Hydraulic efficiency at the whole tree level stably correlated with productivity over years in 9 poplar hybrids clones

Abstract

The rapid growth of trees is largely dependent on the efficient water transport system. Here, we assessed the reliability of breeding high-yield Populus hybrids clones via xylem hydraulic efficiency. Leaf-specific hydraulic conductance at four levels (stem-segment, shoot, root, whole-plant) and growth performance (aboveground biomass, growth rate) were investigated over three successive years on 1–3 years old plants of nine clones issued from I-101 (Populus alba) × 84 K (P. alba × P. tremula var. glandulosa). Gas exchange and leaf water status were also tested the last year. We found significant variations in the nine clones of most of the variables. At the end of the studied period, nine clones reached an average height of about 7.2 m. There was a maximum two-fold difference in aboveground biomass among clones, and the clone ranking for productivity was extremely stable over time. Higher hydraulic efficiency favors more stomata opening and better leaf water status. Hydraulic efficiency at four levels showed a broad positive correlation with productivity for three years; however, the correlation at stem-segment level became weaker year by year, while the correlations at large levels (shoot, root, whole-plant) remained stable over years. Our results suggest that hydraulic efficiency at the large plant level may better reflect the productivity of poplar hybrids than stem-segment in many years of growth, thus it may provide useful information for the breeding of high-yield poplar clones.