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1.
Measurements were made of net rates of CO 2 assimilation in lichens at various ambient concentrations of CO 2 in air and in helox (79% He, 21% O 2). Because of the faster rate of CO 2 diffusion in the pores of lichen thalli when filled with helox than when filled with air, a given net rate of assimilation was achieved at a lower ambient concentration of CO 2 in helox. The differences were used to estimate resistances to diffusion through the gas-filled pore systems in lichens. The technique was first tested with five lichen species, and then applied in a detailed study with Ramalina maciformis, in which gas-phase resistances were determined in samples at four different states of hydration and with two irradiances. By assuming, on the basis of previous evidence, that the phycobiont in R. maciformis is fully turgid and photosynthetically competent at the smallest hydration imposed (equilibration with vapour at 97% relative humidity), and that, with this state of hydration, diffusion of CO 2 to the phycobiont takes place through continuously gas-filled pores, it was possible also to determine both the dependence of net rate of assimilation in the phycobiont on local concentration of CO 2 in the algal layer, and, with the wetter samples, the extents to which diffusion of CO 2 to the phycobiont was impeded by water films. In equilibrium with air of 97% relative humidity, the thallus water content being 0.5 g per g dry weight, the resistance to CO 2 diffusion through the thallus was about twice as large as the resistance to CO 2 uptake within the phycobiont. Total resistance to diffusion increased rapidly with increase in hydration. At a water content of 2 g per g it was about 50 times as great as the resistance to uptake within the phycobiont and more than two-thirds of it was attributable to impedance of transfer by water. The influences of water content on rate of assimilation at various irradiances are discussed. The analysis shows that the local CO 2 compensation concentration of the phycobiont in R. maciformis is close to zero, indicating that photorespiratory release of CO 2 does not take place in the alga, Trebouxia sp., under the conditions of these experiments.Symbols and Units
rate of CO 2 diffusion in air relative to that in carrier gas (unity if the carrier gas is air and 0.43 if is helox)
- A 1
net rate of CO 2 uptake by the lichen
- A p
gross rate of carboxylation minus photorespiratory decarboxylation in the phycobiont, i.e. net rate of light-activated CO 2 exchange
- A *
maximum, CO 2-saturated magnitude of A p
- c
concentration of CO 2
- c a
ambient concentration of CO 2
- c i
c a minus difference in CO 2 concentration across air-filled pore space in the thallus
- c 8
CO 2 concentration equivalent to partial pressure of CO 2 at the surface of the phycobiont
- 1
magnitude of c a at which A 1 = 0
- *
magnitude of c * at which A p = 0
- R
rate of dark respiration in the lichen (mycobiont and phycobiont)
- R
rate of dark respiration in region between the surface of the lichen and an arbitrary distance from the surface within the thallus
- r
resistance to CO 2 transfer from lichen surface to the surface of the phycobiont
- r
resistance to CO 2 transfer between effective source of dark respiration in the lichen and the surface of the phycobiont
- r g, r
g
components of r and r , respectively, attributable to transfer in air-phase
- r w, r
w
components of r and r , respectively, attributable to transfer in water-phase
- r
component of r between surface of lichen and an arbitrary distance from the surface within the thallus
- r *
resistance to CO 2 transfer and carboxylation in the phycobiont
- RH
relative humidity 相似文献
2.
