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1.
1. Plants growing in deep shade and high temperature, such as in the understorey of humid tropical forests, have been predicted to be particularly sensitive to rising atmospheric CO2 . We tested this hypothesis in five species whose microhabitat quantum flux density (QFD) was documented as a covariable. After 7 (tree seedlings of Tachigalia versicolor and Beilschmiedia pendula ) and 18 months (shrubs Piper cordulatum and Psychotria limonensis, and grass Pharus latifolius ) of elevated CO2 treatment ( c. 700 μl litre–1 ) under mean QFD of less than 11 μmol m–2 s–1 , all species produced more biomass (25–76%) under elevated CO2 .
2. Total plant biomass tended to increase with microhabitat QFD (daytime means varying from 5 to 11μmol m–2 s–1 ) but the relative stimulation by elevated CO2 was higher at low QFD except in Pharus .
3. Non-structural carbohydrate concentrations in leaves increased significantly in Pharus (+ 27%) and Tachigalia (+ 40%).
4. The data support the hypothesis that tropical plants growing near the photosynthetic light compensation point are responsive to elevated CO2 . An improved plant carbon balance in deep shade is likely to influence understorey plant recruitment and competition as atmospheric CO2 continues to rise. 相似文献
2. Total plant biomass tended to increase with microhabitat QFD (daytime means varying from 5 to 11μmol m
3. Non-structural carbohydrate concentrations in leaves increased significantly in Pharus (+ 27%) and Tachigalia (+ 40%).
4. The data support the hypothesis that tropical plants growing near the photosynthetic light compensation point are responsive to elevated CO
2.
3.
Changes in the temperature dependence of the photosynthetic rate depending on growth temperature were investigated for a temperate evergreen tree, Quercus myrsinaefolia . Plants were grown at 250 μ mol quanta m–2 s–1 under two temperature conditions, 15 and 30 °C. The optimal temperature that maximizes the light-saturated rate of photosynthesis at 350 μ L L–1 CO2 was found to be 20–25 and 30–35 °C for leaves grown at 15 and 30 °C, respectively. We focused on two processes, carboxylation and regeneration of ribulose-1,5-bisphosphate (RuBP), which potentially limit photosynthetic rates. Because the former process is known to limit photosynthesis at lower CO2 concentrations while the latter limits it at higher CO2 concentrations, we determined the temperature dependence of the photosynthetic rate at 200 and 1000 μ L L–1 CO2 under saturated light. It was revealed that the temperature dependence of both processes varied depending on the growth temperature. Using a biochemical model, we estimated the capacity of the two processes at various temperatures under ambient CO2 concentration. It was suggested that, in leaves grown at low temperature (15 °C), the photosynthetic rate was limited solely by RuBP carboxylation under any temperature. On the other hand, it was suggested that, in leaves grown at high temperature (30 °C), the photosynthetic rate was limited by RuBP regeneration below 22 °C, but limited by RuBP carboxylation above 22 °C. We concluded that: (1) the changes in the temperature dependence of carboxylation and regeneration of RuBP and (2) the changes in the balance of these two processes altered the temperature dependence of the photosynthetic rate. 相似文献
4.
Uptake and turnover of acetate in hypersaline environments 总被引:2,自引:0,他引:2
Aharon Oren 《FEMS microbiology ecology》1995,18(1):75-84
Abstract: Acetate uptake and turnover rates were determined for the heterotrophic community in hypersaline environments (saltern crystallizer ponds, the Dead Sea) dominated by halpphilic Archaea. Acetate was formed from glycerol, which is potentially the major available carbon source for natural communities of halophilic Archaea. Values of [ K t + S n ] (the sum of the substrate affinity and the substrate concentration present in situ) for acetate measured in saltern crystallizer ponds were around 4.5–11.5 μM, while in the Dead Sea during a Dunaliella bloom values up to 12.8 μM were found. Maximal theoretical rates ( V max ) of acetate uptake in saltern crystallizer ponds were 12–56 nmol l−1 h−1 , with estimated turnover times for acetate ( T t ) between 127–730 h at 35°C. V max values measured in the Dead Sea were between 0.8 and 12.8 nmol l−1 h−1 , with turnover times in the range of 320–2190 h. V max values for acetate were much lower than those for glycerol. Comparisons with pure cultures of halophilic Archaea grown under different conditions showed that the natural communities were not adapted for preferential use of acetate. Both in natural brines and in pure cultures of halophilic Archaea, acetate incorporation rates rapidly decreased above the optimum pH value, probably since acetate enters the cell only in its unionized form. The low affinity for acetate, together with low potential utilization rates result in the long acetate turnover times, which explains the accumulation of acetate observed when low concentrations of glycerol are supplied as a nutrient to natural communities of halophilic Archaea. 相似文献
5.
