A simple theoretical framework to explain leaf acclimation to light availability: implications fo... more A simple theoretical framework to explain leaf acclimation to light availability: implications for the evolution of plant form and function. Juan M. Posada, A. Camilo Rey and Ramón Fayad, Faculty of Natural Sciences and Mathematics ...
Background/Question/Methods . Recent climate predictions for the end of this century suggest that... more Background/Question/Methods . Recent climate predictions for the end of this century suggest that soil moisture will decrease and the number of drought days will increase over large parts of the temperate forests in North America. Tolerance of moisture stress is likely to become increasingly important in mediating competitive interactions among tree species, mostly because seedlings are particularly vulnerable to water stress. The goal of our study was to determine how the physiology and growth of seedlings of four temperate tree species were altered by a gradual decrease in soil water content. Ten seedlings of Betula alleghaniensis, Platanus occidentalis, Quercus rubra and Ulmus americana were randomly distributed in a five-block design within a greenhouse. In each block, one seedling per species served as a well-watered control while the other was subjected to drought. As soil gravimetric water content and soil water potential gradually declined, we measured leaf photosynthetic ca...
ABSTRACT The allocation of non-structural carbohydrates (NSCs) to reserves constitutes an importa... more ABSTRACT The allocation of non-structural carbohydrates (NSCs) to reserves constitutes an important physiological mechanism associated with tree growth and survival. However, procedures for measuring NSC in plant tissue are expensive and time-consuming. Near-infrared spectroscopy (NIRS) is a high-throughput technology that has the potential to infer the concentration of organic constituents for a large number of samples in a rapid and inexpensive way based on empirical calibrations with chemical analysis.The main objectives of this study were (i) to develop a general NSC concentration calibration that integrates various forms of variation such as tree species and tissue types and (ii) to identify characteristic spectral regions associated with NSC molecules. In total, 180 samples from different tree organs (root, stem, branch, leaf) belonging to 73 tree species from tropical and temperate biomes were analysed. Statistical relationships between NSC concentration and NIRS spectra were assessed using partial least squares regression (PLSR) and a variable selection procedure (competitive adaptive reweighted sampling, CARS), in order to identify key wavelengths.Parsimonious and accurate calibration models were obtained for total NSC (r2 of 0·91, RMSE of 1·34% in external validation), followed by starch (r2 = 0·85 and RMSE = 1·20%) and sugars (r2 = 0·82 and RMSE = 1·10%). Key wavelengths coincided among these models and were mainly located in the 1740–1800, 2100–2300 and 2410–2490 nm spectral regions.This study demonstrates the ability of general calibration model to infer NSC concentrations across species and tissue types in a rapid and cost-effective way. The estimation of NSC in plants using NIRS therefore serves as a tool for functional biodiversity research, in particular for the study of the growth–survival trade-off and its implications in response to changing environmental conditions, including growth limitation and mortality.
Theory for optimal allocation of foliar nitrogen (ONA) predicts that both nitrogen concentration ... more Theory for optimal allocation of foliar nitrogen (ONA) predicts that both nitrogen concentration and photosynthetic capacity will scale linearly with gradients of insolation within plant canopies. ONA is expected to allow plants to efficiently use both light and nitrogen. However, empirical data generally do not exhibit perfect ONA, and light-use optimization per se is little explored. The aim was to examine to what degree partitioning of nitrogen or light is optimized in the crowns of three tropical canopy tree species. Instantaneous photosynthetic photon flux density (PPFD) incident on the adaxial surface of individual leaves was measured along vertical PPFD gradients in tree canopies at a frequency of 0.5 Hz over 9-17 d, and summed to obtain the average daily integral of PPFD for each leaf to characterize its insolation regime. Also measured were leaf N per area (N(area)), leaf mass per area (LMA), the cosine of leaf inclination and the parameters of the photosynthetic light resp...
Plants are expected to maximize their net photosynthetic gains and efficiently use available reso... more Plants are expected to maximize their net photosynthetic gains and efficiently use available resources, but the fundamental principles governing trade-offs in suites of traits related to resource-use optimization remain uncertain. This study investigated whether Acer saccharum (sugar maple) saplings could maximize their net photosynthetic gains through a combination of crown structure and foliar characteristics that let all leaves maximize their photosynthetic light-use efficiency (ε). A functional-structural model, LIGNUM, was used to simulate individuals of different leaf area index (LAI(ind)) together with a genetic algorithm to find distributions of leaf angle (L(A)) and leaf photosynthetic capacity (A(max)) that maximized net carbon gain at the whole-plant level. Saplings grown in either the open or in a forest gap were simulated with A(max) either unconstrained or constrained to an upper value consistent with reported values for A(max) in A. saccharum. It was found that total ...
A simple theoretical framework to explain leaf acclimation to light availability: implications fo... more A simple theoretical framework to explain leaf acclimation to light availability: implications for the evolution of plant form and function. Juan M. Posada, A. Camilo Rey and Ramón Fayad, Faculty of Natural Sciences and Mathematics ...
