Home About us Contact
|
Home About us Contact | ||
|
|
||
Photosynthetic Parameters (photosynthetic + parameter)
Selected AbstractsPhotosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2 - and O3 - enriched atmospheresPLANT CELL & ENVIRONMENT, Issue 4 2004H. EICHELMANN ABSTRACT Two silver birch (Betula pendula Roth) clones K1659 and V5952 were grown in open-top chambers over 3 years (age 7,9 years). The treatments were increased CO2 concentration (+CO2, 72 Pa), increased O3 concentration (+O3, 2 × ambient O3 with seasonal AOT40 up to 28 p.p.m. h) and in combination (+CO2 + O3). Thirty-seven photosynthetic parameters were measured in the laboratory immediately after excising leaves using a computer-operated routine of gas exchange and optical measurements. In control leaves the photosynthetic parameters were close to the values widely used in a model (Farquhar, von Caemmerer and Berry, Planta 149, 78,90, 1980). The distribution of chlorophyll between photosystem II and photosystem I, intrinsic quantum yield of electron transport, uncoupled turnover rate of Cyt b6f, Rubisco specificity and Km (CO2) were not influenced by treatments. Net photosynthetic rate responded to +CO2 with a mean increase of 17% in both clones. Dry weight of leaves increased, whereas protein, especially Rubisco content and the related photosynthetic parameters decreased. Averaged over 3 years, eight and 17 mechanistically independent parameters were significantly influenced by the elevated CO2 in clones K1659 and V5952, respectively. The elevated O3 caused a significant decrease in the average photosynthetic rate of clone V5952, but not of clone K1659. The treatment caused changes in one parameter of clone K1659 and in 11 parameters of clone V5952. Results of the combined treatment indicated that +O3 had less effect in the presence of +CO2 than alone. Interestingly, changes in the same photosynthetic parameters were observed in chamberless grown trees of clone V5952 as under +O3 treatment in chambers, but this was not observed for clone K1659. These results suggest that during chronic fumigation, at concentrations below the threshold of visible leaf injuries, ozone influenced the photosynthetic parameters as a general stress factor, in a similar manner to weather conditions that were more stressful outside the chambers. According to this hypothesis, the sensitivity of a species or a clone to ozone is expected to depend on the growth conditions: the plant is less sensitive to ozone if the conditions are close to optimal and it is more sensitive to ozone under conditions of stress. [source] Growth rates of phytoplankton under fluctuating lightFRESHWATER BIOLOGY, Issue 2 2000Elena Litchman Summary 1The effect of light fluctuations on the growth rates of four species of freshwater phytoplankton was investigated. Experimental light regimes included constant irradiance and fluctuations of a step function form, with equal proportion of high (maximum of 240 µmol photons m -2 s -1) and low light (minimum of 5 µmol photons m -2 s -1) (or dark) in a period. Fluctuations of 1, 8 and 24-h periods were imposed over several average irradiances (25, 50, 100 and 120 µmol photons m -2 s -1). 2Growth rate responses to fluctuations were species-specific and depended on both the average irradiance and the period of fluctuations. Fluctuations at low average irradiances slightly increased growth rate of the diatom Nitzschia sp. and depressed growth of the cyanobacterium Phormidium luridum and the green alga Sphaerocystis schroeteri compared to a constant irradiance. 3Fluctuations at higher average irradiance did not have a significant effect on the growth rates of Nitzschia sp. and Sphaerocystis schroeteri (fluctuations around saturating irradiances) and slightly increased the growth rates of the cyanobacteria Anabaena flos-aquae and Phormidium luridum (when irradiance fluctuated between limiting and inhibiting levels). 4In general, the effect of fluctuations tended to be greater when irradiance fluctuated between limiting and saturating or inhibiting levels of a species growth-irradiance curve compared to fluctuations within a single region of the curve. 5The growth rates of species under fluctuating light could not always be predicted from their growth-irradiance curves obtained under constant irradiance. When fluctuations occur between limiting and saturating or inhibiting irradiances for the alga and when the period of fluctuations is long (greater than 8 h), steady-state growth-irradiance curves may be insufficient to predict growth rates adequately. Consequently, additional data on physiological acclimation, such as changes in photosynthetic parameters, may be required for predictions under non-constant light supply in comparison to constant conditions. [source] Carbon dioxide assimilation by a wetland sedge canopy exposed to ambient and elevated CO2: measurements and model analysisFUNCTIONAL ECOLOGY, Issue 2 2003D. P. Rasse Summary 1The wetland sedge Scirpus olneyi Gray displays fast rates of CO2 assimilation and responds positively to increased atmospheric CO2 concentration. The present study was aimed at identifying the ecophysiological traits specific to S. olneyi that drive these CO2 -assimilation patterns under ambient and elevated CO2 conditions. 