LAUSR

This study focused on relationships between soil properties, root architecture, and aboveground biomass productivity of Salix miyabeana “SX67”. Roots were excavated at eight short-rotation cultures with contrasted soil/climatic conditions and root system ages from 4 to 14 years. The depth of the root branching points to the initial cuttings, root diameters, and root branching occurrence as well as soil physico-chemical properties were measured. Aboveground biomass had been estimated in a previous study, which allowed to calculate a proxy of root-to-shoot ratio. Root system ages and belowground biomass were related (adj. R2 = 0.88, p < 0.001). However, biomass partitioning in the different tree components was mainly governed by soil properties. Sand content was related to root-to-shoot ratio (adj. R2=0.73, p < 0.01) and the proportion of coarse roots (diameter > 1 cm) deeper than 10 cm (adj. R2 = 0.75, p < 0.01), whereas clay content was related to root branching occurrence-to-aboveground productivity ratio (adj. R2 = 0.80, p < 0.01). Coarse root depth distribution was related to aboveground biomass following a quadratic model that suggested (i) a maximal aboveground biomass productivity when a third of the roots were deeper than 10 cm and (ii) two opposite strategies of biomass allocation, i.e., biomass was allocated “downward” with a higher proportion of deeper roots and root-to-shoot ratio at sites with coarser soils and “upward” with a lower proportion of deeper roots and root-to-shoot ratio at sites with clayey/compacted soils. The study highlights how root plasticity of “SX67” copes with different soil stresses to maintain high aboveground biomass productivity.