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1.
The patterns of diurnal variations in pigmentation and optical cross-section were compared for two cyclostat cultures of Chlorella pyrenoidosa, where the dynamics of the photoperiod differed. Populations were light-limited, nutrient rich and growing on an 8:16 light-dark (LD) cycle. One light regime was an 8 h sine function of the light period (sinusoidal culture), while the second had an 1 h sine function super-imposed on the 8 hour sine function (oscillating sinusoidal culture). Hourly samples were taken throughout a 12 h period including the light period. Determinations were made of chlorophyll (Chl) a and b abundance, in vivo absorption spectra, cell number and volume and used to derive both cell-specific (cell) and optical chlorophyll specific (chl) cross sections, as well as the absorption efficiency, Q, of the cells. The results indicate that C. pyrenoidosa is capable of adapting to dynamics in light intensity within an 8 h photoperiod. The sinusoidal culture showed a constant decrease in the Chl a/b ratio of 28% while the total Chl content per cell increased slightly and chl and Q remained constant, suggesting coordinated changes in reaction centers and light harvesting complexes. Over the oscillating photoperiod, however, the second culture displayed a diurnal variation in Chl a/b ratio, a 20% increase in chl and an apparent oscillation in Q. These observations suggest that an oscillating photoperiod promoted the capability of Chl molecules to collect light and that the fractional area of all Chl molecules exposed to the photon flux is inversely related to the photon flux. 相似文献
2.
Growth and photosynthetic characteristics, P
max (maximum light-saturated oxygen production rate) and (photosynthetic affinity), of Microcystis aeruginosa were studied in continuous cultures under a range of photoperiod lengths and growth irradiances.
Microcystis showed a low specific maintenance rate constant and a high growth affinity for light (typical cyanobacterial features), but required a dark period to obtain maximum growth rate. P
max and per unit dry weight increased, as did pigment content, when less light became available. By regulation in and P
max (crucial in light-limiting and high-light conditions, respectively) this buoyant species can flourish in low light, but also in high-light environments which may arise when buoyancy is lost.The two different types of light conditions affected growth, and photosynthesis, in different ways. One needs thus to discriminate between photoperiod- and irradiance-limitation, which restricts the utility of simple algal growth models. It was emphasized that photosynthetic adaptation patterns of light-limited species may resemble short-term nutrient uptake kinetics of nutrient-limited organisms.With prior knowledge of the growth limitation, we were able to assess the growth rate of a natural population of Microcystis from its photosynthetic response and from data of laboratory cultures of a known physiological state. 相似文献
3.
The photosynthetic response of the purple sulfur bacterium Chromatium vinosum DSM 185 to different degrees of illumination was analyzed. The microorganism was grown in continuous culture, and samples
were taken from the effluent of the culture and incubated at different irradiances to determine the specific rate of sulfur
oxidation as a measure of the photosynthetic activity of the organism. The activities obtained were plotted as a function
of the specific rate of light uptake, and for each set of data a photosynthesis equation was fitted, which allowed the estimation
of P max (photosynthetic capacity), q k (the threshold irradiance for light limitation), and m (maintenance coefficient). The results indicated that cells grown
under light limitation are able to achieve higher photosynthetic activities than cells grown under light saturation. The photosynthetic
capacity (P max) remained constant under all the conditions of illumination tested, while the maintenance expenses (m) were higher under
light limitation. The parameter q k, on the contrary, decreased considerably at limiting irradiances.
Received: 16 January 1998 / Accepted: 7 September 1998 相似文献
4.
