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1.
The effects of two light treatments (photosynthetically active photon flux density of either 650 or 1950 µmol m–2 s–1) on the photochemical efficiency of Photosystem II (PS II) (measured as variable to maximum fluorescence ratio) and on the xanthophyll cycle components was studied in wilted Zea mays leaves. For comparison, these parameters were followed under the same light conditions in well-hydrated leaves maintained either in normal or CO2-free air. The net CO2 assimilation of dehydrated leaves declined rapidly as their relative water content (RWC) decreased from 100 to 60% while the PS II efficiency measured after a prolonged dark period of 16 h declined only when RWC leaves was lower than 60%. Furthermore, drought caused an increase in the pool size of the xanthophyll cycle pigments and the presence of a sustained elevated level of zeaxanthin and antheraxanthin at the end of the long dark period. The leaf water deficit enhanced the sensitivity of PS II efficiency to light exposure. During illumination, strong inhibition of PS II efficiency and large violaxanthin deepoxidation was observed in wilted leaves even under moderate photon flux density compared to control leaves in the same conditions. After 2 h of darkness following the light treatment, the PS II efficiency that is dependent on the previous PPFD, decreased with leaf water deficit. Moreover, zeaxanthin epoxidation led to an accumulation of antheraxanthin in dehydrated leaves. All these drought effects on PS II efficiency and xanthophyll cycle components were also obtained in well-hydrated leaves by short-term CO2 deprivation during illumination. We conclude that the increased susceptibility of PS II efficiency to light in wilted maize leaves is mainly explained by the decrease of CO2 availability and the resulting low net CO2 assimilation. 相似文献
2.
Effects of environmental conditions on isoprene emission from live oak 总被引:12,自引:0,他引:12
Live-oak plants (Quercus virginiana Mill.) were subjected to various levels of CO2, water stress or photosynthetic photon flux density to test the hypothesis that isoprene biosynthesis occurred only under conditions of restricted CO2 availability. Isoprene emission increases as the ambient CO2 concentration decreased, independent of the amount of time that plants had photosynthesized at ambient CO2 levels. When plants were water-stressed over a 4-d period photosynthesis and leaf conductance decreased 98 and 94%, respectively, while isoprene emissions remained constant. Significant isoprene emissions occurred when plants were saturated with CO2, i.e., below the light compensation level for net photosynthesis (100 mol m-2 s-1). Isoprene emission rates increased with photosynthetic photon flux density and at 25 and 50 mol m-2 s-1 were 7 and 18 times greater than emissions in the dark. These data indicate that isoprene is a normal plant metabolite and not — as has been suggested — formed exclusively in response to restricted CO2 or various stresses.Abbreviation PPFD
photosynthetic photon flux density 相似文献
3.
George T. Byrd T. Loboda Clanton C. Black Jr. R. Harold Brown 《Photosynthesis research》1995,44(3):253-260
Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO2 that accumulates within their leaf cavities. Leaf cavity CO2 concentrations ranged from 2250 L L–1 near the leaf base to below atmospheric (<350 L L–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO2 concentrations with minimum values near midday and maximum values at night. Conductance to CO2 from the leaf cavity ranged from 24 to 202 mol m–2 s–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO2 was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO2 concentrations and conductance values or as measured directly by 14CO2 labeling experiments. The photosynthetic responses to CO2 and O2 were measured to determine whether onion leaves exhibited a typical C3-type response. A linear increase in CO2 uptake was observed in intact leaves up to 315 L L–1 of external CO2 and, at this external CO2 concentration, uptake was inhibited 35.4±0.9% by 210 mL L–1 O2 compared to 20 mL L–1 O2. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO2 and greatly restrict the refixation of leaf cavity CO2 by photosynthetic tissue.Abbreviations Ca
external CO2 concentration
- Ci
intercellular CO2 concentration
-
CO2 compensation concentration
- PPFR
photosynthetic photon fluence rate 相似文献
4.
