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1.
The objective of this study was to improve the biological water–gas shift reaction for producing hydrogen (H2) by conversion of carbon monoxide (CO) using an anaerobic thermophilic pure strain, Carboxydothermus hydrogenoformans. Specific hydrogen production rates and yields were investigated at initial biomass densities varying from 5 to 20 mg volatile
suspended solid (VSS) L−1. Results showed that the gas–liquid mass transfer limits the CO conversion rate at high biomass concentrations. At 100-rpm
agitation and at CO partial pressure of 1 atm, the optimal substrate/biomass ratio must exceed 5 mol CO g−1 biomass VSS in order to avoid gas–liquid substrate transfer limitation. An average H2 yield of 94 ± 3% and a specific hydrogen production rate of ca. 3 mol g−1 VSS day−1 were obtained at initial biomass densities between 5 and 8 mg VSS−1. In addition, CO bioconversion kinetics was assessed at CO partial pressure from 0.16 to 2 atm, corresponding to a dissolved
CO concentration at 70°C from 0.09 to 1.1 mM. Specific bioactivity was maximal at 3.5 mol CO g−1 VSS day−1 for a dissolved CO concentration of 0.55 mM in the culture. This optimal concentration is higher than with most other hydrogenogenic
carboxydotrophic species. 相似文献
2.
The oxygen and nutrient dynamics of the zooxanthellate, upside down jellyfish (Cassiopea sp.), were determined both in situ and during laboratory incubations under controlled light conditions. In the laboratory,
Cassiopea exhibited a typical Photosynthesis–Irradiance (P–I) curve with photosynthesis increasing linearly with irradiance, until
saturation was reached at an irradiance of ~400 μE m−2 s−1, with photosynthetic compensation (photosynthesis = respiration) being achieved at an irradiance of ~50 μE m−2 s−1. Under saturating irradiation, gross photosynthesis attained a rate of almost 3.5 mmol O2 kg WW−1 h−1, whereas the dark respiration rate averaged 0.6 mmol O2 kg WW−1 h−1. Based upon a period of saturating irradiance of 9 h, the ratio of daily gross photosynthesis to daily respiration was 2.04.
Thus, photosynthetic carbon fixation was not only sufficient to meet the carbon demand of respiration, but also to potentially
support a growth rate of ~3% per day. During dark incubations Cassiopea was a relatively minor source of inorganic N and P, with the high proportion of NO
X
(nitrate + nitrite) produced indicating that the jellyfish were colonised by nitrifying bacteria. Whereas, under saturating
irradiance the jellyfish assimilated ammonium, NO
X
and phosphate from the bathing water. However, the quantities of inorganic nitrogen assimilated were small by comparison
to carbon fixation rates and the jellyfish would need to exploit other sources of nitrogen, such as ingested zooplankton,
in order to maintain balanced growth. During in situ incubations the presence of Cassiopea had major effects on benthic oxygen and nutrient dynamics, with jellyfish occupied patches of sediment having 3.6-fold higher
oxygen consumption and 4.5-fold higher ammonium regeneration rates than adjacent patches of bare sediment under dark conditions.
In contrast at saturating irradiance, jellyfish enhanced benthic photosynthetic oxygen production almost 100-fold compared
to the sediment alone and created a small sink for inorganic nutrients, whereas unoccupied sediment patches were sources of
inorganic nutrients to the water column. Overall, Cassiopea greatly enhanced the spatial and temporal heterogeneity of benthic fluxes and processes by creating “hotspots” of high activities
which switched between being sources or sinks for oxygen and nutrients over diurnal irradiance cycles, as the metabolism of
the jellyfish swapped between heterotrophy and net autotrophy. 相似文献
3.
Akiko Sasaki Yu Hagimori Ichiro Yuasa Takayuki Nakatsubo 《Landscape and Ecological Engineering》2012,8(1):107-114
To quantify organic matter mineralization at estuarine intertidal flats, we measured in situ sediment respiration rates using
an infrared gas analyzer in estuarine sandy intertidal flats located in the northwestern Seto Inland Sea, Japan. In situ sediment
respiration rates showed spatial and seasonal variations, and the mean of the rates is 38.8 mg CO2-C m−2 h−1 in summer. In situ sediment respiration rates changed significantly with sediment temperature at the study sites (r
2 = 0.70, p < 0.05), although we did not detect any significant correlations between the rates and sediment characteristics. We prepared
a model for estimating the annual sediment respiration based on the in situ sediment respiration rates and their temperature
coefficient (Q
10 = 1.8). The annual sediment respiration was estimated to be 92 g CO2-C m−2 year−1. The total amount of organic carbon mineralization for the entire estuarine intertidal flats through sediment respiration
(43 t C year−1) is equivalent to approximately 25% of the annual organic carbon load supplied from the river basin of the estuary. 相似文献
4.
