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1.
CO2 exchange and water relations of selected lichen species were investigated in the field and also in the laboratory, at a height of 3106 m above sea level in the Austrian Alps, during the short snowless summer period from middle of July to the end of August. In the course of the field investigations, clear summer days were quite rare. Altogether 14 diurnal courses of CO2 exchange were measured spanning a time of 255 h of measurements.The air temperatures measured close to the ground ranged between −0.7 and 17.1 °C and their daily fluctuation was lower than 10.7 °C. Fog was present for more than one-third of the measuring period and relative humidity (RH) exceeded 90% in almost half of the time. Temperature optimum of net photosynthesis (NP) of Xanthoria elegans and Brodoa atrofusca determined in the laboratory increased with increasing photosynthetic photon flux density (PPFD) from 1.5 to 11.3 °C and the maximal CO2 uptake was found to be at 10 °C. In the field the lichens were metabolically active at air temperatures between −0.7 and 12.8 °C. The light compensation points (LCP) of both lichen species ranged in the laboratory between 50 and 200 μmol m−2 s−1 PPFD (0–20 °C) and in the field between 22 and 56 μmol m−2 s−1 PPFD (3–8 °C). At 30 °C the NP of X. elegans surpassed the LCP, whereas B. atrofusca remained below the LCP. NP in X. elegans did not reach light saturation at 1500 μmol m−2 s−1 PPFD. NP in B. atrofusca reached light saturation at low temperatures (−5 to +5 °C). At higher temperatures light saturation was almost detectable. On sunny days the lichens in the field were metabolically active only for 3 h during the early morning. In this time they reached the maximal values or values close to their maximal CO2 uptake in situ. Under dry weather conditions the lichens dried out to a minimal water content (WC) of 5–12% which is below the moisture compensation point (MCP) of 34–25%. The optimal WC was between 90% and 120% dry weight (DW) in B. atrofusca and Umbilicaria cylindrica, in X. elegans between 140% and 180% DW. Species specific differences in water-holding capacity, desiccation intensity and in the compensation points of temperature, light and moisture are responsible for differences in metabolic activity. The lichens were active during less than half of the observation time. Total time of NP of X. elegans was 24% of the measuring period, for U. cylindrica 22% and for B. atrofusca 16%.  相似文献   

2.
《Aquatic Botany》2005,81(2):157-173
The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O2 g−1 dw h−1 and 9.1 μmol O2 g−1 dw h−1/μmol photons m−2 s−1, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O2 g−1 dw h−1 and 2.6 μmol O2 g−1 dw h−1/μmol photons m−2 s−1 respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to Rd (ranging 6.7–794 μmol O2 g−1 dw h−1, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).  相似文献   

3.
Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R > 0.92 (p < 0.01) using regression analysis and photosynthesis-light intensity (P-L) model. Based on this equation, the optimum light intensity (Lmax) and the semi-optimum light intensity range (Ls-opt) that resulted in the maximum growth rate (μmax) and ≥80% μ max values of the four species/phylotypes, respectively, were as follows: (1) the Lmax and Ls-opt of G. australes were 208 μmol photons m−2 s−1 and 91–422 μmol photons m−2 s−1, respectively; (2) those of G. scabrosus were 252 and 120–421 μmol photons m−2 s−1, respectively; (3) those of Gambierdiscus sp. type 2 were 192 and 75–430 μmol photons m−2 s−1, respectively; and (4) those of Gambierdiscus sp. type 3 were ≥427 and 73–427 μmol photons m−2 s−1, respectively. All four Gambierdiscus species/phylotypes required approximately 10 μmol photons m−2 s−1 to maintain growth. The light intensities in coastal waters at a site in Tosa Bay were measured vertically at 1 m intervals once per season. The relationships between the observed light intensity and depth were formulated using Beer’s Law. Based on these equations, the range of the attenuation coefficients at Tosa Bay site was determined to be 0.058–0.119 m−1. The values 1700 μmol photons m−2 s−1, 500 μmol photons m−2 s−1, and 200 μmol photons m−2 s−1 were substituted into the equations to estimate the vertical profiles of light intensity at sunny midday, cloudy midday and rainy midday, respectively. Based on the regression equations coupled with the empirically determined attenuation coefficients for each of the four seasons, the ranges of the projected depths of Lmax and Ls-opt for the four Gambierdiscus species/phylotypes under sunny midday conditions, cloudy midday conditions, and rainy midday conditions were 12–38 m and 12–54 m, 1–16 m and 1–33 m, and 0 m and 0–16 m, respectively. These results suggest that light intensity plays an important role in the bloom dynamics and vertical distribution of Gambierdiscus species/phylotypes in Japanese coastal waters.  相似文献   