Leaf Conductance in Relation to Rate of CO(2) Assimilation: II. Effects of Short-Term Exposures to Different Photon Flux Densities 总被引:1,自引:1,他引:0
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When photon flux density incident on attached leaves of Zea mays L. was varied from the equivalent of 0.12 of full sunlight to full sunlight, leaf conductance to CO2 transfer, g, changed in proportion to the change in rate of CO2, assimilation, A, with the result that intercellular partial pressure of CO2 remained almost constant. The proportionality was the same as that previously found in g and A measured at one photon flux density in plants of Zea mays L. grown at different levels of mineral nutrition, light intensities, and ambient partial pressures of CO2. In shade-grown Phaseolus vulgaris L. plants, A as photon flux density was increased from about 0.12 up to about 0.5 full sunlight, the proportionality being almost the same in plants grown at low and at high light intensity.
When photon flux density incident on the adaxial and abaxial surfaces of the isolateral leaves of Eucalyptus pauciflora Sieb. ex Spreng was varied, g and A also varied proportionally. The leaf conductance in a particular surface was affected by the photon flux density at the opposite surface to a greater extent than was expected on the basis of transmittance. The results indicated that stomata may, in some way, be sensitive to the photon flux absorbed within the leaf as a whole.
相似文献5.
Taro and cocoyam were grown outdoors in either full sun or under 40% shade. Leaves were tagged as they emerged and the effect of leaf age on net CO2 assimilation rate (A) was determined. The effects of shading on A, transpiration (E), stomatal conductance for CO2 (gc) and H2O (gs), and water use efficiency (WUE) were also determined for leaves of a single age for each species. The effect of leaf age on A was similar for both species. Net CO2 assimilation rates increased as leaf age increased up to 28 days with the exception of a sharp decline in A for 21 day-old leaves which corresponded to unusually low temperatures during the period of leaf expansion. A generally decreased as leaves aged beyond 28 days. Cocoyam had higher A rates than taro. Leaves of shade-grown plants had higher rates of A and E for both species at photosynthetic photon flux densities (PPFD) up to 1600 mol s–1 m–2. Shade-grown leaves of cocoyam had greater leaf dry weights per area (LW/A) and a trend toward higher gc and gs than sun-grown leaves. Shade leaves of taro had greater gc and g3 rates than sun-grown leaves. The data suggest that taro and cocoyam are highly adapted to moderate shade conditions. 相似文献
6.
Damage to primary photosynthetic reactions by drought, excess light and heat in leaves of Macroptilium atropurpureum Dc. cv. Siratro was assessed by measurements of chlorophyll fluorescence emission kinetics at 77 K (-196°C). Paraheliotropic leaf movement protected waterstressed Siratro leaves from damage by excess light (photoinhibition), by heat, and by the interactive effects of excess light and high leaf temperatures. When the leaves were restrained to a horizontal position, photoinhibition occurred and the degree of photoinhibitory damage increased with the time of exposure to high levels of solar radiation. Severe inhibition was followed by leaf death, but leaves gradually recovered from moderate damage. This drought-induced photoinhibitory damage seemed more closely related to low leaf water potential than to low leaf conductance. Exposure to leaf temperatures above 42°C caused damage to the photosynthetic system even in the dark and leaves died at 48°C. Between 42 and 48°C the degree of heat damage increased with the time of exposure, but recovery from moderate heat damage occurred over several days. The threshold temperature for direct heat damage increased with the growth temperature regime, but was unaffected by water-stress history or by current leaf water status. No direct heat damage occurred below 42°C, but in water-stressed plants photoinhibition increased with increasing leaf temperature in the range 31–42°C and with increasing photon flux density up to full sunglight values. Thus, water stress evidently predisposes the photosynthetic system to photoinhibition and high leaf temperature exacerbates this photoinhibitory damage. It seems probable that, under the climatic conditions where Siratro occurs in nature, but in the absence of paraheliotropic leaf movement, photoinhibitory damage would occur more frequently during drought than would direct heat damage.Abbreviations and symbols PFD
photon flux area density
- PSI, PSII
photosyntem I, II
-
F
M, F
O, F
V
maximum, instantaneous, variable fluorescence emission
- PLM
paraheliotropic leaf movement; all data of parameter of variation are mean ± standard error 相似文献
7.
