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1.
Variation in the carbon isotopic composition of ecosystem respiration ('13CR) was studied for 3 years along a precipitation gradient in western Oregon, USA, using the Keeling plot approach. Study sites included six coniferous forests, dominated by Picea sitchensis, Tsuga heterophylla, Pseudotsuga menziesii, Pinus ponderosa, and Juniperus occidentalis, and ranged in location from the Pacific coast to the eastern side of the Cascade Mountains (a 250-km transect). Mean annual precipitation across these sites ranged from 227 to 2,760 mm. Overall '13CR varied from -23.1 to -33.1‰, and within a single forest, it varied in magnitude by 3.5-8.5‰. Mean annual '13CR differed significantly in the forests and was strongly correlated with mean annual precipitation. The carbon isotope ratio of carbon stocks (leaves, fine roots, litter, and soil organic matter) varied similarly with mean precipitation (more positive at the drier sites). There was a strong link between '13CR and the vapor saturation deficit of air (vpd) 5-10 days earlier, both across and within sites. This relationship is consistent with stomatal regulation of gas exchange and associated changes in photosynthetic carbon isotope discrimination. Recent freeze events caused significant deviation from the '13CR versus vpd relationship, resulting in higher than expected '13CR values.  相似文献   

2.
Specific conductivity (ks, m2s-1MPa-1) describes the permeability of xylem and is determined by all aspects of xylem anatomy that create resistance to the flow of water. Here we test the hypothesis that ks is a function of radial and vertical position within the stem, rather than solely a function of cambial age (ring number from the pith), by measuring ks on samples excised from 35-year-old Douglas-fir [Pseudotsuga menziesii var. menziesii (Mirb.) Franco] trees at six heights and two or three radial positions. Sapwood ks decreased from the cambium to the heartwood boundary, and the difference between outer and inner sapwood increased with height in the tree. Beneath the live crown, inner sapwood had 80-90% the ks of outer sapwood, but only 55% just 10 m higher in the stem (about 10 nodes down from the tree top). Outer sapwood ks peaked near the base of the crown and declined toward both the base and top of the stem. These patterns can be explained by two superimposed effects: the effect of cambial age on the dimensions of tracheids as they are produced, and the effect of xylem aging, which may include accumulation of emboli and aspiration of bordered pits. Tracheid lumen diameter and earlywood and latewood density and width, all factors known to vary with cambial age, were measured on different trees of the same age and from the same stand. Lumen diameter increased with cambial age, whereas the proportion of latewood and growth ring density increased after an initial decrease in the first 5 years. Our results suggest that the effect of cambial age on xylem anatomy is not sufficient to explain variation in ks. Instead, physical position (both vertical and radial) in the stem and cambial age must be considered as determinants of conductivity.  相似文献   

3.
Carbon isotope discrimination in photosynthetic bark   总被引:1,自引:0,他引:1  
We developed and tested a theoretical model describing carbon isotope discrimination during photosynthesis in tree bark. Bark photosynthesis reduces losses of respired CO2 from the underlying stem. As a consequence, the isotopic composition of source CO2 and the CO2 concentration around the chloroplasts are quite different from those of photosynthesizing leaves. We found three lines of evidence that bark photosynthesis discriminates against 13C. First, in bark of Populus tremuloides, the '13C of CO2 efflux increased from -24.2‰ in darkness to -15.8‰ in the light. In Pinus monticola, the '13C of CO2 efflux increased from -27.7‰ in darkness to -10.2‰ in the light. Observed increases in '13C were generally in good agreement with predictions from the theoretical model. Second, we found that '13C of dark-respired CO2 decreased following 2-3 h of illumination (P<0.01 for Populus tremuloides, P<0.001 for Pinus monticola). These decreases suggest that refixed photosynthate rapidly mixes into the respiratory substrate pool. Third, a field experiment demonstrated that bark photosynthesis influenced whole-tissue '13C. Long-term light exclusion caused a localized increase in the '13C of whole bark and current-year wood in branches of P. monticola (P<0.001 and P<0.0001, respectively). Thus bark photosynthesis was shown to discriminate against 13C and create a pool of photosynthate isotopically lighter than the dark respiratory pool in all three experiments. Failure to account for discrimination during bark photosynthesis could interfere with interpretation of the '13C in woody tissues or in woody-tissue respiration.  相似文献   

