Internal pressurization and convective gas flow in some emergent freshwater macrophytes

Abstract

Internal pressurization and convective through-flow are demonstrated to be common attributes of wetland plants with cylindrical culms or linear leaves. Eight of 14 species tested produced static internal gas pressure differentials of 200-1,300 Pa relative to ambient and internal convective airflows of 0.2 to > 10 cm3 min-' culm-I, depending on species. Four species produced internal static pressure differentials of < 100 Pa. Two species did not pressurize. The driving forces are gradients in temperature and water vapor between the internal gas spaces of the plants and the ambient atmosphere (thermal transpiration and humidity-induced pressurization). A clear diel variation in pressurization and convective flow was observed; rates were highest in the afternoon and lowest at night, responding to ambient changes in light, temperature, and humidity. The resistance to airflow at the stem-rhizome junction was very high for some species, resulting in a low ability to convert internal pressurization into convective airflow through the rhizomes. Species with a high potential for internal pressurization and a low internal resistance to convective flow seem to have a competitive advantage over species that rely exclusively on diffisive gas transport, which allows them to grow in deeper waters.

Methanogenesis and methane emissions: effects of water table, substrate type and presence of Phragmites australis

“…Enhancement occurs through production and release of organic matter (Holzapfel-Pschorn et al, 1986;Schütz et al, 1991), and by transportation of CH 4 via molecular diffusion or convective flow through the internal gas spaces of the plants, thus bypassing oxidation in the anoxic/oxic interface (Shannon and White, 1994;Sorrell and Boon, 1994;Shannon et al, 1996). Many species of emergent macrophytes possess a convective flow mechanism which is many times more efficient in transporting gases than diffusion alone (Brix et al, 1992), and hence these species may accelerate the emission of CH 4 from wetlands (Brix et al, 1996). On the other hand, emergent macrophytes may attenuate CH 4 emission by providing oxygen to the methanotrophic bacteria associated with the rhizosphere.…”

“…ex Steud.) is a dominant plant species in much of the land-water ecotone throughout Europe, and is known to have particularly high rates of convective flow (Brix et al, 1992;Armstrong et al, 1996). Phragmitesdominated wetlands therefore provide a significant source of CH 4 emission to the atmosphere (Brix et al, 1996).…”

Water level-dependent morphological plasticity in Sagittaria montevidensis Cham. and Schl. (Alismataceae).

“…Plants with lignified petioles present a higher resource investment in these tissues when submitted to adverse conditions, such as flood periods (Cooling et al, 2001). This investment could increase resistance to gas flow (Brix et al, 1992). We suggest that S. montevidensis invests in external lignification of its petioles in flood periods as occurs in other aquatic plant species, such as Phragmites australis (Cav.)…”

Amino acids as indicators of physiological stress in common reed Phragmites australis affected by an extreme flood

“…australis exhibits an outstanding capacity to vent its underground tissue by pressurised gas-throughflow, to supply oxygen from the atmosphere to their roots and rhizomes, which grow in the flooded, anoxie sediment, and to remove microbial metabolie end products (CH4, C02) from the rhizosphere (Armstrong and Armstrong, 1990). A reduced convective gas-flow rate affects the oxygen supply and may induce hypoxia in the below-ground organs (Annstrong and Annstrong, 1990;Brix et al , 1992). Convective gas flows may be impaired by a change of the water level, by the mechanical damage of culms, insect and fungal attack or by callus formation (Armstrong et al, 1996).…”