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1.
The light-dependent modulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity was studied in two species: Phaseolus vulgaris L., which has high levels of the inhibitor of Rubisco activity, carboxyarabinitol 1-phosphate (CA1P), in the dark, and Chenopodium album L., which has little CA1P. In both species, the ratio of initial to fully-activated Rubisco activity declined by 40–50% within 60 min of a reduction in light from high a photosynthetic photon flux density (PPFD; >700 mol · m–2 · s–1) to a low PPFD (65 ± 15 mol · m–2 · s–1) or to darkness, indicating that decarbamylation of Rubisco is substantially involved in the initial regulatory response of Rubisco to a reduction in PPFD, even in species with potentially extensive CA1P inhibition. Total Rubisco activity was unaffected by PPFD in C. album, and prolonged exposure (2–6 h) to low light or darkness was accompanied by a slow decline in the activity ratio of this species. This indicates that the carbamylation state of Rubisco from C. album gradually declines for hours after the large initial drop in the first 60 min following light reduction. In P. vulgaris, the total activity of Rubisco declined by 10–30% within 1 h after a reduction in PPFD to below 100 mol · m–2 · s–1, indicating CA1P-binding contributes significantly to the reduction of Rubisco capacity during this period, but to a lesser extent than decarbamylation. With continued exposure of P. vulgaris leaves to very low PPFDs (< 30 mol · m–2 · s–1), the total activity of Rubisco declined steadily so that after 6–6.5 h of exposure to very low light or darkness, it was only 10–20% of the high-light value. These results indicate that while decarbamylation is more prominent in the initial regulatory response of Rubisco to a reduction in PPFD in P. vulgaris, binding of CA1P increases over time and after a few hours dominates the regulation of Rubisco activity in darkness and at very low PPFDs.Abbreviations CA1P 2-carboxyarabinitol 1-phosphate - CABP 2-carboxyarabinitol 1,5-bisphosphate - kcat substrate-saturated turnover rate of fully carbamylated enzyme - PPFD photosynthetically active photon flux density (400–700 nm) - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose-1,5-bisphosphate  相似文献   

2.
An empirical light simulation model was applied to estimate stand scale photosynthesis in a deciduous broadleaved forest in central Japan. Based on diurnal courses of photosynthetically active photon flux density (PPFD), we characterized the components of incoming light within the forest canopy, and found that the instantaneous relative PPFD (PPFD under the canopy relative to that above the canopy) under diffuse light condition was a reliable estimator of the intensity and duration of PPFD. We calculated the daily photosynthesis (Aday) for each PPFD class using photosynthesis–light response curves. Model simulated Aday were corroborated with the estimates obtained from the nearby CO2 flux tower. The result demonstrated the potential of the light simulation model. The light use efficiency of two dominant species, Betula ermanii as overstory and Sasa senanensis as understory species, were then evaluated. At the forest understory, PPFD under 50 mol m–2 s–1 contributed to 77% of the sunshine duration on a completely clear day. Therefore, a higher apparent quantum yield for S. senanensis enhanced the utilization of low PPFD for photosynthesis. On the other hand, at the upper forest canopies, B. ermanii with a higher light-saturated photosynthetic rate used high PPFD efficiently. Consequently, potential of daily net photosynthesis for both B. ermanii and S. senanensis was high under each light condition. Such interspecific difference in the patterns of light utilization was suggested as one of factors allowing coexistence of the two species in the study forest.  相似文献   

