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1.
Summary Gas exchange patterns, diurnal malic acid fluctuations, and stable carbon isotope ratios of five species of Sedum were investigated to assess the ecophysiological characteristics of three different photosynthetic pathways under well-watered and drought-stressed conditions. All five species have succulent leaves and stems and were examined under identical environmental conditions. When well-watered, Sedum integrifolium (Raf.) Nels. and S. ternatum Michx. displayed C3 photosynthesis, S. telephioides Michx. and S. nuttallianum Raf. exhibited CAM-cycling, and S. wrightii A. Gray showed CAM. When grown under a less frequent watering regime, S. integrifolium and S. ternatum exhibited CAM-cycling, whereas S. telephioides and S. nuttallianum displayed CAM-cycling simultaneously with low-level CAM. Sedum wrightii retained its CAM mode of photosynthesis. In general, leaf 13C values reflected these variations in photosynthetic pathways. While all values of water-use efficiency (WUE) were greater than those reported for most C3 and C4 species, no correlation of malic acid accumulation in the CAM and CAM-cycling (including low-level CAM) species with increased WUE was found. Sedum wrightii (CAM) had the highest WUE value at night, yet its 24-h WUE was not different from S. ternatum when the latter was in the C3 mode. Thus, relative water-use efficiencies of these species of Sedum were not predictable based on photosynthetic pathways alone.  相似文献   

2.
Under well-watered conditions in the laboratory, Sedum pulchellum assimilated CO2 only during the day, yet exhibited small nocturnal increases in tissue acid content followed by deacidification in the light (CAM-cycling). When drought-stressed, little CO2 was fixed in the day and none at night, yet even greater acid fluctuations were observed (CAM-idling). Calculations indicate that water savings associated with CAM-cycling when water is available are small. Water saving is more likely to be significant during CAM-idling when water supply is limited and stomata are closed day and night. Thus, in this species, CAM-idling may be of greater benefit to the plant, relative to CAM-cycling, in surviving habitats prone to frequent drought stress.Abbreviations A CO2 exchange rate - CAM Crassulacean acid metabolism - ci shoot internal CO2 concentration - gc shoot conductance to CO2 - PPFD photosynthetic photon flux density - WUE water-use efficiency Supported by National Science Foundation Grant No. DMB 8506093.  相似文献   

3.
Summary The degree of CAM-cycling was examined in plants from 23 populations representing five morphologically similar species of Talinum to determine how CAM-cycling correlates with site aridity and drought stress. In the field, CAM-cycling, as indicated by the amount of malic acid accumulated in plant tissues overnight, and stable carbon isotope ratio (13C) were positively correlated with an index of site aridity. The relative levels of CAM-cycling and 13C values among populations in the field reversed when plants were grown under less arid conditions in a growth chamber such that populations with the highest average CAM-cycling and 13C in the field had the lowest averages in the growth chamber. In both cases, plants from all populations showed significantly higher levels of CAM-cycling under drought-stressed conditions relative to conditions known or predicted to be less arid. CAM-cycling was also positively correlated with tissue water content in both well-watered and drought-stressed plants, possibly reflecting greater water conservation associated with reductions in stomatal conductance. Biomass accumulation in plants exhibiting the greatest degree of CAM-cycling in the growth chamber was suppressed by drought stress to a similar degree as in the other plants, yet reproductive biomass of these plants was inhibited to a smaller degree. Thus, the importance of CAM-cycling increases in these species of Talinum during drought stress, due to increased malic acid accumulation overnight, potentially enhancing their water status, survival, and reproduction.  相似文献   

