Growth, wood density, and ethylene production in response to mechanical perturbation in Pinustaeda

Ethylene, emitted by the first internode of intact stems of 3-year-old Pinustaeda L. (loblolly pine), was trapped before and after mechanical perturbation. The analysis was conducted as a 2 × 2 design on eight different half-sib families grown (i) without exposure to shaking (control) or (ii) with preconditioning to mechanical perturbation for a 2-year period. Ethylene production was determined per gram fresh weight of stem tissue and per square centimetre of cambial tissue. Ethylene produced over a 14-h period varied from 0.15 to 0.55 nmol/g fresh weight among families in the control group prior to mechanical perturbation. Mechanical perturbation increased ethylene emission from all stems of control and preconditioned trees from all families. Ethylene production per gram fresh weight correlated positively with juvenile wood density (p < 0.005, r 2 = 0.76) and negatively with stem diameter (p < 0.032, r 2 = 0.56) in the control trees. Ethylene production per square centimetre of vascular cambium correlated negatively with wood density (p < 0.05, r 2 = 0.50) and positively with stem diameter (p < 0.02, r 2 = 0.62) in preconditioned trees.