Summary The photosynthetic characteristics for the intertidal macroalga Ascophyllum nodosum were examined in air and water. Under ambient conditions of temperature (10° C) inorganic carbon concentrations (15.63 mmol CO 2 m -3 or 2.0 mol TIC m -3) and light (500 mol photons m -2 s -1) photosynthesis was slightly greater by the exposed alga than by the submerged alga. In both environments photosynthesis was light saturated at 200 mol photons m -2 s -1. The relationship between CO 2 concentration and photosynthesis in air could be accurately analysed using Michaelis-Menten kinetics, although the range of concentrations used were not saturating. In contrast the application of the Lineweaver-Burk and Woolf plots to aquatic photosynthesis was not suitable as the experimental data was similar to the Blackman type curves and not rectangular hyperbolae. This was reflected by the applicability of the Hill-Whittingham equation to describe the photosynthesis curves. The effect of unstirred layers and other limiting factors is discussed in relation to the kinetic parameters, V
max and K
m. 相似文献
5.
In outdoor thin-layer sloping reactors algae are batch cultured and harvested at biomass concentrations of about 15 g (dw) I -1 whereafter a portion is used as inoculum for the next cycle. Light saturation curves of the oxygen evolution (PII curves) of the algae were measured using diluted aliquots of suspension taken from the reactors. The maximum specific photosynthetic rates ( P
B
max) and the light intensity at the onset of saturated photosynthesis (I
k
) decreased whilst the maximum specific photosynthetic efficiency (
B
) increased with an increase in the biomass concentration, during the production cycle. These differences reflect transition from light- to dark-acclimated state of the algae that occurs as a result of an increase of the suspension concentration during the production cycle. During these experiments the thin-layered smooth sloping cultures (TLSS, culture depth 5–7 mm) had higher photosynthetic rates per volume than the thin-layered baffled sloping cultures (TLBS, culture depth 5–15 mm). This was ascribed to the higher P
B
max values of the algae grown in the TLSS cultures, allowing them to utilise high incident irradiancies more effectively. However, the areal productivity of the TLBS was higher than the TLSS indicating a higher photosynthetic efficiency of the TLBS reactors. The specific productivity decreased rapidly with an increase in the biomass concentration, but the yield remained linear during the batch production cycle, even at high areal densities. 相似文献
6.
Photosynthetic capacity and leaf properties of sun and shade leaves of overstorey sweetgum trees ( Liquidambar styraciflua L.) were compared over the first 3 years of growth in ambient or ambient + 200 μL L ?1 CO 2 at the Duke Forest Free Air CO 2 Enrichment (FACE) experiment. We were interested in whether photosynthetic down‐regulation to CO 2 occurred in sweetgum trees growing in a forest ecosystem, whether shade leaves down‐regulated to a greater extent than sun leaves, and if there was a seasonal component to photosynthetic down‐regulation. During June and September of each year, we measured net photosynthesis ( A) versus the calculated intercellular CO 2 concentration ( Ci) in situ and analysed these response curves using a biochemical model that described the limitations imposed by the amount and activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase ( Vcmax) and by the rate of ribulose‐1,5‐bisphosphate (RuBP) regeneration mediated by electron transport ( Jmax). There was no evidence of photosynthetic down‐regulation to CO 2 in either sun or shade leaves of sweetgum trees over the 3 years of measurements. Elevated CO 2 did not significantly affect Vcmax or Jmax. The ratio of Vcmax to Jmax was relatively constant, averaging 2·12, and was not affected by CO 2 treatment, position in the canopy, or measurement period. Furthermore, CO 2 enrichment did not affect leaf nitrogen per unit leaf area ( Na), chlorophyll or total non‐structural carbohydrates of sun or shade leaves. We did, however, find a strong relationship between Na and the modelled components of photosynthetic capacity, Vcmax and Jmax. Our data over the first 3 years of this experiment corroborate observations that trees rooted in the ground may not exhibit symptoms of photosynthetic down‐regulation as quickly as tree seedlings growing in pots. There was a strong sustained enhancement of photosynthesis by CO 2 enrichment whereby light‐saturated net photosynthesis of sun leaves was stimulated by 63% and light‐saturated net photosynthesis of shade leaves was stimulated by 48% when averaged over the 3 years. This study suggests that this CO 2 enhancement of photosynthesis will be sustained in the Duke Forest FACE experiment as long as soil N availability keeps pace with photosynthetic and growth processes. 相似文献
7.
