Home About us Contact
|
Home About us Contact | ||
|
|
||
Compensation Point (compensation + point)
Kinds of Compensation Point Selected AbstractsPhotoheterotrophy and light-dependent uptake of organic and organic nitrogenous compounds by Planktothrix rubescens under low irradianceFRESHWATER BIOLOGY, Issue 10 2003Tatiana Zotina Summary 1. Planktothrix rubescens is the dominant photoautotrophic organism in Lake Zürich, a prealpine, deep, mesotrophic freshwater lake with an oxic hypolimnion. Over long periods of the year, P. rubescens accumulates at the metalimnion and growth occurs in situ at irradiance near the photosynthesis compensation point. Experiments were conducted to evaluate the contribution of photoheterotrophy, heterotrophy and light-dependent uptake of nitrogenous organic compounds to the carbon and nitrogen budget of this cyanobacterium under conditions of restricted availability of light quanta. 2. We used both purified natural populations of P. rubescens from the depth of 9 m and an axenic culture grown under low irradiance at 11 ,mol m,2 s,1 on a light : dark cycle (10 : 14 h) to determine the uptake rates of various amino acids, urea, glucose, fructose, acetate and inorganic carbon. The components were added to artificial lake water in low amounts that simulated the naturally occurring potential concentrations. 3. The uptake rates of acetate and amino acids (glycine, serine, glutamate and aspartate) were strongly enhanced at low irradiance as compared with the dark. However, no difference was observed in the uptake of arginine, which was taken up at high rates under both treatments. The uptake rates of glucose, fructose and urea were very low under all conditions. Similar results were obtained for both axenic P. rubescens and for purified natural populations of P. rubescens that were separated from bacterioplankton and other phytoplankton. 4. Metalimnetic P. rubescens that was stratified at low irradiance for weeks exhibited much higher uptake rates than filaments that were entrained in the deepening surface mixed layer and experienced higher irradiance. The added organic compounds contributed up to 62% to the total carbon uptake of metalimnetic P. rubescens. On the basis of a molar C : N ratio of 4.9, the nitrogen uptake as organic compounds satisfied up to 84% of the nitrogen demand. 5. The experiments indicate that photoheterotrophy and light-dependent uptake of nitrogenous organic compounds may contribute significantly to the carbon and nitrogen budget of filaments at low irradiance typical for growth of P. rubescens in the metalimnion and at the bottom of the surface mixed layer. [source] Trade-offs in low-light CO2 exchange: a component of variation in shade tolerance among cold temperate tree seedlingsFUNCTIONAL ECOLOGY, Issue 2 2000M. B. Walters Abstract 1.,Does enhanced whole-plant CO2 exchange in moderately low to high light occur at the cost of greater CO2 loss rates at very-low light levels? We examined this question for first-year seedlings of intolerant Populus tremuloides and Betula papyrifera, intermediate Betula alleghaniensis, and tolerant Ostrya virginiana and Acer saccharum grown in moderately low (7·3% of open-sky) and low (2·8%) light. We predicted that, compared with shade-tolerant species, intolerant species would have characteristics leading to greater whole-plant CO2 exchange rates in moderately low to high light levels, and to higher CO2 loss rates at very-low light levels. 2.,Compared with shade-tolerant A. saccharum, less-tolerant species grown in both light treatments had greater mass-based photosynthetic rates, leaf, stem and root respiration rates, leaf mass:plant mass ratios and leaf area:leaf mass ratios, and similar whole-plant light compensation points and leaf-based quantum yields. 3.,Whole-plant CO2 exchange responses to light (0·3,600 µmol quanta m,2 s,1) indicated that intolerant species had more positive CO2 exchange rates at all but very-low light (< 15 µmol quanta m,2 s,1). In contrast, although tolerant A. saccharum had a net CO2 exchange disadvantage at light > 15 µmol quanta m,2 s,1, its lower respiration resulted in lower CO2 losses than other species at light < 15 µmol quanta m,2 s,1. 4.,Growth scaled closely with whole-plant CO2 exchange characteristics and especially with integrated whole-plant photosynthesis (i.e. leaf mass ratio × in situ leaf photosynthesis). In contrast, growth scaled poorly with leaf-level quantum yield, light compensation point, and light-saturated photosynthetic rate. 5.,Collectively these patterns indicated that: (a) no species was able to both minimize CO2 loss at very-low light (i.e. < 15 µmol quanta m,2 s,1) and maximize CO2 gain at higher light (i.e. > 15 µmol quanta m,2 s,1), because whole-plant respiration rates were positively associated with whole-plant photosynthesis at higher light; (b) shade-intolerant species possess traits that maximize whole-plant CO2 exchange (and thus growth) in moderately low to high light levels, but these traits may lead to long-term growth and survival disadvantages in very-low light (< 