Nitrogen nutrition of hedged stock plants of Loblolly Pine. II. Influence of carbohydrate and nitrogen status on adventitious rooting of stem cuttings

Hedged stock plants of four full-sib families [27-2 x 27-5, 27-3 x 27-1, 27-2 x 27-1, and 27-6 x 27-1 (designated B, G, R, and W)] of loblolly pine (Pinus taeda L.) were fertilized daily with a complete nutrient solution containing N at either 10, 25, 40, 55, or 70 mg.L-1. May (spring softwood), July (summer softwood), and January (winter hardwood) terminal stem cuttings were taken for tissue analysis and rooting studies. Spring cuttings rooted in the highest percentages (59.5%), followed by winter (40.5%), and summer (34.7%). Maximum rooting for spring (70.0%), summer (48.6%), and winter (55.6%) occurred with cuttings taken from hedges that received N at 55 mg.L-1. Genetic differences among families were evident as families G and W rooted in greater percentages at lower applied N rates and family B was the best rooting family at the highest applied N rate. When internal N levels were considered families G and W also rooted best at low internal N levels, while family B was the best rooting family at high internal N levels. Neither total nonstructural carbohydrates (TNC) nor any of several specific carbohydrates were correlated with rooting and an optimal TNC : N ratio for rooting was not found. Root counts generally increased with increases in applied N. Root number was weakly correlated with TNC (R = 0.29, P less than or equal to 0.01) and several specific sugars, but was not correlated with internal N. Total root dry weight, total root length, and total root area responded similarly.