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1.
The Influence of Nutrient Availability on Soil Organic Matter Turnover Estimated by Incubations and Radiocarbon Modeling 总被引:4,自引:0,他引:4
We investigated the decomposability of soil organic matter (SOM) along a chronosequence of rainforest sites in Hawaii that form a natural fertility gradient and at two long-term fertilization experiments. To estimate turnover times and pool sizes of organic matter, we used two independent methods: (1) long-term incubations and (2) a three-box soil model constrained by radiocarbon measurements. Turnover times of slow-pool SOM (the intermediate pool between active and passive pools) calculated from incubations ranged from 6 to 20 y in the O horizon and were roughly half as fast in the A horizon. The radiocarbon-based model yielded a similar pattern but slower turnover times. The calculation of the 14C turnover times is sensitive to the lag time between photosynthesis and incorporation of organic C into SOM in a given horizon. By either method, turnover times at the different sites varied two- or threefold in soils with the same climate and vegetation community. Turnover times were fastest at the sites of highest soil fertility and were correlated with litter decay rates and primary productivity. However, experimental fertilization at the two least-fertile sites had only a small and inconsistent effect on turnover, with N slowing turnover and P slightly speeding it at one site. These results support studies of litter decomposition in suggesting that while plant productivity can respond rapidly to nutrient additions, decomposition may respond much more slowly to added nutrients. 相似文献
2.
Experiments were carried out to define the effect of mixing upon primary productivity. The method compares the production of a water column with 14C-labelled samples (i) along a classic vertical profile and (ii) with a rotating system moving between the surface and the bottom of the pond, which was 0·5 m deep. In all the experiments, photosynthesis was best in the moving flask. The effect of mixing is particularly important at sunrise and sunset hours: the vertical photosynthetic budget may be over 2·5 times that of homogeneous non-turbulent water. These results have clear implications for monitoring intensive outdoor algal cultures. 相似文献
3.
A multiple enzyme and multisubstrate cycling system is described for the radiometric determination of cholineacetyltransferase (ChAT) activity in crude tissue homogenates. The methods employs [14C]acetate coupled with the enzymes acetate kinase (AK) and phosphotransacetylase (PTA) for the generation of [14C]acetyl CoA. By recycling it was possible to avoid product inhibition of ChAT by CoA, ATP was maintained constant by rephosphorylation of ADP. Kinetics of the individual enzyme reactions were studied and the parameters obtained were used to select appropriate conditions to maintain linearity of varying amounts ChAT activity over a sixty minute time course. The sensitivity of the method is limited only by the specific activity of commercially available isotope labeled acetate.Special issue dedicated to Dr. O. H. Lowry. 相似文献
4.
Measurements of the uptake and loss of 4C in the light and in the dark in the Tasman and Coral Seas have revealed methodological problems with the estimation of productivity in these waters. Rates of productivity estimated without replication, time series incubations and dark controls frequently overestimated the true rates of autotrophic production. The data showed unexpectedly high rates of both uptake and loss in the dark in oligotrophic waters. In oligotrophic oceanic waters, dark incorporation of 14C sometimes equalled the uptake of 14C in the light bottle. Rapid uptake of isotope in the dark controls appeared to be the result of rapid bacterial growth and metabolism. This problem was exacerbated by agitation of the sample before or during the incubation. Tropical samples were particularly susceptible to problems arising from the agitation of the samples. Latitudinal gradients of dark uptake and loss were revealed in these incubations. The loss of label during 8–12 hours in the dark (after 12 hr in the light) was as high as 50% in subtropical waters. The loss was frequently unmeasurable (< 10%) in temperate waters. The time course of 14C uptake indicated active grazing in the bottles and suggested that most of the nighttime losses of label were due to grazing by microheterotrophs. Respiratory losses appeared to be small. Calculated values of the assimilation number (or photosynthetic capacity) which did not correct for dark 14C uptake were too high to be biochemically realistic. The errors were due to the heterotrophic uptake of label and the lack of dark controls. Rapid release of 14C in the dark after incubation in the light meant that the estimate of productivity was dependant on the trophic state of the sample and on the period of incubation. 相似文献
5.