4.
Water availability and carbon isotope discrimination in conifers   总被引:22,自引:0,他引:22  
The stable C isotope composition ('13C) of leaf and wood tissue has been used as an index of water availability at both the species and landscape level. However, the generality of this relationship across species has received little attention. We compiled literature data for a range of conifers and examined relationships among landscape and environmental variables (altitude, precipitation, evaporation) and '13C. A significant component of the variation in '13C was related to altitude (discrimination decreased with altitude in stemwood, 2.53‰ km-1 altitude, r2=0.49, and in foliage, 1.91‰ km-1, r2=0.42), as has been noted previously. The decrease in discrimination with altitude was such that the gradient in CO2 partial pressure into the leaf (Pa-Pi) and altitude were generally unrelated. The ratio of precipitation to evaporation (P/E) explained significant variation in Pa-Pi of stemwood (r2=0.45) and foliage (r2=0.27), but only at low (<0.8) P/E. At greater P/E there was little or no relationship, and other influences on '13C probably dominated the effect of water availability. We also examined the relationship between plant drought stress (O) and '13C within annual rings of stemwood from Pinus radiata and Pinus pinaster in south-western Australia. Differential thinning and fertiliser application produced large differences in the availability of water, nutrients and light to individual trees. At a density of 750 stems ha-1, O and '13C were less (more negative) than at 250 stems ha-1 indicating greater drought stress and less efficient water use, contrary to what was expected in light of the general relationship between discrimination and P/E. The greater '13C of trees from heavily thinned plots may well be related to an increased interception of radiation by individual trees and greater concentrations of nutrients in foliage - attributes that increase rates of photosynthesis, reduce Pi and increase '13C. '13C was thus modified to a greater extent by interception of radiation and by nutrient concentrations than by water availability and the '13C-O relationship varied between thinning treatments. Within treatments, the relationship between '13C and O was strong (0.38<r2<0.58). We conclude that '13C may well be a useful indicator of water availability or drought stress, but only in seasonally dry climates (P/E<1) and where variation in other environmental factors can be accounted for.  相似文献   

5.
Following a single acute exposure to chlorine gas, persistenteffects on epicuticular waxes, cuticular transpiration, treegrowth and mortality were studied in foliage of Pinus ponderosaand Pseudotsuga menziesii for three growing seasons. Chlorinegas exposure caused foliar injury to both exposed foliage andfoliage that flushed after exposure (P < 0.05). The tendencyto form films of water rather than droplets was greater in directlyexposed foliage (P < 0.001). Rates of cuticular transpirationwere higher for directly and indirectly exposed foliage of Pinusponderosa up to 1 year after exposure and up to 6 months afterexposure for directly exposed Pseudotsuga menziesii(P < 0.001),after which P. menziesii needles defoliated. Total water content(TWC) and relative water content were significantly correlatedwith foliar injury (P < 0.05). TWC was lower for directlyexposed foliage up to 1 year after exposure (P < 0.001).There was no persistent negative effect on Fv/Fm ratios after1 year. Exposure to chlorine gas did not affect needle lengthor annual shoot increment growth, but exposure was correlatedwith increased bud production. Needle longevity of foliage thatflushed 2 months after exposure was reduced significantly (P< 0.001). Annual stem increment growth for both species decreasedover at least three growing seasons following chlorine gas exposure(P < 0.001), and depended on distance from the spill site.Cone production was lower for exposed Pinus ponderosa treescompared to controls (P < 0.05), and tree mortality was higherwithin approx. 50 m of the release site forPseudotsuga menziesii. Growth responses for both conifers agreed well with predictedpatterns of carbon allocation after defoliation caused by chlorinegas exposure. Copyright 2001 Annals of Botany Company Pinus ponderosa, Pseudotsuga menziesii, conifers, chlorine gas, leaf wettability, cuticular transpiration, water relations, growth, mortality  相似文献   