3.
Naramoto  M.  Han  Q.  Kakubari  Y. 《Photosynthetica》2001,39(4):545-552
Photosynthetic induction responses to a sudden increase in photosynthetic photon flux density (PPFD) from lower background PPFD (0, 25, 50, and 100 mol m–2 s–1) to 1 000 mol m–2 s–1 were measured in leaves of Fagus crenata, Acer rufinerve Siebold & Zucc., and Viburnum furcatum growing in a gap and understory of a F. crenata forest in the Naeba mountains. In the gap, A. rufinerve exhibited more than 1.2-fold higher maximum net photosynthetic rate (P Nmax) than F. crenata and V. furcatum. Meanwhile, in the understory F. crenata exhibited the highest P Nmax among the three species. The photosynthetic induction period required to reach P Nmax was 3–41 min. The photosynthetic responses to increase in PPFD depended on the background PPFD before increase in PPFD. The induction period required to reach P Nmax was 2.5–6.5-fold longer when PPFD increased from darkness than when PPFD increased from 100 mol m–2 s–1. The induction period was correlated with initial P N and stomatal conductance (g s) relative to maximum values before increase in PPFD. The relationship was similar between the gap and the understory. As the background PPFD increased, the initial P N and g s increased, indicating that the degrees of biochemical and stomata limitations to dynamic photosynthetic performance decreased. Therefore, photosynthetic induction responses to increase in PPFD became faster with the increasing background PPFD. The differences in time required to reach induction between species, as well as between gap and understory, were mainly due to the varying of relative initial induction states in P N and g s at the same background PPFD.  相似文献   

4.
Morphological and physiological measurements on individual leaves of Leucaena leucocephala seedlings were used to study acclimation to neutral shading. The light-saturated photosynthetic rate (Pn max) ranged from 19.6 to 6.5 mol CO2 m–2 s–1 as photosynthetic photon flux density (PPFD) during growth decreased from 27 to 1.6 mol m–2 s–1. Stomatal density varied from 144 mm–2 in plants grown in high PPFD to 84 mm–2 in plants grown in low PPFD. Average maximal stomatal conductance for H2O was 1.1 in plants grown in high PPFD and 0.3 for plants grown in low PPFD. Plants grown in low PPFD had a greater total chlorophyll content than plants grown in high PPFD (7.2 vs 2.9 mg g–1 on a unit fresh weight basis, and 4.3 vs 3.7 mg dm–2 on a unit leaf area basis). Leaf area was largest when plants were grown under the intermediate PPFDs. Leaf density thickness was largest when plants were grown under the largest PPFDs. It is concluded that L. leucocephala shows extensive ability to acclimate to neutral shade, and could be considered a facultative shade plant.Abbreviations the initial slope of the photosynthesis vs PPFD curve - Pn max the light-saturated photosynthetic rate - PPFD photosynthetic photon flux density  相似文献   

5.
Micropropagated plantlets are fragile and often lack sufficient vigour to survive the acclimatization shock during transplantation to the soil. Effects of photosynthetic photon flux densities (PPFDs) on growth, photosynthesis and anatomy of micropropagated Doritaenopsis were studied after 4 months of acclimatization in a greenhouse at 25 °C. The plantlets were transferred to three different PPFDs for four months, i.e. low light (175), intermediate light (270) and high light (450 mol m–2 s–1). For most of the growth parameters measured i.e. leaf length, leaf area, leaf width, fresh weight, dry weight, chlorophyll (Chl) a/b ratio, were greater for the intermediate light levels after 4 months of acclimatization. The only exception was leaf thickness, which was increased more under high light levels. Results showed that the survival of Doritaenopsis plantlets was greatest (90%) in low light and intermediate light (89%) compared with only (73%) at high light. However, at low light levels, pigment concentrations (chlorophyll a, b and total chlorophyll) were higher. Net CO2 assimilation (A), stomatal conductance (g) and transpiration (E) were higher in plantlets grown at high level PPFD than at low after 4 months of acclimatization. Photosynthetic efficiency (Fv/Fm) decreased insignificantly; only at mid day for the high light treatment whereas leaf temperature and stomatal closure increased compared to low light. Scanning electron microscopic (SEM) images of leaves from acclimatized plantlets showed an increase in wax formation for the high light grown plantlets compared to those at low light. Microscopic analysis of acclimatized root sections showed highly developed multiseriate-velamen layers and higher root cell activity; while shoots had larger leaf air spaces than those of in vitro grown plantlets. These results suggest that physiological acclimation occurs at the intermediate PPFD (270 mol m–2 s–1) in Doritaenopsis compared to treatment at the high light level.  相似文献   

