Leaf gas films contribute to rice (Oryza sativa) submergence tolerance during saline floods

Floods and salinization of agricultural land adversely impact global rice production. We investigated whether gas films on leaves of submerged rice delay salt entry during saline submergence. Two-week-old plants with leaf gas films (+GF) or with gas films experimentally removed (-GF) were submerged in artificial floodwater with 0 or 50mm NaCl for up to 16d. Gas films were present >9d on GF plants after which gas films were diminished. Tissue ion analysis (Na⁺, Cl^- and K⁺) showed that gas films caused some delay of Na⁺ entry, as leaf Na⁺ concentration was 36-42% higher in -GF leaves than +GF leaves on days 1-5. However, significant net uptakes of Na⁺ and Cl^-, and K⁺ net loss, occurred despite the presence of gas films, indicating the likely presence of some leaf-to-floodwater contact, so that the gas layer must not have completely separated the leaf surfaces from the water. Natural loss and removal of gas films resulted in severe declines in growth, underwater photosynthesis, chlorophyll_a and tissue porosity. Submergence was more detrimental to leaf P_N and growth than the additional effect of 50mm NaCl, as salt did not significantly affect underwater P_N at 200μm CO₂ nor growth.