The characteristics of gas exchange and carbon isotope discrimination were determined for a number of lichen species, representing contrasting associations between fungal (mycobiont) and photosynthetic (photobiont) organism. These parameters were evaluated with regard to the occurrence of any CO 2-concentrating mechanism (CCM) expressed specifically by the green algal (phycobiont) or cyanobacterial (cyanobiont) partner. Carbon isotope discrimination () fell into three categories. The highest , found in lichens comprising a phycobiont plus cyanobacteria limited to pockets in the thallus (known as cephalodia), ranged from 24 to 28, equivalent to a carbon isotope ratio ( 13C) of around -32 to-36 vs. Pee Dee Belemnite (PDB) standard. Further evidence was consistent with CO 2 supply to the carboxylating system entirely mediated by diffusion rather than a CCM, in that thallus CO 2 compensation point and online instantaneous were also high, in the range normally associated with C 3 higher plants. For lichens consisting of phycobiont or cyanobiont alone, organic material formed two distinct ranges around 15 (equivalent to a 13C of -23%.). Thallus compensation point and instantaneous were lower in the cyanobiont group, which also showed higher maximum rates of net photosynthesis, whether expressed on the basis of thallus dry weight, chlorophyll content or area. These data provide additional evidence for the activity of a CCM in cyanobiont lichens, which only show photosynthetic activity when reactivated with liquid water. Rates of net CO 2 uptake were lower in both phycobiont associations, but were relatively constant across a wide working range of thallus water contents, usually in parallel with on-line . The phycobiont response was consistent whether photosynthesis had been reactivated with liquid water or water vapour. The effect of diffusion limitation could generally be seen with a 3–4 decrease in instantaneous at the highest water contents. The expression of a CCM in phycobiont algae, although reduced compared with that in cyanobacteria, has already been related to the occurrence of pyrenoids in chloroplasts. In view of the inherent requirement of cyanobacteria for some form of CCM, and the smaller pools of dissolved inorganic carbon (DIC = CO 2 + HCO
inf3
su–
+ CO
inf3
su2–
) associated with phycobiont lichens, it appears that characteristics provide a good measure of the magnitude of any CCM, albeit tempered by diffusion limitation at the highest thallus water contents.Abbreviations ANOVA
analysis of variance
- CCM
CO 2-concentrating mechanism
- cyanobiont
cyanobacterium
- DIC
CO 2 + HCO
inf3
su–
+ CO
inf3
su2–
(dissolved inorganic carbon)
- photobiont
photosynthetic organism present in the association
- phycobiont
green alga
- phycobiont + cephalodia
green algae + cyanobacteria in cephalodia
- Pmax
maximum photosynthetic rate
- PPFD
photosynthetic photon flux density, 400–700 nm
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
-
carbon isotope discrimination ()
- 13C
carbon isotope ratio ()
We would like to thank Dr. Enrico Brugnoli (CNR, Porano, Italy) and E.C. Smith (University of Newcastle) for many helpful discussions. Dr. Kristin Palmqvist (Department of Plant Physiology, University of Umeå, Sweden) kindly provided the samples of Peltigera apthosa. In particularly, Cristina Máguas would like to thank to Prof. Fernando Catarino (University of Lisbon) for his support throughout this study. Cristina Máguas has been supported by JNICT-Science Programme studentship (BD/153/90-RN). 相似文献
3.
Summary Thalli of Ramalina maciformis were moistened to their maximal water holding capacity, thus, simulating actual conditions following a heavy rainfall. Time courses of net photosynthesis at 17° C and 750 E m -2 s -1 light intensity (PAR) were obtained during drying of the thalli. At ambient CO 2 concentrations from 200 to 1,000 ppm, CO 2 uptake of the moist lichens was depressed at high water content. After a certain water loss, net photosynthesis increased to a maximal value and decreased again with further drying of the thalli. The degree of initial depression of photosynthesis decreased with increasing ambient CO 2 concentration, and it was fully absent at 1,600 ppm ambient CO 2. Under these conditions of CO 2 saturation, net photosynthesis remained constant at maximum for many hours and decreased only when substantial amounts of water had been lost. We conclude that the carboxylation capacity of the lichen is not affected by high contents of liquid water. Therefore, the depression of CO 2 uptake of the water saturated lichen at lower (e.g. natural) ambient CO 2 must be due exclusively to increased resistance to CO 2 diffusion from the external air to the sites of carboxylation. 相似文献
4.
The CO 2 dependence of net CO 2 assimilation was examined in a number of green algal and cyanobacterial lichens with the aim of screening for the algal/cyanobacterial CO 2-concentrating mechanism (CCM) in these symbiotic organisms. For the lichens Peltigera aphthosa (L.) Willd., P. canina (L.) Willd. and P. neopolydactyla (Gyeln.) Gyeln., the photosynthetic performance was also compared between intact thalli and their respective photobionts, the green alga Coccomyxa PA, isolated from Peltigera aphthosa and the cyanobacterium Nostoc PC, isolated from Peltigera canina. More direct evidence for the operation of a CCM was obtained by monitoring the effects of the carbonic-anhydrase inhibitors acetazolamide and ethoxyzolamide on the photosynthetic CO 2use efficiency of the photobionts. The results strongly indicate the operation of a CCM in all cyanobacterial lichens investigated and in cultured cells of Nostoc PC, similar to that described for free-living species of cyanobacteria. The green algal lichens were divided into two groups, one with a low and the other with a higher CO 2-use efficiency, indicative of the absence of a CCM in the former. The absence of a CCM in the low-affinity lichens was related to the photobiont, because free-living cells of Coccomyxa PA also apparently lacked a CCM. As a result of the postulated CCM, cyanobacterial Peltigera lichens have higher rates of net photosynthesis at normal CO 2 compared with Peltigera aphthosa. It is proposed that this increased photosynthetic capacity may result in a higher production potential, provided that photosynthesis is limited by CO 2 under natural conditions. 相似文献
5.