Electron flow around photosystem II was investigated in Chlorella pyrenoidosa. Using a bare platinum O 2 electrode, simultaneous measuremnts were made of steady-state photosynthesis in continuous light, the yield of oxygen (Y o2) produced by a superimposed saturating xenon flash, and the change in fluorescence yield of a weak flash triggered before and 70 microseconds after the saturating flash. Throughout most of the continuous photosynthesis-irradiance curve, normalized O 2 flash yields (Y o2/Y o2max) and normalized variable fluorescence yields (Δ/Δ′) were linearly correlated with a slope of 1.0. As photosynthetic rates reached light saturation, however, the variable fluorescence yields remained relatively constant while O 2 flash yields decreased. These results strongly suggest that there is a cyclic electron flow around photosystem II in unpoisoned intact cells at light saturation and supraoptimal light intensities. 相似文献
8.
The photosynthetic characteristics of the Cymbidium plantlet in vitro cultured on Hyponex-agar medium with 2% sucrose were determined based on the measurements of CO 2 concentration inside and outside of the culture vessels. The CO 2 measurements were made with a gas chromatograph at a PPF (photosynthetic photon flux) of 35, 102 and 226 mol m -2 s -1, a chamber air temperature of 15, 25 and 35°C and a CO 2 concentration outside the vessel of approximately 350, 1100 and 3000 ppm. The net photosynthetic rates were determined on individual plantlets and were expressed on a dry weight basis. The steady-state CO 2 concentration during the photoperiod was lower inside the vessel than outside the vessel at any PPF greater than 35 mol m -2s -1 and at any chamber air temperature. The photosynthetic response curves relating the net photosynthetic rate, PPF, and CO 2 concentration in the vessel and chamber air temperature were similar to those for Cymbidium plants grown outside and other C 3 plants grown outside under shade. The results indicate that CO 2 enrichment for the plantlets in vitro at a relatively high PPF would promote photosynthesis and hence the growth of chlorophyllous shoots/plantlets in vitro and that the plantlets in vitro would make photoautotrophic growth under environmental conditions favorable for photosynthesis.Abbreviations C in
CO 2 concentration in the culture vessel
- C out
CO 2 concentration outside the vessel (in the culture room)
- PPF
photosynthetic photon flux 相似文献
9.
Chlorella pyrenoidosa was grown in three continuous cultures each receiving a different light regime during the light period of a diurnal cycle. Hourly samples taken during the light period were subjected to medium frequency light/dark oscillations of equal duration, ranging from 3 to 240 seconds. The oxygen consumption and production of each sample were measured with an oxygen electrode in a small oxygen chamber. Although the light/dark cycles had little overall influence on photosynthetic activity, the microalgae appeared to adapt to the light regime to which they were subjected. Large differences were found between the maximum chlorophyll-specific production rates (P
infmax
supB
), the chlorophyll-specific production rates (P B) and the respiration rates between the cultures and treated subsamples. Respiration rates increased during the light period, whilst P B either increased, or had a mid light period minimum or maximum. The culture which received an hourly light oscillation during the light period had the highest P
infmax
supB
and lowest respiration rates, and it is suggested that these algae react as in nature, whereas either a sinusoidal or a block light pattern is unnatural. The latter light regime is commonly used in laboratory studies. 相似文献
10.
SUMMARY. - 1 The macrophyte community of Lake George, New York is diverse, composing of forty-eight submersed species representing a wide range of habitats, depth ranges and life-history strategies. The photosynthetic rates of seven representative submersed aquatic macrophytes were determined in laboratory studies using measurements of short-term changes in oxygen concentration at eight light intensities from 0 to 1000 μmol m?2 s?1 at 20°C. The species examined were: Elodea canadensis, Myriophyllum spicatum, Potamogeton amplifolius, P. gramineus, P. praelongus, P. robbinsii, and Vallisneria americana.
- 2 Comparisons of maximum net photosynthesis, Michaelis–Menten Vmax and Km for photosynthesis versus irradiance, and dark respiration rates correlated with changes in community composition and species distribution with depth.