Photosystem II chlorophyll fluorescence and leaf net gas exchanges (CO2 and H2O) were measured simultaneously on bean leaves (Phaseolus vulgaris L.) submitted either to different ambient CO2 concentrations or to a drought stress. When leaves are under photorespiratory conditions, a simple fluorescence parameter F/ Fm (B. Genty et al. 1989, Biochem. Biophys. Acta 990, 87–92; F = difference between maximum, Fm, and steady-state fluorescence emissions) allows the calculation of the total rate of photosynthetic electron-transport and the rate of electron transport to O2. These rates are in agreement with the measurements of leaf O2 absorption using 18O2 and the kinetic properties of ribulose-1,5bisphosphate carboxylase/oxygenase. The fluorescence parameter, F/Fm, showed that the allocation of photosynthetic electrons to O2 was increased during the desiccation of a leaf. Decreasing leaf net CO2 uptake, either by decreasing the ambient CO2 concentration or by dehydrating a leaf, had the same effect on the partitioning of photosynthetic electrons between CO2 and O2 reduction. It is concluded that the decline of net CO2 uptake of a leaf under drought stress is only due, at least for a mild reversible stress (causing at most a leaf water deficit of 35%), to stomatal closure which leads to a decrease in leaf internal CO2 concentration. Since, during the dehydration of a leaf, the calculated internal CO2 concentration remained constant or even increased we conclude that this calculation is misleading under such conditions.Abbreviations Ca, Ci
ambient, leaf internal CO2 concentrations
- Fm, Fo, Fs
maximum, minimal, steady-state fluorescence emission
- Fv
variable fluorescence emission
- PPFD
photosynthetic photon flux density
- qp, qN
photochemical, non-photochemical fluorescence quenching
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase 相似文献
8.
Exchange of CO2 and O2 and chlorophyll fluorescence were measured in the presence of 360 1 · 1–1 CO2 in nitrogen in Helianthus annuss L. leaves which had been preconditioned in the dark or at a photon flux density (PFD) of 24 mol · m–2 · s–1 either in 21 or 0% O2. An initial light-dependent O2 outburst of 6 mol · m–2 was measured after aerobic dark incubation. It was attributed to the reduction of electron carriers, predominantly plastoquinone. The maximum initial rate of O2 evolution at PFD 8000 mol · m–2 · s–1 was 170 mol · m–2 · s–2 or about four times the steady CO2-and light-saturated rate of photosynthesis. Fluorescence measurements showed that the rate was still acceptor-limited. Fast O2 evolution ceased after electron carriers were reduced in the dark-adapted leaf, but continued for a short time at the lower rate of 62 mol · m–2 · s–1 in the light-adapted leaf. The data are interpreted to show that enzymes involved in 3-phosphoglycerate reduction are dark-inhibited, but were fully active in low light. In a dark-adapted leaf, respiratory CO2 evolution continued under nitrogen; it was partially inhibited by illumination. Prolonged exposure of a leaf to anaerobic conditions caused reducing equivalents to accumulate. This was shown by a slowly increasing chlorophyll fluorescence yield which indicated the reduction of the PSII acceptor QA in the dark. When the leaf was illuminated, no O2 evolution was detected from short light pulses, although transient O2 production was appreciable during longer light pulses. This indicates that an electron donor (pool size about 2–3 e/PSII reaction center) became reduced in the dark and the first photons were used to oxidise this donor instead of water.Abbreviations Chl
chlorophyll
- CRC
carbon reduction cycle
- GAPDH
NADP-glyceraldehyde-phosphate dehydrogenase
- PFD
photon flux density
- PGA
3-phosphoglycerate
- RuBP
ribulose bisphosphate
- TCA
tricarboxylic acid cycle
To whom correspondence should be addressedThis work received support by the Estonian Academy of Sciences, the Gottfried-Wilhelm-Leibniz Program of the Deutsche For-schungsgemeinschaft and the Sonderforschungsbereich 251 of the University of Würzburg. 相似文献
9.
