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1.
Impact of soil vertical water movement on the energy balance of different land surfaces 总被引:4,自引:0,他引:4
The soil heat flux determination method proposed by Gao (Boundary-Layer Meteorol 114:165–178, 2005) is discussed for (1) dry
surfaces, (2) bare soil or sparse short-grass lands, and (3) dense-grass surfaces or forest. Our analysis shows that, when
neglecting the contribution of soil vertical water movement to soil heat flux, the energy components measured independently
will (1) still achieve balance over dry surfaces, and (2) be significantly in imbalance over bare soil or sparse short-grass
lands. The mean of bare ground evaporation modeled by SiB2 is 1.58 × 10−5 m3 s−1 m−2, and the mean of soil water flux obtained by the method of Gao is 1.22 × 10−5 m3 s−1 m−2 for the Naqu site in the summer of 1998. Comparison of the bare ground evaporation with the mean of soil water flux shows
a difference, the causes of which are investigated. Physically, the bare ground evaporation is equal to the sum of soil water
flux and water content change in the soil surface layer. Because the bare ground evaporation is very limited for the dense-grass
surfaces or forest, our analysis implies that the energy imbalance encountered over the dense-grass or forest is not caused
by the fact that previous researchers neglected soil water movements in their energy budget analyses. 相似文献
2.
Ichiro Aoki 《Bulletin of mathematical biology》1987,49(4):449-460
From an energy budget of a deciduous plant leaf in moderate conditions, entropy fluxes into or out of the leaf due to solar
radiation, infrared radiation, evaporation of water and heat conduction are calculated. Net entropy flow into the leaf is
negative. On the assumption that the entropy in the leaf is in a steady state, the entropy production in the typical deciduous
leaf in moderate conditions [the solar energy absorbed by both sides of the leaf isE
solar=0.0602 (J cm−2 s−1)] becomesS
prod=1.8×10−4 (J cm−2 s−1 K−1). The positiveness of the entropy production shows that the Second Law of Thermodynamics certainly holds in the plant leaf.
Entropy productions in other conditions are also calculated. The entropy production in the leafS
prod becomes a linear function of the solar energy absorbed by the leafE
solar:S
prod≈-(29.5E
solar)×10−4. A theorem is presented: the entropy production in plant leaves oscillates during the period of one day, paralleling the
daily solar energy absorbed by leaves. 相似文献
3.
Fathia Aouidi Eltaeif Khelifi Nedra Asses Lamia Ayed Moktar Hamdi 《Journal of industrial microbiology & biotechnology》2010,37(8):877-882
Geotrichum candidum is a yeast-like filamentous fungus that has attracted industrial interest. The present work investigated G. candidum biomass production in agro-industrial wastewaters (olive mill wastewater (OMW) and cheese whey (CW)) as the only substrate.
Different solid media (Sabouraud dextrose agar (SDA), CW, OMW, and OMW/CW mixtures in different proportions) were tested.
OMW/CW mixtures proved to be suitable for optimal mycelia growth of G. candidum with a very high hyphae density. The highest fungal and expansion rate growth of 83 ± 1 mm and 12.4 day−1, respectively, were obtained on a 20:80 mixture of OMW/CW, which was incubated for 7 days. This optimal mixture was used
to study the biomass production and the OMW decolorization ability of G. candidum in the presence of CW in liquid medium. Liquid cultures were also conducted in OMW and CW separately. After 5 days of incubation,
fungal biomass reached 9.26 g l−1 in the OMW/CW mixture and only 2.83 g l−1 in CW, while no biomass production was observed in OMW alone. OMW decolorization and dephenolization by G. candidum also improved in the presence of CW with a decolorization efficiency of 54.5% and a total phenolic reduction of 55.3%, compared
with the control which yielded values of about 10% and 15%, respectively. These results suggested that OMW/CW—as the only
substrate—could be used as a cost-effective medium to produce G. candidum biomass, without the need for water dilution or supplementation with other nutriments. 相似文献
4.