2·8%) owing, in part, to high respiration. In contrast, shade-tolerant species may minimize CO2 losses in very-low light at the expense of maximizing CO2 gain potential at higher light levels, but to the possible benefit of long-term survival in low light. [source] Seasonal Variation and Correlation with Environmental Factors of Photosynthesis and Water Use Efficiency of Juglans regia and Ziziphus jujubaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 2 2008Hai-Bo Yang Abstract Both the photosynthetic light curves and CO2 curves of Juglans regia L. and Ziziphus jujuba Mill. var. spinosa in three seasons were measured using a LI-6400 portable photosynthesis system. The maximal net photosynthetic rate (Amax), apparent quantum efficiency(,), maximal carboxylation rate (Vcmax) and water use efficiency (WUE) of the two species were calculated based on the curves. The results showed that Amax of J. regia reached its maximum at the late-season, while the highest values of Amax of Z. jujuba occurred at the mid-season. The Amax of J. regia was more affected by relative humidity (RH) of the atmosphere, while that of Z. jujuba was more affected by the air temperature. Light saturation point (LSP) and Light compensation point (LCP) of J. regia had a higher correlation with RH of the atmosphere, those of Z. jujuba, however, had a higher correlation with air temperature. Vcmax of both J. regia and Z. jujuba had negative correlation with RH of the atmosphere. WUE of J. regia would decrease with the rise of the air temperature while that of Z. jujuba increased. Thus it could be seen that RH, temperature and soil moisture had main effect on photosynthesis and WUE of J. regia and Z. jujuba. Incorporating data on the physiological differences among tree species into forest carbon models will greatly improve our ability to predict alterations to the forest carbon budgets under various environmental scenarios such as global climate change, or with differing species composition. [source] PHOTOSYNTHETIC UTILIZATION OF INORGANIC CARBON IN THE ECONOMIC BROWN ALGA, HIZIKIA FUSIFORME (SARGASSACEAE) FROM THE SOUTH CHINA SEA,JOURNAL OF PHYCOLOGY, Issue 6 2003Dinghui Zou The mechanism of inorganic carbon (Ci) acquisition by the economic brown macroalga, Hizikia fusiforme (Harv.) Okamura (Sargassaceae), was investigated to characterize its photosynthetic physiology. Both intracellular and extracellular carbonic anhydrase (CA) were detected, with the external CA activity accounting for about 5% of the total. Hizikia fusiforme showed higher rates of photosynthetic oxygen evolution at alkaline pH than those theoretically derived from the rates of uncatalyzed CO2 production from bicarbonate and exhibited a high pH compensation point (pH 9.66). The external CA inhibitor, acetazolamide, significantly depressed the photosynthetic oxygen evolution, whereas the anion-exchanger inhibitor 4,4,-diisothiocyano-stilbene-2,2,-disulfonate had no inhibitory effect on it, implying the alga was capable of using HCO3, as a source of Ci for its photosynthesis via the mediation of the external CA. CO2 concentrations in the culture media affected its photosynthetic properties. A high level of CO2 (10,000 ppmv) resulted in a decrease in the external CA activity; however, a low CO2 level (20 ppmv) led to no changes in the external CA activity but raised the intracellular CA activity. Parallel to the reduction in the external CA activity at the high CO2 was a reduction in the photosynthetic CO2 affinity. Decreased activity of the external CA in the high CO2 grown samples led to reduced sensitiveness of photosynthesis to the addition of acetazolamide at alkaline pH. It was clearly indicated that H. fusiforme, which showed CO2 -limited photosynthesis with the half-saturating concentration of Ci exceeding that of seawater, did not operate active HCO3, uptake but used it via the extracellular CA for its photosynthetic carbon fixation. [source] NH3 and NO2 fluxes between beech trees and the atmosphere , correlation with climatic and physiological parametersNEW PHYTOLOGIST, Issue 3 2000ARTHUR GESSLER The dynamic-chamber technique was used to investigate the correlation between NH3 and NO2 fluxes and different climatic and physiological parameters: air temperature; relative air humidity; photosynthetic photon fluence rate; NH3 and NO2 concentrations; transpiration rate; leaf conductance for water vapour; and photosynthetic activity. The experiments were performed with twigs from the sun crown of mature beech trees (Fagus sylvatica) at a field site (Höglwald, Germany), and with 12-wk-old beech seedlings under controlled conditions. Both sets of experiments showed that NO2 and NH3 fluxes depended linearly on NO2 and NH3 concentration, respectively, in the concentration ranges representative for the field site studied, and on water-vapour conductance as a measure for stomatal aperture. The NO2 compensation point determined in the field studies (the atmospheric NO2 concentration with no net NO2 flux) was 1.8,1.9 nmol mol,1. The NH3 compensation point varied between 3.3 and 3.5 nmol mol,1 in the field experiments, and was 3.0 nmol mol,1 in the experiments under controlled conditions. The climatic factors T and PPFR were found to influence both NO2 and NH3 fluxes indirectly, by changing stomatal conductance. Whilst NO2 flux showed a response to changing relative humidity that could be explained by altered stomatal conductance, increased NH3 flux with increasing relative humidity (>50%) depended on other factors. The exchange of NO2 between above-ground parts of beech trees and the atmosphere could be explained exclusively by uptake or emission of NO2 through the stomata, as indicated by the quotient between measured and predicted NO2 conductance of approx. 