses of two Lupinus species with different altitudinal ranges (L. meridanus, 1,800-3,600 and L. eromonomos, 3,700-4,300 m of altitude). Are there differences in night low temperature resistance mechanisms between the species along the gradient? How do these species respond, in terms of optimum temperature for photosynthesis, to increasing altitude? Lupinus meridanus shows frost avoidance, in contrast to L. eromonomos, which tolerates freezing at higher altitudes. Optimum temperature for photosynthesis decreases along the gradient for both species. Maximum CO 2 assimilation rates were higher in L. meridanus, while L. eromonomos showed decreasing CO 2 assimilation rates at the higher altitude. In most cases, measured daily leaf temperature is always within the 80 % of optimum for photosynthesis. L. meridanus' upper distribution limit seems to be restricted by cold resistance mechanisms, while L. eromonomos' to a combination of both cold resistance and to CO 2 assimilation responses at higher altitudes.
Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-li... more Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-line formation at a global scale. We studied gas exchange and water relations of Polylepis tarapacana in the field, considering the possible effects of water stress limitations imposed on net photosynthetic rate (P N). Daily courses of microclimatic variables, gas exchange, and leaf water potential were measured in both dry-cold and wet-warm seasons at an altitude of 4 300 m. Marked differences in environmental conditions between seasons resulted in differences for the dry-cold and wet-warm seasons in mean leaf water potentials (-1.67 and-1.02 MPa, respectively) and mean leaf conductances (33.5 and 58.9 mmol m-2 s-1 , respectively), while differences in mean P N (2.5 and 2.8 µmol m-2 s-1 , respectively) were not as evident. This may be related to limitations imposed by water deficit and lower photon flux densities during dry and wet seasons, respectively. Hence P. tarapacana has coupled its gas exchange characteristics to the extreme daily and seasonal variations in temperature and water availability of high elevations.
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