Photosynthetic responses of selected Antarctic plants to solar radiation in the southern maritime Antarctic   总被引：1，自引：0，他引：1  

Pedro Montiel  rew Smith  Don Keiller 《Polar research》1999,18(2):229-235

The effects of UV-B exclusion and enhancement of solar radiation on photosynthesis of the two phanerogams which occur in the maritime Antarctic, Deschampsia antarctica and Colobanthus quitensis , and the moss Sanionia uncinats were investigated. Data on air temperature and solar radiation illustrate a drastic seasonal variation. Daily O₃ column mean values and UV-B measured at ground level document the occurrence of the O₃"hole" in the spring of 1997, with a concomitant increase in UV-B. The grass, D. antarctica , exhibited a broad temperature optimum for photosynthesis between 10–25°C while photosynthesis did not saturate even at high irradiance. The high water use efficiencies measured in the grass may be one of the features explaining the presence of this species in the maritime Antarctic. The net photosynthesis response to intercellular CO₂ (A/c_i) for D. antarctica was typical of a C₃ plant. Exposure to a biologically effective UV-B irradiance of 0.74 W M^-2 did not result in any significant change in either the maximum rate of photosynthesis at saturating CO₂ and light, or in the initial carboxylation efficiency of Rubisco. (V_c,max). Furthermore while ambient (or enhanced) solar UV-B did not affect photochemical yield, measured in the field, of C. quitensis and D. antarctica , UV-B enhancement did affect negatively photochemical yield in S. uncinata . In D. antarctica plants, exposure to UV-B at low irradiances elicited increased flavonoid synthesis. The observed effects of UV-B enhancement on the moss (decreased photochemical yield) and the grass (increase in flavonoids) require further, separate investigation.  相似文献   

南北朝以前陕西天文人物     

刘次沅  窦忠 《时间频率学报》1994

  相似文献   

Mercurian volcanism questioned     

Don E. Wilhelms 《Icarus》1976,28(4):551-558

The Mariner 10 television team has argued that extensive plains on Mercury were formed by volcanism and compared them with the demonstrably lunar maria. I believe, however, that in stratigraphic relations, surface morphology, and albedo contrast, the Mercurian plains more closely resemble the lunar light plains. These lunar plains were interpreted as volcanic on the basis of data comparable to that available to the Mariner 10 investigators but have been shown by the Apollo missions to be of impact origin. The plains on Mercury might also be formed of impact materials, perhaps of impact melt or other basin ejecta that behaved more like a fluid when emplaced that did lunar basin ejecta.  相似文献   

WELL FIELD CONTAMINATION NEAR BALD KNOB,ALLEGANY COUNTY,MARYLAND     

Don W. Duckson 《The Professional geographer》1981,33(4):445-449

A case study from Allegany County, Maryland illustrates that, in the absence of a baseline of water quantity and quality established prior to coal mining, resolution of conflicts is neither fully possible nor equitable.  相似文献   

Temperature Dependence of Single-Crystal Spinel (MgAl₂O₄) Elastic Constants from 293 to 423°K Measured by Light-Sound Scattering in the Raman-Nath Region     

Hsi-Ping Liu  R. N. Schock  Don L. Anderson 《Geophysical Journal International》1975,42(1):217-250

Summary. The temperature dependence of single-crystal elastic constants of synthetic stoichiometric MgAl₂O₄ spinel has been measured by the light-sound scattering technique in the Raman-Nath region. The crystal is set into forced vibration by a single crystal LiNbO₃ transducer coupled to one crystal face. A He-Ne Laser beam is diffracted by the stress-induced birefringence inside the crystal. The diffraction angle is determined from the distance between two spots exposed on a photographic plate by the first order diffracted beams as measured by a microdensitometer. The sound wavelength inside the crystal is then inferred from the laser diffraction angle. Combining the sound wavelength with the measured transducer frequency, the velocity inside the crystal is determined typically to a precision of 0·05 per cent. In this method, the measurement of velocity is not dependent on either the determination of sample length or on phase shifts at sample-transducer interface. Velocities of four pure modes, L //[001], T //[001], L //[110], and T //[110]( P //[1 1 0] are measured in the temperature range between 293 and 423 °K. A linear temperature dependence is fit to the data by a least square method. Values obtained at 25 °C from this linear fit are
The temperature dependence of the adiabatic elastic constants and bulk and shear (VRH average) moduli is computed using the density and literature value of thermal expansion coefficient. Values obtained are:
A comparison with previous measurements by pulse superposition and ultrasonic interferometry methods is made. Disagreement, when present, is discussed in terms of the separate measuring techniques. Finally, the present method, with its possibility for further improvement, is evaluated as a new method to measure temperature and pressure dependence of elastic constants.  相似文献   

Leonard Medal Citation for Robert M. Walker     

Don Burnett 《Meteoritics & planetary science》1994,29(4):434-435

  相似文献   

The structure of the lowermost mantle determined by short-period P-wave amplitudes     

Larry J. Ruff  Don V. Helmberger 《Geophysical Journal International》1982,68(1):95-119

  相似文献   

Morgan, W.B. and Moss, R.P. Fuelwood and rural energy production and supply in the humid tropics : Dun Laoghaire: Tycooly International, 1981. Natural resources and the environment series, vol. 4, 224 pp. £21 hardback; £15.70 paperback     

Don Scott-Kemmis 《Applied geography (Sevenoaks, England)》1983,3(4):345-346

  相似文献   

Geochemistry of diabase dikes from the Lewis Hills Massif, Bay of islands ophiolite: evidence for partial melting of oceanic crust in transform faults     

D. Elthon  J.A. Karson  J.F. Casey  J. Sullivan  F.X. Siroky   《Earth and Planetary Science Letters》1986,78(1)

  相似文献   

The petrogenesis of the Lac Guyer komatiites and basalts and the nature of the komatiite-komatiitic basalt compositional gap     

Karen Stamatelopoulou-Seymour  Don Francis  John Ludden 《Contributions to Mineralogy and Petrology》1983,84(1):6-14

A sequence of ultramafic rocks in the Lac Guyer Archean greenstone belt exhibit brecciated flow tops, pillow structures, and spinifex textures testifying to their volcanic origin. Massive, spinifex-textured and differentiated flows in the sequence have the chemical characteristics of peridotitic komatiite, with MgO ranging from 19–25 wt.%. Associated pillowed flows have compositions that straddle the conventional boundary between komatiite and komatiitic basalt with MgO contents ranging from 16 to 19 wt.% MgO and are best termed pyroxenitic komatiites. Unlike other komatiitic occurrences, the peridotitic and pyroxenitic komatiites at Lac Guyer constitute a continuous chemical spectrum with no evidence of population minimum near 18 wt.% MgO. The contrasting behaviour of highly compatible elements, such as Ni and Cr, versus incompatible elements, such as Zr, indicate that this compositional spectrum was produced by a variation in the extent of partial melting (10–40%) of a garnet lherzolite source in the Archean mantle. The pyroxenitic komatiites represent liquids produced during lower (10–20%) degrees of melting during which garnet remained in the mantle residue. However, a change in slope in the distribution of Zr vs. Y between the pyroxenitic and the peridotitic komatiites indicates that garnet was completely consumed at the more extensive degrees of melting which produced the peridotitic komatiites. The Lac Guyer volcanic rocks display a population minimum at 15 wt.% MgO separating komatiitic magmas whose compositions are controlled by partial melting from basalts whose composition is controlled by crystal fractionation. The population minimum near 18 wt.% MgO which is taken as the boundary between komatiite and komatiitic basalt may have a similar origin.  相似文献