- • Many wetland plants have gas films on submerged leaf surfaces. We tested the hypotheses that leaf gas films enhance CO2 uptake for net photosynthesis (PN) during light periods, and enhance O2 uptake for respiration during dark periods.
- • Leaves of four wetland species that form gas films, and two species that do not, were used. Gas films were also experimentally removed by brushing with 0.05% (v/v) Triton X. Net O2 production in light, or O2 consumption in darkness, was measured at various CO2 and O2 concentrations.
- • When gas films were removed, O2 uptake in darkness was already diffusion-limited at 20.6 kPa (critical O2 pressure for respiration, COPR≥ 284 mmol O2 m−3), whereas for some leaves with gas films, O2 uptake declined only at approx. 4 kPa (COPR 54 mmol O2 m−3). Gas films also improved CO2 uptake so that, during light periods, underwater PN was enhanced up to sixfold.
- • Gas films on submerged leaves enable continued gas exchange via stomata and thus bypassing of cuticle resistance, enhancing exchange of O2 and CO2 with the surrounding water, and therefore underwater PN and respiration.