CO 2 exchange of the endolithic lichen Verrucaria baldensis was measured in the laboratory under different conditions of water content, temperature, light, and CO 2 concentration. The species had low CO 2 exchange rates (maximum net photosynthesis: c. 0.45 μmol CO 2 m −2 s −1; maximum dark respiration: c. 0.3 μmol CO 2 m −2 s −1) and a very low light compensation point (7 μmol photons m −2 s −1 at 8°C). The net photosynthesis/respiration quotient reached a maximum at 9–15°C. Photosynthetic activity was affected only
after very severe desiccation, when high resaturation respiratory rates were measured. Microclimatic data were recorded under
different weather conditions in an abyss of the Trieste Karst (northeast Italy), where the species was particularly abundant.
Low photosynthetically active radiation (normally below 40 μmol photons m −2 s −1), very high humidities (over 80%), and low, constant temperatures were measured. Thallus water contents sufficient for CO 2 assimilation were often measured in the absence of condensation phenomena.
Received: 22 September 1996 / Accepted: 26 April 1997 相似文献
6.
Earlier experiments (T.D. Brock 1975, Planta 124, 13–23) addressed the question whether the fungus of the lichen thallus might enable the algal component to function when
moisture stress is such that the algal component would be unable to function under free-living conditions. It was concluded
that the liberated phycobiont in ground lichen thalli could not photosynthesize at water potentials as low as those at which
the same alga could when it was present within the thallus. However, our experience with lichen photosynthesis has not substantiated
this finding. Using instrumentation developed since the mid-1970's to measure photosynthesis and control humidity, we repeated
Brock's experiments. When applying “matric” water stress (equilibrium with air of constant relative humidity) we were unable
to confirm the earlier results for three lichen species including one of the species, Letharia vulpina, had also been used by Brock. We found no difference between the effects of low water potential on intact lichens and their
liberated algal components (ground thallus material and isolated algae) and no indication that the fungal component of the
lichen symbiosis protects the phycobiont from the adverse effects of desiccation once equilibrium conditions are reached.
The photosynthetic apparatus of the phycobiont alone proved to be highly adapted to water stress as it possesses not only
the capability of functioning under extremely low degrees of hydration but also of becoming reactivated solely by water vapor
uptake. 相似文献
7.
Uptake of NH
4
+
and NO
3
-
by the N 2-fixing lichens Peltigera praetextata (two-component lichen) and P. aphthosa (three-component lichen) was studied. In addition, the effects of these ions, separately and in combination, on C 2H 2 reduction and CO 2 exchange were examined. Both NH
4
+
and NO
3
-
were utilized by the lichens. NH 4NO 3 caused an increased liberation of NO
3
-
from the lichens as compared to the release observed in untreated lichen thalli. NH
4
+
and NO
3
-
led to reduced C 2H 2 reduction by P. praetextata, which, however, was less pronounced than when the two ions were given in combination. In P. aphthosa the C 2H 2 reduction was inhibited by NH
4
+
and NH 4NO 3, but not by NO
3
-
alone. NH
4
+
and NO
3
-
had no effect on the net photosynthesis of P. praetextata, while, in combination, they led to inhibition, although only at a concentration higher than that inhibitory to the C 2H 2 reduction of P. aphthosa. The photsynthesis was inhibited by all salts, but only initially, probably a salt effect. Effects of NH
4
+
on the membrane potential of the cyanobiont are suggested as an important factor causing the depression of net photosynthesis. 相似文献
8.
