Root habit of Jatroptia cardiopliylla of which the horizontal extensions of the rool-syslcin were shown in plate 12 52 Plate 14. Horizontal and vertical extensions of root-systems of Carnegiea gigantea, Covilka tridcntala. and Parkinsonia microphylla Plate 15. (a) The anchorinK roots and bases of sonic lateral roots of Carnegiea gigantea 6.8 in. high. {/>) Tap root and secondary roots making up the anchoring system, and the bases of some of the superficial roots of a specimen of Carnegiea 1.2 m. high from same habitat as cactus shown in (a), (c) Tap root and bases of laterals of Parkinsonia microphylla growing near Carnegiea shown in (6) and which appears in plate 14 56 Plate 16. (o) Covillea tridentata. Horizontal and vertical extensions of roots of this plant arc shown in fig. 8. (6) Covillea from flood-plain near West Wash, showing the large number of slender adventitious roots springing from upper portion of the main roots and long tap root of which only a i)art appears, (c) Fouquieria splendens from bajada where Covillea shown in (a) was growing. Horizontal extension of roots of this plant shown in fig. 8 64 Plate 17. (a) Franscria deltoidea from flood-plain near West Wash, showing part of tap root, (b) Lateral of the first order bearing filamentous roots in groups, which, at time photograph was made, were no longer functional, (c) Krameria canescens from the flood-plain near West Wash, showing essential superficial placing of roots. (d) Lycium andersonii from near West Wash 64 Plate 18. Bird's-eye view of superficial roots of Opuntia arbuscula from bajada a mile east of Santa Cruz, showing tieir fleshy character 68 Plate 19. (o) Riddellia cooperi showing the large number of slender laterals arising from crown of tap root, and the branching feature of the bases of the laterals, (b) Riddellia from red clay soil, to illustrate lack of slender roots at crown of tap root, (c) Dasylirion texanum, with root-system partly exposed, (d) Shoot and root habit of Yucca sp. (e) Root character of Yucca radiosa 72 Plate 20. Root habit of Koeberliniaspinosa. (a) Isolated plant with prominent tap root. (b) Several shoots arising from a single sucker which still keeps its connection with parent tap root, (c) Adventitious absorption roots arising from a sucker which has not formed an independent tap root, (d) Secondary formation of tap root in a group with connecting sucker root no longer living So Plate 21. (a) Peniocereus greggii showing fleshy main root and the most important laterals, (b) Condalia spathulata. (c) Root-system of Prosopis velutina partly exposed by the caving bank of the Santa Cruz. The vertical distance from the ground surface to the water is approximately 5 m. (d) Young plant of Prosopis. The squares are centimeters, (e, f, g) Cuttings of Opuntia arbuscula (Tucson), O. arbuscula (Sacaton), and O. vivipara, respectively, all grown under similar conditions and with a large water supply Plate 22. (o) Cultures of Fouquieria splendens and of garden watermelon showing differences in character and development of ...