4.
Summary The effects of irradiance during growth on biomass allocation, growth rates, leaf chlorophyll and protein contents, and on gas exchange responses to irradiance and CO2 partial pressures of the evergreen, sclerophyllous, chaparral shrub, Ceanothus megacarpus were determined. Plants were grown at 4 irradiances for the growth experiments, 8, 17, 25, 41 nE cm-2 sec-1, and at 2 irradiances, 9 and 50 nE cm-2 sec-1, for the other comparisons.At higher irradiances root/shoot ratios were somewhat greater and specific leaf weights were much greater, while leaf area ratios were much lower and leaf weight ratios were slightly lower than at lower irradiances. Relative growth rates increased with increasing irradiance up to 25 nE cm-2 sec-1 and then leveled off, while unit leaf area rates increased steeply and unit leaf weight rates increased more gradually up to the highest growth irradiance.Leaves grown at 9 nE cm-2 sec-1 had less total chlorophyll per unit leaf area and more per unit leaf weight than those grown at 50 nE cm-2 sec-1. In a reverse of what is commonly found, low irradiance grown leaves had significantly higher chlorophyll a/b than high irradiance grown leaves. High irradiance grown leaves had much more total soluble protein per unit leaf area and per unit dry weight, and they had much higher soluble protein/chlorophyll than low irradiance grown leaves.High irradiance grown leaves had higher rates of respiration in very dim light, required higher irradiances for photosynthetic saturation and had higher irradiance saturated rates of photosynthesis than low irradiance grown leaves. CO2 compensation irradiances for leaves of both treatments were very low, <5 nE cm-2 sec-1. Leaves grown under low and those grown under high irradiances reached 95% of their saturated photosynthetic rates at 65 and 85 nE cm-2 sec-1, respectively. Irradiance saturated rates of photosynthesis were high compared to other chaparral shrubs, 1.3 for low and 1.9 nmol CO2 cm-2 sec-1 for high irradiance grown leaves. A very unusual finding was that leaf conductances to H2O were significantly lower in the high irradiance grown leaves than in the low irradiance grown leaves. This, plus the differences in photosynthetic rates, resulted in higher water use efficiencies by the high irradiance grown leaves. High irradiance grown leaves had higher rates of photosynthesis at any particular intercellular CO2 partial pressure and also responded more steeply to increasing CO2 partial pressure than did low irradiance grown leaves. Leaves from both treatments showed reduced photosynthetic capability after being subjected to low CO2 partial pressures (100 bars) under high irradiances. This treatment was more detrimental to leaves grown under low irradiances.The ecological implications of these findings are discussed in terms of chaparral shrub community structure. We suggest that light availability may be an important determinant of chaparral community structure through its effects on water use efficiencies rather than on net carbon gain.  相似文献   

5.
Kurasová  I.  Čajánek  M.  Kalina  J.  Špunda  V. 《Photosynthetica》2000,38(4):513-519
The adaptation of barley (Hordeum vulgare L. cv. Akcent) plants to low (LI, 50 µmol m–2 s–1) and high (HI, 1000 µmol m–2 s–1) growth irradiances was studied using the simultaneous measurements of the photosynthetic oxygen evolution and chlorophyll a (Chl a) fluorescence at room temperature. If measured under ambient CO2 concentration, neither increase of the oxygen evolution rate (P) nor enhancement of non-radiative dissipation of the absorbed excitation energy within photosystem 2 (PS2) (determined as non-photochemical quenching of Chl a fluorescence, NPQ) were observed for HI plants compared with LI plants. Nevertheless, the HI plants exhibited a significantly higher proportion of QA in oxidised state (estimated from photochemical quenching of Chl a fluorescence, qP), by 49–102 % at irradiances above 200 µmol m–2 s–1 and an about 1.5 fold increase of irradiance-saturated PS2 electron transport rate (ETR) as compared to LI plants. At high CO2 concentration the degree of P stimulation was approximately three times higher for HI than for LI plants, and the irradiance-saturated P values at irradiances of 2 440 and 2 900 µmol m–2 s–1 were by 130 and 150 % higher for HI plants than for LI plants. We suggest that non-assimilatory electron transport dominates in the adaptation of the photosynthetic apparatus of barley grown at high irradiances under ambient CO2 rather than an increased NPQ or an enhancement of irradiance-saturated photosynthesis.  相似文献   