Oxygen evolution activity of Spirulina platensis cells ttached to nitro-cellulose filters or glass fiber filters (GF/C) was measured using the leaf disc electrode (LD-2 Hansatech
Ltd, Kings Lynn, U.K.), originally designed for its use with leaves of higher plants. Measurements were performed in saturating
(CO2) as described previously for leaf discs and pieces. Photoinhibition could be induced in cells on the solid support as indicated
by a significant increase in their quantum requirement (from 11 to 33 after 25 min exposure to a photon flux density of 2500
μE m-2s-1 and a smaller effect on the photosynthetic rate at light saturation. Photoinhibited cells showed recovery from the photoinhibitory
treatment when illuminated under dim light. 相似文献
10.
A system for measuring leaf gas exchange based on regulating vapour pressure difference 总被引:2,自引:0,他引:2
Waichi Agata Yoshinobu Kawamitsu Susumu Hakoyama Yasuo Shima 《Photosynthesis research》1986,9(3):345-357
A system for measurement of leaf gas exchange while regulating leaf to air vapour pressure difference has been developed; it comprises an assimilation chamber, leaf temperature controller, mass flow controller, dew point controller and personal computer. A relative humidity sensor and air and leaf temperature sensors, which are all used for regulating the vapour pressure difference, are mounted into the chamber. During the experiments, the computer continuously monitored the photosynthetic parameters and measurement conditions, so that accurate and intenstive measurements could be made.When measuring the light-response curve of CO2 assimilation for single leaves, in order to regulate the vapour pressure difference, the leaf temperature and relative humidity in the chamber were separately and simultaneously controlled by changing the air temperature around the leaf and varying the air flow rate through the chamber, respectively. When the vapour pressure difference was regulated, net CO2 assimilation, transpiration and leaf conductance for leaves of rice plant increased at high quantum flux density as compared with those values obtained when it was not regulated.When measuring the temperature-response curve of CO2 assimilation, the regulation of vapour pressure difference was manipulated by the feed-forward control of the dew point temperature in the inlet air stream. As the vapour pressure difference was regulated at 12 mbar, the maximum rate of and the optimum temperature for CO2 assimilation in rice leaves increased 5 molCO2 m–2 s–1 and 5°C, respectively, as compared with those values obtained when the vapour pressure difference took its own course. This was reasoned to be due to the increase in leaf conductance and the decrease in transpiration rate. In addition, these results confirmed that stomatal conductance essentially increases with increasing leaf temperature under constant vapour pressure difference conditions, in other words, when the influence of the vapour pressure difference is removed.This system may be used successfully to measure inter- and intra-specific differences and characteristics of leaf gas exchange in plants with a high degree of accuracy.Abbreviations A
CO2 assimilation rate
- Amax
Maximum rate of CO2 assimilation
- Aopt
Optimum teperature for CO2 assimilation
- CTWB
Controlled-temperature water bath
- DPC
Dew point controller
- E
Transpiration rate; gl, leaf conductance
- HCC
Humidity control circuit
- IRGA
Infrared gas analyzer
- LT
Leaf temperature
- LTC
Leaf temperature controller
- MFC
Mass flow controller
- QFD
Quantum flux density
- RH
Relative humidity
- RHC
Relative humidity controller
- VPD
Vapour pressure difference
- CO2
Difference of CO2 concentration between inlet and outlet air 相似文献
11.
The effect of leaf temperature on stomatal conductance and net CO2 uptake was studied on French bean (Phaseolus vulgaris L.) using either dehydrated attached leaves (25–40% water deficit) or cut leaves supplied with 10–4 M abscisic acid (ABA) solution to the transpiration stream. Decreasing leaf temperature caused stomatal opening and increased net CO2 uptake (which was close to zero at around 25° C) to a level identical to that of control leaves (without water deficit) at around 15° C. (i) The ABA effect on stomatal closure was modulated by temperature and, presumably, ABA is at least partly responsible for stomatal closure of french bean submitted to a drought stress. (ii) For leaf temperatures lower than 15° C, net CO2 uptake was no longer limited by water deficit even on very dehydrated leaves. This shows that dehydrated leaves retain a substantial part of their photosynthetic capacity which can be revealed at normal CO2 concentrations when stomata open at low temperature. In contrast to leaves fed with ABA, decreasing the O2 concentration from 21% to 1% O2 did not increase either the rate of net CO2 uptake or the thermal optimum for photosynthesis of dehydrated leaves. The quantum yield of PSII electron flow (measured by F/Fm) was lower in 1% O2 than in 21% O2 for each leaf pretreatment given (non-dehydrated leaves, dehydrated leaves, and leaves fed with ABA) even within a temperature range in which leaf photosynthesis at normal CO2 concentration was the same in these two O2 concentrations. It is concluded that this probably indicates an heterogeneity of photosynthesis, since this difference in quantum yield disappears when using high CO2 concentrations during measurements.Abbreviations and Symbols ABA
abscisic acid
- Fm
maximum chlorophyll fluorescence
- F
difference between steady-state chlorophyll fluorescence and Fm
- PPFD
photosynthetic photon flux density
We would like to thank Dr. J.-M. Briantais (Laboratoire d'écologie végétale, Orsay, France) for help during fluorescence measurements and Ms. J. Liebert for technical assistance. 相似文献
12.