Summary The influence of seasonal variation on nitrogenase (N2-ase) activity of undisturbed soil-plant cores ofPanicum maximum var.trichoglume was measured using the C2H2 reduction assay.
The largest N2-ase activity in the field, 14.7 g N ha−1 day−1, occurred in spring when soil moisture was high, soil temperature was low and nitrogenous fertiliser influence was at a minimum.
The potential N2-ase activity of the cores, measured under controlled conditions, reached a maximum of 27.2 g N ha−1 day−1 and averaged 26.3 g N ha−1 day−1 over the 14 month sampling period.
N2-ase activity was positively correlated (P=0.05) with field soil moisture and negatively correlated with field soil temperature (r=0.59 and −0.78 respectively). Multiple
regression showed that 69% of the variation of N2-ase activity in the field was associated with the combined effects of soil moisture and soil temperature.
Nitrogen fixing bacteria were isolated from the roots ofP. maximum and based upon morphology, biochemical tests and fluorescent antibody reaction, were found to be closely related toAzospirillum lipoferum. 相似文献
5.
The impact of the oxygen supply rate (OSR) on the metabolic activity and on the composition of hexadecane-degrading bacterial
communities in a quasi-anoxic milieu (nominal DOT=0%) was studied in continuous cultures containing intertidal sediment. The
dilution rate was kept constant at 0.035 h−1. The OSR was stepwise reduced from 3.5 mmol O2L−1 h−1 to 0.06 mmol O2L−1 h−1. Activity was determined by analyzing the respiration quotient (RQ) and the rates of hexadecane degradation (QHex), of hexadecane mineralization, and of protein production (PPR). The community composition and size were investigated by
fluorescence in situ hybridization (FISH), by dilution plating (colony forming units or CFU), and by most probable number (MPN). The culture showed
an aerobic hexadecane metabolism down to an OSR of 0.35 mmol O2L−1 h−1. Below this OSR, anaerobic metabolism was initiated. The relationship among the RQ, PPR, QHex, and the OSR can be approximated by hyperbola (Michaelis-Menten kinetics). We suggest that the metabolic adaptation of the
culture to low OSRs is due to regulation of protein expression and enzyme activity. Reducing the OSR resulted in minor but
significant changes in the concentration of different physiological and phylogenetic groups. This means that, in addition
to protein expression and activity regulation, the adaptation of the population to low OSRs is due to changes in the community
composition. 相似文献
6.
Part of the Larsen A Ice Shelf (64°15′S to 74°15′S) collapsed during January 1995. A first oceanographic and biological data
set from the newly free waters was obtained during December 1996. Typical shelf waters with temperatures near and below the
freezing point were found. A nutrient-rich water mass (max: PO4
3− 1.80 μmol L−1 and NO3
− 27.64 μmol L−1) was found between 70 and 200 m depth. Chlorophyll-a (Chl-a) values (max 14.24 μg L−1) were high; surface oxygen saturation ranged between 86 and 148%. Diatoms of the genera Nitzschia and Navicula and the prymnesiophyte Phaeocystis sp. were the most abundant taxa found. Mean daily primary production (Pc) estimated from nutrient consumption was 14.80 ± 0.17 mgC m−3 day−1. Pc was significantly correlated with total diatom abundance and Chl-a. Calculated ΔpCO2 (difference of the CO2 partial pressure between surface seawater and the atmosphere) was –30.5 μatm, which could have contributed to a net CO2 flux from the atmosphere to the sea and suggests the area has been a CO2 sink during the studied period. High phytoplankton biomass and production values were found in this freshly open area, suggesting
its importance for biological CO2 pumping. 相似文献
7.