6.
 Although Pinaceae and Betulaceae have been reported to contain Glomus–type root endophytes, its ecological importance and the conditions influencing this symbiosis are poorly understood. Seedlings of Abies lasiocarpa, Alnus rubra, Pinus contorta, Pinus ponderosa, Pseudotsuga menziesii, and Tsuga heterophylla were inoculated with Glomus intraradices to determine the vesicular-arbuscular mycorrhizae (VAM) development and responsiveness of these hosts. The role of companion VAM host plants on mycorrhizal colonization and nutrient uptake by Pseudotsuga menziesii was also examined by growing seedlings of Pseudotsuga menziesii in dual culture with VAM hosts Thuja plicata or Calamagrostis rubescens. After 8 weeks, no seedlings were colonized. At 16 weeks, 8 of 17 Thuja plicata seedlings grown with Pseudotsuga menziesii and all 18 inoculated Thuja plicata seedlings grown alone were colonized with vesicles and hyphae. Two of 17 inoculated Pseudotsuga menziesii seedlings grown in dual culture with Thuja plicata were colonized with abundant vesicles and hyphae. No ectomycorrhizal seedlings grown in monoculture were colonized. At 9 months, all 10 Calamagrostis rubescens and all 10 inoculated Pseudotsuga menziesii seedlings grown in dual culture were colonized by vesicles and hyphae. Two of 10 inoculated Pseudotsuga menziesiiand 1 of 10 inoculated Pinus ponderosa seedlings grown in monoculture were similarly colonized. The mean phosphorus content in the needles of colonized Pseudotsuga menziesii seedlings grown with Calamagrostis rubescens was about twice as high as in noncolonized Pseudotsuga menziesiiseedlings grown with Calamagrostis rubescens. Tissue nitrogen did not differ between these treatments. The results show that Glomus intraradices colonization of Pinaceae is most successful when a VAM host is present, although some vesicular colonization of Pinaceae occurred in the absence of a VAM host. Accepted: 24 September 1997  相似文献   

7.
In-situ estimates of fast-ice algal productivity at Cape Evans, McMurdo Sound, in 1999 were lower than at the same site in previous years. Under-ice irradiance was between 0 and 8 µmol photons m-2 s-1; the ice was between 1.9 and 2.0 m thick and the algal biomass averaged 150 mg chl a m-2, although values as high as 378 mg chl a m-2 were recorded. Production on 11 and 12 November was between 0.053 and 1.474 mg C m-2 h-1. When the data from 11 November were fitted to a hyperbolic tangent function, a multilinear regression gave estimates for Pmax of 0.571 nmol O2 cm-2 s-1, an ! of 0.167 nmol O2 cm-2 s-1 µmol-1 photons m-2 s-1 and an Ek of 3.419 µmol photons m-2 s-1. A Pmax of 2.674 nmol O2 cm-2 s-1, an ! of 0.275 nmol O2 cm-2 s-1 µmol-1 photons m-2 s-1, r of 0.305 nmol O2 cm-2 s-1 and an Ek of 9.724 µmol-1 photons m-2 s-1 were estimated from the 12 November data. The sea-ice algal community was principally comprised of Nitzschia stellata, Entomoneis kjellmanii and Berkeleya adeliensis. Other taxa present included N. lecointei, Fragilariopsis spp., Navicula glaciei, Pleurosigma spp. and Amphora spp. Variations in the method for estimating the thickness of the diffusive boundary layer were not found to significantly affect the measurements of oxygen flux. However, the inability to accurately measure fine-scale variations in biomass is thought to contribute to the scatter of the P versus E data.  相似文献   

8.
A common cylindropuntia in the northwestern Sonoran Desert, Opuntia acanthocarpa, was investigated for the following hypotheses: its lower elevational limit is set by high temperatures, so its seedlings require nurse plants; its upper elevational limit is set by freezing; spine shading is the least at intermediate elevations; and changes in plant size and frequency with elevation reflect net CO2 uptake ability. For four elevations ranging from 230 m to 1,050 m, the mean height of O. acanthocarpa approximately doubled and its frequency increased 14-fold. Nurse plants were associated with only 4% of O. acanthocarpa less than 20 cm tall at the two lower elevations compared with 57% at 1,050 m, where putative freezing damage was especially noticeable, suggesting that nurse plants protect from low temperature damage. Spine shading of the stem doubled from the lowest to the highest elevation. Net CO2 uptake, which followed a Crassulacean acid metabolism pattern, was maximal at day/night air temperatures of 25/15°C and was halved by 4 weeks of drought and by reducing the photosynthetic photon flux from 30 to 12 mol m-2 day-1. The root system of O. acanthocarpa was shallow, with a mean depth of only 9 cm for the largest plants. Root growth was substantial and similar for plants at 25/15°C and 35/25°C, decreasing over 70-fold at 15/5°C and 45/35°C. Based on cellular uptake of the vital stain neutral red, neither roots nor stems tolerated tissue temperatures below -5°C for 1 h while both showed substantial high temperature acclimation, roots tolerating 1 h at 61°C and stems 1 h at 70°C for plants grown at 35/25°C. The increase in height and frequency of O. acanthocarpa with elevation apparently reflected both a greater ability for net CO2 uptake and greater root growth and hence water uptake. This species achieves its greatest ecological success at elevations where it becomes vulnerable to low temperature damage.  相似文献   

