Water availability preceding long-term drought defines the tolerance of Eucalyptus to water restriction

Abstract

Plantations of Eucalyptus species are expanding across South America into regions where drought conditions can reduce growth rate and result in substantial commercial loss. Understanding the mechanisms of drought tolerance in Eucalyptus is essential for the successful production in drought-regions. The main objectives of this study were to evaluate how water availability preceding a long-term drought period affects morphological, physiological and molecular traits of four Eucalyptus clones grown under field conditions. The study areas are located in north-eastern Brazil with an average rainfall of 800 and 1500 mm per year. At each rainfall regime, the following clones were evaluated: 1404 (Eucalyptus urophylla), 1407 (E. urophylla × E. camaldulensis), 1296 and 6500 (E. grandis × E. urophylla). Our results indicate that trees growing in the area with higher annual precipitation were more stressed after long-term drought, compared to those stands previously exposed to mild water-restriction period. The genetic materials showed distinct responses to drought, which allowed their separation in two groups: drought-tolerant (1404 and 1407) and drought sensitive (6500 and 1296). The former group shows some important adaptations to drought, such as decreased leaf area (avoiding excessive transpiration rates), higher antioxidant activity and carotenoid concentration (leading to lower lipid peroxidation). In conclusion, previous exposure to water deficit may provide the benefit of increased defense protection during future water deficit. From all measured variables, the leaf area, antioxidant compounds and changes in 13C and 18O isotope abundance reflect some of the most important morphological and physiological alterations in order to mitigate the water stress damage in drought-tolerant genotypes.