Tatiana G. Sazykina A. I. Kryshev K. D. Sanina 《Radiation and environmental biophysics》2009,48(4):391-404
Databases on effects of chronic low-LET radiation exposure were analyzed by non-parametric statistical methods, to estimate
the threshold dose rates above which radiation effects can be expected in vertebrate organisms. Data were grouped under three
umbrella endpoints: effects on morbidity, reproduction, and life shortening. The data sets were compiled on a simple ‘yes’
or ‘no’ basis. Each data set included dose rates at which effects were reported without further details about the size or
peculiarity of the effects. In total, the data sets include 84 values for endpoint “morbidity”, 77 values for reproduction,
and 41 values for life shortening. The dose rates in each set were ranked from low to higher values. The threshold TDR5 for
radiation effects of a given umbrella type was estimated as a dose rate below which only a small percentage (5%) of data reported
statistically significant radiation effects. The statistical treatment of the data sets was performed using non-parametric
order statistics, and the bootstrap method. The resulting thresholds estimated by the order statistics are for morbidity effects
8.1 × 10−4 Gy day−1 (2.0 × 10−4–1.0 × 10−3), reproduction effects 6.0 × 10−4 Gy day−1 (4.0 × 10−4–1.5 × 10−3), and life shortening 3.0 × 10−3 Gy day−1 (1.0 × 10−3–6.0 × 10−3), respectively. The bootstrap method gave slightly lower values: 2.1 × 10−4 Gy day−1 (1.4 × 10−4–3.2 × 10−4) (morbidity), 4.1 × 10−4 Gy day−1 (3.0 × 10−4–5.7 × 10−4) (reproduction), and 1.1 × 10−3 Gy day−1 (7.9 × 10−4–1.3 × 10−3) (life shortening), respectively. The generic threshold dose rate (based on all umbrella types of effects) was estimated
at 1.0 × 10−3 Gy day−1. 相似文献
5.
The distribution of picoplankton and nanoplankton in Kongsfjorden,Svalbard during late summer 2006 总被引:2,自引:0,他引:2
Abundance and biomass of pico- (<2 μm) and nanoplankton (2–20 μm) were investigated in relation to hydrography in Kongsfjorden,
Svalbard (79°N, 12°E) during late summer 2006. Autotrophic and heterotrophic picoplankton abundance ranged from 0.1 × 106 to 35.2 × 106 cells L−1 and from 0.4 × 106 to 20.3 × 106 cells L−1, respectively. The highest number of bacteria in the entire water column was recorded at station 2 at 10 m (22.3 × 108 cells L−1); the lowest concentration was observed at station 1 (6.0 × 108 cells L−1). The abundance of autotrophic and heterotrophic nanoplankton varied from 0.4 × 105 cells L−1 to 46 × 105 cells L−1 and from 0.3 × 106 to 9.1 × 106 cells L−1, respectively. Our results demonstrated that heterotrophic nanoflagellates and bacteria in Kongsfjorden microbial community
were relatively important. The structure of plankton communities integrated with environmental variables could act as indicators
of the variability of the inflow of Atlantic Water into Kongsfjorden. 相似文献
6.
This article reports rate constants for thiol–thioester exchange (k
ex), and for acid-mediated (k
a), base-mediated (k
b), and pH-independent (k
w) hydrolysis of S-methyl thioacetate and S-phenyl 5-dimethylamino-5-oxo-thiopentanoate—model alkyl and aryl thioalkanoates, respectively—in water. Reactions such as
thiol–thioester exchange or aminolysis could have generated molecular complexity on early Earth, but for thioesters to have
played important roles in the origin of life, constructive reactions would have needed to compete effectively with hydrolysis
under prebiotic conditions. Knowledge of the kinetics of competition between exchange and hydrolysis is also useful in the
optimization of systems where exchange is used in applications such as self-assembly or reversible binding. For the alkyl
thioester S-methyl thioacetate, which has been synthesized in simulated prebiotic hydrothermal vents, k
a = 1.5 × 10−5 M−1 s−1, k
b = 1.6 × 10−1 M−1 s−1, and k
w = 3.6 × 10−8 s−1. At pH 7 and 23°C, the half-life for hydrolysis is 155 days. The second-order rate constant for thiol–thioester exchange
between S-methyl thioacetate and 2-sulfonatoethanethiolate is k
ex = 1.7 M−1 s−1. At pH 7 and 23°C, with [R″S(H)] = 1 mM, the half-life of the exchange reaction is 38 h. These results confirm that conditions
(pH, temperature, pK
a of the thiol) exist where prebiotically relevant thioesters can survive hydrolysis in water for long periods of time and
rates of thiol–thioester exchange exceed those of hydrolysis by several orders of magnitude. 相似文献
7.
