Submergence-induced damage of photosynthetic apparatus in Phragmites australis

Phragmites australis colonises new areas by seedling establishment after drop down of water levels and exposure of mud flats. Seedlings may subsequently be subjected to submergence resulting from fluctuations of the water level. Seedling survival depends on tolerance to total or partial submersion. In particular, the response to short submergence periods may be related to the tolerance of green tissues. Three-month-old plants were partially or totally submerged in tanks for 2–17 days, and subsequently re-exposed to the air. The effects of submergence on photosystem II (PSII) activity and pigment contents and the reversibility of changes were analysed at the level of individual leaves. Pigment contents decreased during submergence and failed to recover following a return to non-submerged conditions. PSII photochemical efficiency was affected by submergence and exhibited varying recovery levels depending on duration and degree of submergence. Emerged leaves of partially submerged plants displayed an increase in both photochemical efficiency in the light adapted state and in pigment content, whereas submerged leaves of the same plants were negatively affected and did not recover. The effects of short-term stress were found to be reversible. Over longer periods, partially submerged reed favoured top emerged leaves at the expense of submerged ones, thus suggesting short-term avoidance of anoxia rather than tolerance.