Genetic variation in productivity, leaf traits and carbon isotope discrimination in hybrid poplars cultivated on contrasting sites

? We examined the relationships between productivity, leaf traits and carbon isotope discrimination in bulk leaf matter (Δ₁) and in phloem sap (Δ_s) from more than 5-year-old trees belonging to Populus deltoides × P. nigra and Populus trichocarpa × P. deltoides; trees were grown in alluvial and non alluvial sites in a commercial poplar plantation.

? On both sites, a large genetic variability was evidenced for all variables. The genotypic ranking remained stable between years for all variables, while it differed between sites. Δ₁ scaled positively with Δ_s and neither Δ₁ nor Δ_s were correlated with productivity. A significant genotype by site interaction was evident for all variables. The non alluvial site resulted in lower productivity, and in thicker/denser leaves with lower nitrogen and carbon contents. Noteworthy, the genotypic ranking for Δ₁ measured at the alluvial site was similar to that previously established in a glasshouse.

? As observed in previous studies from younger trees, there is a potential to select genotypes, combining high productivity and high water-use efficiency, for growth in moderately drought-prone areas.