6.
Due to their rapid growth and nutrient assimilation,Porphyra spp. are good candidates for bioremediation and polyculture. The production potential of two strains of P. purpurea and P. umbilicalis from north-east USA was evaluated by measuring rates of photosynthesis (as O2evolution) of material grown at 20 °C. Photosynthetic rates of P. umbilicalis were 80%higher than P. purpurea over the temperature range 5–20 °C, at both sub-saturating andsaturating irradiances (37 and 289 μmol photonm-2 s-1). Porphyra umbilicalis was more efficient at low irradiances (higher α) and had a higher Pmax (23.0 vs 15.6 μmolO2 g-1 DW min-1) than P.purpurea, suggesting that P. umbilicalis is a better choice for mass culture, where self-shading maybe severe. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

7.
The relationship between O2-based gross photosynthesis (GP) and in vivo chlorophyll fluorescence of Photosystem II-based electron transport rate (ETR) as well as the relationship between effective quantum yield of fluorescence (ΦPSII) and quantum yield of oxygen evolution (ΦO_2) were examined in the green algae Ulva rotundata and Ulva olivascens and the red alga Porphyra leucosticta collected from the field and incubated for 3 days at 100 μmol m−2 s−1 in nutrient enriched seawater. Maximal GP was twice as high in Ulva species than that measured in P. leucosticta. In all species ETR was saturated at much higher irradiance than GP. The initial slope of ETR versus absorbed irradiance was higher than that of GP versus absorbed irradiance. Only under absorbed irradiances below saturation or at values of GP <2 μmol O2 m−2 s−1 a linear relationship was observed. In the linear phase, calculated O2 evolved /ETR molar ratios were closed to the theoretical value of 0.25 in Ulva species. In P. leucosticta, the estimated GP was associated to the estimated ETR only at high irradiances. ETR was determined under white light, red light emitting by diodes and solar radiation. In Ulva species the maximal ETR was reached under red light and solar radiation whereas in P. leucosticta the maximal ETR was reached under white light and minimal under red light. These results are in agreement with the known action spectra for photosynthesis in these species. In the case of P. leucosticta, GP and ETR were additionally determined under saturating irradiance in algae pre-incubated for one week under white light at different irradiances and at white light (100 μmol m−2 s−1) enriched with far-red light. GP and growth rate increased at a growth irradiance of 500 μmol m−2 s−1 becoming photoinhibited at higher irradiances, while ETR increased when algae were exposed to the highest growth irradiance applied (2000 μmol m−2 s−1). The calculated O2 evolved /ETR molar ratios were close to the theoretical value of 0.25 when algae were pre-incubated under 500–1000 μmol m−2 s−1. The enrichment by FR light provoked a decrease in both GP and ETR and an increase of nonphotochemical quenching although the irradiance of PAR was maintained at a constant level. In addition to C assimilation, other electron sinks, such as nitrogen assimilation, affected the GP–ETR relationship. The slopes of GP versus ETR or ΦPSII versus ΦO_2 were lower in the algae with the highest N assimilation capacity, estimated as nitrate reductase activity and internal nitrogen contents, i.e., Ulva rotundata and Porphyra leucosticta, than that observed in U. olivascens. The possible mechanisms to explain this discrepancy between GP and ETR are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

8.
Water stress and root formation in pea cuttings   总被引:1,自引:0,他引:1  
The stock plants of pea (Pistum sativium L. cv. Alaska) grown for 11 days at 16 W m?2 38 W m?2 were subjected to different degrees of moisture stress, simulated with polyethyleneglycol (PEG, 6000) for different periods. The cuttings were made at the end of stress treatments, planted in perlite and allowed to root in a mist propagation chamber. The number of adventitious roots formed on the cuttings from non-stressed plants was significantly higher under low (16 W m?2) than under high (38 W m?2) irradiance. However, under the influence of short duration stress the number of roots increased significantly under high but not under low irradiance. There was significantly poor rooting after prolonged stress under both irradiances. The leaf osmotic potential ψπ showed a greater reduction with increasing degree and duration of stress at 38 W m?2 than at 16 W m?2. The differential rooting behaviour as a result of stress levels and irradiances is discussed in the light of available literature on adventitious root formation.  相似文献   