Denis V. Abramochkin Natalia V. Tennova Elizaveta E. Hirazova Anna V. Pizgareva Vladislav S. Kuzmin Galina S. Sukhova 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(5):645-651
Standard microelectrode technique was used to study electrical activity of the isolated heart of the polychaete annelid, Arenicola marina. Typical pacemaker activity with slow diastolic depolarization was observed in all recordings. The average maximum diastolic
potential (−58.4 ± 3.2 mV), the average amplitude of the action potential (28.7 ± 4.7 mV) and the average total duration of
the action potential (2,434 ± 430 ms) were determined. There has been no gradient of automaticity observed in our studies,
which suggests that all regions of the Arenicola heart could possess pacemaker functions. Acetylcholine (ACh) produced a concentration dependent (5 × 10−8–5 × 10−5 M) increase of the beating rate via increase in the rate of the diastolic depolarization. ACh (5 × 10−5 M) increased beating rate by 2.5-fold compared to the control rate. A stronger action of ACh resulted in depolarization,
block of action potential generation and contracture of the heart. The non-hydrolysable ACh analog carbacholine (10−8–10−6 M) produced similar effects. All effects of ACh and carbacholine were abolished by 5 × 10−6 M atropine. d-Tubocurarine (5 × 10−5 M) did not significantly alter effects of ACh or carbacholine. Epinephrine (10−8–10−6 M) caused the slowing of pacemaker activity and marked decrease of action potential duration. 10−6 M epinephrine produced complete cardiac arrest. The effects of epinephrine were not significantly altered by the β-blocker
propranolol (5 × 10−6 M). The β-agonist isoproterenol (10−7–10−5 M) and the α-agonist xylometazoline (10−6–10−5 M) did not produce significant effects. Thus, cholinergic effects in the Arenicola heart are likely to be mediated via muscarinic receptors, while the nature of adrenergic effects needs further investigation. 相似文献
8.
A thorough understanding of the reproductive phenology of introduced species is crucial for effective management and control.
Undaria pinnatifida is an invasive macroalga from the Northwest Pacific which has been recently introduced into three countries in the Southern
Hemisphere: Australia, New Zealand and Argentina. Reproductive phenological studies in Port Phillip Bay, Australia, were undertaken
and compared with other populations in the Southern Hemisphere, especially with those from Tasmania which were suspected to
be very different. The growth season began earlier in Port Phillip Bay than in Tasmanian populations, and abundance was higher.
Growth rates were lower in Port Phillip Bay, but this might be due to the different morphology of both populations. The maximum
spore release competency of U. pinnatifida in Port Phillip Bay was 12.1 × 105 spores cm−2 h−1 which is 20 times the maximum obtained in Tasmania (0.6 × 105 spores cm−2 h−1). For most of the growth season, spore release competency ranged between 2 and 3 × 105 spores cm−2 h−1, 3–5 times more than in Tasmania. Undaria pinnatifida has not been established outside Port Phillip Bay in continental Australia, but a precautionary approach should be undertaken
in order to avoid further spread. Monitoring for early detection and removal of immature sporophytes prior to spore release
seem to be the best options. This monitoring should be continuous since new recruits may appear throughout the growth season
(April–February) and it should be combined with informative programmes to reduce the chances of spread. 相似文献
9.