Christopher Freeman Douglas M. Fiebig Maurice A. Lock 《Journal of Aquatic Ecosystem Stress and Recovery (Formerly Journal of Aquatic Ecosystem Health)》1993,2(4):329-334
A method is described which enables lipid biosynthesis to be determined within intact river biofilms. Significantly different rates of biosynthesis were detected in rivers of differing nutrient availability and during different seasons. Rapid changes in microbial physiology could be detected within 24 hours. The technique appeared to be well suited to investigation of factors affecting lipid biosynthesis within biofilms. Although in contrast, acetate incorporation did not correlate with microcalorimetric total activity measurements over a 12-month period, and so the method did not appear suitable for determining total metabolic activity. However, microbial lipid biosynthesis produces a valuable food resource for the ecosystems higher tropic levels and thus the acetate incorporation technique could prove useful as an indicator of aspects of aquatic ecosystem health. 相似文献
6.
Marco A. Martins 《Mycorrhiza》1992,2(2):69-73
The transfer of 14C from Lolium perenne (the donor) to Plantago lanceolata (the receiver), mediated by vesicular-arbuscular (VA) mycorrhizal fungi, was examined when the two species were grown together or separately. The VA mycorrhizal infection led to a significant increase, relative to that in uninfected plants, in the 14C transferred from donor to receiver plants, not only when the roots of the two plants were growing in intimate mixture, but also when they were separated by a root-free zone of 2.33 cm. The majority of isotope transfer between the two plant species was along the direct pathway via VA mycelium. 相似文献
7.
The allocation of carbon to shoots, roots, soil and rhizosphere respiration in barrel medic (Medicago truncatulaGaertn.) before and after defoliation was determined by growing plants in pots in a labelled atmosphere in a growth cabinet.
Plants were grown in a 14CO2-labelled atmosphere for 30 days, defoliated and then grown in a 13CO2-labelled atmosphere for 19 days. Allocation of 14C-labelled C to shoots, roots, soil and rhizosphere respiration was determined before defoliation and the allocation of 14C and 13C was determined for the period after defoliation. Before defoliation, 38.4% of assimilated C was allocated below ground,
whereas after defoliation it was 19.9%. Over the entire length of the experiment, the proportion of net assimilated carbon
allocated below ground was 30.3%. Of this, 46% was found in the roots, 22% in the soil and 32% was recovered as rhizosphere
respiration. There was no net translocation of assimilate from roots to new shoot tissue after defoliation, indicating that
all new shoot growth arose from above-ground stores and newly assimilated carbon. The rate of rhizosphere respiration decreased
immediately after defoliation, but after 8 days, was at comparable levels to those before defoliation. It was not until 14
days after defoliation that the amount of respiration from newly assimilated C (13C) exceeded that of C assimilated before defoliation (14C).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Isotype analyses were performed on biochemical fractions isolated from leaves of Kalanchoe blossfeldiana Tom Thumb. during aging under long days or short days. Irrespective of the age or photoperiodic conditions, the intermediates of the starch-malate sequence (starch, phosphorylated compounds and organic acids) have a level of 13C higher than that of soluble sugars, cellulose and hemicellulose. In short days, the activity of the crassulacean acid metabolism pathway is predominant as compared to that of C3 pathway: leaves accumulate organic acids, rich in 13C. In long days, the activity of the crassulacean acid metabolism pathway increases as the leaves age, remaining, however, relatively low as compared to that of C3 pathway: leaves accumulate soluble sugars, poor in 13C. After photoperiodic change (long daysshort days), isotopic modifications of starch and organic acids suggest evidence for a lag phase in the establishment of the crassulacean acid metabolism pathway specific to short days. The relative proportions of carbon from a C3-origin (RuBPC acitivity as strong discriminating step, isotope discrimination in vivo=20) or C4-origin (PEPC activity as weak discriminating step, isotope discrimination in vivo=4) present in the biochemical fractions were calculated from their 13C values. Under long days, 30 to 70% versus 80 to 100% under short days, of the carbon of the intermediates linked to the starch-malate sequence, or CAM pathway (starch, phosphorylated compounds and organic acids), have a C4-origin. Products connected to the C3 pathway (free sugars, cellulose, hemicellulose) have 0 to 50% of their carbon, arising from reuptake of the C4 from malate, under long days versus 30 to 70% under short days.Abbreviations CAM
