Preconditioning effects of nitrogen relative addition rate and drought stress on container-grown lodgepole pine seedlings

Abstract

Five-week-old Pinuscontorta var. latifolia Engelm. seedlings were subjected to 6 weeks of preconditioning with four combinations of watering and nitrogen fertilization, followed by a second 6-week period to evaluate the continuing effects of the preconditioning treatments. In both phases, the seedlings were fertilized with nitrogen at either 3 or 6%•d−1 relative addition rate and were either subjected to drought or well watered. Preconditioning treatments were crossed with second-phase treatments to give a 24 factorial design. Nitrogen and watering preconditioning effects on biomass, water relations, nutrients, and metabolic constituents persisted at least 6 weeks regardless of the second-phase treatments. Interaction between nitrogen and watering treatments applied simultaneously was found only in relative growth rate and foliar potassium concentration. Interactions between preconditioning and second-phase treatments were found in foliar nitrogen, potassium, and α-amino nitrogen concentrations, root water content, and xylem pressure potential. Foliar starch concentration increased when either nitrogen or water were limiting, but showed no evidence of interaction or preconditioning effect. Preconditioning at the lower nitrogen rate resulted in elevated reducing sugar concentration in the leaves, which persisted during the second-phase period. We did not detect an effect of increased reducing sugars on osmotic potential. Preconditioning at the lower nitrogen rate increased subsequent root weight ratio and reducing sugars concentration, which could contribute to drought resistance. Turgor regulation occurred via changes in cell wall elasticity rather than osmotic adjustment.