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1.
Given their rapid growth and nutrient assimilation rates, Porphyra spp. are good candidates for bioremediation. The production potential of two northeast U.S. Porphyra species currently in culture ( P. purpurea and P. umbilicalis ) was evaluated by measuring rates of photosynthesis (as O2 evolution) of samples grown at 20° C. Gametophytes of P. umbilicalis photosynthesized at rates that were 80% higher than those of P. purpurea over 5–20° C at both sub-saturating and saturating irradiances (37 and 289 μmol photons m−2 s−1 ). Porphyra umbilicalis was both more efficient at low irradiances (higher alpha) and had a higher Pmax than did P. purpurea (23.0 vs. 15.6 μmol O2 g−1 DW min−1 ), suggesting that P. umbilicalis is a better choice for mass culture where self-shading may be severe. The photosynthesis-irradiance relationship for the Conchocelis stage of P. purpurea was also examined. Tufts of filaments, grown at 10, 15, and 20° C, were assayed at growth temperatures at irradiances ranging from 0–315 μmol photons m−2 s−1 . Tufts were slightly more productive at 15° than at 10° C, but only ca. 4–6% as productive as gametophytes. Maximum rates of net photosynthesis were reduced by 66–74% in tufts grown at 20° C (only about 2% of gametophytes). The Conchocelis stage, however, need not limit mariculture operations; once Conchocelis cultures are established, they can be maintained over the long-term as ready sources of spores for net seeding. 相似文献
2.
Klaus Lüning 《Journal of phycology》2001,37(1):52-58
The circadian rhythm in growth of the red macroalga Porphyra umbilicalis (Linnaeus) J. Agardh was investigated under different spectral light conditions in laboratory-grown thalli. A free-running rhythm was observed in constant green or red light at irradiances of 2.5 to 20 μmol photons·m−2 ·s−1 , whereas arhythmicity occurred in constant blue light at 6–20 μmol photons·m−2 ·s−1 . The circadian oscillator controlling growth rhythmicity in Porphyra uses most of the visible sunlight spectrum and possibly multiple photoreceptors with a high sensitivity for blue light and a lower sensitivity for red light. This was inferred from three experimental results: (1) The free-running period, τ, of the growth rhythm decreased with increasing irradiance, from approximately 25 h at 2.5 μmol photons·m−2 ·s−1 to 22 h at 20 μmol photons·m−2 ·s−1 in red or green light, (2) Dark pulses of 3 h duration, interrupting otherwise continuous green or red light, caused advances during the subjective day and delays during the subjective night; the circadian oscillator in Porphyra can discriminate darkness from green or red light, and (3) Low-irradiance blue light pulses (2.5 μmol photons·m−2 ·s−1 ) shifted the growth rhythm in red light of higher irradiance (e.g. 10 μmol photons·m−2 ·s−1 ), and a strong, high amplitude, type 0 phase response curve was obtained that is usually observed with light pulses shifting a circadian rhythm in otherwise continuous darkness. 相似文献
3.
Abstract A diatom biofilm was grown in a chamber developed for culture of biofilms in chemical gradients. The diatoms grew on a polycarbonate membrane filter which separated a sterile reservoir, with added phosphate, from a reservoir without phosphate. Within 3 weeks of inoculation, a thick biofilm developed on the surface of the filter. The biofilms were homogeneous and therefore suitable for calculations of O2 diffusion fluxes from concentration profiles of O2 . Profiles of O2 , pH, and gross photosynthesis at different light intensities and liquid medium concentrations of dissolved inorganic carbon and O2 were measured with microelectrodes. Respiratory activity in a layer of the biofilm was determined as the difference between gross photosynthesis and outflux of O2 from that layer. The photosynthetic activity in a well-developed biofilm grown at 360 μEinst m−2 s−1 and 2.4 mM HCO3 − was limited by the supply of inorganic carbon. Exposure to light above 360 μEinst m−2 s−1 stimulated gross photosynthesis as well as respiratory processes without affecting net outflux of O2 . Higher concentrations of inorganic carbon, on the other hand, enhanced gross photosynthesis without concurrent increase in respiratory rate, resulting in an increased outflux of O2 . High concentrations of O2 in the liquid medium decreased the net outflux of O2 with little effect on the gross photosynthesis. The effects of inorganic carbon and O2 on the metabolic activities of the biofilm were consistent with the presence of photorespiratory activity. 相似文献
4.
Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. I. Photosynthesis in vivo 总被引:2,自引:0,他引:2
The floating angiosperm Lemna gibba L. was exposed for 2 h to various combinations of photosynthetic photon flux densities and temperature. The extent of photoinhibition of photosynthesis was assayed by measuring the net CO2 uptake before and after a photoinhibitory treatment, and the time course for photoinhibition was studied. It was found that the maximum quantum yield and the light-saturated rate of CO2 uptake were affected by the interaction between light and temperature during the photoinhibitory treatment. At a constant photon flux density of 650 μmol m−2 s−1 the extent of photoinhibition increased with decreasing temperature showing that even a chilling-resistant plant like L. gibba is much more susceptible to photoinhibition at chilling temperatures. About 60% photoinhibition of the quantum yield for CO2 uptake could be obtained either by a high photon flux density of 1 750 μmol m−2 s−1 and 25°C or by a moderate photon flux density of 650 μmol m−2 s−1 and 3°C. The time courses of recovery from 60% photoinhibition produced by either of these two treatments were similar, indicating that the nature of the photoinhibition was intrinsically similar. The extent of photoinhibition was related to the amount of light absorbed in excess to what could be handled by photosynthesis at that temperature. The vital importance of photosynthesis in alleviating photoinhibition is discussed. 相似文献
5.
Choline Uptake in Cultured Human Y79 Retinoblastoma Cells: Effect of Polyunsaturated Fatty Acid Compositional Modifications 总被引:6,自引:6,他引:0
Abstract: Choline uptake in Y79 human retinoblastoma cells occurs through two kinetically distinguishable processes. The high-affinity system shows little sodium or energy dependence, and it does not appear to be linked to acetyl CoA: choline O -acetyltransferase. When the cells are grown in a culture medium containing 10% fetal bovine serum, the high-affinity system has a K' m = 2.16 ± 0.13 μ m and V' max = 27.0 ± 2.9 pmol min−1 mg−1 , whereas the low-affinity system has K' m = 20.4 ± 1.3 μ m and V' max = 402 ± 49 pmol min−1 mg−1 . Under these conditions, the polyunsaturated fatty acid content of the cell membranes is relatively low. When the polyunsaturated fatty acid content of the microsomal membrane fraction was increased by supplementing the culture medium with linolenic or docosahexaenoic acids (n-3 polyunsaturated fatty acids) or arachidonic acid (n-6 polyunsaturated fatty acid), the K' m of the high-affinity choline transport system was reduced by 40–60%. The V' max also was reduced by 20–40%. Supplementation with oleic acid, the most prevalent monounsaturated fatty acid, did not affect either kinetic parameter. The results suggest that one functional effect of the high unsaturated fatty acid content of neural cell membranes is to facilitate the capacity of the high-affinity choline uptake system to transport low concentrations of choline. This effect appears to be specific for polyunsaturated fatty acids but not for a single type, for it is produced by members of both the n-3 and n-6 classes of polyunsaturated fatty acids. 相似文献
6.
Reaction of Muscimol with 4-Aminobutyrate Aminotransferase 总被引:1,自引:1,他引:0
Abstract: The reaction of muscimol as amino donor substrate for GABA transaminase (GABA-T) has been studied using enzyme purified from rabbit brain. Enzyme activity was assayed by measuring the glutamate produced using glutamate dehydrogenase. Kinetic parameters determined at 37°C were for GABA, K m (app) = 1.92 ± 0.24 m M , specific activity = 7.33 ± 0.27 μmol/min/mg ( k cat = 13.7s−1 ), and for muscimol, K m (app) = 1.27 ± 0.15 m M , specific activity = 0.101 ± 0.009 μmol/min/mg ( k cat = 0.19s−1 ). Addition of muscimol to the enzyme caused the spectral changes associated with conversion of the pyridoxaldimine form to the pyridoxamine form, and the first-order rate constant for the reaction showed a dependence on muscimol concentration that followed saturation kinetics, with a K = 1.1 ±0.18 m M and k max = 0.065 ± 0.004 s−1 (19°C). The rate of spectral change observed on addition of muscimol to ornithine transaminase was extremely slow—at least an order of magnitude slower than that seen with GABA-T. 相似文献
7.