4.
《Aquatic Botany》2005,83(2):129-140
Bisexual populations of the charophyte Chara canescens (Desv. et Loisel. in Loisel., 1810) containing male and female individuals are rarely found. Two experiments were carried out to study whether male and female algae from the same site exhibit different physiological capacities, especially with respect to light acclimation.Algae from two different shore levels and from laboratory cultures acclimated to six irradiance conditions (35–500 μmol photons m−2 s−1) were compared. Field measurements showed that both female and male algae of C. canescens are able to acclimate to daily changes in solar irradiance. The quantum yield of Photosystem II (PSII) decreased with increasing irradiance in the morning and increased with decreasing irradiance in the afternoon. Growth experiments showed increasing growth rates from 35 μmol photons m−2 s−1 (∼7 mg FW) up to 500 μmol photons m−2 s−1 (∼27 mg FW) in female and male C. canescens. The irradiance saturation point for photosynthesis (Ek) was about 140 μmol m−2 s−1 for both sexes within the whole range of acclimation irradiances. The maximum photosynthesis rate at saturating irradiances (Pmax) of male algae was highest at Ek, whereas Pmax of female algae was highest at 500 μmol photons m−2 s−1. The photosynthetic efficiency in the light-limited range (α) increased in female C. canescens and decreased in male C. canescens. The ratio of the non-photochemical quenching parameter (NPQ) to the relative electron transport rates rETR(MT) increased in both sexes with irradiance, but showed a steeper increase in male than in female algae. Pigment analysis showed similar acclimation pattern for male and female C. canescens. Chl a/Chl b ratios of both sexes were constant over the whole range of Eg, whereas Chl a/carotenoid ratios in male and female C. canescens decreased from 70 μmol photons m−2 s−1 upwards. Pigment analysis pointed out that the carotenes α-, β- and γ-carotene were more prominent in male than in female algae.Our results indicate that female C. canescens are more efficient in light acclimation than male algae from the same site. Nevertheless, further investigations of bisexual C. canescens populations resolving CO2-uptake mechanisms and/or genetic differences are needed.  相似文献   

5.
The introduced shrub Tamarix ramosissima invades riparian zones, but loses competitiveness under flooding. Metabolic effects of flooding could be important for T. ramosissima, but have not been previously investigated. Photosynthesis rates, stomatal conductance, internal (intercellular) CO2, transpiration, and root alcohol dehydrogenase (ADH) activity were compared in T. ramosissima across soil types and under drained and flooded conditions in a greenhouse. Photosynthesis at 1500 μmol quanta m−2 s−1 (A1500) in flooded plants ranged from 2.3 to 6.2 μmol CO2 m−2 s−1 during the first week, but A1500 increased to 6.4–12.7 μmol CO2 m−2 s−1 by the third week of flooding. Stomatal conductance (gs) at 1500 μmol quanta m−2 s−1 also decreased initially during flooding, where gs was 0.018 to 0.099 mol H2O m−2 s−1 during the first week, but gs increased to 0.113–0.248 mol H2O m−2 s−1 by the third week of flooding. However, photosynthesis in flooded plants was reduced by non-stomatal limitations, and subsequent increases indicate metabolic acclimation to flooding. Root ADH activities were higher in flooded plants compared to drained plants, indicating oxygen stress. Lower photosynthesis and greater oxygen stress could account for the susceptibility of T. ramosissima at the onset of flooding. Soil type had no effect on photosynthesis or on root ADH activity. In the field, stomatal conductance, leaf water potential, transpiration, and leaf δ13C were compared between T. ramosissima and other flooded species. T. ramosissima had lower stomatal conductance and water potential compared to Populus deltoides and Phragmites australis. Differences in physiological responses for T. ramosissima could become important for ecological concerns.  相似文献   