9.
Yoldia hyperborea is a deposit-feeding circumpolar protobranch that also inhabits muddy sediments of the cold water boreal system of Conception Bay, Newfoundland, Canada. Little is known about this species, despite its wide distribution and frequent high density in the benthos. The present work deals with oxygen consumption and ammonia excretion under cold ambient conditions. Y. hyperborea showed low basal metabolism [0.051 ml O2 hу·(g dry weight)у, T=у°C] and low ammonia excretion rates [4.212 µg·NH4-N·hу·(g dry weight)у, T=у°C]. Low metabolic activity could prove a useful strategy during periods of low food availability. In addition, Y. hyperborea was able to regulate its O2 consumption rate at very low pO2 levels, which may be advantageous for a species that may experience periods of hypoxia.  相似文献   

10.
The mixing behaviour of the liquid phase in concentric-tube airlift bioreactors of different scale (RIMP: VL=0.070 m3; RIS-1: VL=2.50 m3; RIS-2: VL=5.20 m3) in terms of mixing time was investigated. This mixing parameter was determined from the output curves to an initial Dirac pulse, using the classical tracer response technique, and analyzed in relation to process and geometrical parameters, such as: gas superficial velocity, xSGR; top clearance, hS; bottom clearance, hB, and ratio of the resistances at downcomer entrance, Ad/AR. A correlation between the mixing time and the specified operating and geometrical parameters was developed, which was particularized for two flow regimes: bubbly and transition (xSGRА.08 m/s) and churn turbulent flow (xSGR> 0.08 m/s) respectively. The correlation was applied in bioreactors of different scale with a maximum error of ᆲ%.  相似文献   

11.
Post-storage gas exchange parameters like CO2 assimilation, stomatal conductance, transpiration, water use efficiency and intercellular CO2 concentrations, together with several chlorophyll a fluorescence parameters: Fo, Fv, Fv/Fm, Fm/Fo and Fv/Fo were examined in radiata pine (Pinus radiata D. Don) seedlings that were stored for 1, 8 or 15 days at 4° or 10°C with or without soil around the roots. Results were analysed in relation to post-storage water potential and electrolyte leakage in order to forecast their vitality (root growth potential) following cold storage, and post-planting survival potential under optimal conditions. During storage at 4° and 10°C, photosynthesis was reduced, being more pronounced in bare-root seedlings than in seedlings with soil around the roots. The depletion of CO2 assimilation seemed not to be solely a stomatal effect as effects on chloroplasts contributed to this photosynthetic inhibition. Thus, the fall in the ratios Fv/Fm, Fv/Fo and Fm/Fo indicated photochemical apparatus damage during storage. Photosynthetic rate was positively correlated with the root growth index and new root length showing that new root growth is dependent primarily on current photosynthesis. Pre-planting exposure of bare-root radiata pine seedlings to temperatures of 10°C for more than 24 h during transportation or storage is not recommended.  相似文献   

12.
 Isolates from two species of Morchella were tested for ability to form mycorrhizae in pure culture synthesis with Arbutus menziesii, Larix occidentalis, Pinus contorta, Pinus ponderosa, andPseudotsuga menziesii. Ectomycorrhizal structures (mantle and Hartig net) formed with the four species of the Pinaceae but not with A. menziesii. Results are compared to previous studies on morel mycorrhizae and discussed in an ecological context. Accepted: 23 October 1999  相似文献   