6.
Husen  Jia  Dequan  Li 《Photosynthetica》2002,40(1):139-144
The responses to irradiance of photosynthetic CO2 assimilation and photosystem 2 (PS2) electron transport were simultaneously studied by gas exchange and chlorophyll (Chl) fluorescence measurement in two-year-old apple tree leaves (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd). Net photosynthetic rate (P N) was saturated at photosynthetic photon flux density (PPFD) 600-1 100 (mol m-2 s-1, while the PS2 non-cyclic electron transport (P-rate) showed a maximum at PPFD 800 mol m-2 s-1. With PPFD increasing, either leaf potential photosynthetic CO2 assimilation activity (Fd/Fs) and PS2 maximal photochemical activity (Fv/Fm) decreased or the ratio of the inactive PS2 reaction centres (RC) [(Fi – Fo)/(Fm – Fo)] and the slow relaxing non-photochemical Chl fluorescence quenching (qs) increased from PPFD 1 200 mol m-2 s-1, but cyclic electron transport around photosystem 1 (RFp), irradiance induced PS2 RC closure [(Fs – Fo)/Fm – Fo)], and the fast and medium relaxing non-photochemical Chl fluorescence quenching (qf and qm) increased remarkably from PPFD 900 (mol m-2 s-1. Hence leaf photosynthesis of young apple leaves saturated at PPFD 800 mol m-2 s-1 and photoinhibition occurred above PPFD 900 mol m-2 s-1. During the photoinhibition at different irradiances, young apple tree leaves could dissipate excess photons mainly by energy quenching and state transition mechanisms at PPFD 900-1 100 mol m-2 s-1, but photosynthetic apparatus damage was unavoidable from PPFD 1 200 mol m-2 s-1. We propose that Chl fluorescence parameter P-rate is superior to the gas exchange parameter P N and the Chl fluorescence parameter Fv/Fm as a definition of saturation irradiance and photoinhibition of plant leaves.  相似文献   

7.
Measurement of the light response of photosynthetic CO2 uptake is often used as an implement in ecophysiological studies. A method is described to calculate photosynthetic parameters, such as the maximum rate of whole electron transport and dissimilative respiration in the light, from the light response of CO2 uptake. Examples of the light-response curves of flag leaves and ears of wheat (Triticum aestivum cv. ARKAS) are shown.Abbreviations and symbols A net photosynthesis rate - D 1 rate of dissimilative respiration occurring in the light - f loss factor - I incident PPFD - I effective absorbed PPFD - J rate of whole electron transport - J m maximum rate of whole electron transport - p c intercellular CO2 partial pressure - PPFD photosynthetic photon flux density - q effectivity factor for the use of light (electrons/quanta) - absorption coefficient - I * CO2 compensation point in the absence of dissimilative respiration (bar) - II conversion factor for calculation of CO2 uptake from the rate of whole electron transport - convexity factor Gas-exchange rates relate to the projective area and are given in mol·m-2·s-1. Electron-transport rates are given in mol electrons·m-2·s-1; PPFD is given in mol quanta·m-2·s-1.  相似文献   

8.
Vats  S.K.  Pandey  S.  Nagar  P.K. 《Photosynthetica》2002,40(4):625-628
Net photosynthetic rate (P N) of Valeriana jatamansi plants, grown under nylon net shade or under different tree canopies, was saturated with photons at 1 000 mol m–2 s–1 photosynthetic photon-flux-density (PPFD), whereas open-grown plants were able to photosynthesise even at higher PPFD, e.g. of 2 000 mol m–2 s–1. Plants grown under net shade had higher total chlorophyll (Chl) content per unit area of leaf surface. However, Chl a/b ratio was maximal in open-grown plants, but remained unchanged in plants grown in nylon net shade and under different tree canopies. Sun-grown plants had thicker leaves (higher leaf mass per leaf area unit), higher wax content, and higher P N than shade grown plants. Thus V. jatamansi is able to acclimate to high PPFD and therefore this Himalayan species may be cultivated in open habitat to meet the ever-increasing industrial demand.  相似文献   