6.
《Aquatic Botany》2002,72(3-4):219-233
We studied the potential role of dissolved inorganic carbon (DIC) in determining vegetation dominance of Potamogeton pectinatus L. and Chara aspera Deth. ex Willd. by monitoring the seasonal dynamics of DIC in a shallow lake and comparing the use of DIC of the two species. The HCO3-concentration in summer dropped from 2.5 to <0.5 mM with seasonally increasing Chara biomass, whereas outside the vegetation concentrations remained at 2.5 mM. Inside Potamogeton spp. vegetation DIC decreased from 2.5 to ca. 0.75 mM HCO3. A growth experiment showed ash-free biomass for P. pectinatus was nearly two times as high as for C. aspera at 3 mM HCO3, but almost two times lower at 0.5 mM than at 3.0. In a separate experiment, P. pectinatus precultured at a relatively low HCO3-level had a lower net photosynthetic rate (Pmax, 0.1 mmol O2 g−1 DW h−1) than C. aspera (Pmax, 0.1 mmol O2 g−1 DW h−1) over the range of HCO3-concentrations tested (Pmax, 0.14 mmol O2 g−1 DW h−1). In response to CO2 no significant differences between the compensation points (P. pectinatus, 28 mM; C. aspera 66 mM), were observed, but the photosynthetic rate increased faster than for C. aspera than for P. pectinatus. Under field conditions, the use of CO2 is not important since inside vegetation CO2-concentrations were below 10 μM, and thus, not available for photosynthesis of either species during the main part of the growth season. It is suggested that C. aspera may be a better competitor for HCO3 than P. pectinatus in conditions with a low HCO3 supply. As HCO3 is a strong limiting factor for growth inside the vegetation and probably the only carbon source available, the superior ability of C. aspera to use HCO3 may be an important factor explaining its present dominance in Veluwemeer.  相似文献   

7.
《Aquatic Botany》2005,82(4):239-249
The activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as photosynthetic pigment contents and free malondialdehyde (MDA), were determined in senescent batch cultures of Tetraselmis gracilis (Kylin) Butcher, under a cyclic light regime. A 2.6-fold increase in SOD activity (from 53 to 137 U mg−1 protein) was observed in the light phase, contrasting with a 9-fold increase in CAT (from 1 to 9 μmol H2O2 min−1 mg−1 protein) and a 1.7-fold increase in APX (from 3 to 5 μmol ascorbate min−1 mg−1 protein) activities, both enzymes peaking in the dark phase. The β-carotene and lycopene content did not vary significantly with the light–dark cycle. The Chl a, Chl b, lutein, zeaxanthin, violaxanthin and neoxanthin pigments exhibited the highest values in the first half (3–6 h) of the light phase, followed by a declining trend and a plateau or a slight increase 3 h from the beginning of the dark phase onwards. The highest values for prasinoxanthin were observed in the second half of the dark phase and the first half of the light phase. None of the pigments displayed any discernible cyclic trend. The possibility of the xanthophyll cycle occurring during senescence is discussed in light of the high value (∼0.9) obtained for the zeaxanthin/(zeaxanthin + violaxanthin) ratio. The free MDA content was enhanced during the experimental period, which may be an indicator of oxidative stress in aging cell cultures. Our results indicated the occurrence of an imbalance between the production of reactive oxygen species and the antioxidant defense in stationary T. gracilis cells.  相似文献   

8.
《Aquatic Botany》2007,87(1):43-48
CH4 and CO2 fluxes across the water–atmosphere interface were measured over a 24 h day–night cycle in a shallow oxbow lake colonized by the water chestnut (Trapa natans L.) (Lanca di Po, Northern Italy). Only exchanges mediated by macrophytes were measured, whilst gas ebullition was not considered in this study. Measurements were performed from 29 to 30 July 2005 with short incubations, when T. natans stands covered the whole basin surface with a mean dry biomass of 504 ± 91 g m−2. Overall, the oxbow lake resulted net heterotrophic with plant and microbial respiration largely exceeding carbon fixation by photosynthesis. The water chestnut stand was a net sink of CO2 during the day-light period (−60.5 ± 8.5 mmol m−2 d−1) but it was a net source at night (207.6 ± 6.1 mmol m−2 d−1), when the greatest CO2 efflux rate was measured across the water surface (28.2 ± 2.4 mmol m−2 h−1). The highest CH4 effluxes (6.6 ± 1.8 mmol m−2 h−1) were determined in the T. natans stand during day-time, whilst CH4 emissions across the plant-free water surface were greatest at night (6.8 ± 2.1 mmol m−2 h−1). Therefore, we assumed that the water chestnut enhanced methane delivery to the atmosphere. On a daily basis, the oxbow lake was a net source to the atmosphere of both CO2 (147.1 ± 10.8 mmol m−2 d−1) and CH4 (116.3 ± 8.0 mmol m−2 d−1).  相似文献   