Kalanchoë pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism p... more Kalanchoë pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism plant, was grown in open-top chambers at ambient and elevated (two times ambient) CO2 concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO2 treatments. However, under elevated CO2, dry matter accumulation increased by 42–51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six-to eightfold at both CO2 concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO2. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day-night fluctuations.
After defoliation by herbivores, some plants exhibit enhanced rates of photosynthesis and growth ... more After defoliation by herbivores, some plants exhibit enhanced rates of photosynthesis and growth that enable them to compensate for lost tissue, thus maintaining their fitness relative to competing, undefoliated plants. Our aim was to determine whether compensatory photosynthesis and growth would be altered by increasing concentrations of atmospheric CO2. Defoliation of developing leaflets on seedlings of a tropical tree, Copaifera aromatica, caused increases in photosynthesis under ambient CO2, but not under elevated CO2. An enhancement in the development of buds in the leaf axils followed defoliation at ambient levels of CO2. In contrast, under elevated CO2, enhanced development of buds occurred in undefoliated plants with no further enhancement in bud development due to exposure to elevated CO2. Growth of leaf area after defoliation was increased, particularly under elevated CO2. Despite this increase, defoliated plants grown under elevated CO2 were further from compensating for tissue lost during defoliation after 51/2 weeks than those grown under ambient CO2 concentrations.Luego de ser defoliadas por herbívoros, algunas plantas muestran aumentos en las tasas de fotosíntesis y crecimiento que les permiten compensar por el tejido perdido y así mantener su aptitud (fitness), relativo a plantas no defoliadas que están compitiendo con ellas. Nuestro propósito era determinar si la fotosíntesis compensatoria y el crecimiento eran alterados, o no, por incrementos en la concentración de CO2 atmosférico. La defoliación de foliolos en desarrollo, de plántulas del árbol tropical Copaifera aromatica, causó incrementos en fotosíntesis bajo CO2 ambiente, pero no bajo CO2 elevado. Una mejora en el desarrollo de yemas localizadas en el eje de las hojas ocurrió, luego de que las plantas en niveles de CO2 ambiente fueran defoliadas. En cambio, una mejora en el desarrollo de yemas ocurrió en plantas control no defoliadas creciendo bajo CO2 elevado, sin que se observaran mejoras adicionales en la produción de yemas en plantas defoliadas. El crecimiento del área foliar después de la defoliación fue incrementado, especialmente bajo CO2 elevado. Pero, a pesar de este aumento, después de 5′/2 semanas las plantas defoliadas que crecieron bajo CO2 elevado estaban mas lejos de haber compensado por el tejido perdido durante la defoliación, que aquellas que crecieron bajo concentraciones de CO2 ambiente.
A simple theoretical framework to explain leaf acclimation to light availability: implications fo... more A simple theoretical framework to explain leaf acclimation to light availability: implications for the evolution of plant form and function. Juan M. Posada, A. Camilo Rey and Ramón Fayad, Faculty of Natural Sciences and Mathematics ...
Background/Question/Methods . Recent climate predictions for the end of this century suggest that... more Background/Question/Methods . Recent climate predictions for the end of this century suggest that soil moisture will decrease and the number of drought days will increase over large parts of the temperate forests in North America. Tolerance of moisture stress is likely to become increasingly important in mediating competitive interactions among tree species, mostly because seedlings are particularly vulnerable to water stress. The goal of our study was to determine how the physiology and growth of seedlings of four temperate tree species were altered by a gradual decrease in soil water content. Ten seedlings of Betula alleghaniensis, Platanus occidentalis, Quercus rubra and Ulmus americana were randomly distributed in a five-block design within a greenhouse. In each block, one seedling per species served as a well-watered control while the other was subjected to drought. As soil gravimetric water content and soil water potential gradually declined, we measured leaf photosynthetic ca...
ABSTRACT The allocation of non-structural carbohydrates (NSCs) to reserves constitutes an importa... more ABSTRACT The allocation of non-structural carbohydrates (NSCs) to reserves constitutes an important physiological mechanism associated with tree growth and survival. However, procedures for measuring NSC in plant tissue are expensive and time-consuming. Near-infrared spectroscopy (NIRS) is a high-throughput technology that has the potential to infer the concentration of organic constituents for a large number of samples in a rapid and inexpensive way based on empirical calibrations with chemical analysis.The main objectives of this study were (i) to develop a general NSC concentration calibration that integrates various forms of variation such as tree species and tissue types and (ii) to identify characteristic spectral regions associated with NSC molecules. In total, 180 samples from different tree organs (root, stem, branch, leaf) belonging to 73 tree species from tropical and temperate biomes were analysed. Statistical relationships between NSC concentration and NIRS spectra were assessed using partial least squares regression (PLSR) and a variable selection procedure (competitive adaptive reweighted sampling, CARS), in order to identify key wavelengths.Parsimonious and accurate calibration models were obtained for total NSC (r2 of 0·91, RMSE of 1·34% in external validation), followed by starch (r2 = 0·85 and RMSE = 1·20%) and sugars (r2 = 0·82 and RMSE = 1·10%). Key wavelengths coincided among these models and were mainly located in the 1740–1800, 2100–2300 and 2410–2490 nm spectral regions.This study demonstrates the ability of general calibration model to infer NSC concentrations across species and tissue types in a rapid and cost-effective way. The estimation of NSC in plants using NIRS therefore serves as a tool for functional biodiversity research, in particular for the study of the growth–survival trade-off and its implications in response to changing environmental conditions, including growth limitation and mortality.