The photosynthetic properties of a range of lichens containing both green algal (11 species) and cyanobacterial (6 species) photobionts were examined with the aim of determining if there was clear evidence for the operation of a CO 2-concentrating mechanism (CCM) within the photobionts. Using a CO 2-gas-exchange system, which allowed resolution of fast transients, evidence was obtained for the existence of an inorganic carbon pool which accumulated in the light and was released in the dark. The pool was large (500–1000 nmol · mg Chl) in cyanobacterial lichens and about tenfold smaller in green algal lichens. In Hypogymnia physodes (L.) Nyl., which contains the green alga Trebouxia jamesii, a small inorganic carbon pool was rapidly formed in the light. Carbon dioxide was released from this pool into the gas phase upon darkening within about 20 s when photosynthesis was inhibited by the carbon-reduction-cycle inhibitor glycolaldehyde. In the absence of this inhibitor, release appeared to be obscured by carboxylation of ribulose bisphosphate. The kinetics of CO 2 uptake and release were monophasic. The operation of an active CCM could be distinguished from passive accumulation and release accompanying the reversible light-dependent alkalization of the stroma by the presence of saturation characteristics with respect to external CO 2. In Peltigera canina (L.) Willd., which contains the cyanobacterium Nostoc sp., a larger CO 2 pool was taken up over a longer period in the light and the release of this pool in the dark was slow, lasting 3–5 min. This pool also accumulated in the presence of glycolaldehyde, and under these conditions the CO 2 release was biphasic. In both species, photosynthesis at low CO 2 was inhibited by the carbonic-anhydrase inhibitor ethoxyzolamide (EZ). Inhibition could be reversed fully or to a considerable extent by high CO 2. In Peltigera, EZ decreased both the accumulation of the CO 2 pool by the CCM and the rate of photosynthesis. Free-living cultures of Nostoc sp. showed a similar effect of EZ on photosynthesis, although it was more dramatic than that seen with the lichen thalli. In contrast, in Hypogymnia, EZ actually increased the size of the CO 2 pool, although it inhibited photosynthesis. This effect was also seen when glycolaldehyde was present together with EZ. Surprisingly, EZ did not alter the kinetics of either CO 2 uptake or release. Taken together, the evidence indicates the operation in cyanobacterial lichens of a CCM which is capable of considerable elevation of internal CO 2 and is similar to that reported for free-living cyanobacteria. The CCM of green algal lichens accumulates much less CO 2 and is probably less effective than that which operates in cyanobacterial lichens. 相似文献
9.
The total resistances to CO 2 uptake by Sticta latifrons Rich, and Pseudocyphellaria amphisticta Kremp. were separated into transport and carboxylation components by calculation after transformation of net photosynthesis rate against CO 2 concentration curves into a linear form. The use of this technique circumvented the problem of measuring the internal CO 2 concentration of the lichen thalli. Both species exhibited an increase in transport resistance at high thallus water contents and an increase in both transport and carboxylation resistances at low water contents. At low and intermediate water contents internal transport resistances were larger than carboxylation resistances when measured at limiting CO 2 concentrations. However, at ambient CO 2 concentrations carboxylation processes were the dominant factors limiting photosynthesis at all, except the high, water contents. 相似文献
10.
Leaf gas exchange rates, predawn wp and daily minimum wm leaf water potentials were measured during a wet-to-dry season transition in pioneer ( Jacaranda copaia, Goupia glabra and Carapa guianensis) and late stage rainforest tree species ( Dicorynia guianensis and Eperua falcata) growing in common conditions in artificial stands in French Guiana. Carbon isotope discrimination () was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The values were 2.7 higher in the pioneer species than in the late stage species. The calculated time integrated C
i values derived from the values averaged 281 mol mol –1 in the pioneers and 240 mol mol –1 in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency [ratio CO 2 assimilation rate ( A)/leaf conductance ( g)] ranged from 37 to 47 mmol mol –1 in the pioneers and the values were 64 and 74 mmol mol –1 for the two late stage species. The high values were associated—at least in J. copaia—with high maximum g values and with high plant intrinsinc specific hydraulic conductance [Cg/( wm– wp], which could reflect a high competitive ability for water and nutrient uptake in the absence of soil drought in the pioneers. A further clear discriminating trait of the pioneer species was the very sensitive stomatal response to drought in the soil, which might be associated with a high vulnerability to cavitation in these species. From a methodological point of view, the results show the relevance of for distinguishing ecophysiological functional types among rainforest trees. 相似文献
11.
