The effect of mechanical perturbation on the conductivity, mechanical strength, and aboveground biomass of seven hybrid poplars (Populus trichocarpa, Populus deltoides)

To mimic the wind-induced back and forth motion of plants under greenhouse conditions, mechanical perturbation, MP, (20 flexures per day) was applied to stems of sapling poplar clones for 70–90 days. This study quantifies the effect of MP on the wood properties of hydraulic conductivity and mechanical strength, and total aboveground biomass for seven hybrids of a cross between Populus trichocarpa (black cottonwood) and P. deltoides (eastern cottonwood). Mechanical perturbation of stems was expected to decrease hydraulic conductivity (k_h) and aboveground biomass, and increase mechanical strength. Mechanical perturbation significantly decreased specific conductivity (k_s or k_h per conductive xylem cross sectional area) and aboveground biomass. Flexural rigidity (EI), wood density, and xylem transverse area at point of flexure increased while modulus of elasticity (MOE) and modulus of rupture (MOR) decreased in most of the mechanically perturbed stems. Surprisingly, k_{h max} was positively correlated with EI (P < 0.0001, R2 = 0.507) with some hybrids having both great mechanical strength and water conduction (e.g. Hybrid 19–61) while others were deficient in both properties. Similarly, both k_s and MOE were positively correlated with percent vessel lumen area (P < 0.0001 and P = 0.002, respectively).