Oxygen uptake rates and yolk-inclusive dry weiGhts were measured during the egg and yolk-sac larval stages of milkfish, Chanos chanos (Forsskal). Oxygen uptake by eggs and yolk-sac larvae was measured to assess the effects of four salinities (20,25,30,35 ppt) at 28°C. The effects of three temperatures (23,28,33°C) on oxygen uptake by yolk-sac larvae were determined at a salinity of 35 ppt. Dry weights were measured throughout embryonic development at 28°C and the yolk-sac stage at 23.28 and 33°C.
Oxygen uptake rates of eggs increased more than fivefold during embryogenesis (0.07±0.03 to 0.40 ± 03 μl O2 egg −1 h −1 ;blastula to prehatch stage). Larval oxygen uptake did not change with age but was affected by rearing temperature (0.33 ± 0.08, 0.44 ± 0.07 and 0.63 ± 0.13 μl O2 larva −1 h−1 at 23, 28 and 33°C, respectively; Q10 = 1.93). Acute temperature changes from 28 to 33°C caused significant increases in oxygen uptake by embryos (Q 10 = 1.69–3.58) and yolk-sac larvae (Q 10 =2.55). Salinity did not affect metabolic rates.
Dry weight of eggs incubated at 28°C decreased 13% from fertilization to hatching. Incubation temperatures from 23–33°C did not affect dry weights at hatching. Rearing temperatures significantly affected the rate of larval yolk absorption (Q10 = 2.25). 相似文献
Oxygen uptake rates of eggs increased more than fivefold during embryogenesis (0.07±0.03 to 0.40 ± 03 μl O
Dry weight of eggs incubated at 28°C decreased 13% from fertilization to hatching. Incubation temperatures from 23–33°C did not affect dry weights at hatching. Rearing temperatures significantly affected the rate of larval yolk absorption (Q
8.
Regulation of phosphate influx in barley roots: Effects of phosphate deprivation and reduction of influx with provision of orthophosphate 总被引:4,自引:0,他引:4
Barley plants were grown in nutrient solutions, which were maintained at either 0 (-P) or 15 μ M orthophosphate (+P). After 11 days phosphate influx into the intact roots of the -P plants began to increase by comparison with +P plants. During this period differences became apparent between the treatments in absolute growth rates, as well as in the root:shoot ratios. Phosphate influx in the -P plants continued to increase as a function of time, to a maximum value of 2.4 μmol (g fresh wt)-1 h-1 at 16 days after germination. This rate was 6 times higher than influx values for +P plants of the same age. During the period of enhanced uptake phosphate was strongly correlated (r2 = 0.77) with root organic phosphate concentration. – The enhancement of inorganic phosphate influx into intact roots of -P plants was rapidly reduced by the provision of 15 μ M orthophosphate. Typically, within 4 h of exposure to this concentration of phosphate, influx values fell from 1.80 ± 0.20 to 0.75 ± 0.03 μmol (g fresh wt)-1 h-1 , while inorganic phosphate concentrations of the roots increased from 0.12 to 1.15 μmol (g fresh wt)-1 during the same period. Hill plots of the influx data obtained during this period, treating root inorganic phosphate as an inhibitor of influx, gave Hill coefficients close to 2. The rapidity of the reduction of influx associated with increased root inorganic phosphate together with the Hill plot data provide evidence for an allosteric inhibition of influx by internal inorganic phosphate. 相似文献
9.