Namaqualand, a semi-arid winter rainfall region of South Africa, supports an exceptional diversity of geophytic species. The survey focused on gas exchange reactions and chlorophyll a fluorescence in geophytes with different leaf orientation in relation to environmental variability. Although the above ground life cycle of geophytes can be extremely short, unlike desert annuals, they are not characterized by a high photosynthetic CO2 uptake. Maximum CO2 uptake ranged from 4 to 20 mol CO2 m-2 s-1. Temperature optima of photosynthetic CO2 uptake were comparably low and ranged from 12 to 22°C for eleven species tested, with only one species above 19°C. The decrease of CO2 uptake with rising temperatures was associated with a substantial increase of photorespiration. Net photosynthesis was saturated between 500 and 900 mol photons m-2 s-1 while electron transport through PSII was saturated at higher photon flux densities. At light intensities beyond saturation, a high variability of PSII efficiency occurred. It was highest for horizontal leaves and lowest for upright leaves. However, the maximum quantum yield of PSII (Fv/Fm)remained constant during the course of a day, regardless of leaf orientation. This indicates the absence of photoinhibitory effects and a well protected photosynthetic apparatus. Leaf orientation determined interception of solar radiation and thus leaf temperature which was highest for horizontal leaves. In conclusion, Namaqualand geophytes show photosynthetic characteristics that are well adapted to the mild and generally moist conditions during the growing season. 相似文献
13.
Response of epidermal diffusive conductance to simultaneous changes in leaf water potential and photon flux density was studied in primary bean leaves. Values of epidermal conductance corresponding to every photon flux density decreased with decreasing leaf water potential below - 6.9 x 105Pa; slight deorease was followed by a rapid one at water potential ranging from - 8.0 to -10.5 x 105 Pa. In the leaves with water potential lower than -10.5 x 105 Pa neither the saturated photon flux density (1200 [xeinstein m-2s-1) induced photoactive stomatal opening. Negative influence of one factor could be partially compensated by positive influence of the other. These results were in good agreement with the considered mechanism of action of leaf water potential and photon flux density on epidermal conductance. 相似文献
14.
Abstract Using an open-system leaf chamber, gas exchange measurements on attached leaves of 3-4-year-old Golden Delicious apple trees, made through two seasons, provided data from which the parameters of a leaf photosynthesis model could be derived. The equation is: where C1 is internal CO2 concentration and Qp is the incident quantum flux. There was considerable leaf to leaf variation in the values of the parameters but no clear seasonal trends were established. The initial slope (a) had an average value of about 2.5 × 10?3 mg μmol?1? (i.e. quantum yield ~ 0.057); the mesophyll conductance (gm) was about 3.5 mm s?1 in extension leaves of trees carrying fruit and 2.5 mm s?1 in extension leaves of defruited trees. Differences between the values of gm for spur leaves with and without subtending fruits were not significant; 2.5 mm s?1 may be used. Dark respiration (Rd, mg m?2 s?1) increased exponentially with temperature (T°C); Rd~ 0.006 exp (0.09 T). At saturating photon flux density Pn was linearly related to Ci, up to Ci~ 250 mg m?3. Optimum temperatures for Pn were slightly different in the two years and were in the range 16-26°C. 相似文献
15.
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
16.
