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1.
Soil Temperature Influences on Root Resistance of Pinus contorta Seedlings 总被引:2,自引:1,他引:1 下载免费PDF全文
The influence of low temperature in the root zone on water uptake in lodgepole pine (Pinus contorta Dougl. ex Loud.) was studied under laboratory conditions. To remove soil hydraulic influences, two-year-old seedlings were transferred to solution cultures and maintained in temperature controlled water baths. Short term measurements of leaf conductance, leaf water potential and tritiated water movement were taken at root temperatures from 22 C down to 0 C. Root resistance was calculated to be 67% of total plant resistance at 7 C and 93% at 0 C. In addition an Arrhenius break was found in a plant resistance versus temperature plot, suggesting a significant change with temperature in the membrane pathway in the root water uptake system. 相似文献
2.
Thomas Horn Brian D. Warner Joyce A. Running Kristi Downing Jennifer Clyne Mickey S. Urdea 《Nucleosides, nucleotides & nucleic acids》2013,32(5-6):875-877
Abstract Branched oligonucleotides have been synthesized using phosphoramidite derivatives with two protected hydroxyl functions. These molecules are employed for a label amplification strategy used in DNA probe diagnostics. 相似文献
3.
Two dimensional liquid phase separations of proteins using online fractionation and concentration between chromatographic dimensions 总被引:1,自引:0,他引:1
Karty JA Running WE Reilly JP 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,847(2):103-113
Multi-dimensional liquid chromatography is often presented as an alternative to two-dimensional (2-D) gel electrophoresis for separating complex protein mixtures. The vast majority of analytical-scale 2-D LC systems have employed either off-line fractionation or stepped gradients in the first dimension separation. The latter severely restrict flexibility in setting up the first dimension gradient. We propose a novel two-dimensional LC system that employs online fractionation of proteins into a series of small reversed phase trapping columns. These traps effectively decouple the two separation dimensions and avoid problems associated with off-line fraction collection. Flexibility in determining the gradient programs for the two separations is thus enhanced. The reduced diameter of the trapping columns concentrates analyte between chromatographic dimensions. The apparatus is coupled with online electrospray time-of-flight mass spectrometry to characterize ribosomal proteins of Caulobacter crescentus. 相似文献
4.
The impact of growing-season length variability on carbon assimilation and evapotranspiration over 88 years in the eastern US deciduous forest 总被引:17,自引:0,他引:17
Recent research suggests that increases in growing-season length (GSL) in mid-northern latitudes may be partially responsible
for increased forest growth and carbon sequestration. We used the BIOME-BGC ecosystem model to investigate the impacts of
including a dynamically regulated GSL on simulated carbon and water balance over a historical 88-year record (1900–1987) for
12 sites in the eastern USA deciduous broadleaf forest. For individual sites, the predicted GSL regularly varied by more than
15 days. When grouped into three climatic zones, GSL variability was still large and rapid. There is a recent trend in colder,
northern sites toward a longer GSL, but not in moderate and warm climates. The results show that, for all sites, prediction
of a long GSL versus using the mean GSL increased net ecosystem production (NEP), gross primary production (GPP), and evapotranspiration
(ET); conversely a short GSL is predicted to decrease these parameters. On an absolute basis, differences in GPP between the
dynamic and mean GSL simulations were larger than the differences in NEP. As a percentage difference, though, NEP was much
more sensitive to changes in GSL than were either GPP or ET. On average, a 1-day change in GSL changed NEP by 1.6%, GPP by
0.5%, and ET by 0.2%. Predictions of NEP and GPP in cold climates were more sensitive to changes in GSL than were predictions
in warm climates. ET was not similarly sensitive. First, our results strongly agree with field measurements showing a high
correlation between NEP and dates of spring growth, and second they suggest that persistent increases in GSL may lead to long-term
increases in carbon storage.
Received: 26 May 1998 / Accepted: 6 July 1998 相似文献
5.
6.
Reconciling Carbon-cycle Concepts, Terminology, and Methods 总被引:5,自引:1,他引:4
F. S. Chapin III G. M. Woodwell J. T. Randerson E. B. Rastetter G. M. Lovett D. D. Baldocchi D. A. Clark M. E. Harmon D. S. Schimel R. Valentini C. Wirth J. D. Aber J. J. Cole M. L. Goulden J. W. Harden M. Heimann R. W. Howarth P. A. Matson A. D. McGuire J. M. Melillo H. A. Mooney J. C. Neff R. A. Houghton M. L. Pace M. G. Ryan S. W. Running O. E. Sala W. H. Schlesinger E.-D. Schulze 《Ecosystems》2006,9(7):1041-1050
Recent projections of climatic change have focused a great deal of scientific and public attention on patterns of carbon (C)
cycling as well as its controls, particularly the factors that determine whether an ecosystem is a net source or sink of atmospheric
carbon dioxide (CO2). Net ecosystem production (NEP), a central concept in C-cycling research, has been used by scientists to represent two different
concepts. We propose that NEP be restricted to just one of its two original definitions—the imbalance between gross primary
production (GPP) and ecosystem respiration (ER). We further propose that a new term—net ecosystem carbon balance (NECB)—be
applied to the net rate of C accumulation in (or loss from [negative sign]) ecosystems. Net ecosystem carbon balance differs
from NEP when C fluxes other than C fixation and respiration occur, or when inorganic C enters or leaves in dissolved form.