9.
Past studies of the effects of varying levels of photosynthetic photon flux density (PPFD) on the morphology and physiology of the epiphytic Crassulacean acid metabolism (CAM) plant Tillandsia usneoides L. (Bromeliaceae) have resulted in two important findings: (1) CAM, measured as integrated nocturnal CO2 uptake or as nocturnal increases in tissue acidity, saturates at relatively low PPFD, and (2) this plant does not acclimate to different PPFD levels, these findings require substantiation using photosynthetic responses immediately attributable to different PPFD levels, e.g., O2 evolution, as opposed to the delayed, nocturnal responses (CO2 uptake and acid accumulation). In the present study, instantaneous responses of O2 evolution to PPFD level were measured using plants grown eight weeks at three PPFD (20–45, 200–350, and 750–800 mol m-2s-1) in a growth chamber, and using shoots taken from the exposed upper portions (maximum PPFD of 800 mol m-2s-1) and shaded lower portions (maximum PPFD of 140 mol m-2s-1) of plants grown ten years in a greenhouse. In addition, nocturnal increases in acidity were measured in the growth chamber plants. Regardless of the PPFD levels during growth, O2 evolution rates saturated around 500 mol m-2s-1. Furthermore, nocturnal increases in tissue acidity saturated at much lower PPFD. Thus, previous results were confirmed: photosynthesis saturated at low PPFD, and this epiphyte does not acclimate to different levels of PPFD.Abbreviations ANOVA analysis of variance - CAM Crassulacean acid metabolism - DW dry weight - PPFD photosynthetic photon flux density - SNK Student-Newman-Keuls (to whom all correspondence should be sent-present address and reprint requests);  相似文献   

10.
The growth yield of the PUFA-producing marine microalgaIsochrysis galbana ALII-4 grown in a light limited chemostat, was measured under a wide variety of conditions of incident irradiance (I O ) and dilution rates (D). The experiments were conducted under laboratory conditions at 20 °C under continuous light. D ranged from 0.0024 to 0.0410 h–1 at three intensities of Io (820, 1620 and 3270 µmol photon m–2 s–1) close to those found in outdoor cultures. A maximum efficiency max = 0.616 g mol photon–1 was obtained at I O = 820 µmol photon m–2 s–1 and D = 0.030 h–1 and the maximum capacity of the biomass to metabolize the light harvested was found to be 13.1 µmol photon g–1 s–1. Above this value, a significant drop in the system efficiency was observed. A new approach based in the averaged irradiance is used to assess the photon flux absorbed by the biomass.  相似文献   

11.
Interspecific ecophysiological differences in response to different light environments are important to consider in regeneration behavior and forest dynamics. The diurnal changes in leaf gas exchange and chlorophyll fluorescence of two dipterocarps, Shorea leprosula (a high light-requiring) and Neobalanocarpus heimii (a low light-requiring), and a pioneer tree species (Macaranga gigantea) growing in open and gap sites were examined. In the open site, the maximum net photosynthetic rate (Pn), photosystem II (PSII) quantum yield (; F/Fm), and relative electron transport rate (r-ETR) through PSII at a given photosynthetic photon flux density (PPFD) was higher in S. leprosula and M. gigantea than in N. heimii, while non-photochemical quenching (NPQ) at a given PPFD was higher in N. heimii. The maximum values of net photosynthetic rate (Pn) in M. gigantea and S. leprosula was higher in the open site (8–11 mol m–2 s–1) than in the gap site (5 mol m–2 s–1), whereas that in N. heimii was lower in the open site (2 mol m–2 s–1) than in the gap site (4 mol m–2 s–1), indicating that N. heimii was less favorable to the open site. These data provide evidence to support the hypothesis that ecophysiological characteristics link with plants regeneration behavior and successional status. Although Pn and stomatal conductance decreased at midday in M. gigantea and S. leprosula in the open site, both r-ETR and leaf temperature remained unchanged. This indicates that stomatal closure rather than reduced photochemical capacity limited Pn in the daytime. Conversely, there was reduced r-ETR under high PPFD conditions in N. heimii in the open site, indicating reduced photochemical capacity. In the gap site, Pn increased in all leaves in the morning before exposure to direct sunlight, suggesting a relatively high use of diffuse light in the morning.  相似文献   