2The net ecosystem exchange (NEE) of CO2 between S. olneyi communities and the atmosphere was measured in open-top chambers. 3We developed a new mechanistic model for S. olneyi communities based on published ecophysiological data and additional measurements of photosynthetic parameters. 4Our NEE measurements confirmed that S. olneyi communities have a high rate of summertime CO2 assimilation, with noontime peaks reaching 40 µmol CO2 m,2 ground s,1 on productive summer days, and that elevated CO2 increased S. olneyi CO2 assimilation by c. 35,40%. 5Using S. olneyi -specific ecophysiological parameters, comparison with measured NEE showed that the model accurately simulated these high rates of CO2 uptake under ambient or elevated CO2. 6The model pointed to the Rubisco capacity of Scirpus leaves associated with their high total nitrogen content as the primary explanation for the high rates of CO2 assimilation, and indicated that the vertical-leaf canopy structure of S. olneyi had comparatively little influence on CO2 assimilation. [source] Daily dynamics of photosynthesis of the freshwater red alga Sirodotia delicatula (Batrachospermales, Rhodophyta)PHYCOLOGICAL RESEARCH, Issue 4 2009Thiago Kusakariba SUMMARY The daily course of photosynthetic parameters of a population of the freshwater red alga Sirodotia delicatula from São Paulo State, Brazil (20°43,24,S, 49°18,21,W) was investigated under natural and laboratory conditions using dissolved oxygen and in vivo chlorophyll fluorescence techniques. Field specimens in laboratory conditions showed a defined daily pattern for net photosynthesis (NP) with two peaks observed in marine macroalgae and some freshwater red algae: the first (the highest) during the morning, and the second (the lowest and less evident) during the afternoon. Values of electron transport rate did not show a clear pattern of daily variation. NP results suggest the existence of an endogenous rhythm controlling photosynthesis. The study under natural conditions in two contrasting periods (autumn (June) and spring (October)) showed that the daily course of effective and potential quantum yield values was negatively correlated with irradiance and values were similar in the beginning and end of the day. These data evidenced, respectively, high excitement pressure on photosystem II and good recovery capacity (with lower values in spring) and a lack of irreversible photodamage to photosynthetic apparatus due to the prolonged exposure to high irradiances. Non-photochemical quenching values were also negatively correlated with the irradiance, suggesting a low dissipation capacity of excess energy absorbed by reaction centers. The results evidenced a typical pattern of daily variation with evident response to irradiance. [source] Effects of chronic elevated ozone concentration on antioxidant capacity, photosynthesis and seed yield of 10 soybean cultivarsPLANT CELL & ENVIRONMENT, Issue 9 2010AMY M. BETZELBERGER ABSTRACT Crops losses to tropospheric ozone (O3) in the United States are estimated to cost $1,3 billion annually. This challenge is expected to increase as O3 concentrations ([O3]) rise over the next half century. This study tested the hypothesis that there is cultivar variation in the antioxidant, photosynthetic and yield response of soybean to growth at elevated [O3]. Ten cultivars of soybean were grown at elevated [O3] from germination through maturity at the Soybean Free Air Concentration Enrichment facility in 2007 and six were grown in 2008. Photosynthetic gas exchange, leaf area index, chlorophyll content, fluorescence and antioxidant capacity were monitored during the growing seasons in order to determine if changes in these parameters could be used to predict the sensitivity of seed yield to elevated [O3]. Doubling background [O3] decreased soybean yields by 17%, but the variation in response among cultivars and years ranged from 8 to 37%. Chlorophyll content and photosynthetic parameters were positively correlated with seed yield, while antioxidant capacity was negatively correlated with photosynthesis and seed yield, suggesting a trade-off between antioxidant metabolism and carbon gain. Exposure response