Unbalanced nutrient status and epicuticular wax of Scots pine needles

Abstract

Different combinations of normal and excessive foliar levels of nitrogen and normal and deficient foliar levels of K, Mg, and Ca were induced in Scots pine (Pinussylvestris L.) seedlings in an experiment with a completely randomized 24 factorial design during the growing season in 1991 and 1992. For scanning electron microscope analysis of epicuticular wax, the needles were sampled from the same part of the shoot on the same seedlings in September 1991 and 1 year later. The quantity and quality of the structural epicuticular wax were estimated by five-class scales based on the wax coverage or morphology. The effects of foliar nutrients on the quantity and quality of the wax were analyzed by logistic models. The deleterious effect of unbalanced nutrition first became visible in the stomatal furrows; the changes in wax coverage and morphology were clear already one growing season after the start of the nutrient treatments. Changes in the epistomatal chambers did not become discernible until 1 year later. The effect of different nutrients on the wax was somewhat different in stomatal and in nonstomatal areas. Deficiencies of Ca and Mg significantly decreased wax coverage in both the stomatal furrows and epistomatal chambers of the needles. Coverage in the epistomatal chambers was also significantly decreased by K deficiency, N excess, and consequently increased N/K ratios. The wax morphology in both the stomatal furrows and epistomatal chambers changed from tubelike to more fused and netlike structures as a result of deficiencies of K, Mg, and Ca and consequently increased N/K, N/Mg, and N/Ca ratios.