Spatio-temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps 总被引:3,自引:0,他引:3
1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity.
2. Nitrogen concentrations were high (nitrate-N values were 130–274 μg L–1 ), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m–2 dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus .
3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m–2 , although peaking as high as 9000 ind. m–2 . Average annual biomass ranged from 102 to 721 mg m–2 , and reached >2000 mg m–2 at one site in autumn.
4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina , and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer. 相似文献
2. Nitrogen concentrations were high (nitrate-N values were 130–274 μg L
3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m
4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina , and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer. 相似文献
6.
Abstract The kinetics of glucose uptake by soil microbial communities in 16 different soild (7 under monocultures and 9 under crop rotations) differing in microbial biomass content, % Corg , pH and clay content were investigated at 22°C. The V max value of microbial bimasses under monoculture, was o.27 μg Cgluc · μg−1 Cmic · h−1 (range 0.18–0.44), twice as high as the mean value of V max of microbial biomasses under rotations (0.13 μg Cgluc , range 0.07–0.19). Mean values of K m were 714 μg Cgluc and 290 μg Cgluc · g−1 soil, respectively.
These differences were highly significant ( P =0.001, based on SE) and could not be relate to particle size distribution of the soils, pH or Corg . A Michaelis-Menten type uptake response was apparent over the total range of glucose concentrations used (45.4–1453.3 μg Cgluc · g−1 soil) for microbial biomasses under rotation while the majority of microbial biomasses under monocultures showed a similar response only at low glucose concentrations. A different uptake mechanism appeared to be involved at higher glucose concentrations (similar to diffusion) in monoculture soils. 相似文献
These differences were highly significant ( P =0.001, based on SE) and could not be relate to particle size distribution of the soils, pH or C
7.
The populations, characterization and activity of suspended bacteria in the Welsh River Dee 总被引:1,自引:1,他引:0
D. Nuttall 《Journal of applied microbiology》1982,53(1):49-59
In a 29 month study of bacterial populations at three sites on the Welsh River Dee, the aerobic heterotrophic bacteria increased from an average basal level of about 1.2 times 104 colony-forming units (cfu)/ml near the source of the river, to 2 times 105 cfu/ml in the lower reaches. The ratio, total bacterial cell count: viable count, decreased from 70 in the upland reaches to 10 in the lower parts of the river. There was no apparent seasonal variation in bacterial numbers but on occasions the bacterial populations in both upland and lowland reaches of the river increased simultaneously. Fluctuations in bacterial numbers over a 50-fold range were observed in this study. Bacterial isolates from both upland and lowland sites were predominated by two groupings of bacteria, the Pseudomonas—Agrobacterium—Alcaligenes group and the Flavobacterium—Cytophaga—Flexibacter group. Results suggested that the latter group may have been part of the autochthonous population. Seasonal variation in heterotrophic potential ( V max ) for acetate uptake was shown to occur over a 30-fold range in the lowland reaches of the River Dee. Peaks in activity at the lowland site occurred during the summer months, the range of V max values for acetate ranged from 0.2 to 30 μg/1/h. Fluctuations in V max values from the upland site were not seasonal but were instead linked to faecal pollution, V max values from this site range from 0.04 to 3 μg/1/h. 相似文献
8.
Of 22 commercial juice-processing enzyme preparations investigated, Clarex ML was found to exhibit the highest xylanase activity. The xylanase from Clarex ML was most active at 50–60°C and pH 5·0–5·5. The K m and V max values of the enzyme with oat-spelt xylan as the substrate were 8·6 mg ml−1 and 42 μmol xylose l−1 min−1 , respectively. Xylobiose was the main product of enzymatic hydrolysis of xylan. 相似文献
9.