Michael Knee 《Physiologia plantarum》1995,95(2):211-216
I considered the possibility that changes in fruit photosynthesis obscure the occurrence of the climacteric rise in respiration in tomato fruits attached to the plant. Internal CO2 and ethylene concentrations in tomatoes ( Lycopersicon esculentum Mill. cv. OH 7814) were analyzed after direct sampling through polyethylene tubes implanted in the external pericarp. Fruits which were shaded with aluminium foil contained up to 60 ml 1−1 CO2 , until the internal ethylene concentration exceeded 1 μl l−1 , when CO2 concentration declined to below 40 ml l−1 ; the CO2 concentration in fruits exposed to light only occasionally exceeded 40 ml 1−1 . The internal CO2 concentration of detached fruits first declined and then increased along with ethylene concentration, as expected for the climacteric. Detached green fruits under continuous low photosynthetic photon flux density (100 μmol m−2 s−1 ) contained almost no internal CO2 and produced no CO2 . Changes in photosynthesis and an associated CO2 -generating system in green fruits are thought to obscure the climacteric rise in tomato fruits developing on the plant. 相似文献
10.
The Uptake of Carnitine by Slices of Rat Cerebral Cortex 总被引:5,自引:3,他引:2
P. J. Huth M. J. Schmidt P. V. Hall R. G. Fariello A. L. Shug 《Journal of neurochemistry》1981,36(2):715-723
Abstract: The properties of carnitine transport were studied in rat brain slices. A rapid uptake system for carnitine was observed, with tissue-medium gradients of 38 ± 3 for L-[14 CH3 ]carnitine and 27 ± 3 for D-[14 CH3 ]carnitine after 180 min incubation at 37°C in 0.64 mM substrate. Uptake of L- and D-carnitine showed saturability. The estimated values of K m for L- and D-carnitine were 2.85 mM and 10.0 mM, respectively; but values of V max (1 μmol/min/ml in-tracellular fluid) were the same for the two isomers. The transport system showed stereospecificity for L-carnitine. Carnitine uptake was inhibited by structurally related compounds with a four-carbon backbone containing a terminal carboxyl group. L-Carnitine uptake was competitively inhibited by γ-butyrobetaine ( K i = 3.22 mM), acetylcarnitine ( K i = 6.36 mM), and γ-aminobutyric acid ( K i = 0.63 mM). The data suggest that carnitine and γ-aminobutyric acid interact at a common carrier site. Transport was not significantly reduced by choline or lysine. Carnitine uptake was inhibited by an N2 atmosphere, 2,4-dinitrophenol, carbonylcyanide- N -chlorophenylhydrazone, potassium cyanide, n-ethylmaleimide, and ouabain. Transport was abolished by low temperature (4°C) and absence of glucose from the medium. Carnitine uptake was Na+ -dependent, but did not require K+ or Ca2+ . 相似文献
11.
Photosynthetic CO2 -fixation, chlorophyll content, growth rate and nitrate reductase activity were used to examine the influence of NH+ 4 -N and NO− 3 -N on Sphagnum magellanicum cultivated under defined conditions in phytotrons. NO− 3 -concentrations up to 322 μ M were found to be favourable. Increased NH+ 4 concentrations, however, resulted in growth inhibition and decreased chlorophyll content at concentrations ≧ 255 μ M ; e.g. 600 μ M NH+ 4 caused a 20% reduction of nitrate reductase activity and net photosynthesis. For raised bog Sphagna an improved standard nutrient solution is proposed with the following ion concentrations (μ M ): 55 Na+ ; 17 K+ ; 95 NH+ 4 ; 22 Ca2+ ; 22 Mg2+ ; 2 Fe3+ ; 20 Cl− ; 100 NO− 3 ; 57 SO2- 4 ; 7.4 H2 PO− 4 ; trace elements: A-Z solution (Hoagland) 50 μl 1000 ml−1 ; pH 5.8. 相似文献
12.