1 under all environmental conditions examined. Neither internal mesophyll resistances nor additional sinks could be observed for adult trees or for beech seedlings. By contrast, the patterns of NH3 flux could not be explained by an exclusive exchange of NH3 through the stomata. Deposition into additional sinks on the leaf surface, as indicated by an increase in the quotient between measured and predicted NH3 conductance, gained importance in high air humidity, when the stomata were closed or nearly closed and/or when atmospheric NH3 concentrations were high. Although patterns of NH3 gas exchange did not differ between different months or years at high NH3 concentrations (c. 140 nmol mol,1), it must be assumed that emission or deposition fluxes at low ambient NH3 concentration (0.8 and 4.5 nmol mol,1) might vary significantly with time because of variation in the NH3 compensation point. [source] A coupled dispersion and exchange model for short-range dry deposition of atmospheric ammoniaTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 618 2006Benjamin Loubet Abstract The MODDAS-2D model (MOdel of Dispersion and Deposition of Ammonia over the Short-range in two dimensions) is presented. This stationary model couples a two-dimensional Lagrangian stochastic model for short-range dispersion, with a leaf-scale bi-directional exchange model for ammonia (NH3), which includes cuticular uptake and a stomatal compensation point. The coupling is obtained by splitting the upward and downward components of the flux, which can be generalized for any trace gas, and hence provides a way of simply incorporating bi-directional exchanges in existing deposition velocity models. The leaf boundary-layer resistance is parametrized to account for mixed convection in the canopy, and the model incorporates a stability correction for the Lagrangian time-scale for vertical velocity, which tends to increase the Lagrangian time-scale in very stable conditions compared with usual parametrizations. The model is validated against three datasets, where concentrations of atmospheric NH3 were measured at several distances from a line source. Two datasets are over grassland and one is over maize, giving a range of canopy structure. The model correctly simulates the concentration in one situation, but consistently overestimates it at further distances or underestimates it at small distances in the two other situations. It is argued that these discrepancies are mainly due to the lack of length of one of the line sources and non-aligned winds. Analysis shows that the surface exchange parameters and the turbulent mixing at the source level are the predominant factors controlling short-range deposition of NH3. Copyright © 2006 Royal Meteorological Society [source] Photosynthesis light curves: a method for screening water deficit resistance in the model legume Medicago truncatulaANNALS OF APPLIED BIOLOGY, Issue 3 2009C. Nunes Abstract The photosynthetic performance of two transgenic Medicago truncatula lines engineered for water deficit (WD) resistance and a non-transformed line was assessed in a growth chamber experiment in well-watered, WD and stress recovery conditions. Direct gas exchange measurements showed that the transgenic plants had lower photosynthetic rates under well-hydrated conditions when compared to the non-transformed line. Photosynthesis light curves confirmed this difference but more importantly showed a progressive change in photosynthetic behaviour with intensity of dehydration. Dehydration led to sharp decreases of maximum photosynthesis (Amax), photosynthetic apparent quantum yield (,) and apparent light compensation point. The recovery rates showed that all plant lines had a similar capacity to regain control photosynthetic values. Furthermore, results suggested that light was more limiting for photosynthesis than atmospheric CO2 concentration. The results are discussed in terms of the use of photosynthesis light response curves as a non-destructive and expeditious approach to select M. truncatula transformants with improved WD resistance. [source] Variation in ecophysiology and carbon economy of invasive and native woody vines of riparian zones in south-eastern QueenslandAUSTRAL ECOLOGY, Issue 6 2010OLUSEGUN O. OSUNKOYA Abstract Exotic and invasive woody vines are major environmental weeds of riparian areas, rainforest communities and remnant