9.
Benthic dinoflagellates of the genus Ostreopsis are found all over the world in temperate, subtropical, and tropical coastal regions. Our recent studies revealed that a putative “cryptic” species of Ostreopsis ovata is present widely along Japanese coasts. This organism, Ostreopsis sp. 1, possesses palytoxin analogs and thus its toxic blooms may be responsible for potential toxification of marine organisms. To evaluate the bloom dynamics of Ostreopsis sp. 1, the present study examined the growth responses of Ostreopsis sp. 1 strain s0716 to various light intensities (photon flux densities: μmol photons m−2 s−1) using a newly devised photoirradiation-culture system. This novel system has white light-emitting diodes (LEDs) capable of more closely simulating the wavelength spectrum of light entering the oceanic water column than do fluorescent tubes and halogen lamps. In this system, the light intensity of the white LEDs was reduced through two polarizing filters by varying the rotation angles of the filters. Thereby, the new system was capable of culturing microalgae under well-controlled light intensity conditions. Ostreopsis sp. 1 grew proportionally when light intensity was increased from 49.5 to 199 μmol photons m−2 s−1, but its growth appeared to be inhibited slightly at ≥263 μmol photons m−2 s−1. The relationship between observed growth rates and light intensity was calculated at R > 0.99 (P < 0.01) using a regression analysis with a modified equation of the photosynthesis-light intensity (P-L) model. The equation determined the critical light intensities for growth of Ostreopsis sp. 1 and the organism's growth potential as follows: (1) the threshold light intensity for growth: 29.8 μmol photons m−2 s−1; (2) the optimum light intensity (Lm) giving the maximum growth rate (μmax = 0.659 divisions day−1): 196 μmol photons m−2 s−1; (3) the optimum light intensity range (Lopt) giving ≥95% μmax: 130–330 μmol photons m−2 s−1; (4) the semi-optimum range (Lsopt) giving ≥80% μmax: 90 to over 460 μmol photons m−2 s−1. The Lsopt represents 4.5–23% ambient light intensity present in surface waters off of a temperate region of the Japanese coast, Tosa Bay; putatively, this semi-optimum range of light intensity appears at depth of 12.9–27.8 m. Considering these issues, our data indicate that Ostreopsis sp. 1 in coastal environments may form blooms at ca. ∼28 m depth in regions along Japanese coasts.  相似文献   

10.
《Aquatic Botany》2005,83(1):71-81
The aquatic plant Elodea nuttallii (Planch.) St. John has been shown to express plasticity in the source of inorganic carbon it uses for photosynthesis. An investigation was undertaken to determine what effect the switch from CO2 to HCO3 use had on the growth of E. nuttallii. Plants were grown under reduced CO2 availability that favoured the switch, together with control plants (CO2 at equilibrium with air) that continued to use CO2 only. The extent to which both sets of plants could utilise HCO3 was determined (as the ratio of oxygen evolution at pH 9 and 6.5), and several measures of growth were made. Although reduced CO2 availability produced an increase in HCO3 utilisation, no differences were found in the measured growth of the plants. Therefore, it was possible to estimate, from the difference between the estimated rate of photosynthesis of the plants utilising HCO3 and those using CO2 only, the approximate cost of constructing, maintaining and running the bicarbonate utilisation mechanism in this species as 69 μmol photons m−2 s−1. This value can be used to estimate an irradiance of circa 80 μmol m−2 s−1 below which HCO3 use would not be expected in this species, an irradiance commonly experienced by submerged macrophytes in the field.  相似文献   

11.
《Process Biochemistry》2014,49(10):1606-1611
The filamentous fungus Paecilomyces lilacinus was grown on n-hexadecane in submerged (SmC) and solid-state (SSC) cultures. The maximum CO2 production rate in SmC (Vmax = 11.7 mg CO2 Lg−1 day−1) was three times lower than in SSC (Vmax = 40.4 mg CO2 Lg−1 day−1). The P. lilacinus hydrophobin (PLHYD) yield from the SSC was 1.3 mg PLHYD g protein−1, but in SmC, this protein was not detected. The PLHYD showed a critical micelle concentration of 0.45 mg mL−1. In addition, the PLHYD modified the hydrophobicity of Teflon from 130.1 ± 2° to 47 ± 2°, forming porous structures with some filaments <1 μm and globular aggregates <0.25 μm diameter. The interfacial studies of this PLHYD could be the basis for the use of the protein to modify surfaces and to stabilize compounds in emulsions.  相似文献   