CO2 exchange of the endolithic lichen Verrucaria baldensis was measured in the laboratory under different conditions of water content, temperature, light, and CO2 concentration. The species had low CO2 exchange rates (maximum net photosynthesis: c. 0.45 μmol CO2 m−2 s−1; maximum dark respiration: c. 0.3 μmol CO2 m−2 s−1) and a very low light compensation point (7 μmol photons m−2 s−1 at 8°C). The net photosynthesis/respiration quotient reached a maximum at 9–15°C. Photosynthetic activity was affected only
after very severe desiccation, when high resaturation respiratory rates were measured. Microclimatic data were recorded under
different weather conditions in an abyss of the Trieste Karst (northeast Italy), where the species was particularly abundant.
Low photosynthetically active radiation (normally below 40 μmol photons m−2 s−1), very high humidities (over 80%), and low, constant temperatures were measured. Thallus water contents sufficient for CO2 assimilation were often measured in the absence of condensation phenomena.
Received: 22 September 1996 / Accepted: 26 April 1997 相似文献
8.
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
9.
Oliveira GR Ribeiro JM Fraga ME Cavaglieri LR Direito GM Keller KM Dalcero AM Rosa CA 《Mycopathologia》2006,162(5):355-362
The intake of mycotoxin-contaminated feeds can lead to nutrient losses and may have adverse effects on animal health and on
productivity. The aims of this study were (1) to determine the mycobiota present in poultry feed samples, and (2) to evaluate
the natural occurrence of aflatoxin B1, fumonisin B1 and zearalenone. Fungal counts were similar between all culture media tested (103 CFU g−1). The most frequent genus isolated was Penicillium spp. (41.26%) followed by Aspergillus spp. (33.33%) and Fusarium spp. (20.63%). High precision liquid chromatography was applied to quantify aflatoxin B1 and fumonisin B1. Thin layer chromatography was used to determine zearalenone levels. Aflatoxin B1 values ranged between 1.2 and 17.5 μg kg−1. Fumonisin B1 levels ranged between 1.5 and 5.5 μg g−1. Zearalenone levels ranged between 0.1 and 7 μg g−1. The present study shows the simultaneous occurrence of two carcinogenic mycotoxins, aflatoxin B1 and fumonisin B1, together with another Fusarium mycotoxin (zearalenone) in␣feed intended for poultry consumption. Many samples contained AFB1 levels near the permissible maximum and it could affect young animals. A synergistic toxic response is possible in animals
under simultaneous exposure. 相似文献
10.
Rates of net photosynthesis (P
N) and transpiration (E), and leaf temperature (TL) of maintenance leaves of tea under plucking were affected by photosynthetic photon flux densities (PPFD) of 200–2 200 μmol
m−2 s−1. P
N gradually increased with the increase of PPFD from 200 to 1 200 μmol m−2 s−1 and thereafter sharply declined. Maximum P
N was 13.95 μmol m−2 s−1 at 1 200 μmol m−2 s−1 PPFD. There was no significant variation of P
N among PPFD at 1 400–1 800 μmol m−2 s−1. Significant drop of P
N occurred at 2 000 μmol m−2 s−1. PPFD at 2 200 μmol m−2 s−1 reduced photosynthesis to 6.92 μmol m−2 s−1. PPFD had a strong correlation with TL and E. Both TL and E linearly increased from 200 to 2 200 μmol m−2 s−1 PPFD. TL and E were highly correlated. The optimum TL for maximum P
N was 26.0 °C after which P
N declined significantly. E had a positive correlation with P
N. 相似文献
11.