Deamination of 5-Hydroxytryptamine by Both Forms of Monoamine Oxidase in the Rat Brain 总被引:8,自引:3,他引:5
Abstract: K m and V max values of monoamine oxidase (MAO) A and B towards 5-hydroxytryptamine were determined for rat brain homogenates after the in vitro inhibition of one of the two forms by the selective inhibitors clorgyline and l -deprenyl. K m values of 178 and 1170μ m , and V max values of 0.73 and 0.09 nmol·mg protein−1 ·min−1 towards 5-hydroxytryptamine were found for MAO-A and -B, respectively. The K 1 for 5-hydroxytryptamine as a competitive inhibitor of β-phenethylamine oxidation by MAO-B was found to be 1400 μm. The significance of these findings is discussed. 相似文献
10.
Competition between anoxygenic phototrophic bacteria and colorless sulfur bacteria in a microbial mat 总被引:2,自引:0,他引:2
Pieter T. Visscher Frank P. van den Ende Bartholomeus E.M. Schaub Hans van Gemerden 《FEMS microbiology letters》1992,101(1):51-58
Abstract The populations of chemolithoautotrophic (colorless) sulfur bacteria and anoxygenic phototrophic bacteria were enumerated in a marine microbial mat. The highest population densities were found in the 0–5 mm layer of the mat: 2.0 × 109 cells cm−3 sediment, and 4.0 × 107 cells cm−3 sediment for the colorless sulfur bacteria and phototrophs, respectively. Kinetic parameters for thiosulfate-limited growth were assessed for Thiobacillus thioparus T5 and Thiocapsa roseopersicina M1, both isolated from microbial mats. For Thiobacillus T5, growing at a constant oxygen concentration of 43 μmol l−1 , μmax was 0.336 h−1 and K s 0.8 μmol l−1 . Phototrophically grown Thiocapsa strain M1 displayed a μmax of 0.080 h−1 and a K s of 8 μmol l−1 when anoxically grown under thiosulfate limitation. In a competition experiment with thiosulfate as electron donor, Thiocapsa became dominant during a 10-h oxic/14-h anoxic regimen at continuous illumination, despite the higher affinity for thiosulfate of Thiobacillus . 相似文献
11.
Abstract Bradyrhizobium japonicum and Shewanella putrefaciens were unable to oxidize hydrogen at atmospheric concentrations (0.55 ppmv), neither in suspension nor when added to sterile soil. The K m -value of S. putrefaciens for H2 (39 ppmv in gas phase, 0.22 μM in aqueous phase), using Fe(III) as electron acceptor, showed a 4–5-fold higher affinity for H2 than that of B. japonicum (1200 ppmv; 0.84 μM) or other hydrogen-oxidizing bacteria. However, the V max (4.54 fmol H2 h−1 cell −1 ) and threshold (> 0.5 ppmv; 0.35 nM) of S. putrefaciens and the V max (7.19 fmol H2 h−1 cell−1 ) and threshold (> 0.5 ppmv; 0.35 nM) of B. japonicum were in the same order of magnitude as data for Knallgas bacteria from relevant literature. To enable hydrogen oxidation in soil the soil-samples with S. putrefaciens even had to be supplemented with Fe(III). Fresh soil, on the other hand, oxidized hydrogen very efficiently below atmospheric mixing ratios, demonstrating that there must be other oxidation activities in soil. 相似文献
12.
The mechanisms mediating CO2 sensing and light–CO2 interactions in guard cells are unknown. In growth chamber-grown Vicia faba leaves kept under constant light (500 μ mol m–2 s–1 ) and temperature, guard cell zeaxanthin content tracked ambient [CO2 ] and stomatal apertures. Increases in [CO2 ] from 400 to 1200 cm3 m–3 decreased zeaxanthin content from 180 to 80 mmol mol–1 Chl and decreased stomatal apertures by 7·0 μ m. Changes in zeaxanthin and aperture were reversed when [CO2 ] was lowered. Guard cell zeaxanthin content was linearly correlated with stomatal apertures. In the dark, the CO2 -induced changes in stomatal aperture were much smaller, and guard cell zeaxanthin content did not change with chamber [CO2 ]. Guard cell zeaxanthin also tracked [CO2 ] and stomatal aperture in illuminated stomata from epidermal peels. Dithiothreitol (DTT), an inhibitor of zeaxanthin formation, eliminated CO2 -induced zeaxanthin changes in guard cells from illuminated epidermal peels and reduced the stomatal CO2 response to the level observed in the dark. These data suggest that CO2 -dependent changes in the zeaxanthin content of guard cells could modulate CO2 -dependent changes of stomatal apertures in the light while a zeaxanthin-independent CO2 sensing mechanism would modulate the CO2 response in the dark. 相似文献
13.