Pseudo-cubic spline functions were applied to the two atmospheric CO2 concentrations of 340 and 600 l·l–1 CO2 for describing the average daily CO2 gas exchange rates of simplifed grassland model ecosystems. Measurements used were from daily means of photon flux density (PhAR), temperature and relative air humidity, phytomass of each day, leaf area indexes, average phenological states of the vegetation (1–15), and water exchange rates of the entire model ecosystems. The functions were validated with, data from the same experimental year. We also succeeded in verifying the functions with the response data from years other than those used for constructing the model. 相似文献
17.
Strawberry (Fragaria ananassaDuch. cv. Fengxiang) plantlets were cultured under two in vitroenvironments for rooting, and then acclimatized under two ex vitroirradiance conditions. At the end of rooting stage plant height, fresh weight and specific leaf area of T1-plants grown under high sucrose concentration (3 sucrose), low photosynthetic photon flux density (30 mol m–2 s–1) and normal CO2 concentration (350–400 l l–1) were significantly higher than those of T2-plantlets grown under low sucrose concentration (0.5), high photosynthetic photon flux density (90 mol m–2 s–1) and elevated CO2 concentration (700–800 l l–1). But T2-plantlets had higher net photosynthetic rate (Pn), effective photochemical quantum yield of PSII (PSII), effective photosynthetic electron transport rate (ETR), photochemical quenching (qP) and ratio of chlorophyll fluorescence yield decrease (Rfd). After transfer, higher irradiance obviously promoted the growth of plantlets and was beneficial for the development of photosynthetic functions during acclimatization. T2-plantlets had higher fresh weight, leaf area, PSII and ETR under higher ex vitroirradiance condition. 相似文献
18.
The photosynthetic responses of tomato (Lycopersicum esculentum Mill.) leaves to environmental and ontogenetic factors were determined on plants grown in the field under high radiation and high nitrogen fertilization. Response curves showed net photosynthesis to only approach light saturation at a photosynthetic photon flux density (PPFD) of 2200 mol m-2 s-1, with rates of approx. 40 mol CO2 m-2 s-1. A broad temperature optimum was observed between 25° and 35°C, with 50% of the photosynthetic rates remaining even at 47°C. The high rate, the lack of saturation at the equivalent of full sunlight, and the tolerance to high temperature of tomato were unusual in light of the literature on this C3 species. Apparently, acclimation to the field environment of high radiation and hot daytime temperature, coupled with the high nitrogen nutrition, made possible the high photosynthetic performance normally associated with C4 species.Photosynthetic ability of the leaf reached a maximum near the time of its full expansion and declined steadily thereafter, regardless of the time of leaf initiation. Leaf nitrogen content showed a similar decline with leaf ontogeny. Photosynthesis was linearly correlated with nitrogen content, whether the nitrogen variation was due to leaf age or rates of nitrogen fertilization. Internal CO2 concentrations (Ci) of the leaf indicated that stomatal function was well coordinated with photosynthetic capacity as leaf age and fluence rate varied down to a PPFD of 500 mol m-2 s-1. As PPFD decreased further, there was less stomatal control and Ci increased to as high as 320 bar bar-1.Dark respiration was highest for expanding leaves and increased nearly exponentially with temperature. Respiration was also highest for young and expanding fruits, and next highest for fruits just turning pink. Fruit respiration increased approximately linearly with temperature, and was estimated to be an important component of the CO2 flux of the plant near maturity because of the heavy fruit load and low leaf photosynthesis at that time. The results are significant for model simulation of tomato productivity in the field. 相似文献
19.
