Graham's laws: Simple demonstrations of gases in motion: Part II, Experiments

Mason, Edward A.; Love, L. D.; Evans, Richard B.

doi:10.1021/ed046p423

Cited by 12 publications

(2 citation statements)

References 3 publications

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“…1-3) indicates that the diffusion of gases in and out of plant tissues is inversely related to mol wt and is in agreement with Graham's law (16 (Fig. 2), which suggests that a gradient in water vapor pressure is necessary for pressurization in Spartina.…”

Section: Resultssupporting

confidence: 72%

Evidence for Hygrometric Pressurization in the Internal Gas Space of Spartina alterniflora

Hwang

Morris²

1991

Plant Physiol.

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Higher pressure, up to several hundred pascal relative to ambient, is generated by hygrometric pressurization within the central hollow space of the stem in Spartina afterniflora. Dilution of oxygen and nitrogen by water vapor within the plant's internal gas space results in an influx of nitrogen and oxygen from the air and a net increase in the internal gas pressure at steady state. The nature of the pressure gradient suggests that small pores exist in the plant tissues. Moreover, the compact arrangement of leaf mesophyll cells creates a high resistance for the mass flow of gases and contributes to the higher pressure within leaves. After experimentally venting the internal pressure, outside air diffused through the basal area of the adaxial side of the leaves into the internal space and elevated pressure was restored.In wetland plants, oxygen is transported from the ambient air via the stomata through the aerenchyma tissue to the roots to maintain aerobic respiration in highly anoxic and reduced environments (2). Traditionally, the primary process of gas transport in most wetland plants was thought to be passive diffusion (2,3,5,7,24). Recently, several alternative mass flow mechanisms have been proposed, including a convective flow system based either on thermal transpiration and/or hygrometric pressurization (1, 8-10, 12, 13, 19, 20). These mechanisms are capable of generating pressure gradients across a porous membrane when a gradient in temperature, in the former case, or in gas composition such as water vapor, in the latter case, exists across the membrane (see Dacey [9] for a detailed description of these mechanisms). A third mechanism based on the difference in solubility of 02 and CO2 in water coupled with their metabolic consumption and production has also been described in the pneumatophores of mangroves (22) the roots when the root system is contained in a propane atmosphere. Recently, Dacey and Howes (1 1) proposed that the dynamics of root water uptake and transpiration of S. alterniflora could invoke a mass flow of gases. However, Mendelssohn et al. (17) showed that S. alterniflora responds metabolically to anaerobic conditions by increasing the activities of alcohol dehydrogenase, indicating that the mechanism of aeration apparently cannot support total aerobic respiration. Nonetheless, there is clear evidence that the rhizospheres of some root tips are oxidized (18). Our study ofS. alterniflora indicates that pressurization occurs in the internal spaces and that the process is driven primarily by hygrometric pressurization. MATERIALS AND METHODSSpartina alterniflora was grown in sand-filled pots in a greenhouse. The pots were totally submerged in sea water diluted 1:1 with fresh water and were fertilized periodically with dilute Hoagland solution. The plants were collected as cuttings of rhizomes taken originally from the Great Sippewissett Marsh, Cape Cod, MA. When healthy culms had developed after a season ofgrowth to heights ranging between 0.8 and 1.2 m, they were brought into th...

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Section: Resultssupporting

confidence: 72%

Evidence for Hygrometric Pressurization in the Internal Gas Space of Spartina alterniflora

Hwang

Morris²

1991

Plant Physiol.

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“…Air contains about 78.0% nitrogen and 0.94% argon, for a N2/Ar ratio of 83.0; this ratio would not change if air flowed through the partition en masse. If, on the other hand, the partition allowed diffusion alone, the conditions described by Graham (14) for effusion would prevail. According to Graham's law, the N2 and Ar in air would flow through the partition at rates inversely proportional to the square root of their mol wt.…”

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confidence: 99%

Knudsen-Transitional Flow and Gas Pressurization in Leaves of Nelumbo

Dacey¹

1987

Plant Physiol.

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ABSTRACITPressures in gas spaces of leaves of the lotus Nelumbo are higher than ambient pressure. The pressurization capacity of leaves was studied as a function of leaf temperature, and the composition ofair entering evacuated leaves was used to calibrate the pore sizes which determine flow in these leaves. The adaxial side of the leaf of Nelumbo has two distinct regions in terms of gas exchange characteristics. There is a region of relatively high mean pore diameter in the center of the leaf opposite the point of petiole insertion. Gas exchange between the remainder of the leaf (>99% by area) and the atmosphere is restricted by "pores" with an effective mean diameter less than 0.03 micrometer. As a result, a flowthrough ventilation operates within each leaf. Air enters the leaf across the expanse of the lsmins and escapes back to the atmosphere through the highly porous region at the center of the lamina.

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