Modifying sexual expression of containerized jack pine by topping, altering soil nitrogen and water, and applying gibberellins

Abstract

The numbers of seed strobili and pollen strobilus clusters and the extent of branch terminal growth were determined on 6-year-old containerized jack pine (Pinusbanksiana Lamb.) trees following modification of the soil nitrogen (N) supply (NH4NO3 at 3, 100, or 300 mg N/L; NO3− at 100 mg N/L; or NH4+ at 100 mg N/L in a nutrient solution), soil water supply (soil water potentials above −20 kPa compared with potentials near −70 kPa), and tree crown size (intact trees outside polythene shelters and lightly versus severely topped trees under polythene shelters). These factors were tested with or without biweekly foliar applications of spray solutions containing 400 mg/L of GA4/7. Intact trees outside polythene shelters did not display sexual or growth responses to N or GA4/7 treatments. Seed strobilus production on topped trees under shelters was not influenced by the level of topping or N supply, but it was depressed by low soil moisture potentials and stimulated by GA4/7 with high or low soil water potentials. Pollen strobilus production was depressed by severe topping and by low soil water potential; it was stimulated by GA4/7 on lightly topped trees but not on severely topped trees and by a low (3 mg N/L) N supply. In the year after treatment, terminal growth of a branch from the 2-year-old nodal whorl was not influenced by nitrogen supply or by light topping but it was increased by severe topping; it was increased by GA4/7 treatment if soil water potential was high but not with low water potential; it was depressed by low soil water potential.

Sexual expression in container-grown jack pine seedlings

“…For example, Pinus radiata D. Don cuttings produce pollen strobili after 2 years of growth when subjected to nitrogen deficiency (Sweet and Will 1965). We have observed that nitrogen deficiency promotes pollen strobilus production in 5-year-old jack pine seedlings (Fogal et al 1994), and Riemenschneider (1985) reported that short-term soil water deficits enhance seed strobilus production in jack pine seedlings.…”

Pollen cone production in jack pine: spatial and temporal patterns subject to natural disturbance by the jack pine budworm

“…However, we suggest that this pattern is among the most interesting results of our analysis and worthy of further investigation. In general, jack pine pollen cone production can increase in response to stress or in response to improved growth conditions (Fogal et al 1994(Fogal et al , 1999Kozlowski and Pallardy 2002;McCullough and Kulman 1991). It would be interesting to know if jack pine trees are becoming more or less stressed over time in central Ontario and why.…”