9.
14CO2 was applied repeatedly at 3- to 6-h intervals toKalanchoë daigremontiana leaves during continuous light of differing irradiances. The circadian rhythm in net CO2 uptake in gasexchange measurements and its disappearance at high irradiances was confirmed by oscillating rates of14CO2 incorporation. At 10–30 W m-2 a markedly circadian oscillation in the14CO2-uptake rate was measured; with increasing energy fluence rate the oscillation levelled off at a constant high uptake rate. The labelling patterns obtained during the 10 min of14CO2 fixation indicated that the rhythm of CO2 exchange is the consequence of a rhythmic behaviour in the C4 pathway of CO2 fixation. During the mininum of14CO2 uptake no C4 products were labelled; however, substantial amounts of label were transferred to C4 products during the peaks of14CO2 uptake. Metabolism of C3 and C4 products was also studied in pulsechase experiments at different points of the circadian cycle. In bright light (100 W m-2), when the14CO2 uptake was constantly high, the transfer of label into C4 products (malic acid) was high in spite of the fact that the malate pool is known to be reduced to a permanently low level under these conditions. This led us to the conclusion that it is not the capacity of the phosphoenolpyruvatecarboxylase-mediated CO2 fixation but rather the storage of malic acid in the vacuole that is disturbed under bright-light conditions when the circadian oscillation levelled off.Abbreviations CAM Crassulacean acid metabolism - LL continuous light - PEP phosphoenolpyruvate  相似文献   

10.
Batch cultures of the green microalga Chlorella vulgaris and cyanobacterium Planktothrix isothrix and their corresponding co-cultures were grown in municipal wastewater in order to study their growth as well as the nitrogen (NH4–N) and phosphorus (PO43−–P) removal. The cultures were grown under two irradiances of 20 and 60 μmol photons m−2 s−1 in shaken and unshaken conditions. The co-culture of unshaken Chlorella and Planktothrix showed the greatest growth under both irradiances. The monoalgal Planktotrix cultures showed better growth when unshaken than when shaken, whereas Chlorella cultures grew better when mixed, but only at the higher irradiance. The highest percentage of nitrogen removal (up to 80%) was attained by the unshaken co-cultures of Chlorella and Planktothrix. The amount of nitrogen recycled in the biomass reached up to 85% of that removed. Shaken monoalgal cultures of Chlorella showed phosphorus removal under both irradiances. They completely removed the initial phosphorus concentration (7.47 ± 0.17 mg L−1) within 96 and 48 h under 20 and 60 μmol photons m−2 s−1, respectively.  相似文献   

11.
Responses of photosynthetic rates, determined by oxygen evolution using the light and dark bottles technique, to different temperatures, irradiances, pH, and diurnal rhythm were analyzed under laboratory conditions in four charophyte species (Chara braunii Gmelin, C. guairensis R. Bicudo, Nitella subglomerata A. Braun and Nitella sp.) from lotic habitats in southeastern Brazil. Parameters derived from the photosynthesis versus irradiance curves indicated affinity to low irradiances for all algae tested. Some degree of photoinhibition, [β= ‐(0.30–0.13) mg O2 g?1 dry weight Ir1 (μmol photons m?2 s?1)?1], low light compensation points (Ic= 4–20 μmol photons m?2 s?1) were found for all species analyzed, as well as low values of light saturation parameter (Ik) and saturation (Is) 29–130 and 92–169 μmol photons m?2 s?1, respectively. Photoacclimation was observed in two populations of N. subglomerata collected from sites with different irradiances, consisting of variations in photosynthetic parameters (higher values of a, and lower of Ik and maximum photosynthetic rate, Pmax, in the population under lower irradiance). The highest photosynthetic rates for Chara species were observed at 10–15°C, while for Nitella the highest photosynthetic rate was observed at 20–25°C, despite the lack of significant differences among most levels tested. Rates of dark respiration significantly increase with temperature, with the highest values at 25°C. The results from pH experiments showed highest photosynthetic rates under pH 4.0 for all algae, suggesting higher affinity for inorganic carbon in the form of carbon dioxide, except in one population of N. subglomerata, with similar rates under the three levels, suggesting indistinct use of bicarbonate and carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for most algae tested, which was characterized by two peaks: the first (higher) during the morning (07.00–11.00) and the second (lower) in the afternoon (14.00–17.00). This suggests an endogenous rhythm determining the daily variations in photosynthetic rates.  相似文献   