12.
Kübler  Janet E.  Raven  John A. 《Hydrobiologia》1996,326(1):401-406
Palmaria palmata, which is able to use HCO inf3 sup– as a carbon source for photosynthesis, and Lomentaria articulata, which is dependent on diffusive uptake of dissolved CO2, were grown under constant light and light with sunflecks designed to model wave-induced fluctuations of near-shore underwater light. Both species exhibited significantly increased stable carbon isotope discrimination (more negative values of 13C relative to PDB) when grown with sunflecks. More negative 13C values were associated with decreased growth rate of P. palmata but not of L. articulata. The contrasting effects of sunflecks on the carbon-use characteristics of the two species are discussed in terms of the energetic cost of HCO inf3 sup– use and the susceptibility of CO2 diffusion-dependent species to photoinhibition.  相似文献   

13.
AxenicTrentepohlia odorata was cultured at three different NH4Cl levels (3.5 × 10–2, 3.5 × 10–3, 3.5 × 10–4 M) and three different light intensities (48, 76, 122 µmol m–2 s–1). Chloride had no effect on growth over this range of concentration. High light intensity and high NH4Cl concentration enhanced the specific growth rate. The carotenoid content increased under a combination of high light intensity and low N concentration. WhenD. bardawil was exposed to the same combination of growth conditions, there was an increase in its carotenoid content. The light saturation and the light inhibition constants (K s andK i, respectively) for growth, and the saturation constant (K m) for NH4Cl were determined. TheK s andK i values were higher inT. odorata (66.7 and> 122 mol m–2 s–1, respectively) than inD. bardawil (5.1 and 14.7 µmol m–2 s–1, respectively). TheK m value determined at 122 µmol m–2 s–1, however, was lower inT. odorata (0.048 µM) than inD. bardawil (0.062 µM).Author for correspondence  相似文献   

14.
Behavioral and physiological responses to hypoxia were examined in three sympatric species of sharks: bonnethead shark Sphyrna tiburo, blacknose shark, Carcharhinus acronotus, and Florida smoothhound shark, Mustelus norrisi, using closed system respirometry. Sharks were exposed to normoxic and three levels of hypoxic conditions. Under normoxic conditions (5.5–6.4mg l–1), shark routine swimming speed averaged 25.5 and 31.0cm s–1 for obligate ram-ventilating S. tiburo and C. acronotus respectively, and 25.0cm s–1 for buccal-ventilating M. norrisi. Routine oxygen consumption averaged about 234.6 mg O2kg–1h–1 for S. tiburo, 437.2mg O2kg–1h–1 for C. acronotus, and 161.4mg O2 kg–1 h–1 for M. norrisi. For ram-ventilating sharks, mouth gape averaged 1.0cm whereas M. norrisi gillbeats averaged 56.0 beats min–1. Swimming speeds, mouth gape, and oxygen consumption rate of S. tiburo and C. acronotus increased to a maximum of 37–39cm s–1, 2.5–3.0cm and 496 and 599mg O2 kg–1 h–1 under hypoxic conditions (2.5–3.4mg l–1), respectively. M. norrisi decreased swimming speeds to 16cm s–1 and oxygen consumption rate remained similar. Results support the hypothesis that obligate ram-ventilating sharks respond to hypoxia by increasing swimming speed and mouth gape while buccal-ventilating smoothhound sharks reduce activity.  相似文献   