natural vegetation in coastal eastern Australia, where they smother standing vegetation, including large trees, and cause canopy collapse. We investigated, through glasshouse resource manipulative experiments, the ecophysiological traits that might facilitate faster growth, better resource acquisition and/or utilization and thus dominance of four exotic and invasive vines of South East Queensland, Australia, compared with their native counterparts. Relative growth rate was not significantly different between the two groups but water use efficiency (WUE) was higher in the native species while the converse was observed for light use efficiency (quantum efficiency, AQE) and maximum photosynthesis on a mass basis (). The invasive species, as a group, also exhibited higher respiration load, higher light compensation point and higher specific leaf area. There were stronger correlations of leaf traits and greater structural (but not physiological) plasticity in invasive species than in their native counterparts. The scaling coefficients of resource use efficiencies (WUE, AQE and respiration efficiency) as well as those of fitness (biomass accumulated) versus many of the performance traits examined did not differ between the two species-origin groups, but there were indications of significant shifts in elevation (intercept values) and shifts along common slopes in many of these relationships , signalling differences in carbon economy (revenue returned per unit energy invested) and/or resource usage. Using ordination and based on 14 ecophysiological attributes, a fair level of separation between the two groups was achieved (51.5% explanatory power), with AQE, light compensation point, respiration load, WUE, specific leaf area and leaf area ratio, in decreasing order, being the main drivers. This study suggests similarity in trait plasticity, especially for physiological traits, but there appear to be fundamental differences in carbon economy and resource conservation between native and invasive vine species. [source] Colonization Strategies of Two Liana Species in a Tropical Dry Forest CanopyBIOTROPICA, Issue 3 2007Gerardo Avalos ABSTRACT Lianas impose intense resource competition for light in the upper forest canopy by displaying dense foliage on top of tree crowns. Using repeated access with a construction crane, we studied the patterns of canopy colonization of the lianas Combretum fruticosum and Bonamia trichantha in a Neotropical dry forest in Panama. Combretum fruticosum flushed leaves just before the rainy season, and its standing leaf area quickly reached a peak in the early rainy season (May,June). In contrast, B. trichantha built up foliage area continuously throughout the rainy season and reached a peak in the late rainy season (November). Both species displayed the majority of leaves in full sun on the canopy surface, but C. fruticosum displayed a greater proportion of leaves (26%) in more shaded microsites than B. trichantha (12%). Self-shading within patches of liana leaves within the uppermost 40,50 cm of the canopy reduced light levels measured with photodiodes placed directly on leaves to 4,9 percent of light levels received by sun leaves. Many leaves of C. fruticosum acclimated to shade within a month following the strongly synchronized leaf flushing and persisted in deep shade. In contrast, B. trichantha produced short-lived leaves opportunistically in the sunniest locations. Species differences in degree of shade acclimation were also evident in terms of structural (leaf mass per area, and leaf toughness) and physiological characters (nitrogen content, leaf life span, and light compensation point). Contrasting leaf phenologies reflect differences in light exploitation and canopy colonization strategies of these two liana species. RESUMEN Las lianas imponen una competencia intensa por la luz en el dosel superior al desplegar un denso follaje encima de las copas de los árboles. Usando acceso repetido al dosel a través de una grúa de construcción, estudiamos los patrones de colonización del dosel de las lianas Combretum fruticosum y Bonamia trichantha en un bosque neotropical seco en Panamá. Combretum fruticosum produjo hojas nuevas justo antes de la estación lluviosa, y su área foliar total alcanzó rápidamente un pico a inicios de la estación lluviosa (mayo-junio). En contraste, B. trichantha construyó su área foliar de forma continua a través de la estación lluviosa alcanzando un pico al final de esta (noviembre). Ambas especies desplegaron la mayoría de sus hojas bajo alta irradiación en la superficie del dosel, aunque C. fruticosum desplegó una mayor proporción de follaje (26%) en micrositios más sombreados que B. trichantha (12%). El auto sombreo dentro de los parches de hojas de lianas dentro de los primeros 40-50 cm del dosel superior redujo el nivel de radiación medido con fotodiodos colocados directamente sobre las hojas a 4-9% de la luz recibida por las hojas de sol. Muchas hojas de C. fruticosum se aclimataron a la sombra luego de un mes después de la producción inicial de hojas altamente