Elevated CO2 and ozone reduce nitrogen acquisition by Pinus halepensis from its mycorrhizal symbiont
The effects of 700 μmol mol−1 CO2 and 200 nmol mol−1 ozone on photosynthesis in Pinus halepensis seedlings and on N translocation from its mycorrhizal symbiont, Paxillus involutus, were studied under nutrient-poor conditions. After 79 days of exposure, ozone reduced and elevated CO2 increased net assimilation rate. However, the effect was dependent on daily accumulated exposure. No statistically significant differences in total plant mass accumulation were observed, although ozone-treated plants tended to be smaller. Changes in atmospheric gas concentrations induced changes in allocation of resources: under elevated ozone, shoots showed high priority over roots and had significantly elevated N concentrations. As a result of different shoot N concentration and net carbon assimilation rates, photosynthetic N use efficiency was significantly increased under elevated CO2 and decreased under ozone. The differences in photosynthesis were mirrored in the growth of the fungus in symbiosis with the pine seedlings. However, exposure to CO2 and ozone both reduced the symbiosis-mediated N uptake. The results suggest an increased carbon cost of symbiosis-mediated N uptake under elevated CO2 , while under ozone, plant N acquisition is preferentially shifted towards increased root uptake. 相似文献
13.
Roberto Barreiro Juan J. Guiamét José Beltrano Edgardo R. Montaldi 《Physiologia plantarum》1992,85(1):97-101
The main objective of the present work was to examine the effects of the red:far-red ratio (R:FR) prevailing during leaf development on the photosynthetic capacity of mature leaves. Plants of Phaseolus vulgaris L. cv. Balin de Albenga were grown from time of emergence in a controlled environment room, 25 ± 3°C, 12-h photoperiod, with different light treatments:a) high photosynthetic photon flux density (PPFD) = 800 μmol m−1 s−1 + high R:FR= 1.3;b) low PPFD= 300 μmol m−2 s−1 + high R:FR= 1.3; c) high PPFD=800 μmol m−2 s−1 + low R:FR= 0.7; d) low PPFD= 300 μmol m−2 s−1 + low R:FR=0.7. With an R:FR ratio of 1.3, a decrease in irradiance during leaf growth reduced photosynthesis when measured at moderate to high PPFD; but when measured at low PPFD, leaves expanded under low irradiance actually had photosynthesis rates higher than those of leaves grown in high irradiance. A low R:FR ratio during development reduced the photosynthetic capacity of the leaves. In leaves expanded under R:FR = 0.7 and high irradiance photosynthesis was reduced by 42 to 89%, depending on the PPFD at which measurements were made, whereas for leaves developed at R:FR = 0.7 and low irradiance photosynthesis decreased by 21 to 24%, compared to leaves under R:FR = 1.3 and similar irradiance. The reduced photosynthetic capacity under R:FR = 0.7 and high irradiance. In natural environments, leaves may experience low R:FR conditions temporarily during their development, and this may affect their future photosynthetic capacity in full sunlight. 相似文献
14.
Ammonium uptake by field-grown Eriophorum vaginatum roots under laboratory and simulated field conditions 总被引:1,自引:0,他引:1
Nitrogen (N) deficiencies in tundra ecosystems could be caused, in part, by the kinetics of root N uptake. The objectives of this study were to quantify NH4 uptake by field-grown excised roots of Eriophorum vaginatum I. under controlled NH4 concentrations (0-250 μmol I-1 ) and temperatures (5-20°C) and to evaluate this laboratory derived model as a means of estimating field NH4 uptake. There was no consistent temperature effect on root NH4 uptake which suggests a relative in-sensitivity of E. vaginatum roots to short-term temperature fluctuations. The Michaelis-Menten equation parameters for NH4 uptake were Vmax = 22.1 μmol h-1 g-1 and Km = 191 μmol I-1 . Using field NH4 concentrations, field E. vaginatum root biomass data, and the Michaelis-Menten equation, an estimate was made of NH4 uptake over a 42 day period; this estimate of NH4 uptake accounted for 28% of the net incorporation of N into leaves and roots which is a reasonable estimate for E. vaginatum which relies primarily on N retranslocation for supplying new leaves and roots. Major uncertainties in field N uptake rates, model parameterization, and site characterization preclude an accurate model validation and indicate research areas most in need of future study. 相似文献
15.
