1ST-ORDER ROOT DEVELOPMENT FROM CUTTINGS OF POPULUS-TRICHOCARPA X POPULUS-DELTOIDES HYBRIDS

We studied first-order root development of field-grown plants of 44 F1 Populus trichocarpa x P. deltoides hybrids as well 15 clones of P. tr ichocarpa (T) and 20 clones of P. deltoides (D) during their first gro wing season. The cuttings were planted in the field on May 11-12, 1988 and destructively sampled in July, August and September. By September 12, hybrids had an average of 50 first-order roots per cutting (range = 32 to 85) with an average of 25% dead roots (range = 10 to 51%). Th e longest roots of hybrids averaged 107 cm (range = 58 to 182 cm) and originated at the base of the cutting. Roots originating at the side o f the cutting averaged 54 cm in length (range = 12 to 96 cm). For most aboveground and root parameters measured, the values for hybrids exce eded those for both parent species clones. For all clones, aboveground weights were positively correlated with weights of collected roots (R 2 = 0.66 to 0.86). In contrast, aboveground weights were negatively (b ut poorly) correlated with root/shoot ratios (R2 = 0.08 to 0.21). Root s differed allometrically depending on their location on the cutting. Total weight of roots originating along the sides of the cutting was n ot correlated with aboveground weight (R2 = 0.001 to 0.27), whereas to tal weight of roots originating at the base of the cutting was correla ted with aboveground weight (R2 = 0.52 to 0.80). Basal roots dominated the first-order root systems of most clones in terms of maximum lengt h and total mass, but not in total numbers of roots.