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

Abstract

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...

Host-specific ecotype diversity of rhizoplane diazotrophs of the perennial glasswort Salicornia virginica and selected salt marsh grasses

“…This is in contrast to S. alterniflora and the J. roemerianus islands in the low intertidal, where frequent tidal flooding promotes cyclic changes from oxic or suboxic to anoxic conditions. Lacunal transport is the major source of oxygen to roots, rhizomes, and the rhizoplane/rhizosphere (via diffusive losses from roots and rhizomes) at these locations (Teal & Kanwisher 1966, Armstrong 1978, Hwang & Morris 1991. However, oxygen availability in the root microenvironment is likely intermittent and generally low (Lovell 2001 and references therein).…”

Cordgrass Biomass in Salt Marshes

“…average leaf emergence from tidal waters during daylight hours), a potent environmental factor in limiting the survival of Spartina clumps on low marshes, where a few centimeters of elevation in the tidal gradient may determine the lower distribution limit (Castillo et al, 2000). In addition, taller shoots may play a role in improving the oxygenation of rhizomes and roots via aerenchyma in anoxic environments, as in certain non-tidal wetland species (Sorrel et al, 2002); such internal ventilation might be associated with internal pressurization, as has been described for S. alterniflora (Hwang & Morris, 1991). Variations in canopy height of a dominant Spartina species can influence ecological functions and the structure of plant and animal communities in a marsh (Seliskar et al 2002).…”

Trophic interaction of the aerotolerant anaerobe Clostridium intestinale and the acetogen Sporomusa rhizae sp. nov. isolated from roots of the black needlerush Juncus roemerianus

“…Ventilation occurs via the aerenchyma, a tissue containing interconnected intercellular gas-filled spaces that can occupy as much as 70 % of the plant tissue volume. Diffusive and convective airflows through the aerenchyma of stems, rhizomes and roots have been demonstrated for several species (Christensen et al, 1994;Hwang & Morris, 1991). In the case of plants having stomata, such as Juncus and other emergent grasses, ventilation is not dependent upon photosynthesis and thus occurs throughout the day-night cycle.…”