Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Wood density is the product of carbon allocation for structural growth and reflects thetrade-off between mechanical support and water conductivity. We tested a conceptualframework based on the assumption that micro-density depends on direct and indirect rela-tionships with endogenous and exogenous factors.

The dynamics of wood formation, including timings and rates of cell division, cell enlarge-ment, and secondary wall deposition, were assessed from microcores collected weeklybetween 2002 and 2016 from five black spruce stands located along a latitudinal gradient inQuebec, Canada. Cell anatomy and micro-density were recorded by anatomical analyses andX-ray measurements.

Our structural equation model explained 80% of micro-density variation within the tree-ring with direct effects of wall thickness (σ=0.61), cell diameter (σ=-0.51), and photoperiod(σ=-0.26). Wood formation dynamics had an indirect effect on micro-density. Micro-densityincreased under longer periods of cell-wall deposition and shorter durations of enlargement.

Our results fill a critical gap in understanding the relationships underlying micro-densityvariation in conifers. We demonstrated that short-term responses to environmental variationscould be overridden by plastic responses that modulate cell differentiation. Our results pointto wood formation dynamics as a reliable predictor of carbon allocation in trees.