curves indicate that there has not been a significant improvement in soybean tolerance to [O3] in the past 30 years. [source] The effect of temperature on C4 -type leaf photosynthesis parametersPLANT CELL & ENVIRONMENT, Issue 9 2007RAIA-SILVIA MASSAD ABSTRACT C4 -type photosynthesis is known to vary with growth and measurement temperatures. In an attempt to quantify its variability with measurement temperature, the photosynthetic parameters , the maximum catalytic rate of the enzyme ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) (Vcmax), the maximum catalytic rate of the enzyme phosphoenolpyruvate carboxylase (PEPC) (Vpmax) and the maximum electron transport rate (Jmax) , were examined. Maize plants were grown in climatic-controlled phytotrons, and the curves of net photosynthesis (An) versus intercellular air space CO2 concentrations (Ci), and An versus photosynthetic photon flux density (PPFD) were determined over a temperature range of 15,40 °C. Values of Vcmax, Vpmax and Jmax were computed by inversion of the von Caemmerer & Furbank photosynthesis model. Values of Vpmax and Jmax obtained at 25 °C conform to values found in the literature. Parameters for an Arrhenius equation that best fits the calculated values of Vcmax, Vpmax and Jmax are then proposed. These parameters should be further tested with C4 plants for validation. Other model key parameters such as the mesophyll cell conductance to CO2 (gi), the bundle sheath cells conductance to CO2 (gbs) and Michaelis,Menten constants for CO2 and O2 (Kc, Kp and Ko) also vary with temperature and should be better parameterized. [source] The response of photosynthesis and stomatal conductance to rising [CO2]: mechanisms and environmental interactionsPLANT CELL & ENVIRONMENT, Issue 3 2007ELIZABETH A. AINSWORTH ABSTRACT This review summarizes current understanding of the mechanisms that underlie the response of photosynthesis and stomatal conductance to elevated carbon dioxide concentration ([CO2]), and examines how downstream processes and environmental constraints modulate these two fundamental responses. The results from free-air CO2 enrichment (FACE) experiments were summarized via meta-analysis to quantify the mean responses of stomatal and photosynthetic parameters to elevated [CO2]. Elevation of [CO2] in FACE experiments reduced stomatal conductance by 22%, yet, this reduction was not associated with a similar change in stomatal density. Elevated [CO2] stimulated light-saturated photosynthesis (Asat) in C3 plants grown in FACE by an average of 31%. However, the magnitude of the increase in Asat varied with functional group and environment. Functional groups with ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)-limited photosynthesis at elevated [CO2] had greater potential for increases in Asat than those where photosynthesis became ribulose-1,5-bisphosphate (RubP)-limited at elevated [CO2]. Both nitrogen supply and sink capacity modulated the response of photosynthesis to elevated [CO2] through their impact on the acclimation of carboxylation capacity. Increased understanding of the molecular and biochemical mechanisms by which plants respond to elevated [CO2], and the feedback of environmental factors upon them, will improve our ability to predict ecosystem responses to rising [CO2] and increase our potential to adapt crops and managed ecosystems to future atmospheric [CO2]. [source] Photosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2 - and O3 - enriched atmospheresPLANT CELL & ENVIRONMENT, Issue 4 2004H. EICHELMANN ABSTRACT Two silver birch (Betula pendula Roth) clones K1659 and V5952 were grown in open-top chambers over 3 years (age 7,9 years). The treatments were increased CO2 concentration (+CO2, 72 Pa), increased O3 concentration (+O3, 2 × ambient O3 with seasonal AOT40 up to 28 p.p.m. h) and in combination (+CO2 + O3). Thirty-seven photosynthetic parameters were measured in the laboratory immediately after excising leaves using a computer-operated routine of gas exchange and optical measurements. In control leaves the photosynthetic parameters were close to the values widely used in a model (Farquhar, von Caemmerer and Berry, Planta 149, 78,90, 1980). The distribution of chlorophyll between photosystem II and photosystem I, intrinsic quantum yield of electron transport, uncoupled turnover rate of Cyt b6f, Rubisco specificity and Km (CO2) were not influenced by treatments. Net photosynthetic rate responded to +CO2 with a mean increase of 17% in both clones. Dry weight of leaves increased, whereas protein, especially Rubisco content and the related photosynthetic parameters decreased. Averaged over 3 years, eight and 17 mechanistically independent parameters were significantly influenced