- 3 In particular, Myriophyllum spicatum exhibited a high photosynthetic rate (Vmax) and high light requirement (both in compensation point and higher half-saturation constant (Km) indicative of a high light-adapted species. In contrast, the native species exhibited shade-tolerant characteristics.
- 4 Simple daily carbon balance models indicate that M. spicatum has a higher positive carbon balance near the surface than the native species, but carbon balance decreased more rapidly with decreased light. All species showed greatly reduced carbon balances under a simulated M. spicatum canopy, indicating that native species might not survive. Myriopyllum spicatum leaves would experience self-shading and eventual sloughing.
相似文献
11.
Anabaena sp., isolated from a rice paddy, was investigated for its nitrogen fixation as measured by acetylene reduction activity (ARA)
in P-limited continuous and light-limited semi-continuous cultures. Growth rate (μ) under P limitation was a function of cell
P content ( q
p). Both the photosynthetic capacity (P max) and photosynthetic efficiency (α) increased with μ when expressed per cell, but not per unit chl a. The ARA of steady-state cells under P limitation increased with μ and was linearly related to C-fixation rate. This was
apparently a consequence of the control of C-fixation by P limitation. In light-limited cells, steady state ARA, both at the
culture light intensity and in the dark, increased asymptotically with μ, but the activity in the dark was only about 51%
of that in the light. When the light level of steady-state cells grown at a high in intensity was switched to a low level,
ARA decreased exponentially with time. Dark ARA activity also showed a similar decline, but at much lower levels. Thus, ARA
depended not only on light history, but also immediate photosynthesis. Steady-state ARA at the ambient intensity or in the
dark showed a strong correlation with 14C-fixation rate. ARA of light-limited cells showed the same light-saturation characteristics as their 14C-fixation, with the same initial saturation intensity, I
k. The ratios of P max to the maximum ARA (ARA max), and α to the slope of ARA (α ara) were identical. A comparison of gross to net photosynthesis and N 2 fixation suggested that there was little leakage or excretion of fixed C or N. 相似文献
12.
Irradiance continuously fluctuates during the day in the field. The speed of the induction response of photosynthesis in high light affects the cumulative carbon gain of the plant and could impact growth and yield. The photosynthetic induction response and its relationship with the photosynthetic capacity under steady-state conditions ( P max) were evaluated in 37 diverse soybean [ Glycine max (L.) Merr.] genotypes. The induction response of leaf photosynthesis showed large variation among the soybean genotypes. After 5 min illumination with strong light, genotype NAM23 had the highest leaf photosynthetic rate of 33.8 µmol CO 2 m ?2 s ?1, while genotype NAM12 showed the lowest rate at 4.7 µmol CO 2 m ?2 s ?1. Cumulative CO 2 fixation (CCF) during the first 5 min of high light exposure ranged from 5.5 mmol CO 2 m ?2 for NAM23 to 0.81 mmol CO 2 m ?2 for NAM12. The difference in the induction response among genotypes was consistent throughout the growth season. However, there was no significant correlation between CCF and P max among genotypes suggesting that different mechanisms regulate P max and the induction response. The observed variation in the induction response was mainly attributed to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activation, but soybean lines differing in the induction response did not differ in the leaf content of Rubisco activase α- and β-proteins. Future studies will be focused on identifying molecular determinants of the photosynthetic induction response and determining whether this trait could be an important breeding target to achieve improved growth of soybeans in the field. 相似文献
13.
