Leaf gas exchange, chlorophyll fluorescence, non-structural carbohydrate content and growth responses of Distylium chinense during complete submergence and subaerial re-emergence

• All plants of D. chinense survived the submergence and re-emergence periods.
• Submergence reduced the biomass and photosynthesis.
• Biomass and photosynthesis rapidly recovered to control levels after drainage.
• Carbohydrate utilization was slowest during submergence.
• Carbohydrate reserves rebuilt rapidly during the re-emergence period.

We examined outdoor effects of submergence and subaerial re-emergence on photosynthesis, non-structural carbohydrate content and growth of Distylium chinense, an evergreen shrub used in restoration programs under way at the hydro-fluctuation belt of the Three Gorges Reservoir Region. Two-year-old D. chinense seedlings were completely submerged for 150 days, then drained and held for a further 60 days. All the seedlings survived the flooding period. The biomass, root/shoot ratio, net photosynthetic rate, stomatal conductance, maximal photochemical efficiency (Fv/Fm), photochemical quenching (qP) and electron transfer rate (ETR) of submerged seedlings were significantly depressed in relation to control seedlings. We also observed increases in chlorophyll content and reductions in non-photochemical quenching (qN) during submersion. The contents of carbohydrates (soluble sugars and starch) in leaves and roots decreased significantly during submergence, but the levels (especially of starch) gradually stabilized toward the end of the submersion period. All seedlings survived for 60 days after drainage. Biomass had almost completely recovered by the end of the experiment, and the net photosynthetic rate, stomatal conductance, Fv/Fm, qP, qN and ETR increased gradually after draining, rising to the values similar to those of controls by the end of the experiment. Carbohydrate content also recovered to the level of controls by the end of the experiment, although starch and soluble sugar contents decreased and increased, respectively, 30 days into the recovery period. We therefore conclude that D. chinense seedlings are flood-tolerant and have excellent post-submergence recovery abilities that make this a suitable candidate species for vegetation restoration at the hydro-fluctuation belt of the Three Gorges Reservoir Region.