Photosynthetic acclimation to elevated atmospheric carbon dioxide and UV irradiation in Pinus banksiana 总被引:2,自引:0,他引:2
Pinus banksiana seedlings were grown for 9 months in enclosures in greenhouses at CO2 concentrations of 350 or 750 μmol mol−1 with either low (0.005 to 0. 3 W m−2 ) or high (0.25 to 0. 90 W m−2 ) ultraviolet-B (UV-B) irradiances. Total seedling dry weight decreased with high UV treatment but was unaffected by CO2 enrichment. High UV treatment also shifted biomass partitioning in favor of leaf production. Both CO2 and UV treatments decreased the dark respiration rate and light compensation point. High UV light inhibited photosynthesis at 350 but not at 750 μmol mol−1 CO2 due to a UV induced increase in ribulose-1, 5-bisphosphate carboxylase/oxygenase efficiency and ribulose-1, 5-bisphosphate regeneration. Stomatal density was increased by high UV irradiance but was unchanged by CO2 enrichment. 相似文献
16.
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
17.
An experiment was conducted on intact algal assemblages of stream periphyton to test their response to fluctuating and constant light regimes having the same mean intensity. The light regimes (in μmol·m−2 ·s−1 ) were constant light at 100, light fluctuating between 50 and 150 with a period of 5 min, and light fluctuating between 10 and 460 with periods of either 4:1 or 8:2 min. Compared to the rates measured under 100 in μmol·m−2 ·s−1 constant light conditions, fluctuations ranging between 50 and 150 in μmol·m−2 ·s−1 with a 5-min period produced a 23% greater rate of photosynthesis. Conversely, fluctuations between 10 and 460 in μmol·m−2 ·s−1 led to a 59%–74% decrease in photosynthetic activity. Detailed examination of periphytic algal responses to fluctuating light revealed that higher light intensities produced steeper photosynthesis/time slopes, but it was the combined interaction with lower light intensity that ultimately determined overall photosynthetic rate for a given light regime. This study offers compelling evidence that variable light regimes have important consequences for algal photosynthesis in natural streams. 相似文献
18.
Abstract— Uptake and release of glutamine were measured in primary cultures of astrocytes together with the activity of the phosphate activated glutaminase (EC 3.5.1.2). In contrast to previous findings of an effective, high affinity uptake of other amino acids (e.g. glutamate, GABA) no such uptake of glutamine was observed, though a saturable, concentrative uptake mechanism did exist (K m = 3.3 ± 0.5 m m ; V max = 50.2 ± 12.6 nmol ± min−1 ± mg−1 ). The phosphate activated glutaminase activity in the astrocytes (6.9 ± 0.9 nmol ± min−1 ± mg−1 ) was similar to the activity found in whole brain (5.4 ± 0.7 nmol ± min −l ± mg−1 ), which may contrast with previous findings of a higher activity of the glutamine synthetase (EC 6.3.1.2) in astrocytes than in whole brain. The observations are compatible with the hypothesis of an in vivo flow of glutamate (and GABA) from neurons to astrocytes where it is taken up and metabolized, and a compensatory flow of glutamine towards neurons and away from astrocytes although the latter cell type may be more deeply involved in glutamine metabolism than envisaged in the hypothesis. 相似文献
19.
The effects of photon flux density and temperature on net photosynthesis and transpiration rates of mature and immature leaves of three-year-old Japanese larch Larix kaempferi (Lamb.) Sarg. trees were determined with an infrared, differential open gas analysis system. Net photosynthetic response to increasing photon flux densities was similar for different foliage positions and stage of maturity. Light compensation was between 25 and 50 μmol m−2 s−1 . Rates of photosynthesis increased rapidly at photon flux densities above the compensation level and became saturated between 800 and 1000 μmol m−2 s−1 . Transpiration rates at constant temperature likewise increased with increasing photon flux density, and leveled off between 800 and 1000 μmol m−2 s−1 . Photosynthetic response to temperature was determined in saturating light and was similar for all foliage positions; it increased steadily from low temperatures to an optimum range betweeen 15 and 21°C and then decreased rapidly above 21°C. Transpiration rate, however, increased continuously with rising temperature up to the experimental maximum. CO2 compensation concentrations for mature foliage varied between 58 and 59 μl l−1 ; however, foliage borne at the apex of the terminal leader compensated at 75 μl l−1 . None of these data support the claim that Japanese larch possesses C4 photosynthetic characteristics. 相似文献
20.
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