Christophe Sandt Truis Smith-Palmer Jonathan Comeau David Pink 《Applied microbiology and biotechnology》2009,83(6):1171-1182
The Raman spectra, water content, and biomass density of wild-type (WT) Pseudomonas aeruginosa PAO1, small colony variant (SCV) PAO1, and Pseudoalteromonas sp. NCIMB 2021 biofilms were compared in order to determine their variation with strain and species. Living, fully submerged
biofilms were analyzed in situ by confocal Raman microspectroscopy for up to 2 weeks. Water to biomass ratios (W/BRs), which
are the ratios of the O–H stretching vibration of water at 3,450 cm−1 to the C–H stretching band characteristic of biomass at 2,950 cm−1, were used to estimate the biomass density and cell density by comparison with W/BRs of protein solutions and bacterial suspensions,
respectively, on calibration curves. The hydration within SCV biofilm colonies was extremely heterogeneous whereas W/BRs were
generally constant in young WT biofilm colonies. The mean biomass in biofilm colonies of WT or colony cores of SCV was typically
equivalent to 16% to 27% protein (w/v), but was 10% or less for NCIMB 2021. The corresponding cell densities were 7.5 to >10 × 1010 cfu mL−1 for SCV, while the maximum cell density for NCIMB biofilms was 2.8 × 1010 cfu mL−1. 相似文献
10.
Al-Jobori S. M. Shihab K. M. Jalil M. Saad A. Mohsin A. 《Biological trace element research》1990,(1):637-645
INAA has been used for the determination of Na, Mg, Al, Cl, K, Sc, Cr, Mn, Fe, Co, Cu, Zn, As, Se, Br, Rb, Sr, Mo, and W in
grains of rice, wheat, and barley, which were collected from different plant fields in Iraq. Samples and standards were irradiated
in the IRT-5000 reactor, at neutron fluxes of 2 × 1013 cm−2·s−1 and 3.2 × 1011 cm−2·s−1. Interferences of photopeaks with each other were considered, and reaction interferences were calculated and determined experimentally.
Accuracy of our method was assessed by the analysis of IAEA standards Wheat Flour and Bovine liver. A good agreement has been
achieved between the present results and recommended values. The precision and detection limit were determined for all elements
in all types of grain. 相似文献
11.
Han Gil Choi Ki Hoon Lee Hyun Il Yoo Pil Jun Kang Young Sik Kim Ki Wan Nam 《Journal of applied phycology》2008,20(5):729-735
The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance
(10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m−2s−1) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m−2s−1), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day−1 (25°C, 20 μmol photons m−2s−1) and 13% day−1 (8 h daylength). In contrast, the RGRs of the blade weights were 4% day−1 (15°C, 20 μmol photons m−2s−1) and 5% day−1 (12 h daylength). Negative growth rates were found at 20 μmol photons m−2s−1 of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m−2s−1, and 8 h daylength for construction of Sargassum beds and restoration of barren areas. 相似文献
12.
Laccase-catalyzed oxidation of N-substituted phenothiazines and N-substituted phenoxazines was investigated at pH 5.5 and
25°C. The recombinant laccase from Polyporus pinsitus (rPpL) and the laccase from Myceliophthora thermophila (rMtL) were used. The dependence of initial reaction rate on substrate concentration was analyzed by applying the laccase
action scheme in which the laccase native intermediate (NI) reacts with a substrate forming reduced enzyme. The reduced laccase
produces peroxide intermediate (PI) which in turn decays to the NI. The calculated constant (kox) values of the PI formation are (6.1±3.1)×105 M−1s−1 for rPpL and (2.5±0.9)×104 M−1s−1 for rMtL. The bimolecular constants of the reaction of the native intermediate with electron donor (kred) vary in the interval
from 2.2×105 to 2.1×107 M−1s−1 for rPpL and from 1.3×102 to 1.8×105 M-1s−1 for rMtL. The larger reactivity of rPpL in comparison to rMtL is associated with the higher redox potential of type I Cu
of rPpL. The variation of kred values for both laccases correlates with the change of the redox potential of substrates. Following outer sphere (Marcus)
electron transfer mechanism the calculated activationless electron transfer rate and the apparent reorganization energy are
5.0×107 M−1s−1 and 0.29 eV, respectively. 相似文献
13.