12.
Gas exchange in K. blossfeldiana shows a circadian rhythm in net CO2 uptake and transpiration when measured under low and medium irradiances. The period length varies between 21.4 h at 60 W m-2 and 24.0 h at 10 W m-2. In bright light (80 W m-2) or darkness there are no rhythms. High leaf temperatures result in a fast dampening of the CO2-uptake rhythm at moderate irradiances, but low leaf temperatures can not overcome the dampening in bright light. The rhythm in CO2 uptake is accompanied by a less pronounced and more rapidly damped rhythm in transpiration and by oscillations in malate levels with the amplitude being highly reduced. The oscillations in starch content, usually observed to oscillate inversely to the acidification in light-dark cycles, disappear after the first cycle in continuous light. The balance between starch and malate levels depends in continuous light on the irradiance applied. Leaves show high malate and low starch content at low irradiance and high starch and low malate in bright light. During the first 12 h in continuous light replacing the usual dark period, malate synthesis decreases with the increasing irradiance. Up to 50 W m-2 starch content decreases; at higher irradiances it increases above the values usually measured at the end of the light period of the 12:12 h light-dark cycle.Abbreviations CAM Crassulacean acid metabolism - FW fresh weight - PEP phosphoenolpyruvate  相似文献   

13.
1. Streambed light regimes change dramatically when riparian trees gain leaves in spring and lose them in autumn. This study examined the effect of these changes on periphyton photosynthetic characteristics, primary production, and light utilisation efficiency in two eastern Tennessee streams. 2. Photosynthesis–irradiance responses were measured at intervals covering leaf emergence and abscission in spring and autumn. Photosynthetic efficiency (αchl) increased with declining streambed irradiances during spring leaf emergence, but returned to pre‐emergence values after autumn leaf fall. The onset of photosaturation (Ik) displayed the opposite pattern, decreasing during leaf emergence and increasing after leaf fall. Both αchl and Ik were closely associated (P < 0.01) with daily integrated streambed irradiance, as were periphyton carotenoids. Internal shading by photoprotective carotenoids is hypothesised to account for lower αchl when streambed irradiances are high. 3. An in situ shading experiment confirmed that the temporal changes observed in periphyton photosynthetic characteristics and carotenoids were primarily the result of changing light levels and not other environmental factors (e.g. nutrients, temperature). 4. Daily chlorophyll‐specific primary production (PPchl) was calculated with PI models and recorded streambed irradiances. In both streams, PPchl was the highest in early spring when trees were leafless, and then declined markedly as leaves emerged, reaching a minimum in summer. PPchl increased after leaf abscission, but was still lower than it was in early spring, when the sun was higher and daylength was longer. A hyperbolic tangent equation fit to PPchl and daily integrated irradiance (r2=0. 85) suggested that primary production was light saturated at 4–8 mol m–2 d–1. 5. Light utilisation efficiency (Ψ) increased 10‐fold during leaf emergence. Photosaturation at high irradiances and photoacclimation at lower irradiances were responsible for a negative hyperbolic relationship between Ψ and daily integrated irradiance.  相似文献   

14.
Direct comparisons between photosynthetic O2 evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400–600 μmol photons m−2 s−1. O2 exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((Fm′−Ft)/Fm′) decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0–300 μmol photons m−2 s−1), there was a significant correlation between O2 evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O2 evolution tended towards an asymptote. However at high irradiance levels (600–1200 μmol photons m−2 s−1) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO3 ], [NH4 +] and [HPO4 2-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O2 evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O2, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