15.
Xu  Qingzhang  Kirkham  M.B. 《Photosynthetica》2003,41(1):27-32
Grain sorghum [Sorghum bicolor (L.) Moench. cvs. TX430 and KS82] was grown in a Haynie very fine sandy loam (coarse-silty, mixed, superactive, calcareous, mesic Mollic Udifluvents) under constant 47 % shade or full irradiance in a greenhouse under two watering regimes to see the combined and individual effects of low irradiance (LI) and low water (LW) on the sorghum genotypes. Under the high-irradiance (HI) and high-water (HW) treatment (control) and the LI-HW treatment, TX430 grew taller than KS82. Both LI and LW reduced several times the fresh and dry masses. Under the control conditions, TX430 reached its maximum net photosynthetic rate (P Nmax) of 28.93 mol m–2 s–1 at a photosynthetic photon flux density (PPFD) of 1 707 mol m–2 s–1, and KS82 reached its P Nmax of 28.32 mol m–2 s–1 at a PPFD of 2 973 mol m–2 s–1. The fact that TX430 had P Nmax under a lower PPFD than KS82 may relate to its taller growth under LI conditions. Hence genotypes of sorghum might be selected for low irradiance using curves relating P N to PPFD.  相似文献   

16.
Pinus pumila (Pallas) Regel. is a dominant dwarf tree in alpine regions of Japan. The possible factors limiting the net photosynthetic rate (Pn) of the needles of P. pumila were examined in the snow-melting (May) and the summer (August) seasons. In August, in situ maximum Pn was 20 mol kg–1 needle s–1 in the current-year needles and 25 mol kg–1 needle s–1 in the 1-year-old needles. Diurnal trends of Pn in August were positively related to fluctuations in photosynthetic photon flux density (PPFD) and no midday depression of Pn was found, indicating that a decrease in PPFD rather than an increase in needle-to-air vapor pressure deficit (W) might cause the reduction of Pn. Both stomatal conductance (gs) and Pn were lower in May than in August. In May, Pn and gs were almost zero in the morning, but gradually increased with decreasing W, reaching maximum Pn values (4 mol kg–1 needle s–1) and gs (60 mmol kg–1 needle s–1) at 16.00 hours. The daytime Pn in May was positively related to gs. Relative water content in the exposed needles above the snow in May was 83%, which was far above the lethal level. This indicates that the water flow from stems or soils to needles was enough to compensate for a small amount of water loss due to the low gs in May, although the water supplied to needles would be impeded by the low temperatures. Thus, the reduced gs in May would be important for avoiding needle desiccation, and would result in a reduced Pn.  相似文献   

17.
The effect of different light qualities (blue, green, white, red and far-red) on ethylene production in leaf discs and flower petal discs of Begonia × hiemalis cv. Schwabenland Red was studied. All the light qualities, except far-red, reduced the ACC-conversion to ethylene in leaf discs by about 70% at a photosynthetic photon flux density (PPFD) of 20 mol m–2s–1.Blue and green light were less inhibitory than white and red light at lower PPFD. In all treatments far-red light at 0.5 mol m–2s–1 of photon flux density (PFD) stimulated the ACC-conversion to ethylene in leaf discs by about 60–90% compared to the dark-incubated control. White and red light strongly inhibited the -naphthalene-acetic acid (NAA) stimulated ethylene synthesis in leaf discs. The results may suggest that the ethylene production is controlled by phytochrome in the leaves but not in the petals. Lack of coaction of any light quality with silver ions on ethylene production in leaf and petal discs was also observed.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene forming enzyme - NAA -naphthalene-acetic acid - PFD photon flux density - PPFD photosynthetic photon flux density - RH relative air humidity - SAM S-adenosylmethionine - STS silver thiosulphate  相似文献   