12.
In response to an osmotic stress, Dunaliella tertiolecta osmoregulates by metabolizing intracellular glycerol as compatible solute. Upon the application of a salt stress to 0.17 M or 0.7 M NaCl grown D. tertiolecta cells, rates of total glycerol synthesis were substantially higher than that arising from photosynthetic 14CO2 fixation into glycerol. The source of this extra carbon is the reserve starch pool. The contribution of carbon from the starch breakdown to glycerol synthesis was estimated from the difference between the total glycerol synthesized and that arising from 14CO2 fixation. The maximum observed flux of carbon from 14CO2 to glycerol from photosynthesis was of the order of 15–20 μmol 14C-glycerol mg−1 Chl h−1, whereas the total glycerol synthesis reached about 70 μmol glycerol mg−1 Chl h−1. The contribution of products of starch breakdown to glycerol synthesis increased progressively with increasing salt stress. In light, contrary to prevailing assumptions, both the photosynthesis and the starch breakdown contribute carbon to glycerol biosynthesis. The relative contributions of these two processes in the light, while cells were actively photosynthesizing, depended on the magnitude of the salt stress. On application of dilution stress, the flux of carbon from newly photosynthetically fixed 14CO2 into glycerol was reduced progressively with increasing dilution stress that was also accompanied by a decline in total glycerol contents of the cell. The maximum observed rate of glycerol dissimilation was about 135 μmol glycerol mg−1 Chl h−1.  相似文献   

13.
In wild-type Escherichia coli, 1 mol of CO2 was fixated in 1 mol of succinic acid generation anaerobically. The key reaction in this sequence, catalyzed by phosphoenolpyruvate carboxylase (PPC), is carboxylation of phosphoenolpyruvate to oxaloacetate. Although inactivation of pyruvate formate-lyase and lactate dehydrogenase is found to enhance the PPC pathway for succinic acid production, it results in excessive pyruvic acid accumulation and limits regeneration of NAD+ from NADH formed in glycolysis. In other organisms, oxaloacetate is synthesized by carboxylation of pyruvic acid by pyruvate carboxylase (PYC) during glucose metabolism, and in E. coli, nicotinic acid phosphoribosyltransferase (NAPRTase) is a rate-limiting enzyme of the NAD(H) synthesis system. To achieve the NADH/NAD+ ratio decrease as well as carbon flux redistribution, co-expression of NAPRTase and PYC in a pflB, ldhA, and ppc deletion strain resulted in a significant increase in cell mass and succinic acid production under anaerobic conditions. After 72 h, 14.5 g L−1 of glucose was consumed to generate 12.08 g L−1 of succinic acid. Furthermore, under optimized condition of CO2 supply, the succinic acid productivity and the CO2 fixation rate reached 223.88 mg L−1 h−1 and 83.48 mg L−1 h−1, respectively.  相似文献   

14.
Anthropogenic impact on CO2 levels was studied in the Bear Chamber of the Výpustek Cave, a show cave in the Moravian Karst (Czech Republic), during a period of active ventilation and enhanced attendance. The study showed that the natural CO2 levels were controlled by (i) the natural CO2 influxes from soils/epikarst (up to ∼5.64 × 10−2 mol s−1); and, (ii) the advective CO2 fluxes out of cave atmosphere (up to 4.66 × 10−2 mol s−1). During visitor presence, the anthropogenic CO2 flux into the chamber reached up to ∼0.13 mol s−1 and exceeded all other CO2 fluxes. The reachable anthropogenic steady states at sufficient duration of stay (up to 2.65 × 10−1 mol m−3) could exceed the natural CO2 levels by factor of more than nine based on the number of visitors. Recession analysis of anthropogenic pulses showed that intervals between individual visitor groups would have to be up to ∼6 h long if the cave environment has to return to natural conditions. As such pauses between individual tours are hardly realizable, a risk analysis was conducted to find the consequences of breaking natural conditions. It showed that the condition under which dripwater becomes aggressive to calcite (i.e., the point when PCO2 in cave atmosphere exceeds the hypothetical CO2 concentrations in epikarst that has participated on the water formation, PCO2(H) = 10−1.56) is potentially reachable under extreme conditions only (enormous visitor stay period and visitor number). In case of condensed water, however, any increase in CO2 concentration will cause an increase of water aggressiveness to calcite. Therefore, in the periods and sites of enhanced condensation, it is important to strive for preservation of natural conditions.  相似文献   

