Influence of pressurized ventilation on performance of an emergent macrophyte (Phragmites australis)

Abstract

Summary1 Pressurized ventilation, which increases gas exchange between aerial and submerged plant parts, has been found in various emergent macrophyte species. We investigated the potential for this mechanism to aect growth, morphology and biomass allocation in Phragmites australis in glasshouse experiments. 2 Inhibition of pressurized ventilation by perforation of stems above the water surface resulted in decreased oxygen concentrations in stem bases and rhizomes. Perforation caused little mechanical damage. 3 Allometric methods were used to evaluate treatment eects on biomass allocation and morphology. 4 Inhibition of pressurized ventilation resulted in decreased allocation to belowground weight and decreased rhizome penetration into the substrate in two of three experiments. Treatment also decreased growth rate, rhizome length and number of rhizomes when substrate had a high organic content. In the third experiment, growth clearly decreased in deep water, although inhibition of pressurized ventilation did not aect growth, biomass allocation or morphology at either of the water depths tested. 5 Decreased allocation to below-ground parts and decreased rhizome lengths may be adaptations to allow the oxygen concentration in roots and rhizomes to be maintained above a critical level when the oxygen supply is low. 6 Pressurized ventilation may improve the performance of P. australis but only under certain conditions (e.g. not when growth rate is low or the substrate has a high redox potential).

Interactive effects of pressurized ventilation, water depth and substrate conditions on Phragmites australis

“…Evaluation of the method As in a previous study (Vretare and Weisner 2000), perforation of all stems above the water surface successfully prevented pressurized ventilation in P. australis. The lack of pressurized ventilation in the perforated treatment resulted in decreased oxygen concentrations in the stem bases, most likely with decreased oxygen concentrations in soil roots and rhizome apices as a consequence.…”

“…The larger effect of stem perforation in deep water on oxygen concentration is probably due to the lower supply rate with diffusion through stems in deep water. The mechanical damage caused to the plant by stem perforation has previously been shown to be negligible (Vretare and Weisner 2000).…”

“…Before the plants were harvested, 0.5 ml gas was sampled from the lowermost internode above the substrate surface from one stem per plant, using a syringe connected to an injection needle (Once 1 ml). The oxygen concentration in the gas samples was determined with a Clark-type oxygen electrode as in Vretare and Weisner (2000). Three stems per plant were cut at the water surface and connected with rubber tubing to a flow meter (0-20 cm 3 min -1 ; TopTrak, Sierra instruments) for determination of potential flow rates.…”

“…Trin. ex Steudel, grown in an organic substrate (Vretare and Weisner 2000). There was, however, no effect on growth when plants were grown in a minerogenic substrate, suggesting that low redox conditions in the substrate increases the need for pressurized ventilation (Vretare and Weisner 2000).…”

“…ex Steudel, grown in an organic substrate (Vretare and Weisner 2000). There was, however, no effect on growth when plants were grown in a minerogenic substrate, suggesting that low redox conditions in the substrate increases the need for pressurized ventilation (Vretare and Weisner 2000). Further, deep water may result in low internal oxygen concentrations in below-ground parts of emergent macrophytes (Yamasaki 1984;Setter et al 1987;Weisner 1988) and in decreased allocation to root weight (Vretare et al 2001).…”