Changes in gross canopy photosynthetic rate (PGc), produced by long-term exposure to an elevated atmospheric CO2 level (626±50 µmol mol-1), were modelled forLolium perenne L. cv. Vigor andTrifolium repens L. cv. Blanca, using a simple photosynthesis model, based on biochemical and physiological information (leaf gross CO2 uptake in saturating light, Pmax, and leaf quantum efficiency, ) and structural vegetation parameters (leaf area index, LAI, canopy extinction coefficient, k, leaf transmission, M). Correction of PGc for leaf respiration allowed comparison with previously measured canopy net CO2 exchange rates, with the average divergence from model prediction amounting to about 6%. Sensitivity analysis showed that for a three-week old canopy, the PGc increase in high CO2 could be attributed largely to changes in Pmax and , while differences in canopy architecture were no longer important for the PGc-stimulation (which they were in the early growth stages). As a consequence of this increasing LAI with canopy age, the gain of daytime CO2 uptake is progressively eroded by the increasing burden of canopy respiration in high-CO2 grownLolium perenne. Modelling canopy photosynthesis in different regrowth stages after cutting (one week, two weeks,...), revealed that the difference in a 24-h CO2 balance between the ambient and the high CO2 treatment is reduced with regrowth time and completely disappears after 6 weeks.Abbreviations C350
ambient CO2 treatment
- C625
high CO2 treatment
-
k
canopy extinction coefficient
- LAI
leaf area index
- LAImax
fitted LAI-maximum
- M
leaf transmission
- NCER
net CO2 exchange rate
- PGc
gross canopy photosynthetic rate
- Q
photosynthetic photon flux density
- Q0
photosynthetic photon flux density at the top of the canopy
- RDc
canopy dark respiration rate
- RDl
leaf dark respiration rate
-
t
regrowth time after cutting
-
T
air temperature
-
leaf quantum efficiency
- LAI
rate of initial LAI-increase with time 相似文献
20.
Separating the contribution of the upper and lower mesophyll to photosynthesis in Zea mays L. leaves
The appearance of transverse sections of maize leaves indicates the existence of two airspace systems serving the mesophyll, one connected to the stomata of the upper epidermis and the other to the stomata of the lower surface, with few or no connections between the two. This study tests the hypothesis that the air-space systems of the upper and lower mesophyll are separated by a defined barrier of measurable conductance. A mathematical procedure, based on this hypothesis, is developed for the quantitative separation of the contributions made by the upper and lower halves of the mesophyll to carbon assimilation using gasexchange data. Serial paradermal sections and three-dimensional scanning-electron-microscope images confirmed the hypothesis that there were few connections between the two air-systems. Simultaneous measurements of nitrous-oxide diffusion across the leaf and of transpiration from the two surfaces showed that the internal conductance was about 15% of the maximum observed stomatal conductance. This demonstrates that the poor air-space connections, indicated by microscopy, represent a substantial barrier to gas diffusion. By measuring the CO2 and water-vapour fluxes from each surface independently, the intercellular CO2 concentration (c
i) of each internal air-space system was determined and the flux between them calculated. This allowed correction of the apparent CO2 uptake at each surface to derive the true CO2 uptake by the mesophyll cells of the upper and lower halves of the leaf. This approach was used to analyse the contribution of the upper and lower mesophyll to CO2 uptake by the leaf as a whole in response to varying light levels incident on the upper leaf surface. This showed that the upper mesophyll was light-saturated by a photon flux of approx. 1000 mol·m-2·s-1 (i.e. about one-half of full sunlight). The lower mesophyll was not fully saturated by photon fluxes of nearly double full sunlight. At low photon fluxes the c
i of the upper mesophyll was significantly less than that of the lower mesophyll, generating a significant upward flux of CO2. At light levels equivalent to full sunlight, and above, c
i did not differ significantly between the two air space systems. The physiological importance of the separation of the air-space systems of the upper and lower mesophyll to gas exchange is discussed.Abbreviations and symbols
A
net leaf CO2 uptake rate
-
A
upper
app.
and A
lower
app.
net rates of CO2 uptake across the upper and lower surfaces
-
A
upper and A
lower
derived net rates of CO2 uptake by the upper and lower mesophyll
-
A
upward
net flux of CO2 from the lower to upper mesophyll
-
c
a, c
a, upper and c
a, lower
the CO2 concentrations in the air around the leaf above the upper surface and below the lower surface
-
c
N2O
the concentration of N2O in the air around the leaf
-
c
i, c
i, upper and c
i, lower
the mesophyll intercellular CO2 concentration of the whole leaf, the upper mesophyll and the lower mesophyll
-
g
i
leaf internal conductance to CO2
-
g
s, g
s, lower and g
s, upper
the stomatal conductance of the whole leaf, the lower surface and the upper surface
-
g
the total conductance across the leaf
-
Q
the photosynthetically active photon flux density 相似文献