15.
Seagrasses worldwide are highly vulnerable to, and at increasing risk from reduced light availability, and robust light thresholds are required for evaluating future impacts of changing light conditions. We tested the morphological response (shoot density and growth) of four Indo-West Pacific seagrass species (Cymodocea serrulata, Halodule uninervis, Halophila ovalis and Zostera muelleri) to six daily light levels ranging from 0 to 23 mol m−2 d−1 (0–70% surface irradiance) in cool (∼23 °C) and warm temperatures (∼28 °C) over 14 weeks. The impact of light limitation on shoot densities and growth rates was higher at warm than at cool temperatures, and for Z. muelleri and H. ovalis than for C. serrulata and H. uninervis, in terms of both the time taken for the low light treatment to take effect and the predicted time to shoot loss (e.g. 17–143 days at 0 mol m−2 d−1). Using fitted curves we estimated temperature-dependent thresholds (with estimates of uncertainty) for 50% and 80% protection of growth and shoot density, defined here as “potential light thresholds” in recognition that they were derived under experimental conditions. Potential light thresholds that maintained 50% and 80% of seagrass shoot density fell within the ranges 1.1–5.7 mol m−2 d−1 and 3.8–10.4 mol m−2 d−1, respectively, depending on temperature and species. Light thresholds calculated in separate in situ studies for two of the same species produced comparable results. We propose that the upper (rounded) values of 6 mol m−2 d−1 and 10 mol m−2 d−1 can be used as potential light thresholds for protecting 50% and 80% of shoot density for these four species over 14 weeks. As management guidelines should always be more conservative than thresholds for biological declines, we used error estimates to provide a quantitative method for converting potential light thresholds into guidelines that satisfy this criterion. The present study demonstrates a new approach to deriving potential light thresholds for acute impacts, describes how they can be applied in management guidelines and quantifies the timescales of seagrass decline in response to light limitation. This method can be used to further quantify cumulative impacts on potential light thresholds.  相似文献   

16.
We investigated the effects of pH on movement behaviors of the harmful algal bloom causing raphidophyte Heterosigma akashiwo. Motility parameters from >8000 swimming tracks of individual cells were quantified using 3D digital video analysis over a 6-h period in 3 pH treatments reflecting marine carbonate chemistry during the pre-industrial era, currently, and the year 2100. Movement behaviors were investigated in two different acclimation-to-target-pH conditions: instantaneous exposure and acclimation of cells for at least 11 generations. There was no negative impairment of cell motility when exposed to elevated PCO2 (i.e., low pH) conditions but there were significant behavioral responses. Irrespective of acclimation condition, lower pH significantly increased downward velocity and frequency of downward swimming cells (p < 0.001). Rapid exposure to lower pH resulted in 9% faster downward vertical velocity and up to 19% more cells swimming downwards (p < 0.001). Compared to pH-shock experiments, pre-acclimation of cells to target pH resulted in ~30% faster swimming speed and up to 46% faster downward velocities (all p < 0.001). The effect of year 2100 PCO2 levels on population diffusivity in pre-acclimated cultures was >2-fold greater than in pH-shock treatments (2.2 × 105 μm2 s−1 vs. 8.4 × 104 μm2 s−1). Predictions from an advection-diffusion model, suggest that as PCO2 increased the fraction of the population aggregated at the surface declined, and moved deeper in the water column. Enhanced downward swimming of H. akashiwo at low pH suggests that these behavioral responses to elevated PCO2 could reduce the likelihood of dense surface slick formation of H. akashiwo through reductions in light exposure or growth independent surface aggregations. We hypothesize that the HAB alga's response to higher PCO2 may exploit the signaling function of high PCO2 as indicative of net heterotrophy in the system, thus indicative of high predation rates or depletion of nutrients.  相似文献   

