NUTRIENT DEFICITS INCREASE FROST HARDINESS IN SITKA SPRUCE (PICEA-SITCHENSIS) NEEDLES

Frost hardiness of Sitka spruce (Picea sitchensis (Bong.) Carr) trees growing in a nutrient deficiency trial was monitored between September and May by freezing detached shoots in a purpose built cabinet. Hardi ness was assessed visually, as the temperature causing 50% shoot death (LT50), and from measurements of electrolyte leakage. Trees, 14-20 ye ars old, growing on a raised upland peat bog were given fertilizer app lications designed to exacerbate macronutrient (N, P, K) deficiency. D epriving these trees of N, P and K resulted in N, P and K concentratio ns of 1-year-old needles of 1.01; 0.09 and 0.19% dry weight, respectiv ely, whereas fertilized control trees whose nutrient concentrations we re considered normal, resulted in concentrations of 1.43, 0.22 and 0.8 2% dry weight, respectively. The timing of autumn hardiness acquisitio n and the level of mid-winter hardiness were strongly influenced by nu trient deprivation. one-year-old shoots deprived of K were hardy to -2 0 degrees C 5 weeks before shoots from the full nutrient treatment, an d in mid January - K trees were 5 to 10 degrees C harder than trees su pplied with all three macronutrients, Likewise, prior to budburst in s pring, - K trees were approximately 10 degrees C harder than control t rees. Similar, but smaller, effects were induced by deficiency of N an d P. Effects of nutrient deprivation were greatest during the hardenin g phase and smallest over the winter period. Effects of needle age wer e detectable in autumn when 2-year-old needles were hardy to colder te mperatures than 1-year-old needles. The observation that N, P or K dep rivation increases frost hardiness in Sitka spruce is important in vie w of the concern over rising levels of N deposition. (C) 1998 Elsevier Science B.V.