Abstract
In acidic mining-impacted lake sediments, the microbial reduction of Fe(III) is the dominant electron-accepting process, whereas
the reduction of sulfate seems to be restricted to a narrow sediment zone of elevated pH and lower amounts of total and reactive
iron. To evaluate the microbial heterogeneity and the commensal interactions of the microbial community, the flow of supplemental
carbon and reductant was evaluated in four different zones of the sediment in anoxic microcosms at the in situ temperature of 12°C. Substrate consumption, product formation, and the potential to reduce Fe(III) and sulfate were similar
with both upper and lower sediment zones. In the upper acidic iron-rich sediment zone, the rate of Fe(II) formation 204 nmol
ml−1 d−1 was enhanced to 833 nmol ml−1 d−1 and 462 nmol ml−1 d−1 by supplemental glucose and H2, respectively. Supplemental lactate and acetate were not consumed under acidic conditions and decreased the rate of Fe(II)
formation to 130 nmol ml−1 d−1 and 52 nmol ml−1 d−1, respectively. When the pH of the upper sediment increased above pH 5, acetate-dependent reduction of sulfate was initiated
even though the pool of Fe(III) was not depleted. In deeper sediment zones with elevated pH, the rapid consumption of acetate
was always coincident to a decrease in the concentration of sulfate and soluble Fe(II), indicating the formation of Fe(II)
sulfides. Although the reduction of Fe(III) was still an ongoing process in deeper sediment zones, the formation of Fe(II)
was only slightly enhanced by the consumption of glucose or cellobiose, but not by H2 or acetate. H2-utilizing acetogens seemed to be involved in the consumption of H2. These collective results indicated (i) that the reduction of Fe(III) predominated over the reduction of sulfate as long
as the sediment remained acidic and carbon-limited, and (ii) that the sulfate-reducing microbiota in this heterogeneous sediment
were better adapted to the geochemical gradients present than were other neutrophilic dissimilatory Fe(III) reducers.
Received: 17 February 2000; Accepted: 22 June 2000; Online Publication: 28 August 2000 相似文献
12.
Jana Woelfel Rhena Schumann Florian Peine Anita Flohr Aleksandra Kruss Jaroslaw Tegowski Philippe Blondel Christian Wiencke Ulf Karsten 《Polar Biology》2010,33(9):1239-1253
During summer 2007, Arctic microphytobenthic potential primary production was measured at several stations around the coastline
of Kongsfjorden (Svalbard, Norway) at ≤5 m water depth and at two stations at five different water depths (5, 10, 15, 20,
30 m). Oxygen planar optode sensor spots were used ex situ to determine oxygen exchange in the overlying water of intact sediment
cores under controlled light (ca. 100 μmol photons m−2 s−1) and temperature (2–4°C) conditions. Patches of microalgae (mainly diatoms) covering sandy sediments at water depths down
to 30 m showed high biomass of up to 317 mg chl a m−2. In spite of increasing water depth, no significant trend in “photoautotrophic active biomass” (chl a, ratio living/dead cells, cell sizes) and, thus, in primary production was measured at both stations. All sites from ≤5 to
30 m water depth exhibited variable rates of net production from −19 to +40 mg O2 m−2 h−1 (−168 to +360 mg C m−2 day−1) and gross production of about 2–62 mg O2 m−2 h−1 (17–554 mg C m−2 day−1), which is comparable to other polar as well as temperate regions. No relation between photoautotrophic biomass and gross/net
production values was found. Microphytobenthos demonstrated significant rates of primary production that is comparable to
pelagic production of Kongsfjorden and, hence, emphasised the importance as C source for the zoobenthos. 相似文献
13.
P. Becker I. Abu-Reesh S. Markossian G. Antranikian H. Märkl 《Applied microbiology and biotechnology》1997,48(2):184-190
A thermostable lipase was produced in continuous cultivation of a newly isolated thermophilic Bacillus sp. strain IHI-91 growing optimally at 65 °C. Lipase activity decreased with increasing dilution rate while lipase productivity
showed a maximum of 340 U l−1 h−1 at a dilution rate of 0.4 h−1. Lipase productivity was increased by 50% compared to data from batch fermentations. Up to 70% of the total lipase activity
measured was associated to cells and by-products or residual substrate. Kinetic and stoichiometric parameters for the utilisation
of olive oil were determined. The maximal biomass output method led to a saturation constant K
S of 0.88 g/l. Both batch growth data and a washout experiment yielded a maximal specific growth rate, μmax, of 1.0 h−1. Oxygen uptake rates of up to 2.9 g l−1h−1 were calculated and the yield coefficient, Y
X/O, was determined to be 0.29 g dry cell weight/g O2. From an overall material balance the yield coefficient, Y
X/S, was estimated to be 0.60 g dry cell weight/g olive oil.
Received: 8 January 1997 / Received revision: 30 April 1997 / Accepted: 4 May 1997 相似文献
14.
