Mineral Nutrient and Carbohydrate Status of Loblolly Pine during Mist Propagation as Influenced by Stock Plant Nitrogen Fertility

Abstract

Hedged stock plants of four full-sib families [27-2 × 27-5, 27-3 × 27-1, 27-2 × 27-1, and 27-6 × 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 10, 25, 40, 55, or 70 mg·L–1. In May, terminal softwood stem cuttings were taken and placed under intermittent mist. Families were combined to form composite poor-rooting (BR) and good-rooting (GW) families. At 0, 3, 6, 9, and 12 weeks after sticking, cuttings were evaluated for rooting and analyzed for mineral nutrient and carbohydrate content. Percent rooting by week 12 for cuttings from stock plants receiving N between 25 to 70 mg·L–1 was 28% to 33%, whereas significantly fewer (17%) cuttings from plants receiving 10 mg·L–1 had rooted. By week 12, 98% of cuttings taken from stock plants receiving N at 10 mg·L–1 were alive, while significantly fewer (81% and 82%) of the more succulent cuttings receiving 55 and 70 mg·L–1, respectively, had survived. Nearly all increases in cutting height occurred within the first 3 weeks. In contrast, top dry weight increased steadily throughout the experiment. There were no significant differences in rooting between the two composite families until week 12, when 32% of cuttings from family GW had rooted compared with 24% for family BR. Survival of cuttings was greater for the poor-rooting family (BR) (94%) than for the good-rooting family (GW) (82%) after 12 weeks. Levels of total nonstructural carbohydrates (TNC) and individual soluble sugars were initially higher in cuttings taken from stock plants that received higher rates of N, whereas the reverse was true for starch content. With the exception of sucrose, content of TNC and soluble carbohydrates generally increased over time. Starch was nearly depleted by week 3, but had increased by weeks 6 and 9. No correlation was found between TNC: N ratios and rooting percentage. Family GW contained greater quantities of myo-inositol, glucose, fructose, sucrose, total soluble carbohydrates (TSC), and TNC than did family BR. Mineral nutrient content was generally greater in cuttings taken from stock plants that received higher rates of N; these cuttings also maintained higher levels throughout the 12-week rooting period. As with the soluble carbohydrates, the good-rooting composite family (GW) contained greater amounts of all mineral nutrients than did the poor-rooting family BR.