sincronizada y persistieron en sombra profunda. En contraste, B. trichantha produjo hojas de corta longevidad de forma oportunística bajo las condiciones de mayor irradiación. Las diferencias entre especies en el grado de aclimatación a la sombra fueron evidentes en términos de caracteres estructurales (masa foliar por unidad de área, y dureza foliar) y fisiológicos (contenido de nitrógeno, longevidad foliar, y punto de compensación lumínica). Estas fenologías foliares tan contrastantes reflejan diferencias en las estrategias de explotación de luz y colonización del dosel por parte de estas dos lianas. [source] Trade-offs in low-light CO2 exchange: a component of variation in shade tolerance among cold temperate tree seedlingsFUNCTIONAL ECOLOGY, Issue 2 2000M. B. Walters Abstract 1.,Does enhanced whole-plant CO2 exchange in moderately low to high light occur at the cost of greater CO2 loss rates at very-low light levels? We examined this question for first-year seedlings of intolerant Populus tremuloides and Betula papyrifera, intermediate Betula alleghaniensis, and tolerant Ostrya virginiana and Acer saccharum grown in moderately low (7·3% of open-sky) and low (2·8%) light. We predicted that, compared with shade-tolerant species, intolerant species would have characteristics leading to greater whole-plant CO2 exchange rates in moderately low to high light levels, and to higher CO2 loss rates at very-low light levels. 2.,Compared with shade-tolerant A. saccharum, less-tolerant species grown in both light treatments had greater mass-based photosynthetic rates, leaf, stem and root respiration rates, leaf mass:plant mass ratios and leaf area:leaf mass ratios, and similar whole-plant light compensation points and leaf-based quantum yields. 3.,Whole-plant CO2 exchange responses to light (0·3,600 µmol quanta m,2 s,1) indicated that intolerant species had more positive CO2 exchange rates at all but very-low light (< 15 µmol quanta m,2 s,1). In contrast, although tolerant A. saccharum had a net CO2 exchange disadvantage at light > 15 µmol quanta m,2 s,1, its lower respiration resulted in lower CO2 losses than other species at light < 15 µmol quanta m,2 s,1. 4.,Growth scaled closely with whole-plant CO2 exchange characteristics and especially with integrated whole-plant photosynthesis (i.e. leaf mass ratio × in situ leaf photosynthesis). In contrast, growth scaled poorly with leaf-level quantum yield, light compensation point, and light-saturated photosynthetic rate. 5.,Collectively these patterns indicated that: (a) no species was able to both minimize CO2 loss at very-low light (i.e. < 15 µmol quanta m,2 s,1) and maximize CO2 gain at higher light (i.e. > 15 µmol quanta m,2 s,1), because whole-plant respiration rates were positively associated with whole-plant photosynthesis at higher light; (b) shade-intolerant species possess traits that maximize whole-plant CO2 exchange (and thus growth) in moderately low to high light levels, but these traits may lead to long-term growth and survival disadvantages in very-low light (< 2·8%) owing, in part, to high respiration. In contrast, shade-tolerant species may minimize CO2 losses in very-low light at the expense of maximizing CO2 gain potential at higher light levels, but to the possible benefit of long-term survival in low light. [source] Comparison of leaf structure and photosynthetic characteristics of C3 and C4Alloteropsis semialata subspeciesPLANT CELL & ENVIRONMENT, Issue 2 2006O. UENO ABSTRACT Alloteropsis semialata (R. Br.) Hitchcock includes both C3 and C4 subspecies: the C3 subspecies eckloniana and the C4 subspecies semialata. We examined the leaf structural and photosynthetic characteristics of these plants. A. semialata ssp. semialata showed high activities of photosynthetic enzymes involved in phosphoenolpyruvate carboxykinase-type C4 photosynthesis and an anomalous Kranz anatomy. Phosphoenolpyruvate carboxylase; pyruvate, Pi dikinase and glycine decarboxylase (GDC) were compartmentalized between the mesophyll (M) and inner bundle sheath cells, whereas ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) occurred in both cells. A. semialata ssp. eckloniana also showed an anomalous non-Kranz anatomy, in which the mestome sheath cells included abundant chloroplasts and mitochondria. Rubisco and GDC accumulated densely in the M and mestome sheath cells, whereas the levels of C4 enzymes were low. The activity levels of photorespiratory enzymes in both subspecies were intermediate between those in typical C3 and C4 plants. The values of CO2 compensation points in A. semialata ssp. semialata were within the C4 range, whereas those in A. semialata ssp. eckloniana were somewhat lower than the C3 range. These data suggest that the plants are C3 -like and C4 -like but not typical C3 and C4, and when integrated with previous findings, point to important variability in the expression of C4 physiology in this species complex. A. semialata is therefore an intriguing grass species with which to study the evolutionary linkage between C3 and C4 plants. [source] | |||||||||||||||||||