Summary Three laboratory-scale water pipe systems were set up to study the effects of adding two levels of acetic acid (10 and 50
μg acetate eq-C l−1) on the bacterial regrowth in water pipes. The results of the water pipe test showed that nearly all carbon in the acetic
acid could be readily utilized by bacteria and resulted in an increase in biomass concentration. The maximum heterotrophic
plate counts in biofilm were equal to 3.5 × 104, 8.9 × 105 and 2.9 × 107 c.f.u. cm−2 while the maximum heterotrophic plate counts of free bacteria were equal to 1.2 × 103, 5.0 × 103 and 6.8 × 104 c.f.u. ml−1 for the blank and with addition of 10 and 50 μg acetate eq-C l−1. These results showed that addition of acetic acid to drinking water has a positive effect on the assimilable organic carbon
content of drinking water and bacterial regrowth in the distribution system. This effect is enhanced with addition of high-level
acetic acid. Batch tests were also conducted using water samples collected from a Taiwanese drinking water distribution system.
The bacterial regrowth potentials of the blank were equal to 4.3 × 103, 1.5 × 104, 4.9 × 104 and 7.5 × 104 c.f.u. ml−1 for water samples collected from treatment plant effluent, commercial area, mixed area, and residential area, respectively.
These results showed that the biological stability of drinking water is the highest in treatment plant effluent, followed
by distributed water of the commercial area, distributed water of the mixed area, and then the distributed water of residential
area. 相似文献
14.
While global climate change in polar regions is expected to cause significant warming, the annual cycle of light and dark
will remain unchanged. Cultures of three species of Antarctic sea ice diatoms, Fragilariopsis cylindrus (Grunow) Krieger, Thalassiosira antarctica Comber and Entomoneis kjellmanii (P.T. Cleve) Poulin and Cardinal, were incubated in the dark and exposed to differing temperatures. Maximum dark survival times varied between 30 and 60 days.
Photosynthetic parameters, photosynthetic efficiency (α), maximum quantum yield (Fv/Fm), maximum relative electron transport
rate (rETRmax) and non-photochemical quenching (NPQ), showed that dark exposure had a significant impact on photoacclimation.
In contrast, elevated temperatures had a relatively minor impact on photosynthetic functioning during the dark exposure period
but had a considerable impact on dark survival with minimal dark survival times reduced to only 7 days when exposed to 10°C.
Recovery of maximum quantum yield of fluorescence (Fv/Fm) was not significantly impacted by temperature, species or dark exposure
length. Recovery rates of Fv/Fm ranged from −5.06E−7 ± 2.71E−7 s−1 to 1.36E−5 ± 1.53E−5 s−1 for monthly experiments and from −9.63E−7 ± 7.71E−7 s−1 to 2.65E−5 ± 2.97E−5 s−1 for weekly experiments. NPQ recovery was greater and more consistent than Fv/Fm recovery, ranging between 5.74E−7 ± 8.11E−7 s−1 to 7.50E−3 ± 7.1E−4 s−1. The concentration of chl-a and monosaccharides remained relatively constant in both experiments. These results suggest that there will probably be little
effect on Antarctic microalgae with increasing water temperatures during the Antarctic winter. 相似文献
15.
In previous experiments, rates of picoplankton uptake into coral communities were controlled by sponge and ascidian biomass.
