Nitrogen nutrition of hedged stock plants of Loblolly Pine. I. Tissue nitrogen concentrations and carbohydrate status

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, andW)] of loblolly pine (Pinus taeda) were fertilized dailywith a complete nutrient solution containing N supplied fromNH₄NO₃ at either 10, 25, 40, 55, or 70mg·L^–1. In May (spring softwood), July(summer softwood), and January (winter hardwood) terminal stem cuttings weretaken for tissue analysis and rooting studies. Averaged over families, meantissue concentrations of N were higher in spring (1.8%) and summer (1.7%) thanin winter (1.3%). Concentrations of N increased linearly with increasing levelsof applied N. Concentrations of total nonstructural carbohydrates (TNC) inwinter (32.8%) were twice those in spring (17.1%) or summer (16.3%), but wererelatively unaffected by N application. In contrast, starch concentrations weresignificantly higher during spring and summer than winter. The greatest numbersof orthotropic shoots 9 cm in length were produced for thespring, followed by summer, and then winter hedgings. Number of shoots producedper hedge increased with increasing applied N rates, and family B producedsignificantly more shoots than the other three families at all applied N levels.Genetic differences among families were evident as several interactions with Nrates were observed.     

Mist, substrate water potential and cutting water potential influence rooting of stem cuttings of loblolly pine

We investigated the influence of cutting water potential (Psicut) on rooting of juvenile hardwood (dormant) and softwood (succulent) stem cuttings of loblolly pine (Pinus taeda L.) propagated under varying substrate water potentials (Psisub) and volumes of mist application. Mist treatment and Psisub contributed to the Psicut of unrooted stem cuttings. When Psisub was held constant across mist treatments, mist treatment contributed strongly to Psicut. Substrate water potential affected rooting percentage when mist treatment was sub-optimal or excessive, otherwise mist treatment had a stronger effect than Psisub on rooting percentage. Cuttings rooted best when subjected to moderate cutting water potentials (-0.5 to -1.2 MPa) during the initial 4 or 5 weeks of the rooting period. Cuttings experiencing either severe water deficit or no water deficit rooted poorly. We conclude that the rooting environment should impose a moderate water stress on loblolly pine stem cuttings to achieve optimum rooting.     

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 × 27-5, 27-3× 27-1, 27-2 × 27-1, and 27-6 × 27-1 (designated B, G, R, andW)] of loblolly pine (Pinus taeda L.) were fertilizeddailywith a complete nutrient solution containing N at either 10, 25, 40, 55, or 70mg·L^–1. May (spring softwood), July(summersoftwood), and January (winter hardwood) terminal stem cuttings were taken fortissue analysis and rooting studies. Spring cuttings rooted in the highestpercentages (59.5%), followed by winter (40.5%), and summer (34.7%). Maximumrooting for spring (70.0%), summer (48.6%), and winter (55.6%) occurred withcuttings taken from hedges that received N at 55mg·L^–1. Genetic differences among familieswere evident as families G and W rooted in greater percentages at lower appliedN 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 lowinternal N levels, while family B was the best rooting family at high internalNlevels. Neither total nonstructural carbohydrates (TNC) nor any of severalspecific carbohydrates were correlated with rooting and an optimal TNC : Nratiofor rooting was not found. Root counts generally increased with increases inapplied N. Root number was weakly correlated with TNC (R = 0.29, P 0.01) and several specific sugars, but was not correlated with internal N.Totalroot dry weight, total root length, and total root area responded similarly.