Light, transpiration and water use efficiency: contrasts among seedlings of three Eucalyptus urophylla × Eucalyptus grandis clones

Abstract

Accurately measuring water absorption and consumption can help improve understanding of forest dynamics and water resource management, especially in areas with water restrictions. In this study, the objective was to evaluate hourly, daily and accumulated transpiration rates of young Eucalyptus urophylla × Eucalyptus grandis plants. A randomized block experiment was conducted with seedlings of clones I144, CO1407, and A211 transplanted into pots. At 120 days after transplanting, leaf area and root, shoot, and total dry mass were measured. Furthermore, water use efficiency, the relationship between transpiration and leaf area, and the relationship between daily transpiration and energy availability, provided by radiation balance and leaf area ratio, were determined. Leaf transpiration increased concomitantly with plant growth of all clones, reaching a maximum with the highest leaf area. The volume of water consumed at the end of 1689 accumulated degree-days was around 20% higher in clone I144, compared to clones CO1407 and A211. The clones showed differences in hourly transpiration throughout the growth stages. CO2 assimilation varied between clones, with net photosynthesis being higher in clone A211, while clones I144 and CO1407 showed higher quantum yield. The increase in leaf area helped to increase the transpiration rate and improve the efficiency of using the energy balance for water loss from the plants. Dry mass production were higher in clones I144 and A211. Conversely, regarding water use efficiency, clones A211 and CO1407 had higher dry mass yield per gram of water transpired. Thus, we conclude that, among the most productive clones, clone I144 was preferably recommended for areas free from water restrictions, while clone A211, for areas with low water availability.