crassulacean acid metabolism
- CAM pathway
pathway with malate accumulation by -carboxylation of PEP, arising from glycolysis of starch (starch-malate sequence)
- C3-metabolism
metabolism with primary carbon fixed by the Calvin and Benson pathway (C3-origin)
- C4-metabolism
metabolism with primary carbon fixed by the Hatch and Slack pathway (C4-origin)
- C3-pathway
pathway with RuBPC activity and the Calvin and Benson pathway, irrespective of the CO2-source, atmospheric or reuptake of the C4 from malate
- 13C()=(Rsample-RPDR)103/RPDB where PDB
Pee Dee belemnite (belemnite from the Pee Dee formation, South Carolina) and R=13C/12C
- D
isotope discrimination
- PEP
phosphoenolpyruvate
- PEPC (EC 4.1.1.31)
PEP carboxylase
- PGA
phosphoglyceric acid
- Py.di-PK (EC 2.7.9.1)
pyruvate, Pi-dikinase
- RuBP
ribulose bisphosphate
- RuBPC (EC 4.1.1.39)
RuBP carboxylase
- SD
short days
- LD
long days 相似文献
9.
Both the Coulter Counter and 14C method were used to measure the grazing (clearance rates) of the marine calanoid copepod Acartia tonsa on different concentrations of a Chlamydomonas sp. culture. In most cases, clearance rates measured by the Coulter Counter method were higher than those measured by the 14C method by factors of 2 to 3. We explore several possibilities for the differences obtained between the two methods. We suggest that loss of radioactivity through grazer egestion might be the main reason for the discrepancy between methods. Food concentration did not affect the comparability of both methods' measurements. 相似文献
10.
11.
A simple method for determining bioethanol content in gasoline containing bioethanol (denoted as E-gasoline in this study) is urgently required. Liquid scintillation counting (LSC) was employed based on the principle that 14C exists in bioethanol but not in synthetic ethanol. Bioethanol was extracted in two steps by water from E-gasoline containing 3% (E3) or 10% (E10) bioethanol. The 14C radioactivity was measured by LSC and converted to the amount of bioethanol. The bioethanol content in E-gasoline was determined precisely from the partition coefficient in the extraction and the amount of bioethanol in the water phases: 2.98 ± 0.10% for E3 and 10.0 ± 0.1% for E10 (means ± SD; n = 3). It appears that this method can be used to determine bioethanol content in E-gasoline quickly and easily. 相似文献
12.
During the oxidation of various mixtures of glucose and aromatic substrates by four strains of Pseudomonas putida, diauxic growth was not observed. Strain A3.12 grew faster on benzoate than on glucose, whereas three other strains showed faster growth on glucose than on the aromatic test substrates. Growth rates on mixtures of glucose and aromatics were intermediate between those on the single substrates.The presence of glucose in media containing aromatic substrates accelerated in the bacteria the appearance of the ability to oxidize aromatic substrates. During growth of the organisms on binary mixtures of aromatics, simultaneous utilization of these compounds occurred, the utilization ratio depending on the quality of the compounds as carbon and energy sources. Addition of glucose to dual aromatic substrate media greatly increased the utilization ratio in favour of the better aromatic substrate.With decreasing concentration of glucose in relation to that of aromatic substrates, the rate of carbon assimilation from glucose increased. Enzymological and radiochemical studies demonstrated that even in the presence of an excess of aromatic substrates, glucose was exclusively catabolized via the 2-keto-3-deoxy-6-phosphogluconate pathway. In contrast, the rate of carbon assimilation from 14C-ring-labelled benzoate and anisate was unaffected by the presence of an excess of glucose.Abbreviations KDPG
2-keto-3-deoxy-6-phosphogluconate
- PP
pentose-phosphate
- OD
optical density 相似文献
13.