The temporal variations in CO 2, CH 4 and N 2O fluxes were measured over two consecutive years from February 2007 to March 2009 from a subtropical rainforest in south‐eastern Queensland, Australia, using an automated sampling system. A concurrent study using an additional 30 manual chambers examined the spatial variability of emissions distributed across three nearby remnant rainforest sites with similar vegetation and climatic conditions. Interannual variation in fluxes of all gases over the 2 years was minimal, despite large discrepancies in rainfall, whereas a pronounced seasonal variation could only be observed for CO 2 fluxes. High infiltration, drainage and subsequent high soil aeration under the rainforest limited N 2O loss while promoting substantial CH 4 uptake. The average annual N 2O loss of 0.5 ± 0.1 kg N 2O‐N ha ?1 over the 2‐year measurement period was at the lower end of reported fluxes from rainforest soils. The rainforest soil functioned as a sink for atmospheric CH 4 throughout the entire 2‐year period, despite periods of substantial rainfall. A clear linear correlation between soil moisture and CH 4 uptake was found. Rates of uptake ranged from greater than 15 g CH 4‐C ha ?1 day ?1 during extended dry periods to less than 2–5 g CH 4‐C ha ?1 day ?1 when soil water content was high. The calculated annual CH 4 uptake at the site was 3.65 kg CH 4‐C ha ?1 yr ?1. This is amongst the highest reported for rainforest systems, reiterating the ability of aerated subtropical rainforests to act as substantial sinks of CH 4. The spatial study showed N 2O fluxes almost eight times higher, and CH 4 uptake reduced by over one‐third, as clay content of the rainforest soil increased from 12% to more than 23%. This demonstrates that for some rainforest ecosystems, soil texture and related water infiltration and drainage capacity constraints may play a more important role in controlling fluxes than either vegetation or seasonal variability. 相似文献
12.
The gaseous exchange pathways of Sticla latifrons Rich. and Pseudocyphellaria amphisticta Kremp. were examined using both light and scanning electron microscopes. The size and frequency of the pores in the gas exchange structures (cyphellae and pseudocyphellae) and in the medulla were measured and from these CO 2 diffusion resistances were calculated. Pseudocyphellae were found to be smaller and more widely spaced than cyphellae, consequently the resistance of the pseudocyphellae, was much greater than that of the cyphellae. Medulla resistances were low in both lichens and are probably unimportant, even at high water contents. No evidence of hyphal swelling was found. Gas exchange structure resistances were more than five fold greater than medulla resistances. It is suggested that this arrangement of resistances may simultaneously encourage refixation of respired CO 2 and maintain a non desiccating environment for the lichen algae. The internal transport resistances calculated in this work approximate experimentally obtained values. 相似文献
13.
The effect of leaf dehydration on photosynthetic O 2 exchange of potato ( Solanum tuberosum L., cv. Haig) leaf discs was examined using 18O 2 as a tracer and mass spectrometry. In normal air (350 μl·l ?1CO 2) and under an irradiance of 390 μmol photons·m ?2·s 1, a relative water deficit (RWD) of about 30% severely decreased net O 2 evolution and increased O 2 uptake by about 50%, thus indicating an enhancement of photorespiration. Increasing CO 2 concentrations diminished O 2 uptake and stimulated net O 2 evolution both in well-hydrated and in dehydrated (RWD of about 30%) leaves. Much higher CO 2 concentrations (up to 4%) were required to observe a complete effect of CO 2 in dehydrated leaves. The chloroplastic CO 2 concentration at the ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) level (C c) was calculated from O 2-exchange data in both well-hydrated and dehydrated leaves, assuming that the specificity factor of Rubisco was unaffected by desiccation. When plotting net O 2 photosynthesis as a function of C c, a similar relationship was obtained for well-hydrated and waterstressed leaf discs, thus showing that the main effect of water deficit is a decrease of the chloroplastic CO 2 concentration. At saturating CO 2 levels, the non-cyclic electron-transport rate, measured either as gross O 2 photosynthesis or as the chlorophyll fluorescence ratio (F m -F s)/F m, was insensitive to water deficit, provided RWD was below 40%. In this range of RWD, the decrease in gross O 2 photosynthesis observed in normal air was attributed to the inability of oxidative processes to sustain the maximal electron-flow rate at low chloroplastic CO 2 concentration. The maximal efficiency of photosystem II, estimated as the chlorophyll fluorescence ratio (F m -F 0)/F m measured in dark-adapted leaves, was not affected by water deficits up to 60%. 相似文献
14.