Summary
Abies nordmanniana (Stev.) Spach was cultivated in rooting media either rich in nutrients (control) or low in magnesium (low Mg) or low in magnesium and nitrogen (low Mg-N), respectively. Intact, attached needles were exposed, in the light (460 mol photons m -2 s -1), to an atmosphere containing 1 ppm SO 2 for 5 h. Measurements of light- and CO 2-saturated rates of photosynthetic O 2 evolution, A
max, were performed before and after SO 2 treatments. In needles from well fertilized plants, A
max was high (about 50 mol m -2 s -1) and was not affected by SO 2. Needles from low-Mg and low-Mg-N plants had lower photosynthetic rates and showed a marked decline in A
max in response to the SO 2 treatment. Stomatal conductance was similar in the three groups of plants during SO 2 treatments.Abbreviations
A
max
photosynthetic capacity (CO 2- and light-saturated rate of O 2 evolution)
- DW
dry weight
- F o
yield of dark level fluorescence
- F M
maximum yield of fluorescence, induced in a pulse of saturating light
- F v
yield of variable fluorescence (= F M–F O)
- FW
fresh weight; g, conductance to water vapor transfer 相似文献
14.
Calcifying coralline algae are functionally important in many ecosystems but their existence is now threatened by global climate change. The aim of this study is to improve our understanding of coralline algal metabolic functions and their interactions by assessing the respiration, photosynthesis and calcification rates in an articulated (geniculate) coralline alga, Ellisolandia elongata. Algal samples selected for this case study were collected from an intertidal rock-pool on the coast of Brittany (France). Physiological rates were assessed in summer and winter by measuring the concentration of oxygen, dissolved inorganic carbon and total alkalinity fluxes at five irradiance levels and in the dark using incubation chambers. Respiration, photosynthetic and calcification rates were strongly affected by seasonal changes. Respiration increased with temperature, being ten-fold higher in summer than in winter. Photosynthetic parameters of the photosynthesis-irradiance (P-E) curve, Pgmax, Pnmax and Ek, were two- to three-fold higher in summer relative to winter. Photoinhibition was observed under high irradiance indicating an acclimation of E. elongata to low irradiance levels. Parameters of the calcification-irradiance (G-E) curve, Gmax and Ek, were approximately two-fold higher in summer compared with winter. In summer, calcification rates were more strongly inhibited under high irradiance than photosynthetic rates, suggesting a dynamic relationship between these metabolic processes. By inhabiting intertidal rock pools, E. elongata exhibits tolerance to a dynamic physico-chemical environment. Information on respiration, photosynthesis and calcification rates in a calcifying coralline alga inhabiting such dynamic environments in terms of pH and temperature is important in order to better understand how ocean acidification and warming will affect coralline algae in the future. 相似文献
15.
A dependence of the photosynthesis rate on light is characterized by a number of parameters that are often used for comparison between plant species or for finding photosynthesis interconnections with other physiological processes. In order to properly assessed these parameters, we measured the maximum apparent photosynthesis rate ( P max), dark respiration rate ( R d), light compensation point (LCP), quantum yield corresponding to photosynthetic efficiency (QY), and the light saturation constant ( K s), taking into consideration the leaf plastochron index during vegetation of one of the willow species ( Salix dasyclados Wimn.). The P max value was the highest in the beginning of the growth season when the leaf reached 65% of its full area; after that P max slowly declined. The most important cardinal value for R d is its plateau reached by the end of leaf growth, i.e., later than the photosynthesis rate maximum. This plateau value also decreased during vegetation. The LCP value changed in the same way as R d but reached its plateau simultaneously with the photosynthesis rate maximum. QY also reached its maximum at the same time with the photosynthesis rate; during vegetation it changed more than twofold. The K s value also changed almost twofold during the season, reaching its maximum together or slightly later than the photosynthesis maximum and then remained constant. Thus, we have found significant changes in the parameters of the photosynthesis light curve during growth season. This shows that they can be used only after a thorough study of leaf development in each particular plant species. Usually performed measuring gas exchange parameters in fully developed leaves does not yield their maximum values and thus does not have any physiological sense. 相似文献
16.
In this paper, photosynthetic characteristics of green leaves (GL) and green pseudobulbs (GPSB) of C 3 orchid Oncidium Golden Wish were first studied. Light saturation for photosynthesis and maximum photosynthetic rates ( P
max) were significantly higher in GL than in GPSB. The results of the optimal PSII quantum yield (F v/F m ratio), electron transport rate (ETR), the effective photochemical quantum yield (ΔF/F m′) and nonphotochemical quenching (NPQ) of Chl fluorescence revealed that GPSB had lower light utilization than that of GL.