13.
Ethanol synthesis was induced in stem segments from greenhouse-grown conifer seedlings by placing them in a N2 atmosphere at 30 °C for 24 h. Stems from ponderosa pine,Pinus ponderosa Dougl. ex Laws., sugar pine,Pinus lambertiana Dougl., Pacific silver fir,Abies amabalis Dougl. ex Forbes, and lodgepole pine,Pinus contorta Dougl. ex Loud, produced the highest quantities of ethanol. This group also had the smallest and slowest growing stems. Within each of these species the amount of ethanol produced was inversely related to the stem volume. Stems from western hemlock,Tsuga heterophylla (Raf.) Sarg., grand fir, Abies grandis Dougl. ex Forbes, Douglas-fir,Pseudotsuga menziesii (Mirb.) Franco, and western redcedar,Thuja plicata Donn ex D. Don, all produced equivalent but low ethanol concentrations. These species had the largest and fastest growing stems. In this group only grand fir exhibited an inverse relationship between ethanol concentrations and stem volume. The relative amounts of ethanol synthesized by stems from Douglas-fir, western hemlock and western redcedar seedlings were not the same as subsequently observed in logs from mature trees of the same species under field conditions. Differences in the anaerobic environments for the two stem types could have affected the quantities of ethanol produced. The observed high amounts of ethanol produced by the stems from pine species were discussed in terms of their ability to handle periods of anaerobic stress or hypoxia.  相似文献   

14.
Leaves from several desert and woodland species, including gymnosperms and angiosperms with both C3 and C4 physiology, were analyzed to detect trends in '13Cleaf with elevation and slope aspect along two transects in southeastern Utah and south-central New Mexico, USA. The main difference between the two transects is the steeper elevational gradient for mean annual and summer precipitation in the southern transect. For any given species, we found that isotopic differences between individual plants growing at the same site commonly equal differences measured for plants along the entire altitudinal gradient. In C3 plants, '13Cleaf values become slightly enriched at the lowest elevations, the opposite of trends identified in more humid regions. Apparently, increasing water-use efficiency with drought stress offsets the influence of other biotic and abiotic factors that operate to decrease isotopic discrimination with elevation. For some species shared by the two transects (e.g., Pinus edulis and Cercocarpus montanus), '13Cleaf values are dramatically depleted at sites that receive more than 550 mm mean annual precipitation, roughly the boundary (pedalfer-pedocal) at which soils commonly fill to field capacity in summer and carbonates are leached. We hypothesize that, in summer-wet areas, this may represent the boundary at which drought stress overtakes other factors in determining the sign of '13Cleaf with elevation. The opposition of isotopic trends with elevation in arid versus humid regions cautions against standard correction for elevation in comparative studies of '13Cleaf.  相似文献   

15.
Biomechanical responses of stems of 6- to 7-year-old spruce [Picea abies (L.) Karst.] and beech (Fagus sylvatica L) trees were studied after 4 years of growth in elevated atmospheric CO2 in combination with a nitrogen treatment and on two different soil types. At the end of the treatment, stems were harvested and tested in fresh and air-dried status. Bending characteristics of juvenile wood (modulus of elasticity, termed rigidity) were determined by bending tests. Fracture characteristics (termed toughness) were determined by stroke-pendulum tests. From the base disk of each stem densitometric data were obtained. In spruce, wood produced under elevated CO2 was tougher on both soil types; enhanced N deposition made wood less rigid only on acidic soils. In contrast, beech wood samples showed no significant reaction to CO2 but were significantly tougher under high nitrogen depositions on acidic soil. Effects on wood density of both CO2 and N treatments were not significant, but wood density was higher on acidic soil and so were rigidity and toughness (soil effect). Different genotypes of spruce and beech reacted significantly differently to the treatments. Some genotypes reacted strongly to CO2 or N, whereas others did not react or showed interactions between CO2 and N. This underlines the importance of genetic diversity in tree communities.  相似文献   

16.
Changes in the stem radius of young Norway spruce [Picea abies (L.) Karst.] were related to changes in stem water content in order to investigate the relationship between diurnal stem size fluctuations and internally stored water. Experiments were performed on living trees and on cut stem segments. The defoliated stem segments were dried under room conditions and weight (W), volume (V), and xylem water potential (Os) were continuously monitored for 95 h. Additionally, photos of cross-sections of fresh and air-dried stem segments were taken. For stem segments we found that the change in V was linearly correlated to the change in W as long as Os was >-2.3ǂ.3 MPa (phase transition point). Stem contraction occurred almost solely in the elastic tissues of the bark (cambium, phloem, and parenchyma), and the stem radius changes were closely coupled to bark water content. For living trees, it is therefore possible to estimate the daily contribution of "bark water" to transpiration from knowledge of the stem size and continuous measurements of the stem radius fluctuations. When Os reaches the phase-transition point, water is also withdrawn from the inelastic tissue of the stem (xylem), which - in the experiment with stem segments - was indicated by an increasing ratio between (V and (W. We assume that for Os below the transition point, air is sucked into the tracheids (cavitation) and water is also withdrawn from the xylem. Due to the fact that in living P. abies Os rarely falls below -2.3ǂ.3 MPa and the xylem size is almost unaffected by radius fluctuations, dendrometers are useful instruments with which to derive the diurnal changes in the bark water contents of Norway spruce trees.  相似文献   