Actual and potential rates of hydrogen photoproduction by continuous culture of the purple non-sulphur bacterium Rhodobacter capsulatus 总被引:1,自引:1,他引:0
A. A. Tsygankov A. S. Fedorov T. V. Laurinavichene I. N. Gogotov K. K. Rao D. O. Hall 《Applied microbiology and biotechnology》1998,49(1):102-107
The influence of (NH4)2SO4 concentration and dilution rate (D) on actual and potential H2 photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H2 production in a photobioreactor was maximal (approx. 80 ml h−1 l−1) at D = 0.06 h−1 and 4 mM (NH4)2SO4. However, it was lower than the potential H2 evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h−1 l−1 at D = 0.03–0.08 h−1. Taking into account the fact that H2 production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting)
factor should be sought. One possibility is an inhibition of H2 production by the H2 accumulated in the gas phase. This is apparent from the non-linear kinetics of H2 evolution in the vials or from its inhibition by the addition of H2; initial rates were restored in both cases after the vials had been refilled with argon. The actual H2 production in the photobioreactor at D = 0.06 h−1 was shown to increase from approximately 80 ml h−1 l−1 to approximately 100 ml h−1 l−1 under an argon flow at 100 ml min−1. Under maximal H2 production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H2 production and 50% for biomass synthesis.
Received: 22 April 1997 / Received revision: 14 July 1997 / Accepted: 27 July 1997 相似文献
15.
Melzner F Bock C Pörtner HO 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(1):1-17
Venous blood flow was measured for the first time in a cephalopod. Blood velocity was determined in the anterior vena cava
(AVC) of cuttlefish S. officinalis with a Doppler, while simultaneously, ventilatory pressure oscillations were recorded in the mantle cavity. In addition,
magnetic resonance imaging (MRI) was employed to investigate pulsatile flow in other major vessels. Blood pulses in the AVC
are obligatorily coupled to ventilatory pressure pulses, both in frequency and phase. AVC peak blood velocity (vAVC) in animals of 232 (± 30 SD) g wet mass at 15°C was found to be 14.2 (± 7.1) cm s−1, AVC stroke volume (SVAVC) was 0.2 (± 0.1) ml stroke−1, AVC minute volume (MVAVC) amounted to 5.5 (± 2.8) ml min−1. Intense exercise bouts of 1–2 min resulted in 2.2-fold increases in MVAVC, enabled by 1.6-fold increments in both, AVC pulse frequency (f
AVC) and vAVC. As increases in blood flow occurred delayed in time by 1.7 min with regard to exercise periods, we concluded that it is
not direct mantle cavity pressure conveyance that drives venous return in this cephalopod blood vessel. However, during jetting
at high pressure amplitude (> 1 kPa), AVC blood flow and mantle cavity pressure pulse shapes completely overlap, suggesting
that under these conditions, blood transport must be driven passively by mantle cavity pressure. MRI measurements at 15°C
also revealed that under resting conditions, f
AVC and ventilation frequency (f
V) match at 31.6 (± 2.1) strokes min−1. In addition, rates of pulsations in the cephalic artery and in afferent branchial vessels did not significantly differ from
f
AVC and f
V. It is suggested that these adaptations are beneficial for high rates of oxygen extraction observed in S. officinalis and the energy conserving mode of life of the cuttlefish ecotype in general. 相似文献
16.
P. Olguín-Lora S. Le Borgne G. Castorena-Cortés T. Roldán-Carrillo I. Zapata-Peñasco J. Reyes-Avila S. Alcántara-Pérez 《Biodegradation》2011,22(1):83-93
Haloalkaliphilic sulfur-oxidizing mixed cultures for the treatment of alkaline–saline effluents containing sulfide were characterized
and evaluated. The mixed cultures (IMP-PB, IMP-XO and IMP-TL) were obtained from Mexican alkaline soils collected in Puebla
(PB), Xochimilco (XO) and Tlahuac (TL), respectively. The Ribosomal Intergenic Spacer Analysis (RISA) revealed bacteria related
to Thioalkalibacterium and Thioalkalivibrio in IMP-XO and IMP-PB mixed cultures. Halomonas strains were detected in IMP-XO and IMP-TL. In addition, an uncultured Bacteroides bacterium was present in IMP-TL. Mixed cultures were evaluated at different pH and NaCl concentrations at 30°C. IMP-PB and
IMP-TL expressed thiosulfate-oxidizing activity in the 7.5–10.5 pH range, whereas IMP-XO presented its maximal activity with
19.0 mg O2 gprotein−1 min−1, at pH 10.6; it was not affected by NaCl concentrations up to 1.7 M. In continuous culture, IMP-XO showed a growth rate of
15 day−1, productivity of 433.4 mgprotein l−1 day−1 and haloalkaliphilic sulfur-oxidizing activity was also detected up to 170 mM by means of N-methyl-diethanolamine (MDEA). Saline–alkaline soil samples are potential sources of haloalkaliphilic sulfur-oxidizing bacteria
and the mixed cultures could be applied in the treatment of inorganic sulfur compounds in petroleum industry effluents under
alkaline–saline conditions. 相似文献
17.
