The impact of winter flooding with saline water on foliarcarbon uptake and the volatile fraction of leavesand fruits of lemon (Citrus limon) trees

We investigated the consequences of recurrent winter flooding with saline water on a lemon (Citrus limon(L.) Burm.f.) orchard, focussing on photosynthesis limitations and emission of secondary metabolites (isoprenoids)from leaves and fruits. Measurements were carried out immediately after flooding (December), at the end of winter(April) and after a dry summer in which plants were irrigated with optimal quality water (September). Photosynthesis wasnegatively affected by flooding. The effect was still visible at the end of winter, whereas the photosynthetic rate was fullyrecovered after summer, indicating an unexpected resilience capacity of flooded plants. Photosynthesis inhibition byflooding was not due to diffusive limitations to CO2 entry into the leaf, as indicated by measurements of stomatalconductance and intercellular CO2 concentration. Biochemical and photochemical limitations seemed to play a moreimportant role in limiting the photosynthesis of flooded plants. In young leaves, characterised by high rates of mitochondrialrespiration, respiratory rates were enhanced by flooding. Flooding transiently caused large and rapid emission of severalvolatile isoprenoids. Emission of limonene, the most abundant compound, was stimulated in the leaves, and in young andmature fruits. Flooding changed the blend of emitted isoprenoids, but only few changes were observed in the storedisoprenoids pool.7