17.
Phytoplankton photosynthesis was measured during spring-summer 1991-1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quantified by means of the root-mean square expected vertical displacement depth of cells in the water column, Zt. The light attenuation coefficient was used as a measure of the influence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious differences between photosynthetic capacity [P*max; averages 2.6 and 0.6 µg C (µg chlorophyll-a)-1 h-1] and photosynthetic efficiency {!*; 0.073 and 0.0018 µg C (µg chlorophyll-a)-1 h-1 [(µmol m-2 s-1)-1]} values were obtained for both sites during low mixing conditions (Zt from 10 to 20 m), while no differences were found for high mixing situations (Zt>20 m). This suggests different photoacclimation of phytoplankton responses, induced by modifications of the light field, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P*max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area.  相似文献   

18.
Spectral water transparency and phytoplankton light absorbance were studied in the Atlantic sector of the Southern Ocean during the Southern Ocean JGOFS ANT XIII/2 cruise in early austral summer 1995/1996. The study area comprised three zones, which differed markedly with respect to their hydrographic and planktological characteristics: the Antarctic Polar Frontal Zone with adiatom bloom, the Antarctic Circumpolar Current outside frontal systems with phytoplankton-poor water and a higher flagellate abundance than in the other two areas, and the marginal ice zone with a Phaeocystis bloom. The influence of phytoplankton on spectral water transparency was assessed by two independent procedures: the pigment-specific beam absorption coefficient, aJ*[5], at all stations, as estimated by spectroscopy of in vivo light absorption of plankton on glass fibre filters, and the pigment-specific light attenuation, (kc[5]), as derived by regression analysis of spectral in situ vertical light attenuation coefficients in the sea against concomitant pigment concentrations. Values of aJ*[5] and vertical profiles of light attenuation by phytoplankton exhibited regional differences that corresponded with the three zones from which samples had been collected. These differences can be related to the specific characteristics of the three zones with respect to cell size distribution, pigment composition and biomass. The observed variations in aJ*[5] values should be considered when oceanic primary production is to be estimated by biooptical modelling.  相似文献   

19.
The objective of this study was to evaluate the potential contribution of the soil microbial community in the vicinity of two plant covers, Sanionia uncinata and Deschampsia antarctica, at Machu Picchu Station, King George Island, Antarctica. Soil samples were collected at the study site during the southern (pole) summer period from 0-5 cm and 5-10 cm depths, for chemical and biological analyses. Soil microbial biomass reached a maximal value of 144 µg g-1 in soil samples taken from under the S. uncinata upper layer plant. qCO2 ranged from 167 to 239 µg CO2.mgCmic.h-1 at the 0-5 and 5-10 cm depths, respectively. CO2 evolution showed values of 54.3 mg.m-2 h-1 beneath plant cover and 55.9 mg.m-2 h-1 in the open space. CO2 evolved by substrate induced respiration in the soil samples taken under the plant cover in the summer period, oscillated between 0.25 and 4.78 µg CO2 g-1 h-1. The data obtained from this short study may provide evidence that both activity and the composition and substrate utilization of the microbial community appear to change substantially across the moisture level and sample location.  相似文献   

20.
Hydrogen bioproduction from agro-industrial residues by Enterobacter aerogenes in a continuous packed column has been investigated and a complete reactor characterization is presented. Experimental runs carried out at different residence time, liable of interest for industrial application, showed hydrogen yields ranging from 1.36 to 3.02 mmolH2mmolуglucose or, in other words, from 37.5% to 75% of the theoretical hydrogen yield. A simple kinetic model of cell growth, validated by experimental results and allowing the prediction of biomass concentration profile along the reactor and the optimization of superficial velocity, is suggested. By applying the developed approach to the selected operative conditions, the identification of the optimum superficial velocity v0,opt of about 2.2 cm hу corresponding to the maximum hydrogen evolution rate 2g,max, was performed.  相似文献   

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