17.
Among the numerous metalloenzymes known to date, carbonic anhydrase (CA, EC 4.2.1.1) was the first zinc containing one, being discovered decades ago. CA is a hydro-lyase, which catalyzes the following hydration–dehydration reaction: CO2 + H2O  HCO3 + H+. Several CA classes are presently known, including the α-, β-, γ-, δ-, ζ- and η-CAs. In prokaryotes, the existence of genes encoding CAs from at least three classes (α-, β- and γ-class) suggests that these enzymes play a key role in the physiology of these organisms. In many bacteria CAs are essential for the life cycle of microbes and their inhibition leads to growth impairment or growth defects of the pathogen. CAs thus started to be investigated in detail in bacteria, fungi and protozoa with the aim to identify antiinfectives with a novel mechanism of action. Here, we investigated the catalytic activity, biochemical properties and anion inhibition profiles of the three CAs from the bacterial pathogen Vibrio cholera, VchCA, VchCAβ and VchCAγ. The three enzymes are efficient catalysts for CO2 hydration, with kcat values ranging between (3.4  8.23) × 105 s−1 and kcat/KM of (4.1  7.0) × 107 M−1 s−1. A set of inorganic anions and small molecules was investigated for inhibition of these enzymes. The most potent VchCAγ inhibitors were N,N-diethyldithiocarbamate, sulfamate, sulfamide, phenylboronic acid and phenylarsonic acid, with KI values ranging between 44 and 91 μM.  相似文献   

18.
An understanding of detailed kinetic of CO2 removal by plants can lead to an effective design of the phytoremediation process for anthropogenic CO2 reduction. This study examines the CO2 removal rates of five wetland plants (Cyperus alternifolius, Dracaena fragrans, Iris ensata, Iris setosa and Thalia dealbata) by using saturation reaction and first-order reaction kinetic equations. It was determined that the elevation of CO2 levels stimulated the plant-CO2 uptake rate. The maximum CO2 removal rates (k) of plants were found to range between 0.76 and 1.21 g m?2 h?1. The magnitude of first-order kinetic coefficient of plants (k′) had a close relationship with CO2 level at half-velocity (K). For consistency, the same kinetics were applied to the continuous flow experiment. A saturation kinetic approach was well suited to estimate the removal rate of CO2 in continuous flow system, while a first-order kinetic approach was limited to inflow CO2 levels below 500 ppm.  相似文献   

19.
《Process Biochemistry》2014,49(12):2114-2121
The codon-optimized carbonic anhydrase gene of Persephonella marina EX-H1 (PMCA) was expressed and characterized. The gene with the signal peptide removed, PMCA(sp−), resulted in the production of approximately five times more purified protein than from the intact gene PMCA using an Escherichia coli expression system. PMCA(sp−) is formed as homo-dimer complex. PMCA(sp−) has a wide pH tolerance (optimum pH 7.5) and a high thermostability even at 100 °C (88 min of thermal deactivation half-life). The melting temperature for PMCA(sp−) was 84.5 °C. The apparent kcat and Km values for CO2 hydration were 3.2 × 105 s−1 and 10.8 mM. The activity of the PMCA(sp−) enzyme was enhanced by Zn2+, Co2+, and Mg2+, but was strongly inhibited by Cu2+, Fe3+, Al3+, Pb2+, Ag+, and Hg2+. PMCA(sp−) readily catalyzed the hydration of CO2, precipitating CaCO3 as calcite in the presence of Ca2+.  相似文献   

20.
The kinetics of a stomatal response to sudden increases or decreases of CO2 concentrations ([CO2]) was studied in 13 plant species growing in the field. Plants were well supplied with water. In each plant, gas exchange measurements were made on a fully developed leaf that was first left to achieve steady-state stomatal conductance (gs) at 400 μmol (CO2) mol−1) and then exposed to a step change of [CO2] (to 700 μmol mol−1 in one experiment; and to 700 and back to 400 μmol mol−1 in a second experiment). Porometric data were captured in intervals of 3 s until a new steady state was reached.A comparison of t1/2, the half-time needed to achieve new gs, indicates similar responses of stomata in grasses when compared to herbs. The stomata of C4 plants responded in approximately 5 min, the highest closure rate was detected in Echinochloa crus-galli and Digitaria sanguinalis. Opening rates were similar to closing rates and the response as a whole was rather symmetric. In C3 plants, the full response of stomata was much slower. Analysis revealed differences in absolute rates of gs change between C3 and C4 plants. These differences can be related to the specificities of the type of photosynthetic metabolism. C4 photosynthesis enables plants to reduce gs, which can hasten further changes of diffusivity in response to the environmental signals. A possible coupling of C4 metabolism to the regulation of guard cells also has to be taken into account when explaining the observed results.  相似文献   

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