Those experimental communities, however, had relatively few sponges and ascidians. In contrast, turbulent transport of particles
into the momentum boundary layers can limit particle removal by layered, dense bivalve populations. In this study, the role
of water velocity in controlling particulate nutrient-uptake by rubble communities was evaluated, in which the rubble was
more completely covered by sponges and ascidians. Picoplankton uptake was proportional to concentration over a range of cell
concentrations from 3.0 × 105 to 9.5 × 105 heterotrophic bacteria ml−1, 4.1 × 104 to 1.2 × 105
Synechococcus sp. ml−1 and 6.3 × 103 to 1.8 × 104 picoeukaryotes ml−1. The first-order uptake rate constants, normalized to sponge and ascidian biomass, were similar to previous experimental
communities. Picoplankton uptake increased 1.6-fold over a 7-fold change in water velocity, 0.05–0.35 m s−1. This increase has been interpreted as a result of higher turbulent transport within the rough coral community (canopy),
as indicated by a 1.6-fold increase in the bottom friction with increasing water velocity. 相似文献
16.
Highly productive papyrus (Cyperus papyrus L.) wetlands dominate many permanently flooded areas of tropical East Africa; however, the cycling of carbon and water within
these ecosystems is poorly understood. The objective of this study was to utilise Eddy Covariance (EC) techniques to measure
the fluxes of carbon dioxide and water vapour between papyrus vegetation and the atmosphere in a wetland located near Jinja,
Uganda on the Northern shore of Lake Victoria. Peak, midday rates of photosynthetic CO2 net assimilation were approximately 40 μmol CO2 m−2 s−1, while night time losses through respiration ranged between 10 and 20 μmol CO2 m−2 s−1. Numerical integration of the flux data suggests that papyrus wetlands have the potential to sequester approximately 0.48 kg C m−2 y−1. The average daily water vapour flux from the papyrus vegetation through canopy evapotranspiration was approximately 4.75 kg
H2O m−2 d−1, which is approximately 25% higher than water loss through evaporation from open water. 相似文献
17.
Viral abundance, burst sizes, lytic production and temperate phage were investigated in land-fast ice at two sites in Prydz
Bay Antarctica (68°S, 77°E) between April and November 2008. Both ice cores and brine were collected. There was no seasonal
pattern in viral or bacterial numbers. Across the two sites virus abundances ranged between 0.5 × 105 and 5.1 × 105 viruses ml−1 in melted ice cores and 0.6 × 105–3.5 × 105 viruses ml−1 in brine, and bacterial abundances between 2.7 × 104 and 17.3 × 104 cells ml−1 in melted ice cores and 3.9 × 104–32.5 × 104 cells ml−1 in brine. Virus to bacterium ratios (VBR) showed a clear seasonal pattern in ice cores with lowest values in winter (range
1.2–20.8), while VBRs in brine were lower (0.2–4.9). Lytic viral production range from undetectable to 2.0 × 104 viruses ml−1 h−1 in ice cores with maximum rates in September and November. In brine maximum, lytic viral production occurred in November
(1.18 × 104 viruses ml−1 h−1). Low burst sizes were typical (3.94–4.03 viruses per bacterium in ice cores and 3.16–4.0 viruses per bacterium in brine)
with unusually high levels of visibly infected cells—range 40–50%. This long-term investigation revealed that viral activity
was apparent within the sea ice throughout its annual cycle. The findings are discussed within the context of limited data
available on viruses in sea ice. 相似文献
18.
Brass coupons (70% Cu 30% Zn) were exposed to a cooling freshwater system of an oil refinery, in order to investigate susceptibility
of the metal to biofilm formation. The coupons were fixed on bypasses at points which allowed the circulation of makeup, cooling
and return water. The number of aerobic, anaerobic and sulfate-reducing bacteria was determined in both the planktonic and
the sessile phases. Maximum bacterial concentrations were detected in the cooling water, corresponding to 2.1 ± 0.1 × 106 CFU ml−1 (planktonic phase) and 1.3 ± 0.2 × 105 CFU cm−2 (sessile phase) for aerobic bacteria and to 3.2 ± 0.3 × 105 cells ml−1 (planktonic phase) and 6.2 ± 0.7 × 105 cells cm−2 (sessile phase) for anaerobic bacteria. Sulfate-reducing bacteria (SRB) were observed only in the planktonic phase, being
found in greater numbers in the return water. Scanning electron microscopy (SEM) analysis indicated that biofilm formation
occurred at the three monitored sites and showed a diversity in cell morphology. Nonetheless, no evidence of corrosion was
observed on the brass coupons during the experimental period.