15.
Eco-physiological responses of nitrogen-fixing cyanobacteria to light   总被引:1,自引:0,他引:1  
The eco-physiological responses of three nitrogen-fixing cyanobacteria (N-fixing cyanobacteria), Aphanizomenon gracile, Anabaena minderi, and Ana. torques-reginae, to light were assessed under nutrient saturation. The N-fixing cyanobacteria were isolated into monocultures from a natural bloom in a shallow colored lake and their growth irradiance parameters and pigment composition were assessed. The different ecological traits related to light use (μmax, α, I k) suggest that these N-fixing cyanobacteria are well adapted to low light conditions at sufficient nutrients, yet interspecific differences were observed. Aphanizomenon gracile and Anabaena minderi had high relative growth rates at low irradiances (ca. 70% of those in high light), low half saturation constant for light-limited growth (I k < 9.09 μmol photon m−2 s−1) and high efficiency (α < 0.11 day−1 μmol photon−1 m2 s). Conversely, Ana. torques-reginae showed poorer light competitiveness: low relative growth rates at low irradiances (ca. 40% of those in high light), low α (0.009 day−1 μmol photon−1 m2 s) and higher I k (35.5 μmol photon m−2 s−1). Final densities in Aphanizomenon gracile and Anabaena minderi reached bloom densities at irradiances above 30 μmol photon m−2 s−1 with different hierarchy depending on irradiance, whereas Ana. torques-reginae never achieved bloom densities. All species had very low densities at irradiances ≤17 μmol photon m−2 s−1, thus no N-fixing blooms would be expected at these irradiances. Also, under prolonged darkness and at lowest irradiance (0 and 3 μmol photon m−2 s−1) akinetes were degraded, suggesting that in ecosystems with permanently dark sediments, the prevalence of N-fixing cyanobacteria should not be favored. All species displayed peaks of phycocyanin, but no phycoeritrin, probably due to the prevailing red light in the ecosystem from which they were isolated.  相似文献   

16.
Pea plants (Pisum sativum L. cv. Alaska) were grown from seeds for eleven days at different irradiances. Cuttings were then excised and rooted at 16 W × m?2. Gibberellic acid (GA3, 10?11 to 10?3M) was applied to the cuttings immediately after excision. Cuttings from stock plants grown at the highest level of irradiance (38 W × m?2) formed the lowest number of roots. An increasing number of roots per cutting was obtained by decreasing the irradiance to the stock plants. In cuttings from stock plants grown at low irradiances, low concentrations of GA3 (10?8 and 10?7M) promoted root formation further. No effect on rooting by these GA3 concentrations was observed when applied to cuttings originating from stock plants grown at the high irradiances. Root formation in all cuttings was inhibited by GA3 at concentrations higher than 10?6M. The degree of inhibition by GA3 was influenced by the irradiance pretreatment and was increased with an increase in the irradiance during the stock plant growth. Seeds from different years produced cuttings with different response patterns regarding the irradiance and GA3 effects on rooting.  相似文献   

17.
Although sea‐ice represents a harsh physicochemical environment with steep gradients in temperature, light, and salinity, diverse microbial communities are present within the ice matrix. We describe here the photosynthetic responses of sea‐ice microalgae to varying irradiances. Rapid light curves (RLCs) were generated using pulse amplitude fluorometry and used to derive photosynthetic yield (ΦPSII), photosynthetic efficiency (α), and the irradiance (Ek) at which relative electron transport rate (rETR) saturates. Surface brine algae from near the surface and bottom‐ice algae were exposed to a range of irradiances from 7 to 262 μmol photons · m?2 · s?1. In surface brine algae, ΦPSII and α remained constant at all irradiances, and rETRmax peaked at 151 μmol photons · m?2 · s?1, indicating these algae are well acclimated to the irradiances to which they are normally exposed. In contrast, ΦPSII, α, and rETRmax in bottom‐ice algae reduced when exposed to irradiances >26 μmol photons · m?2 · s?1, indicating a high degree of shade acclimation. In addition, the previous light history had no significant effect on the photosynthetic capacity of bottom‐ice algae whether cells were gradually exposed to target irradiances over a 12 h period or were exposed immediately (light shocked). These findings indicate that bottom‐ice algae are photoinhibited in a dose‐dependent manner, while surface brine algae tolerate higher irradiances. Our study shows that sea‐ice algae are able to adjust to changes in irradiance rapidly, and this ability to acclimate may facilitate survival and subsequent long‐term acclimation to the postmelt light regime of the Southern Ocean.  相似文献   