Significantly higher photosynthetic pigments were found in GL than in GPSB. Alteration of source/sink ratio had no impact
on all photosynthetic parameters for both GL and GPSB after a short term of 3 days or even a long term of 2 weeks of treatments
although there were significant decreases in GL carbohydrate concentration of GL-darkened plants by the end of the day. However,
decreases of all photosynthetic parameters of GL were observed in GL-darkened plants after 4 weeks of treatment compared to
those of fully illuminated (FI) and GPSB-darkened plants. These results indicate that the level of carbohydrates in GL plays
an important role in regulating their photosynthesis. Due to their lower photosynthetic capacities, GPSB function mainly as
sinks. Darkening GPSB up to 2 weeks did not affect their own P
max and the P
max of GL and thus, did not result in significant decreases of total carbohydrate concentration of GPSB. As GPSB store a large
amount of carbohydrates, it could also act as a source when the level of carbohydrates decreased. Thus, GL could depend on
GPSB carbohydrates to regulate their photosynthesis when their source capacity was removed. However, 4 weeks after treatments,
photosynthetic capacities of GL were significantly lower in GL- and GPSB-darkened plants than in FI plants, which could be
due to the lower total soluble and insoluble sugar concentrations of both GL and GPSB in these plants. 相似文献
17.
The primary production of Ulva populations relies on their photosynthetic performance, which is dependent on the light availability under natural conditions. This study concerns the light attenuation characteristics in Ulva canopies and the seasonal photosynthetic performance of two different species ( Ulva rotundata Blid., Ulva curvata (Kütz.) De Toni) blooming in the Palmones river estuary. Light within canopies differed from that reaching the surface. Light availability was reduced through the water column (at high tide) and Ulva canopies. In addition, light was spectrally filtered. As a result, the photosynthetically usable radiation (PUR) was further attenuated through Ulva canopies, increasing the photosynthetically active radiation/PUR ratio. The muddy sediment deposited on and between the Ulva thalli also drastically restricted the light availability. Thick Ulva mats are frequently found covering the intertidal mudflats, and therefore, thalli within these mats may be subjected to steep light gradients. As a consequence, individual Ulva growth rates cannot be extrapolated to estimate the primary production of Ulva canopies. Interspecific differences were observed for light-saturated photosynthetic rates (P max) and light compensation points (L CP), with Ulva curvata generally displaying higher values than did U. rotundata. For both species, maxima were recorded in winter for P max, quantum yield, chlorophyll content, and absorptance, whereas minima were found in summer. Dark respiration (R d) was not seasonally affected, and a maximum L CP was found in summer. To extrapolate these data to field situations, the temperature dependence of photosynthesis should be considered. The Q 10 values were 2.44 for R d and 1.79 for P max, whereas the photosynthesis rate at subsaturating light levels was unaffected. The Q 10 values showed an enhanced respiratory rate in summer and a minimum in winter, whereas the seasonal differences on P max were damped. 相似文献
18.
Young sporophytes of short-stipe ecotype of Ecklonia cavafrom a warmer locality (Tei, Kochi Pref., southern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the transplanted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were assessed per unit area, per unit chlorophyll acontent and per unit dry weight. In photosynthesis-light curves at 10–29 °C, light saturation occurred at 200–400 mol photon m –2s –1in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate ( P
max) at 10–29 °C and the light-saturation index ( I
k) at 25–29 °C in sporophytes from both localities were generally higher in winter than in summer. P
maxat 25–29 °C (per unit area and chlorophyll a) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 °C in winter and 27 °C in summer at high light intensities of 100–400 mol photon m –2s –1. However, at lower light intensities of 12.5–50 mol photon m –2s –1, it was 20 °C in winter and 25–27 °C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 °C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation. 相似文献
19.