Translocation of radioactive 14C and 32P between the pyrgomatine barnacle Savignium milleporum and the hydrocoral Millepora dichotoma in the Red Sea was investigated in order to discover any mutual nutritional benefits. Translocation of photosynthetic products from endosymbiotic zooxanthellae to the hydrocoral was demonstrated. There was no evidence that carbon was further translocated to the barnacle. However, hydrocorals bearing barnacles accumulated significantly more 14C and 32P than those with no barnacles. The possibility that the hydrocorals recycle substances excreted by the barnacles is discussed in the context of the oligotrophic environment of the Red Sea. 相似文献
14.
15.
Summary An investigation was carried out in order to study the effect of salts namely NaC1 and Na2SO4 on the rate of translocation of photosynthates in pigeonpea, at the pod filling stage. At the concentration of 10 EC NaC1
only 17% of the14C assimilates are translocated from the source leaf to the other parts of the plant. Out of this pods receive about 8%. On
the other hand even at a concentration of 15 EC Na2SO4 about 30% of the total14C assimilates get translocated and out of this pods receive about 12%. From this it may be concluded that under salt-stress
conditions the rate of translocation of photosynthates is adversely affected and between the two salts, NaC1 was discovered
to have a marked inhibitory effect. 相似文献
16.
A14C labeling apparatus was developed to permit the labeling of four-year-old Ponderosa pine with14CO2 in the field. The labeling system is a completely closed canopy system with14CO2 monitored by a GM tube ratemeter apparatus. The level of14CO2 corresponding to ambient levels is monitored by a microloggercomputer which controls a14CO2 generating system. The generated14CO2 is mixed in the canopy by circulating the atmosphere with 12V diaphram pumps. The portable system requires little operator
attention.
At approximately monthly intervals over a one-year period two four-year-old Ponderosa pine trees were labeled for three to
five days using this labeling apparatus. After an assimilate distribution period, one tree was excavated and analyzed for14C distribution. During late spring and early summer most of the carbon assimilated (>60%) was found in the active growing
tips and new needles, with little being allocated to the roots (<10%) or woody material (<20%). During mid to late fall there
was an increase in root labeling along with an increase in carbon going to woody material. Over the winter period, most of
the fixed carbon (65%) resided in the older leaves. The early spring labeling period showed another pulse of root labeling
along with some labeling of woody tissues. 相似文献
17.
R. M. Schmid 《Hydrobiologia》1990,197(1):305-308
The travertine structure containing Mountford Spring is in the only surface accumulation of CaCO3 on Lake Torrens, a playa in South Australia. Here the first 14C data on Lake Torrens is presented. 14C ages for travertine samples surrounding Mountford Spring, range from 13 770 ± 130 years BP to 22 700 ± 290 years BP, giving a time frame for lacustrine sediments wedged in between. In the absence of recent tectonic movements, the old travertine (22 700 ± 130 years) on the clifftop, surrounded by younger spring deposits (13770 ± 130 years) at a lower level, prove a deflation event at this playa. 相似文献
18.