18.
Shoots of Sedum nuttallianum exhibited CAM* acid fluctuations in the field. These nocturnal acid accumulations persisted in the laboratory under well-watered and water-stressed conditions. Simultaneous measurements of transpiration, however, indicated daytime stomatal opening and nocturnal stomatal closure. Measurements of CO2 and H2O vapor exchange continuously for six days after watering substantiated these results in part: the majority of CO2 uptake occurred during the day early in the experiment; however, after several days without water, nighttime CO2 uptake was stimulated and eventually was greater than the drastically reduced daytime CO2 uptake. This nighttime uptake was never quite sufficient to account for all estimated increases in tissue acidity. Thus, a combination of CAM and CAM-cycling occurred early in the desiccation experiment. Evidence for CAM and a form of CAM-idling was found later in the experiment. Though nighttime CO2 uptake occurred and persisted after only one day without water, rates were too low to alter the tissue 13C/12C value from a C3-like number (–30). Thus, although CAM and CAM-idling may have survival value during extended droughts, shoots of S. nuttallianum apparently utilize the C3 pathway to obtain most of their carbon.Abbreviations C3 pathway - CO2 fixation pathway in which an intermediate containing 3 carbon atoms is formed - CAM Crassulacean acid metabolism - Chl Chlorophyll - ci internal CO2 concentration - DW Dry weight - gc mean conductance to CO2 - FW Fresh weight - PAR Photosynthetically active radiation - SD Standard deviation - vpd Vapor pressure deficit - WUE Water use efficiency  相似文献   

19.
Light acclimatisation capabilities of Elodea nuttallii at nearly ambient DIC conditions were investigated by determining growth characteristics, main photosynthetic parameters and pigmentation of plants incubated at 5 different irradiances (10–146 μmol photons m−2 s−1). Positive net growth was observed under all light treatments tested. Maximum ratio root versus shoot (r:s) of 1.86 was achieved at medium irradiances (72–94 μmol photons m−2 s−1), whereas at low (10 μmol photons m−2 s−1) and high irradiances (146 μmol photons m−2 s−1) r:s was significantly lower (0.39 and 1.05, respectively). With respect to main photosynthetic parameters, an increase of light compensation points (E c), attended by decreasing ratios of light saturation points of photosynthesis (E k)/irradiance were observed. E c values were comparable to other low-light adapted macrophytes, which indicate that E. nuttallii can be regarded as a low-light adapted plant, under photorespiratory conditions. This was also confirmed by maximum E k values of just 73 μmol photons m−2 s−1. Further support was achieved from pigmentation and non-photochemical quenching (NPQ) data, both indicating rather limited acclimatisation ability at light treatments above 90 μmol photons m−2 s−1. These results are discussed with respect to the competitive abilities of E. nuttallii under nearly ambient (photorespiratory) DIC conditions, especially in dense stands and turbid phytoplankton-dominated waters.  相似文献   

20.
The aim of this study was to investigate acclimation of micropropagated plants of Rhododendron ponticum subsp. baeticum to different irradiances and recovery after exposure to high irradiance. Plants grown under high (HL) or intermediate (IL) irradiances displayed higher values of maximum electron transport rate (ETRmax) and light saturation coefficient (Ek) than plants grown under low irradiance (LL). The capacity of tolerance to photoinhibition (as assessed by the response of photochemical quenching, qp) varied as follows: HL > IL > LL. Thermal energy dissipation (qN) was also affected by growth irradiance, with higher saturating values being observed in HL plants. Light-response curves suggested a gradual replacement of qp by qN with increasing irradiance. Following exposure to irradiance higher than 1500 μmol m−2 s−1, a prolonged reduction of the maximal photochemical efficiency of PS 2 (Fv/Fm) was observed in LL plants, indicating the occurrence of chronic photoinhibition. In contrary, the decrease in Fv/Fm was quickly reverted in HL plants, pointing to a reversible photoinhibition.  相似文献   

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