Phytochemical changes in leaves of subtropical grasses and fynbos shrubs at elevated atmospheric CO₂ concentrations     

D. Hattas  W.D. Stock  W.T. Mabusela  I.R. Green 《Global and Planetary Change》2005,47(2-4):181

The effects of elevated atmospheric CO₂ concentrations on plant polyphenolic, tannin, nitrogen, phosphorus and total nonstructural carbohydrate concentrations were investigated in leaves of subtropical grass and fynbos shrub species. The hypothesis tested was that carbon-based secondary compounds would increase when carbon gain is in excess of growth requirements. This premise was tested in two ecosystems involving plants with different photosynthetic mechanisms and growth strategies. The first ecosystem comprised grasses from a C₄-dominated, subtropical grassland, where three plots were subjected to three different free air CO₂ enrichment treatments, i.e., elevated (600 to 800 μmol mol⁻¹), intermediate (400 μmol mol⁻¹) and ambient atmospheric CO₂. One of the seven grass species, Alloteropsis semialata, had a C₃ photosynthetic pathway while the other grasses were all C₄. The second ecosystem was simulated in a microcosm experiment where three fynbos species were grown in open-top chambers at ambient and 700 μmol mol⁻¹ atmospheric CO₂ in low nutrient acid sands typical of south western coastal and mountain fynbos ecosystems. Results showed that polyphenolics and tannins did not increase in the grass species under elevated CO₂ and only in Leucadendron laureolum among the fynbos species. Similarly, foliar nitrogen content of grasses was largely unaffected by elevated CO₂, and among the fynbos species, only L. laureolum and Leucadendron xanthoconus showed changes in foliar nitrogen content under elevated CO₂, but these were of different magnitude. The overall decrease in nitrogen and phosphorus and consequent increase in C:N and C:P ratio in both ecosystems, along with the increase in polyphenolics and tannins in L. laureolum in the fynbos ecosystem, may negatively affect forage quality and decomposition rates. It is concluded that fast growing grasses do not experience sink limitation and invest extra carbon into growth rather than polyphenolics and tannins and show small species-specific chemical changes at elevated atmospheric CO₂ concentrations. Responses of fynbos species are varied and were species-specific.  相似文献   

B and V lightcurves and pole positions of three S-class asteroids     

R.S. McCheyne  N. Eaton  S.F. Green  A.J. Meadows 《Icarus》1984,59(2):286-295

B. anb V lightcurves have been obtained for three S-class asteroids—29 Amphitrite, 39 Laetitia, and 43 Ariadne. Pole positions and shapes for each of these asteroids are derived, and comments on small features present in their lightcurves are made. A small color variation for 39 Laetitia is also found.  相似文献   

On the evolution of interacting,magnetized, galactic plasmas     

Anthony L. Peratt  James C. Green 《Astrophysics and Space Science》1983,91(1):19-33

The advent of three-dimensional, electromagnetic, and fully relativistic particle simulations allows a detailed study of a magnetized, rotating plasma, galaxy model. When two such models are simulated, an interaction yielding results resembling observational data from double radio sources, including the emission of synchrotron radiation, are obtained. Simulation derived morphologies, radiation intensities, frequency spectra, and isophote patterns are directly compared to observations. The constituent plasma parameters associated with the source Cygnus A are found to ben _e =1.8×10^?3 cm^?3,T=2.8 keV,B=20–30 gamma, with a small population of electrons accelerated to GeV energies by a rotation induced electric field. The results of these simulations, involving a computational resource of five CDC 7600 and five Cray-1 computers, strongly supports an inhomogeneous version of the Klein world model.  相似文献   

The problem of auroral NO+ concentration and the intensity of 1·27μ bands of O2     

S.S. Prasad  D.R. Furman  A.E.S. Green 《Planetary and Space Science》1975,23(9):1341-1343