Summary Different response patterns in net photosynthesis ( A) leaf conductance ( g) and water use efficiency (WUE= a/transpiration) in three subalpine plants occurred during experimental sun/shade transitions that simulated natural cloudcover. In Frasera speciosa Dougl., a large-leaved herb characteristic of open sites, g was relatively insensitive to transitions in irradiance and variations in A. However, large decreases in leaf temperature resulted in reduced transpiration during shade intervals and relatively constant WUE throughout the experimental sun/shade regime. In the understory herb, Arnica cordifolia Hook., patterns of A and g were similar during sun/shade transitions, but WUE was substantially reduced compared to steady-state levels. A third, somewhat intermediate pattern of A, g, and WUE was found in Artemisia tridentata L., an open site shrub. Higher intercellular CO 2 values in A. tridentata suggested that internal, cellular limitations to A were high relative to stomatal limitations in this shrub when compared to the herbaceous species. 相似文献
15.
Although the coastal zone of the Central Namib Desert (Namibia) has negligible rainfall, frequent fog, dew and high air humidity support a luxurious lichen flora. Large areas of soil crust communities are dominated by the multibranched, fruticose Teloschistes capensis interspersed by a (still indeterminable) Ramalina species. In earlier communications, based on field measurements in autumn, we began the analysis of functional mechanisms that allow these lichens to exist under the special conditions of a fog desert. We have extended this work by monitoring lichen CO 2 exchange and water relations in spring and by experiments under controlled conditions.In both seasons, nocturnal hydration, by fog and/or dew, activated dark respiration of the lichens which was followed, after sunrise, by a short period of positive net photosynthesis (NP) that continued until metabolic inactivation occurred from desiccation. Dry thalli of T. capensis were able to reactivate NP through water vapour uptake alone, beginning at an air relative humidity of 82%, i.e. at a water potential of −26.3 MPa; the moisture compensation point during desiccation was at 13% thallus water content (WC, dry weight related). Optimal WC for photosynthesis was around 100%, and both species showed a large and extended suprasaturation depression of CO 2 assimilation. Light response showed “sun-plant” characteristics with saturation >1000 μmol m −2 s −1 photosynthetically active photon flux density (PPFD). However, due to rapid desiccation, the combination of light saturation with optimal WC very rarely occurred under field conditions. Light compensation point after sunrise was highly dependent on actual WC: at low hydration, it amounted to only ca. 10 μmol m −2 s −1 PPFD so that even the smallest levels of hydration could be used for carbon gain before desiccation took place again. This phenomenon was probably due to a hydration gradient in the thallus branches during transient moistening so that the outer photobiont layer was favoured in contrast to the internal mycobiont which remained dry longer and did not contribute respiratory CO 2 loss. Fully hydrated thalli had light compensation points around 50 μmol m −2 s −1 PPFD. Extended desiccation of 1–3 days had no impact on the magnitude and recovery of photosynthesis but, imposed desiccation of 10 days reduced NP in lab and field experiments and caused an extended period of recovery. “Resaturation respiration” was not detected in the field data, although it was present after experimental moistening of dry thalli.In spring, the higher fog frequency and intensity increased maximal nocturnal WC, maximal attained NP as well as integrated daily carbon income (ΣNP) compared to the autumn measurements. NP max and ΣNP depended on maximal nocturnal WC with a saturation-type response. In terms of carbon gain both species seem to be optimally adapted to nocturnal moistening up to 160% WC and were not able to make use of higher degrees of hydration, a feature that might well influence their habitat selection.Maximal daily carbon-related ΣNP for T. capensis was 4.6 mg C (g C) −1 day −1. A rough estimate of the annual (projected) area-related carbon balance (photosynthetic income minus respiratory losses) based on published fog and dew frequencies and personal observations was 15–34 mg C m −2 yr −1. 相似文献
16.