Evidence for cytochrome P-450 and P-450-mediated benzo(a) pyrene hydroxylation in the white rot fungus Phanerochaete chrysosporium 总被引:2,自引:0,他引:2
Segula Masaphy Dan Levanon Yigal Henis K. Venkateswarlu Steven L. Kelly 《FEMS microbiology letters》1996,135(1):51-55
Abstract The presence of cytochrome P-450 and P-450-mediated benzo(a)pyrene hydroxylase activity in both microsomal and soluble fractions of the white rot fungus Phanerochaete chrysosporium was shown. The reduced carbon monoxide difference spectrum showed maxima at 448–450 and 452–454 nm for microsomal and cytosolic fractions, respectively. Both P-450 fractions produced a Type I substrate binding spectrum on addition of benzo(a)pyrene. Activity for benzo(a)pyrene hydroxylation was NADPH-dependent and inhibited by carbon monoxide. K m values for activity showed a difference between the cellular fractions with a K m of 89 μM for microsomal P-450 and 400 μM for cytosolic P-450. The V max values observed were 0.83 nmol min− (nmol microsomal P-450) −1 and 0.4 nmol min−1 (nmol cytosolic P-450)−1 . The results indicate that P-450-mediated benzo(a)pyrene hydroxylase activity could play a role in xenobiotic transformation by this fungus beside the known ligninolytic exocellular enzymes. 相似文献
14.
Jill E. Cremer Vincent J. Cunningham William M. Pardridge Leon D. Braun William H. Oldendorf 《Journal of neurochemistry》1979,33(2):439-445
Abstract— The kinetics of the uptake from blood to brain of pyruvate, lactate and glucose have been determined in rats of different ages. The carotid artery single injection technique was used in animals anaesthetized with pentobarbital. The rates of influx for each substrate were determined over a range of concentrations for the different age-groups. Data were analysed in terms of the Michaelis-Menten equation with a component to allow for non-saturable diffusion. Values are given for K m , V max and K d . In suckling rats (15-21 days) the V max values for both pyruvate and lactate were 2.0 μmol g−1 min−1 . In 28-day-old rats the V max values had fallen to one-half and in adults they were less than one-tenth. K m , values were higher in the younger animals. The rate of glucose transport in suckling rats was half that of 28-day-old and adults although there was no difference with age in the K m values.
The results are discussed in relation to the net flux of these substrates in and out of brain during different stages of post-natal development. 相似文献
The results are discussed in relation to the net flux of these substrates in and out of brain during different stages of post-natal development. 相似文献
15.
Wild cherry ( Prunus avium L.) shoots were cultured in closed vessels on a proliferation medium and the volatile substances released during incubation at photosynthetic photon flux density of 30 μmol m–2 S–1 were determined. Ethylene and CO2 started forming at the beginning of the incubation period and a linear relationship between their formation was observed even at high CO2 concentrations. After 30 days of culture, CO2 reached a concentration of 30%. Shoots released elhanol and acetaldehyde after several days of incubation. 相似文献
16.
We present, for the first time, the oxygen response kinetics of mitochondrial respiration measured in intact leaves (sunflower and aspen). Low O2 concentrations in N2 (9–1500 ppm) were preset in a flow-through gas exchange measurement system, and the decrease in O2 concentration and the increase in CO2 concentration as result of leaf respiration were measured by a zirconium cell O2 analyser and infrared-absorption CO2 analyser, respectively. The low O2 concentrations little influenced the rate of CO2 evolution during the 60-s exposure. The initial slope of the O2 uptake curve on the dissolved O2 concentration basis was relatively constant in leaves of a single species, 1.5 mm s−1 in sunflower and 1.8 mm s−1 in aspen. The apparent K 0.5 (O2 ) values ranged from 0.33 to 0.67 μ M in sunflower and from 0.33 to 1.1 μ M in aspen, mainly because of the variation of the maximum rate, V max (leaf temperature 22°C). The initial slope of the O2 response of respiration characterizes the catalytic efficiency of terminal oxidases, an important parameter of the respiratory machinery in leaves. The plateau of the response characterizes the activity of the mitochondrial electron transport chain and is subject to regulations in accordance with the necessity for ATP production. The relatively low oxygen conductivity of terminal oxidases means that in leaves, less than 10% of the photosynthetic oxygen can be reassimilated by mitochondria. 相似文献
17.