by the elevated CO2 in clones K1659 and V5952, respectively. The elevated O3 caused a significant decrease in the average photosynthetic rate of clone V5952, but not of clone K1659. The treatment caused changes in one parameter of clone K1659 and in 11 parameters of clone V5952. Results of the combined treatment indicated that +O3 had less effect in the presence of +CO2 than alone. Interestingly, changes in the same photosynthetic parameters were observed in chamberless grown trees of clone V5952 as under +O3 treatment in chambers, but this was not observed for clone K1659. These results suggest that during chronic fumigation, at concentrations below the threshold of visible leaf injuries, ozone influenced the photosynthetic parameters as a general stress factor, in a similar manner to weather conditions that were more stressful outside the chambers. According to this hypothesis, the sensitivity of a species or a clone to ozone is expected to depend on the growth conditions: the plant is less sensitive to ozone if the conditions are close to optimal and it is more sensitive to ozone under conditions of stress. [source] Sub-optimal morning temperature induces photoinhibition in dense outdoor cultures of the alga Monodus subterraneus (Eustigmatophyta)PLANT CELL & ENVIRONMENT, Issue 10 2001A. Vonshak Abstract Diel changes in photosynthetic oxygen evolution and several photochemical parameters measured by chlorophyll fluorescence quenching and induction were measured in outdoor dense cultures of the alga Monodus subterraneus (Eustigmatophyta). Cultures were maintained under two temperature regimes. In one, a rise in temperature was initiated in the morning by the increase in solar radiation up to the optimal temperature of 28 °C; in the other, a heating device was used to increase the rate of warming up in early morning. Although the two cultures were maintained at the same temperature and light intensity for most of the day, cultures exposed for only a short time to suboptimal morning temperature showed a larger decrease in almost all the photosynthetic parameters. By comparing the diel changes in maximal photochemistry efficiency of photosystem II, the electron transport rate and the photochemical and non-photochemical chlorophyll fluorescence quenching of the cultures, we concluded that even a relatively short exposure to suboptimal morning temperatures induced photoinhibitory damage. The higher photochemical activity of the heated culture was also reflected in a significant increase in productivity, which was 60% higher in the morning heated cultures than in the non-heated cultures. [source] Changes in leaf photosynthetic parameters with leaf position and nitrogen content within a rose plant canopy (Rosa hybrida)PLANT CELL & ENVIRONMENT, Issue 4 2000M. M. Gonzalez-Real ABSTRACT This paper deals with changes in leaf photosynthetic capacity with depth in a rose (Rosa hybrida cv. Sonia) plant canopy. Measurements of leaf net CO2 assimilation (Al) and total nitrogen content (Nl) were performed in autumn under greenhouse conditions on mature leaves located at different layers within the plant canopy, including the flower stems and the main shoots. These leaves were subjected (i) to contrasting levels of CO2 partial pressure (pa) at saturating photosynthetic photon flux density (I about 1000 ,mol m,2 s,1) and (ii) to saturating CO2 partial pressure (pa about 100 Pa) and varying I, while conditions of temperature were those prevailing in the greenhouse (20,38 °C). A biochemical model of leaf photosynthesis relating Al to intercellular CO2 partial pressure (pi) was parameterized for each layer of leaves, supplying corresponding values of the photosynthetic Rubisco capacity (Vlm) and the maximum rate of electron transport (Jm). The results indicated that rose leaves growing at the top of the canopy had higher values of Jm and Vlm, which resulted from a higher allocation of nitrogen to the uppermost leaves. Mean values of total leaf nitrogen, Nl, decreased about 35% from the uppermost leaves of flower stem to leaves growing at the bottom of the plant. The derived values of non-photosynthetic nitrogen, Nb, varied from 76 mmolN m,2leaf (layer 1) to 60 mmolN m,2leaf (layer 4), representing a large fraction of Nl (50 and 60% in layer 1 and 4, respectively). Comparison of leaf photosynthetic nitrogen (Np=Nl,Nb) and I profiles supports the hypothesis that rose leaves acclimate to the time-integrated absorbed I. The relationships between I and Np, obtained during autumn, spring and summer, indicate that rose leaves seem also to acclimate their photosynthetic capacity seasonally, by allocating more photosynthetic nitrogen to leaves in autumn and spring than in summer. [source] | ||||||||||