INHERENT DIFFERENCES IN RESPONSE OF DOUGLAS-FIR FAMILIES TO NITROGEN AND PHOSPHORUS SUPPLY LEVELS

Douglas fir (Pseudotsuga menziessi [Mirb.] Franco) seedlings from a half diallel mating design showed significant family by nutrient interactions when grown in a 3N x 3P x 15 family factorial experiment for 2 yr. Differences in response of these families to N and P treatment levels were related to nutrient productivity (dry matter production nutrient-1 time-1), but unrelated to the proportion of dry matter allocated to root growth, or to nutrient net uptake rate. Significance of general combining ability for N and K productivity showed clonal control of these characters. Evidence for genetic control of tissue N% and K%, shoot:root ratio and N uptake rate were also shown.