The kinetics of active sodium uptake in dechorionated embryos, yolk-sac fry and start-feed fry of Atlantic salmon were compared in two groups reared either in low conductivity, untreated, river water (conductivity ∼ 46 μS cm−1 , pH 5.75), or in 'improved' river water buffered with sea water (conductivity ∼2200 μS cm 1 , pH 6.56), the latter treatment often being used in commercial hatcheries to avoid problems associated with periodic acidification.
Maximal transport rate ( Vmax ) increased during development in both groups but was always significantly higher in embryos and fry maintained in untreated river water. Values for K m were not seen to vary during development up to 12 weeks after hatching and were not significantly different between groups, or from values reported for adult Atlantic salmon in fresh water.
The results are discussed with respect to the influence of Na+ concentrations in the perivitelline fluid of developing eggs and in the external medium surrounding fry on V max and K m . The ability of fry reared entirely in buffered river water to maintain sodium balance following transfer to untreated river water is also considered. 相似文献
Maximal transport rate ( V
The results are discussed with respect to the influence of Na
18.
Symbiotic N2 fixation in a high Alpine grassland: effects of four growing seasons of elevated CO2 总被引:1,自引:0,他引:1
J. A. Arnone Iii 《Functional ecology》1999,13(3):383-387
1. Increasing carbon dioxide concentration (E: 680 μl CO2 litre–1 vs ambient, A: 355 μl CO2 litre–1 ) around late-successional Alpine sedge communities of the Swiss Central Alps (2450 m) for four growing seasons (1992–1995) had no detectable effect on symbiotic N2 fixation in Trifolium alpinum —the sole N2 -fixing plant species in these communities (74 ± 30 mg N m–2 year–1 , A and E plots pooled).
2. This result is based on data collected in the fourth growing season showing that elevated CO2 had no effect on Trifolium above-ground biomass (4·4 ± 1·7 g m–2 , A and E plots pooled, n = 24) or N content per unit land area (124 ± 51 mg N m–2 , A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N2 fixation (%Ndfa: 61·0 ± 4·1 across A and E plots) estimated using the 15 N dilution method.
3. Thus, it appears that N inputs to this ecosystem via symbiotic N2 fixation will not be dramatically affected in the foreseeable future even as atmospheric CO2 continues to rise. 相似文献
2. This result is based on data collected in the fourth growing season showing that elevated CO
3. Thus, it appears that N inputs to this ecosystem via symbiotic N
19.
Cyanophytes dominated the phytoplankton of shallow Lake Mikri Prespa during the period May 1990 to September 1992 (76.5 and 52.0% of the total phytoplankton biomass in 1990–1991 and 1991–1992, respectively). Biomass peaks were observed in autumn (from 5.2 to 34.5 g m-3 ) when low dissolved inorganic nitrogen, high phosphate phosphorus and low Zcu to Zmix ratio prevailed. The dominant species were Microcystis aeruginosa and M. wesenbergii. These represented 64 and 86% of the cyanophyte biomass in 1990–1991 and 1991–1992, respectively and revealed similar patterns of seasonality forming biomass peaks in late summer - autumn. Small chroococcalean cyanophytes (< 2 μm) showed also similar temporal distributions. Of the filamentous cyanophytes, the most important species was Anabaena lemmermannii var. minor which formed peaks in late summer and autumn (2.6 and 1.1 g m-3 in 1990 and 1992, respectively). Rainfall and the N:P ratio were probably the main factors influencing the seasonality of all of the filamentous cyanophytes in the lake. Cyanophytes, tended to increase at temperatures higher than 16 °C and at inorganic nitrogen concentrations lower than 100 μg 1- -1 . The frequent mixing of the water column did not seem to prohibit the substantial increase of the group. 相似文献