Microautoradiographs showed that [14C]sucrose taken up in the xylem of small and intermediate (longitudinal) vascular bundles of Zea mays leaf strips was quickly accumulated by vascular parenchyma cells abutting the vessels. The first sieve tubes to exhibit 14C-labeling during the [14C]sucrose experiments were thick-walled sieve tubes contiguous to the more heavily labeled vascular parenchyma cells. (These two cell types typically have numerous plasmodesmatal connections.) With increasing [14C]sucrose feeding periods, greater proportions of thick- and thin-walled sieve tubes became labeled, but few of the labeled thin-walled sieve tubes were associated with labeled companion cells. (Only the thin-walled sieve tubes are associated with companion cells.) When portions of leaf strips were exposed to 14CO2 for 5 min, the vascular parenchyma cells-regardless of their location in relation to the vessels or sieve tubes-were the most consistently labeled cells of small and intermediate bundles, and label (14C-photosynthate) appeared in a greater proportion of thin-walled sieve tubes than thick-walled sieve tubes. After a 5-min chase with 12CO2, the thin-walled sieve tubes were more heavily labeled than any other cell type of the leaf. After a 10-min chase with 12CO2, the thin-walled sieve tubes were even more heavily labeled. The companion cells generally were less heavily labeled than their associated thin-walled sieve tubes. Although all of the thick-walled sieve tubes were labeled in portions of leaf strips fed 14CO2 for 5 min and given a 10-min 12CO2 chase, only five of 72 vascular bundles below the 14CO2-exposed portions contained labeled thick-walled sieve tubes. Moreover, the few labeled thick-walledsieve tubes of the transport region always abutted 14C-labeled vascular parenchyma cells. The results of this study indicate that (1) the vascular parenchyma cells are able to retrieve at least sucrose from the vessels and transfer it to the thick-walled sieve tubes, (2) the thick-walled sieve tubes are not involved in long-distance transport, and (3) the thin-walled sieve tubes are capable themselves of accumulating sucrose and photosynthates from the apoplast, without the companion cells serving as intermediary cells. 相似文献
19.
Below-ground carbon distribution in barley (Hordeum vulgare L.) with and without nitrogen fertilization 总被引:5,自引:0,他引:5
Gerd Johansson 《Plant and Soil》1992,144(1):93-99
The distribution of net assimilated C in barley (Hordeum vulgare L.) grown at two N-levels was determined in a growth chamber. The N-fertilization involved 0 and 3.61 mol N g-1 dry soil. After growth for seven weeks in an atmosphere with continuously 14C-labelled CO2, 14C was determined in shoots, roots, rhizosphere respiration and soil. At the low N-level, 32% of the net assimilated 14C was translocated below ground, whereas at the high N-level 27% was translocated below ground. The release of C from roots (root respiration, microbial respiration originating from decomposition of 14C-labelled root material and 14C remaining in soil) was greater with no N-supply (19% of net assimilated 14C) than in the treatment with N-supply (15%). Thus, the effect of N-supply on both translocation of assimilated 14C below ground and the release of 14C from growing roots was relatively small. 相似文献
20.
John A. Hawley Steven C. Dennis Andrea Nowitz Fred Brouns Timothy D. Noakes 《European journal of applied physiology and occupational physiology》1992,64(6):523-527
Intestinal perfusion studies have shown that glucose absorption from maltose occurs faster than from isocaloric glucose. To determine whether ingested maltose might be a superior source of carbohydrate (CHO) for endurance athletes, we compared the rates of gastric emptying, absorption and oxidation of 15 g.100 ml-1 solutions of maltose and glucose. Six endurance-trained cyclists drank 1200 ml of either U-14C maltose or U-14C glucose as a 400-ml loading bolus immediately before exercise, and as 8 x 100-ml drinks at 10-min intervals during a 90-min ride at 70% of maximal oxygen consumption. The rates of gastric emptying [maltose 690 (SD 119) ml.90 min-1; glucose 655 (SD 93) ml.90 min-1], the appearance of U-14C label in the plasma, and the peak rates of exogenous CHO oxidation [maltose 1.0 (SD 0.09) g.min-1; glucose 0.9 (SD 0.09) g.min-1] were not significantly different. Further, the 51 (SD 8) g of maltose and the 49 (SD 9) g of glucose oxidised during exercise were similar. Each accounted for approximately 20% of the total CHO oxidised during the 90 min of exercise. Since only half of the CHO delivered to the intestine was oxidised in the 90-min ride (maltose 49%; glucose 50%), we conclude that neither the rate of gastric emptying, nor digestion limited the rate of ingested CHO utilisation during the early stages of exercise.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献