Changes in Biomass and Root Architecture During Axillary Bud Development of Pinus yunnanensis

Pinus yunnanensis , a member of the genus Pinus , a dominant coniferous species on the Yunnan-Guizhou Plateau, shows great potential for asexual propagation owing to the difficulty of retaining desirable traits in afforestation. Eight month old P. yunnanensis seedlings were used to divide axillary bud development into four stages. Seedling growth traits, biomass allocation and root architecture were investigated from axillary bud dormancy to elongation. The main findings were that seedling height and basal diameter followed a logistic growth pattern throughout axillary bud development, with the rapid growth phase occurring during bud dormancy, and both height and basal diameter were highly correlated with axillary bud number. Seedling roots were dominated by 0–2 mm fine roots. Most root morphological indices peaked at the axillary‑bud elongation stage except average root diameter, which kept increasing. Mantel test revealed a significant correlation between axillary bud elongation and root architecture. With axillary bud development, plant organ biomass increased continuously, and the root-stem ratio first increased and then decreased, reaching the maximum value in the development stage. Biomass was mainly allocated to roots and needles with a low stem proportion. During axillary bud formation, resources are preferentially allocated to roots, while axillary bud elongation shifts growth priority to above ground needles. In summary, axillary bud development is closely linked to seedling growth, root‑architecture formation and biomass allocation strategies. These findings provide a theoretical basis for scion cultivation of elite P. yunnanensis clones.