Inorganic phosphorus (P i) and carbon (here, CO 2) potentially limit the photosynthesis of phytoplankton simultaneously (colimitation). A single P i limitation generally reduces photosynthesis, but the effect of a colimitation is not known. Therefore, photosynthesis was measured under P i‐limited conditions and high and low CO 2, and osmo‐mixotrophic (i.e., growth in the presence of glucose) conditions that result in colimiting conditions in some cases. The green alga Chlamydomonas acidophila Negoro was used as a model organism because low P i and CO 2 concentrations likely influence its photosynthetic rates in its natural environment. Results showed a decreasing maximum photosynthetic rate ( Pmax) and maximum quantum yield (Φ II) with increasing P i limitation. In addition, a P i limitation enhanced the relative contribution of dark respiration to Pmax ( Rd: Pmax) but did not influence the compensation light intensity. Pmax positively correlated with the cellular RUBISCO content. Osmo‐mixotrophic conditions resulted in similar Pmax, Φ II, and RUBISCO content as in high‐CO 2 cultures. The low‐CO 2 cultures were colimited by P i and CO 2 and had the highest Pmax, Φ II, and RUBISCO content. Colimiting conditions for P i and CO 2 in C. acidophila resulted in an enhanced mismatch between photosynthesis and growth rates compared to the effect of a single P i limitation. Primary productivity of colimited phytoplankton could thus be misinterpreted. 相似文献
20.
We investigated to what extent south-exposed leaves (E-leaves) of the evergreen ivy ( Hedera helix L.) growing in the shadow of two deciduous trees suffered from photoinhibition of photosynthesis when leaf-shedding started in autumn. Since air temperatures drop concomitantly with increase in light levels, changes in photosynthetic parameters (apparent quantum yield,
i and maximal photosynthetic capacity of O 2 evolution, P max; chlorophyll-a fluorescence at room temperature) as well as pigment composition were compared with those in north-exposed leaves of the same clone (N-leaves; photosynthetic photon flux density PPFD< 100 mol · m –2 · s –2) and phenotypic sun leaves (S-leaves; PPFD up to 2000 mol · m –2 · s –1).In leaves exposed to drastic light changes during winter (E-leaves) strong photoinhibition of photosynthesis could be observed as soon as the incident PPFD increased in autumn. In contrast, in N-leaves the ratio of variable fluorescence to maximum fluorescence (F V/F Mm) and
i did not decline appreciably prior to severe frosts (up to -12° C) in January. At this time,
i was reduced to a similar extent in all leaves, from about 0.073 mol O 2 · mol –1 photons before stress to about 0.020. Changes in
i were linearly correlated with changes in f v/f m ( r = 0.955). The strong reduction in F V/F M on exposure to stress was caused by quenching in F M. The initial fluorescence (F 0), however, was also quenched in all leaves. The diminished fluorescence yield was accompanied by an increase in zeaxanthin content. These effects indicate that winter stress in ivy primarily induces an increase in non-radiative energy-dissipation followed by photoinhibitory damage of PSII. Although a pronounced photooxidative bleaching of chloroplast pigments occurred in January (especially in E-leaves), photosynthetic parameters recovered completely in spring. Thus, the reduction in potential photosynthetic yield in winter may be up to three times greater in leaves subjected to increasing light levels than in leaves not exposed to a changing light environment.Abbreviations and Symbols F 0, F M
initial and maximal fluorescence yield when all PSII centres are open and closed
- F V
variable fluorescence (F M-F 0)
- P max
maximal photosynthetic capacity at 1000 umol · m –2 · s –1 PPFD and CO 2 saturation
- PPFD
photosynthetic photon flux density
-
i
apparent quantum yield of photosynthetic O 2 evolution
- E-leaves, N-leaves
shade leaves exposed, not exposed to drastic light changes during winter
- S-leaves
sun leaves from an open ivy stand
Dedicated to Professor Otto Härtel on the occasion of his 80th birthdayThis work was supported by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung. 相似文献
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