Gas film retention and underwater photosynthesis during field submergence of four contrasting rice genotypes

Floods can completely submerge some rice (Oryza sativa L.) fields. Leaves of rice have gas films that aid O(2) and CO(2) exchange under water. The present study explored the relationship between gas film persistence and underwater net photosynthesis (P(N)) as influenced by genotype and submergence duration. Four contrasting genotypes (FR13A, IR42, Swarna, and Swarna-Sub1) were submerged for 13 days in the field and leaf gas films, chlorophyll, and the capacity for underwater P(N) at near ambient and high CO(2) were assessed with time of submergence. At high CO(2) during the P(N) assay, all genotypes initially showed high rates of underwater P(N), and this rate was not affected by time of submergence in FR13A. This superior photosynthetic performance of FR13A was not evident in Swarna-Sub1 (carrying the SUB1 QTL) and the declines in underwater P(N) in both Swarna-Sub1 and Swarna were equal to that in IR42. At near ambient CO(2) concentration, underwater P(N) declined in all four genotypes and this corresponded with loss of leaf gas films with time of submergence. FR13A retained leaf gas films moderately longer than the other genotypes, but gas film retention was not linked to SUB1. Diverse rice germplasm should be screened for gas film persistence during submergence, as this trait could potentially increase carbohydrate status and internal aeration owing to increased underwater P(N), which contributes to submergence tolerance in rice.