Contrasting ethylene-mediated responses to waterlogging in four Eucalyptus globulus Labill. clones

We investigated the effects of overabundant watering in Eucalyptus globulus, a widely used species for pulp production with a low to moderate tolerance to waterlogging. We hypothesized that (1) overabundant watering would result stressful and trigger some of the well-known physiological responses to waterlogging and (2) different clones may show a different response to overabundant watering. Twelve potted plants from four E. globulus clones were watered with nozzles for twenty minutes, twice a day along 21 days. Other eight plants per clone were kept as controls and watered every two to four days. Overabundant watering caused a decrease in total leaf area after 21 days of treatment. Chlorophyll content and net photosynthetic rate were lower in plants under overabundant watering with no significant decrease in the rate of transpiration and no photoinhibition. Root pressure-generated xylem sap exudation was 3-17 times higher in plants under overabundant watering. We found significant differences between clones in ethylene production, growth, chlorophyll fluorescence parameters and root thickening. The highest increase in ethylene production was measured in clone c14, in which we measured the highest decrease in growth, chlorophyll content and the electron transport rate under over-abundant watering. In conclusion, overabundant watering imposed a moderate stress, which allowed the plants to respond at the root and leaf level trying to drain the excess of soil water through transpiration. Our results support the viability of early testing for waterlogging resistance in Eucalyptus globulus clones, in order to select the best attributes to identify waterlogging-resistant genotypes.