18.
About 70% of the shoots developed from nodal explants ofGentiana triflora flowered in vitroondouble strength WPM medium containing 3% (w/v) sucrose, 0.5mg/l BA after 12 weeks of culture in a growth room at 22°Cwith continuous illumination (PPFD=60molm–2 s–1). The influences oninvitro shoot development and flowering of several factors includingthe position of the explant, requirements for sucrose, cytokinin orGA3, variations of pH and photosynthetic photon flux density (PPFD)were investigated. In vitro flowering but not shootdevelopment of G. triflora decreased notably withincreaseddistance from the apex of the shoot, indicating the presence of a floralgradient in the micropropagated shoots. Conversely, as little as 0.01mg l–1 GA3 in the medium promotedshootdevelopment but even up to 0.2 mg l–1GA3 did not induce in vitro flowering.Even though BA could substitute GA3 for a high level of shootdevelopment, it also promoted a high level of in vitroflowering at the PPFD of 60 molm–2 s–1. Sucrose was required for shootdevelopment and flowering in vitro and higher levels ofPPFD could not compensate effectively for the omission of the sugar from themedium. In general, the effects of different concentrations of BA in the mediumor variations of pH on shoot development and flowering invitro were found to be influenced by PPFD. A novel observation isthat precocious flowering of micropropagated gentian shoots did not occur ifthey were first cultured for 5 weeks in the dark before transfer to the lightcondition.  相似文献   

19.
In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m-2 s-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m-2 s-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO2 response. At PPFD-saturation CE was 0.018 mol m-2 s-1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO2 was 0.05–0.08 mol/mol. and PPFD-saturated CO2 exchange was 6–8 mol m-2 s-1. The ratio of internal CO2 concentration to external (C i /C a ) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C i /C a during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO2 exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols A measured photosynthetic rate under any set of conditions (mol m-2 s-1) - A m (atm) measured photosynthetic rate at saturating PPFD, 350 l/l CO2 and 21% (v/v) O2 (mol m-2 s-1) - C constant in equation of Smith (1937, 1938) - C a CO2 concentration in the air (l/l) - C i CO2 concentration in the intercellular air space (l/l) - C i /* C i corrected for CO2 compensation point, i.e., C i -I *, (l/l) - CE initial slope of the CO2 response of photosynthesis (mol m-2 s-1/(l/l)) - CEM CE at PPFD saturation - E transpiration rate (mmol m-2 s-1) - F predicted photosynthetic rate (mol m-2 s-1) - G leaf conductance to H2O (mol m-2 s-1) - I photosynthetic photon flux density (mol m-2 s-1) - N number of data points - P m predicted photosynthetic rate at saturating CO2 and given PPFD (mol m-2 s-1) - P ml predicted photosynthetic rate at saturating CO2 and PPFD (mol m-2 s-1) - R d residual respiratory rate (mol m-2 s-1) - T a air temperature (°C) - T l leaf temperature (°C) - V reaction velocity in equation of Smith (1937, 1938) - V max saturated reaction velocity in equation of Smith (1937, 1938) - VPA vapor pressure of water in the air (mbar/bar) - VPD vapor pressure difference between leaf and air (mbar/bar) - X substrate concentration in equation of Smith (1937, 1938) - initial slope of the PPFD response of photosynthesis at saturating CO2 (mol CO2/mol quanta) - (atm) initial slope of the PPFD response of photosynthesis at 340 l/l CO2 and 21% (v/v) O2 (mol CO2/mol quanta) - I * CO2 compensation point after correction for residual respiration (l/l) - PPFD compensation point (mol m-2 s-1)  相似文献   

20.
The effect of varying light regimes on in vitro rooting of microcuttings of two pear (Pyrus communis L.) cultivars was investigated. Cultures of the easy to-root Conference and the difficult-to-root Doyenne d'Hiver were incubated for 21 days with or without indole-3-butyric acid (IBA) in the medium in darkness or under continuous far-red (8 µmol m–2 s–1), blue, white or red (15 or 36 µmol m–2 s–1) light. Conference rooted without IBA when exposed to red, blue or white light while no rooting was observed under far-red light and in darkness. The high rooting efficiency under red and, by contrast, the inhibition under far-red light and darkness suggest the involvement of the phytochrome system in rhizogenesis. The addition of IBA to the culture medium enhanced root production under all light regimes in both cultivars. Red light, especially at the lower photon fluence rate, had a positive effect by increasing root extension (number × length of roots) and stimulating secondary root formation.Abbreviations IBA Indole-3-butyric acid - R red light - B blue light - FR far-red light - W white light - D darkness - Pfr active (far-red light absorbing) form of phytochrome - Ptot total phytochrome - BA benzyl-adenine  相似文献   

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