Received 22 May 1997/ Accepted in revised form 19 September 1997 相似文献
19.
Theodoros Goulas Athanasios Goulas George Tzortzis Glenn R. Gibson 《Applied microbiology and biotechnology》2009,82(6):1079-1088
Four different β-galactosidases (previously named BbgI, BbgII, BbgIII and BbgIV) from Bifidobacterium bifidum NCIMB41171 were overexpressed in Escherichia coli, purified to homogeneity and their biochemical properties and substrate preferences comparatively analysed. BbgI was forming
a hexameric protein complex of 875 kDa, whereas BbgII, BbgIII and BbgIV were dimers with native molecular masses of 178, 351
and 248 kDa, respectively. BbgII was the only enzyme that preferred acidic conditions for optimal activity (pH 5.4–5.8), whereas
the other three exhibited optima in more neutral pH ranges (pH 6.4–6.8). Na+ and/or K+ ions were prerequisite for BbgI and BbgIV activity in Bis–Tris-buffered solutions, whereas Mg++ was strongly activating them in phosphate-buffered solutions. BbgII and BbgIII were slightly influenced from the presence
or absence of cations, with Mg++, Mn++ and Ca++ ions exerting the most positive effect. Determination of the specificity constants (k
cat/K
m) clearly indicated that BbgI (6.11 × 104 s−1 M−1), BbgIII (2.36 × 104 s−1 M−1) and especially BbgIV (4.01 × 105 s−1 M−1) are highly specialised in the hydrolysis of lactose, whereas BbgII is more specific for β-d-(1→6) galactobiose (5.59 × 104 s−1 M−1) than lactose (1.48 × 103 s−1 M−1). Activity measurements towards other substrates (e.g. β-d-(1→6) galactobiose, β-d-(1→4) galactobiose, β-d-(1→4) galactosyllactose, N-acetyllactosamine, etc.) indicated that the β-galactosidases were complementary to each other by hydrolysing different substrates and thus contributing in a different
way to the bacterial physiology. 相似文献
20.
Litter Decomposition and Nutrient Dynamics in a Phosphorus Enriched Everglades Marsh 总被引:3,自引:0,他引:3
A field study was conducted in a nutrient-impacted marsh in Water Conservation Area 2A (WCA-2A) of the Everglades in southern
Florida, USA, to evaluate early stages of plant litter (detritus) decomposition along a well-documented trophic gradient,
and to determine the relative importance of environmental factors and substrate composition in governing decomposition rate.
Vertically stratified decomposition chambers containing native plant litter (cattail and sawgrass leaves) were placed in the
soil and water column along a 10-km transect coinciding with a gradient of soil phosphorus (P) enrichment. Decomposition rate
varied significantly along the vertical water–soil profile, with rates typically higher in the water column and litter layer
than below the soil surface, presumably in response to vertical gradients of such environmental factors as O2 and nutrient availability. An overall decrease in decomposition rate occurred along the soil P gradient (from high- to low-impact).
First-order rate constant (k) values for decomposition ranged from 1.0 to 9.2 × 10−3 day−1 (mean = 2.8 ×10−3 day−1) for cattails, and from 6.7 × 10−4 to 3.0 × 10−3 day−1 (mean = 1.7 × 10−3 day−1) for sawgrass. Substantial N and P immobilization occurred within the litter layer, being most pronounced at nutrient-impacted
sites. Nutrient content of the decomposing plant tissue was more strongly correlated to decomposition rate than was the nutrient
content of the surrounding soil and water. Our experimental results suggest that, although decomposition rate was significantly
affected by initial substrate composition, the external supply or availability of nutrients probably played a greater role
in controlling decomposition rate. It was also evident that nutrient availability for litter decomposition was not accurately
reflected by ambient nutrient concentration, e.g., water and soil porewater nutrient concentration. 相似文献