The problem of the theoretical computation of the emission intensities and ion composition in a weak aurora which has been preceded by a stronger event is examined. For this purpose a model auroral precipitation consisting of biexponential primaries is considered. The softer of the two components is brighter, and begins to decay after remaining steady for ten to fifteen minutes. The other, harder component starts to build up at that instant. Our results suggest that at least a part of the high $\text{n(}\text{NO}{}^{\mathrm{+}}\text{)}\text{n(}\text{O}{}_2{}^{\mathrm{+}}\text{)}\text{or}\text{I}\text{(1·27 μ)}\text{I}\text{(3914}\text{A}\text{?}\text{)}$ ratios could be attributed to the retention, by the atmosphere, of the memory of previous auroral precipitations. Thus, the serious energy paradox in the context of 1·27 μ intensity need not arise, and, in the context of the large NO⁺ density, it may perhaps be unnecessary to invoke any major conversion of O₂ to NO thus avoiding the associated energy problem.  相似文献   

An Induction Study at Micropulsation Periods in the British Isles     

C. A. Green 《Geophysical Journal International》1975,40(2):225-240

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Deep Ocean Mining — Opportunities for the UK. Seminar sponsored by the UK Science Research Council (SRC): London,UK, 7 February 1980     

David Green 《Marine Policy》1980,4(3):257-259

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SPATIAL PERSPECTIVES OF THE FLOWS THROUGH THE SOUTHEAST ELECTRICAL TRANSMISSION NETWORK     

Milford B. Green  R. L. Mitchelson 《The Professional geographer》1981,33(1):83-94

Cooperative effort among electrical energy utilities is one possible response to increasing stress on generation and transmission systems. Increased interregional flows are a direct consequence of cooperative efforts. Any inefficient electrical flows that may occur among cooperating utilities represent a real cost to society because energy is lost. The Southeast region of the United States provides an ideal situation for investigating the efficiency of flows of electricity. The out-of-kilter algorithm (OKA) is applied to the electrical system of the Southeast abstracted as a graph. Flows are analyzed under various assumptions concerning generative efficiency. Texas and Florida are established as areas where cooperative efforts are inhibited by lack of transmission capacity under possible stress.  相似文献   

Reply to the comment by Nikhely and Davies on 'Magnetic profile analysis' by Green (1972)     

A. G. Green 《Geophysical Journal International》1980,62(3):725-725

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Dissociative recombination contributions to I(5577) and I(6300) [OI] and N_mF2 enhancements resulting from moderate proton PCA events     

H.S. Porter  B.C. Edgar  A.E.S. Green 《Planetary and Space Science》1975,23(6):935-944

We investigate the dissociative recombination contribution to I(5577) and I(6300) of [OI] as a function of low energy cutoff for two measured solar proton spectra. The volume ionization rate profiles used in the calculation are obtained using a detailed atomic cross section approach in the continuous slowing down approximation. The ratio of the dissociative recombination contribution to the direct impact contribution for both the 5577 Å and 6300 Å [OI] emissions is found to be dependent upon the low energy cutoff. This ratio has a nominal value of ～2.0 for the 5577 Å [OI] emission and ～0.25 for the 6300 Å [OI] emission. The I(5577)/I(3914) and I(6300)/I(3914) ratios including the direct and dissociative recombination contributions are strongly dependent upon the low energy cutoff of the spectrum. We have also investigated F-layer enhancements resulting from the low energy spectrum component. For the Mizera et al. (1972) spectrum with a low energy cutoff of 12.4 keV, we find an N_mF2 of ～4.5 × 10³ electrons/cm³ or about 10 per cent of the ionization required to maintain the dip pole at a value of 5 × 10⁴ electrons/cm³. Extension of the cutoff to 1 keV results in ～1 × 10⁴ electrons/cm³, or about 20 per cent of the required maintenance ionization.  相似文献   

WHEN ARE STORE LOCATIONS GOOD? THE CASE OF THE NATIONAL TEA COMPANY IN DETROIT     

Howard L. Green  William Applebaum  Herbert Dupree 《The Professional geographer》1978,30(2):162-167

Testing the theoretical notion that differences in entrepreneurial skill can enhance the viability of a poor location or detract from the qualities of a good location, this study reviews the historical experience of a number of retailing establishments operated by different firms at the same sites. The ultimate success of stores that had done poorly under previous management tends to confirm that a location is “good'’only so long as the retailer employs effective merchandising and operating policies.  相似文献