Estimates have been made of the capacity of the Martian regolith to exchange adsorbed H20 and CO2 with the atmosphere-plus-cap system (APCS). These estimates are based upon measured isotherms for H:O and CO: adsorption on pulverized basalt at low temperatures and on theoretical considerations. A unit column (1 cm :) of regolith with a deep subsurface temperature of -77øC, considered average for the disk, will contain 40.4 g of adsorbed CO: and --• 1 g of adsorbed H•O per meter of depth. Under favorable circumstances the top 3 cm can exchange much more H•O with the lower atmosphere each day than is necessary to produce the diurnal brightening. The process appears to be seasonally reversible. The total regolith may contain, in the adsorbed phase alone, as much as 1% of the H•O and 5% of the CO2 surface inventories expected for a hypothetical Mars that has experienced degassing as intensive as that 9f earth. Long-term (• 105 yr) variations in surface insolation caused by variations in the obliquity of Mars could cause efficient desorption of adsorbed CO: and H:O from a 100-m regolith, and variations in solar output with periods >1 m.y. may well desorb H•O and CO2 efficiently from all the unconsolidated material onMars. Enough CO: could be desorbed to initiate major climatic change even if there is not enough in the APCS. The paradox presented by the fact that the APCS contains barely enough CO: molecules to form caps is mitigated by the observation that the APCS is itself in transient equilibrium with a much larger reservoir of adsorbed CO2.One approach to assessing the extent of Martian degassing is to assay all sinks into which volatiles supplied to the Martian surface might have eventually found their way. An analogous approach to the history of earth volatiles was employed by Rubey [1951] in his classical paper on the subject. He pointed out that the atmosphere, the polar caps, and even the oceans contain only a trivial fraction of certain released earth volatiles and that by far the most important fate of CO•. and some other volatiles that had been released to the surface was chemical recombination with igneous materials, resulting in incorporation into sediments. We will show that within the constraints currently supplied by observations of Mars it is possible and even likely that orders of magnitude more H•.O and CO•. are adsorbed on the Martian regolith than are present in the atmosphere-plus-caps system (APCS). Therefore any estimates of the degree of degassing of Mars based exclusively on the volatile inventory in the APCS are likely to be much too low for this reason alone, even if large amounts of H•.O and CO2 have not been removed by permafrost formation, chemical recombination, or exospheric escape. Further, we will attempt to show that exchange of adsorbed H•.O and CO•. between the Martian regolith and the APCS may play a major role in (1) seasonal and diurnal atmospheric phenomena, as discussed by Pollack et al. [1970] and Fanale and Cannon [ 1971 ], and (2) producing changes in atmospheric pressure...
We report results on the adsorbate-adsorbent system CO2-nontronite at 230øK, 196øK, and 158øK, covering the range of subsurface regolith temperature on Mars. These results, together with Viking observations have allowed construction of a three-part regolith-atmosphere-cap model describing storage and exchange of atmosphere-exchangeable CO2. Cold nontronite, and 'expanding' clays in general, are far better adsorbers for CO2 than cold pulverized basalt and exhibit far more complex adsorptive properties as well. Both observations result from a limitation on interlayer H20 content of clays at low temperature (even when the humidity is high). This makes available energetically favorable adsorption sites for CO2 and creates a micropore structure allowing capillary condensation of CO2 at Martian near-polar temperatures. The layered terrain, and possibly the adjacent debris mantle, contains ---2% or more by mass of atmosphere-exchangeable CO2 (---12 cc STP/g) and the total regolith inventory of available adsorbed CO2 is estimated to be •6 x 1020 g or 4 X 102 g/cm 2 as a global average. Thus the 'ocean' of adsorbed CO2 in the regolith, not the atmosphere or surface caps, is the main repository of atmosphere-exchangeable CO2. Such a large near-polar subsurface reservoir of CQ2 at relatively constant temperature can, either directly or via a small quasi-permanent cap, buffer the atmospheric CO2 pressure on a long-term basis while allowing annual caps to form in response to the wide seasonal variations in surface temperature. For example, isothermal removal (or addition) of atmospheric CO2 causes the large regolith buffer to contribute (or adsorb) atmospheric CO2 in response. Thermal changes also cause important buffering responses. The best understood of these is the obliquity variation, which can produce a ---15 ø increase or decrease in near-polar temperatures relative to present values. An increase would produce rapid dissipation of any quasi-permanent CO2 cap and then the regolith would buffer pressures which could rise to ---20 mb. A decrease would give rise to a situation in which the cap would buffer the pressure as it falls to a minimum of <1 mb. As the pressure falls, the regolith probably transfers much larger amounts of CO2 to the growing cap than the cap would acquire from the atmosphere. The predicted variation in atmospheric pressure (greater than a factor of 10 independent of postulates concerning the existence of a massive surface CO2 reservoir) together with the predicted periodic variations in cap size may have helped generate the layered terrain and other surface features. Also the predicted periodic 'flushing' of the atmosphere resulting from regolith-cap CO2 transfer can explain the near absence of 180 enrichment in the atmosphere observed by the Viking probe mass spectrometer, while other aspects of the model are consistent with and help to explain certain of the Viking lander gas chromatograph-mass spectrometer (GCMS) and gas exchange experiment (GEX) gas evolution observations. tion of circumstantial...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.