Thorén AK 《Microbial ecology》2007,53(2):221-232
Transformation of urea to ammonium is an important link in the nitrogen cycle in soil and water. Although microbial nitrogen
transformations, such as nitrification and denitrification, are well studied in freshwater sediment and epiphytic biofilm
in shallow waters, information about urea transformation in these environments is scarce. In this study, urea transformation
of sedimentary, planktonic, and epiphytic microbial communities was quantified and urea transformation of epiphytic biofilms
associated with three different common wetland macrophyte species is compared. The microbial communities were collected from
a constructed wetland in October 2002 and urea transformation was quantified in the laboratory at in situ temperature (12°C) with the use of the 14C-urea tracer method, which measures the release of 14CO2 as a direct result of urease activity. It was found that the urea transformation was 100 times higher in sediment (12–22 mmol
urea-N m−2 day−1) compared with the epiphytic activity on the surfaces of the submerged plant Elodea canadensis (0.1–0.2 mmol urea-N m−2 day−1). The epiphytic activity of leaves of Typha latifolia was lower (0.001–0.03 mmol urea-N m−2 day−1), while urea transformation was negligible in the water column and on the submerged leaves of the emergent plant Phragmites australis. However, because this wetland was dominated by dense beds of the submerged macrophyte E. canadensis, this plant provided a large surface area for epiphytic microbial activity—in the range of 23–33 m2 of plant surfaces per square meter of wetland. Thus, in the wetland system scale at the existing plant distribution and density,
the submerged plant community had the potential to transform 2–7 mmol urea-N m−2 day−1 and was in the same magnitude as the urea transformation in the sediment. 相似文献
18.
Chunhui Cao Shichun Sun Xuekui Wang Wenling Liu Ying Liang 《Journal of applied phycology》2011,23(6):1039-1043
Experimental ecology methods and chlorophyll fluorescence technology were used to study the effects of different concentrations
of manganese (10−12– 10−4 mol L−1) on the growth, photosystem II and superoxide dismutase (SOD) activity of Amphidinium sp. MACC/D31. The results showed that manganese had a significant effect on the growth rate, fluorescence parameters (maximal
photochemical efficiency of PSII (F
v
/F
m
), photochemical quenching (qP) and non-photochemical quenching (NPQ)) in the exponential stage (days 1–3) and SOD activity
of Amphidinium sp. (P < 0.05). F
v/F
m in the exponential stage in 10−12 mol L−1 manganese concentration was significantly lower whilst qP and NPQ significantly higher than those in the other concentrations.
F
v
/F
m
(days 6–9) in 10−4 mol L−1 manganese was significantly higher than those in the other concentrations. F
v
/F
m
(days 3–6) increased with increased concentration of manganese from 10−12 to 10−4 mol L−1. The values of qP and NPQ decreased with decreased concentrations of manganese, except for those in days 4–6. F
v
/F
m
under each concentration increased earlier and decreased later with culture stage whilst NPQ decreased earlier and increased
later. The SOD activity increased with increased concentration of manganese from 10−12 to 10−8 mol L−1. The SOD activity in 10−4 mol L−1 manganese was significantly higher than those in the other concentrations and in 10−12 mol L−1 manganese, it was significantly lower than those in the other concentrations. 相似文献
19.
To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending
on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a
control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite
content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase
and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar
under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate.
This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase
and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate.
This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献
20.
Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities
of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth
profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the
redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient
over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change
the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to
be 6 × 10−8 cm2 s−1. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused
by the irrigational activities of the benthic fauna. 相似文献