We re-examined the question of whether the stomata limit photosynthesis in dehydrated sunflower ( Helianthus annuus L.) plants having low leaf water potentials. A gas-exchange apparatus was modified to operate at external CO 2 partial pressures as high as 3000 Pa (3%), which were much higher than previously achieved. This allowed photosynthesis and stomatal behavior to be monitored simultaneously at very high CO 2 in the same leaf. The data were compared with those from leaves treated with abscisic acid (ABA) where effects on photosynthesis are entirely stomatal. Photosynthesis was inhibited at low water potential and was only slightly enhanced by increasing the external CO 2 partial pressure from 34 Pa (normal air) to 300 Pa. Photosynthesis in ABA-treated leaves was similarly inhibited but recovered fully at 300 Pa. In both cases, the stomata closed to the same extent as judged from the average conductance of the leaves. Because the ABA effect resulted from diffusion limitation for CO 2 caused by stomatal closure, the contrasting data show that most of the dehydration effect was nonstomatal at low water potentials. When CO 2 partial pressures were raised further to 3000 Pa, photosynthesis increased somewhat at low water potentials but not in ABA-treated leaves. This indicates that some nonstomatal component of photosynthesis responded differently in leaves at low water potential and leaves treated with ABA. Because this component was only partially restored by very high CO 2, it was likely to be metabolic and was an important source of photosynthetic inhibition.Abbreviations and Symbol ABA
abscisic acid
- Chl
chlorophyll
- p a
external partial pressure of CO 2
- P i
intercellular partial pressure of CO 2
-
w
water potential
This work was supported by grant DE-FG02-87ER13776 from the Department of Energy and a grant from E.I. DuPont de Nemours and Company. 相似文献
17.
The physiology, morphology and growth of first-year Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. seedlings, which differ widely in reported successional affinity and shade tolerance, were compared in a controlled high-resource environment. Relative to late-successional, shade-tolerant Acer and Ostrya species, early-successional, shade-intolerant Betula species had high relative growth rates (RGR) and high rates of photosynthesis, nitrogen uptake and respiration when grown in high light. Fire-adapted Quercus rubra had intermediate photosynthetic rates, but had the lowest RGR and leaf area ratio and the highest root weight ratio of any species. Interspecific variation in RGR in high light was positively correlated with allocation to leaves and rates of photosynthesis and respiration, and negatively related to seed mass and leaf mass per unit area. Despite higher respiration rates, early-successional Betula papyrifera lost a lower percentage of daily photosynthetic CO 2 gain to respiration than other species in high light. A subset comprised of the three Betulaceae family members was also grown in low light. As in high light, low-light grown Betula species had higher growth rates than tolerant Ostrya virainiana. The rapid growth habit of sarly-successional species in low light was associated with a higher proportion of biomass distributed to leaves, lower leaf mass per unit area, a lower proportion of biomass in roots, and a greater height per unit stem mass. Variation in these traits is discussed in terms of reported species ecologies in a resource availability context. 相似文献
18.
Light and temperature-response curves and their resulting coefficients, obtained within ecophysiological characterization of gas exchanges at the leaf level, may represent useful criteria for breeding and cultivar selection and required tools for simulation models aimed at the prediction of potential plant behaviour in response to environmental conditions. Leaf-scale gas exchanges, by means of an IRGA open-flow system, were measured in response to light intensity (8 levels from 0 up to 2000 μmol m−2 s−1), CO2 concentrations (ambient—350 μmol mol−1 and short-term enriched—700 μmol mol−1) and air temperature (from 7 up to 35 °C) on three Vicia faba L. genotypes, each representing one of the three cultivated groups: major, equina and minor. The net assimilation rate response to light intensity was well described by an exponential rise to max function. The short-term CO2 enrichment markedly increased the values of light response curve parameters such as maximum photosynthetic rate (+80%), light saturation point (+40%) and quantum yield (+30%), while less homogenous behaviour was reported for dark respiration and light compensation point. For each light intensity level, the major and minor genotypes studied showed assimilation rates at least a 30% higher than equina. The positive effects of short-term CO2 enrichment on photosynthetic water use efficiency (WUE) indicate a relevant advantage in doubling CO2 concentration. In the major and minor genotypes studied, similar assimilation rates, but different WUE were observed. The optimum leaf temperature for assimilation process, calculated through a polynomial function, was 26–27 °C and no relevant limitations were observed in the range between 21 and 32 °C. Analysis at the single leaf level provided both rapid information on the variations in gas exchange in response to environmental factors and selection criteria for the screening of genotypes. 相似文献
19.
The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a standard time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO 2 pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO 2 uptake. Midday depression of CO 2 uptake is the result of i) a decrease in CO 2-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO 2 response curve (carboxylation efficiency), and iii) a substantial increase in the CO 2 compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO 2 pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO 2 may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.Abbreviations and symbols CE
carboxylation efficiency
- NP
net photosynthesis rate
- PAR
photosynthetically active radiation
- P i
leaf internal CO 2 partial pressure
- W
water vapor mole fraction difference between leaf and air
-
T
CO 2 compensation pressure
Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday 相似文献
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