Application of Härtel's turbidity test across Europe

Abstract

The history and development of Härtel's turbidity test ("Trübungstest") for investigating the effects of sulphur dioxide on conifer needles are briefly reviewed. The turbidity test was applied to samples of Norway spruce (Piceaabies (L.) Karst.) and Scots pine (Pinussylvestris L.) needles from 13 sites in western Europe, from southwestern Germany to northeastern Scotland. Turbidity and electrical conductivity of the needle extracts were measured on duplicate samples of current-year, 1-year-old, and 2-year-old needles. The greatest differences among sites were observed for 2-year-old needles, but these differences were not related to needle sulphur content, nor to exposure to sulphur dioxide. The largest values were from British sites, and the smallest were from Dutch sites, with German sites intermediate. Turbidity values for both tree species were positively correlated (p < 0.01) with electrical conductivity of extracts, amounts of leaf surface dust, and total foliar calcium and magnesium; they were negatively correlated with amounts of chloroform-extractable wax and the acidity of macerated needles. Turbidity values for 2-year-old Norway spruce needles and conductivity values for 2-year old Scots pine needles were significantly greater (p < 0.05) within sites for trees with visible decline symptoms (needle loss and discoloration). The large differences in turbidity values among sites suggest that the turbidity test provides a simple method for characterizing conifer needles, and that a better understanding of the basis of the test may lead to a better understanding of the physiological and biochemical status of conifer foliage.