These fluxes include the leaching loss or lateral transfer of C from the ecosystem; the emission of volatile organic C, methane,
and carbon monoxide; and the release of soot and CO2 from fire. Carbon fluxes in addition to NEP are particularly important determinants of NECB over long time scales. However,
even over short time scales, they are important in ecosystems such as streams, estuaries, wetlands, and cities. Recent technological
advances have led to a diversity of approaches to the measurement of C fluxes at different temporal and spatial scales. These
approaches frequently capture different components of NEP or NECB and can therefore be compared across scales only by carefully
specifying the fluxes included in the measurements. By explicitly identifying the fluxes that comprise NECB and other components
of the C cycle, such as net ecosystem exchange (NEE) and net biome production (NBP), we can provide a less ambiguous framework
for understanding and communicating recent changes in the global C cycle. 相似文献
7.
Viral particles are biological machines that have evolved to package, protect, and deliver the viral genome into the host via regulated conformational changes of virions. We have developed a procedure to modify lysine residues with S-methylthioacetimidate across the pH range from 5.5 to 8.5. Lysine residues that are not completely modified are involved in tertiary or quaternary structural interactions, and their extent of modification can be quantified as a function of pH. This procedure was applied to the pH-dependent structural transitions of brome mosaic virus (BMV). As the reaction pH increases from 5.5 to 8.5, the average number of modified lysine residues in the BMV capsid protein increases from 6 to 12, correlating well with the known pH-dependent swelling behavior of BMV virions. The extent of reaction of each of the capsid protein's lysine residues has been quantified at eight pH values using coupled liquid chromatography-tandem mass spectrometry. Each lysine can be assigned to one of three structural classes identified by inspection of the BMV virion crystal structure. Several lysine residues display reactivity that indicates their involvement in dynamic interactions that are not obvious in the crystal structure. The influence of several capsid protein mutants on the pH-dependent structural transition of BMV has also been investigated. Mutant H75Q exhibits an altered swelling transition accompanying solution pH increases. The H75Q capsids show increased reactivity at lysine residues 64 and 130, residues distal from the dimer interface occupied by H75, across the entire pH range. 相似文献
8.
This communication reports gelation of lambda-carrageenan, for the first time, in the presence of trivalent iron ions. Kappa-, iota- and lambda-carrageenans are sulfated polysaccharides used extensively in food, pharmaceutical and medical applications. Kappa- and iota-carrageenans show gelation in the presence of mono- and di-valent ions, but lambda-carrageenan yields only viscous solutions. Our results show that gelation in lambda-carrageenan indeed is possible, but with trivalent ions. X-ray fiber diffraction patterns of iron (III)-lambda-carrageenan are characteristic of highly oriented and polycrystalline fibers containing well resolved Bragg reflections. The elastic modulus (G′) of the product is far greater than the loss modulus (G″) indicating the thermal stability of lambda-carrageenan in the presence of iron (III) ions. This novel finding has potential to expand lambda-carrageenan's current utility beyond a viscosifying agent. 相似文献
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10.
Comparing global models of terrestrial net primary productivity (NPP): the importance of water availability 总被引:1,自引:0,他引:1
G. Churkina S. W. Running A. L. Schloss ThE. Participants OF. ThE. Potsdam NpP. Model Intercomparison 《Global Change Biology》1999,5(Z1):46-55
Given that neither absolute measures nor direct model validations of global terrestrial net primary productivity (NPP) are feasible, intercomparison of global NPP models provides an effective tool to check model consistency. For this study, we tested the assumption that water availability is the primary limiting factor of NPP in global terrestrial biospheric models. We compared a water balance coefficient (WBC), calculated as the difference of mean annual precipitation and potential evapotranspiration to NPP for each grid cell (0.5° × 0.5° longitude/latitude) in each of 14 models. We also evaluated different approaches used for introducing water budget limitations on NPP: (1) direct physiological control on evapotranspiration through canopy conductance; (2) climatological computation of constraints from supply/demand for ecosystem productivity; and (3) water limitation inferred from satellite data alone. Plots of NPP vs. WBC showed comparable patterns for the models using the same method for water balance limitation on NPP. While correlation plots revealed similar patterns for most global models, other environmental controls on NPP introduced substantial variability. 相似文献