Theory for optimal allocation of foliar nitrogen (ONA) predicts that both nitrogen concentration ... more Theory for optimal allocation of foliar nitrogen (ONA) predicts that both nitrogen concentration and photosynthetic capacity will scale linearly with gradients of insolation within plant canopies. ONA is expected to allow plants to efficiently use both light and nitrogen. However, empirical data generally do not exhibit perfect ONA, and light-use optimization per se is little explored. The aim was to examine to what degree partitioning of nitrogen or light is optimized in the crowns of three tropical canopy tree species. Instantaneous photosynthetic photon flux density (PPFD) incident on the adaxial surface of individual leaves was measured along vertical PPFD gradients in tree canopies at a frequency of 0.5 Hz over 9-17 d, and summed to obtain the average daily integral of PPFD for each leaf to characterize its insolation regime. Also measured were leaf N per area (N(area)), leaf mass per area (LMA), the cosine of leaf inclination and the parameters of the photosynthetic light resp...
Plants are expected to maximize their net photosynthetic gains and efficiently use available reso... more Plants are expected to maximize their net photosynthetic gains and efficiently use available resources, but the fundamental principles governing trade-offs in suites of traits related to resource-use optimization remain uncertain. This study investigated whether Acer saccharum (sugar maple) saplings could maximize their net photosynthetic gains through a combination of crown structure and foliar characteristics that let all leaves maximize their photosynthetic light-use efficiency (ε). A functional-structural model, LIGNUM, was used to simulate individuals of different leaf area index (LAI(ind)) together with a genetic algorithm to find distributions of leaf angle (L(A)) and leaf photosynthetic capacity (A(max)) that maximized net carbon gain at the whole-plant level. Saplings grown in either the open or in a forest gap were simulated with A(max) either unconstrained or constrained to an upper value consistent with reported values for A(max) in A. saccharum. It was found that total ...
A simple theoretical framework to explain leaf acclimation to light availability: implications fo... more A simple theoretical framework to explain leaf acclimation to light availability: implications for the evolution of plant form and function. Juan M. Posada, A. Camilo Rey and Ramón Fayad, Faculty of Natural Sciences and Mathematics ...
Kalanchoë pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism p... more Kalanchoë pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism plant, was grown in open-top chambers at ambient and elevated (two times ambient) CO2 concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO2 treatments. However, under elevated CO2, dry matter accumulation increased by 42–51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six-to eightfold at both CO2 concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO2. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day-night fluctuations.
After defoliation by herbivores, some plants exhibit enhanced rates of photosynthesis and growth ... more After defoliation by herbivores, some plants exhibit enhanced rates of photosynthesis and growth that enable them to compensate for lost tissue, thus maintaining their fitness relative to competing, undefoliated plants. Our aim was to determine whether compensatory photosynthesis and growth would be altered by increasing concentrations of atmospheric CO2. Defoliation of developing leaflets on seedlings of a tropical tree, Copaifera aromatica, caused increases in photosynthesis under ambient CO2, but not under elevated CO2. An enhancement in the development of buds in the leaf axils followed defoliation at ambient levels of CO2. In contrast, under elevated CO2, enhanced development of buds occurred in undefoliated plants with no further enhancement in bud development due to exposure to elevated CO2. Growth of leaf area after defoliation was increased, particularly under elevated CO2. Despite this increase, defoliated plants grown under elevated CO2 were further from compensating for tissue lost during defoliation after 51/2 weeks than those grown under ambient CO2 concentrations.Luego de ser defoliadas por herbívoros, algunas plantas muestran aumentos en las tasas de fotosíntesis y crecimiento que les permiten compensar por el tejido perdido y así mantener su aptitud (fitness), relativo a plantas no defoliadas que están compitiendo con ellas. Nuestro propósito era determinar si la fotosíntesis compensatoria y el crecimiento eran alterados, o no, por incrementos en la concentración de CO2 atmosférico. La defoliación de foliolos en desarrollo, de plántulas del árbol tropical Copaifera aromatica, causó incrementos en fotosíntesis bajo CO2 ambiente, pero no bajo CO2 elevado. Una mejora en el desarrollo de yemas localizadas en el eje de las hojas ocurrió, luego de que las plantas en niveles de CO2 ambiente fueran defoliadas. En cambio, una mejora en el desarrollo de yemas ocurrió en plantas control no defoliadas creciendo bajo CO2 elevado, sin que se observaran mejoras adicionales en la produción de yemas en plantas defoliadas. El crecimiento del área foliar después de la defoliación fue incrementado, especialmente bajo CO2 elevado. Pero, a pesar de este aumento, después de 5′/2 semanas las plantas defoliadas que crecieron bajo CO2 elevado estaban mas lejos de haber compensado por el tejido perdido durante la defoliación, que aquellas que crecieron bajo concentraciones de CO2 ambiente.
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