1 Pressurized ventilation, which increases gas exchange between aerial and
submerged plant parts, has been found in various emergent macrophyte specie
s. We investigated the potential for this mechanism to affect growth, morph
ology and biomass allocation in Phragmites australis in glasshouse experime
2 Inhibition of pressurized ventilation by perforation of stems above the w
ater surface resulted in decreased oxygen concentrations in stem bases and
rhizomes. Perforation caused little mechanical damage.
3 Allometric methods were used to evaluate treatment effects on biomass all
ocation 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 le
ngth and number of rhizomes when substrate had a high organic content. In t
he third experiment, growth clearly decreased in deep water, although inhib
ition of pressurized ventilation did not affect 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 o
nly under certain conditions (e.g. not when growth rate is low or the subst
rate has a high redox potential).