The influence of ozone, acid mist and soil nutrient status on Norway spruce [Picea abies (L.) Karst.

Abstract

SUMMARYThree‐year old Norway spruce [Picea abies (L.) Karst.] trees established from two clones (4076 and 2470) of a medium‐altitude southern German provenance, were transplanted in May 1986 into two acid brown earth soils which differed particularly in the amounts of exchangeable Ca2+and Mg2+. During the summers of 1987 and 1988 trees were exposed in large‐scale fumigation chambers (solardomes) to ozone at 200 or 40 μg−3(control). Each day trees were treated with acid (pH 3‐6) or control (pH 5‐5) mist solution. In late autumn 1988 certain aspects of tree water relations were investigated. In clone 4076 ozone and acid mist reduced stomatal conductance in the light, but resulted in incomplete stomatal closure at night, reducing the diel range of stomatal conductance in treated trees grown on both soils. In addition, current year's needles excised from clone 4076 dried more rapidly following exposure to ozone and/or acid mist than needles from control trees, indicating impaired stomatal performance. However, evidence of both clonai and soil variation in this response was found. Cellular water relations of current year's shoots of clone 4076 were investigated using pressure‐volume analysis. Exposure to ozone and/or acid mist resulted in a marked increase in the plasticity of tissues (reduction in ɛ) compared with controls, indicating that the pollutants induced cell wall loosening. In trees exposed to acid mist this was associated with lower cellular solute concentrations and a decrease in maximum turgor. Throughout this study, where interactions between ozone and acid mist were significant, they were always antagonistic. It is concluded that effects of ozone and acid mist on stomata, which would be expected to enhance the sensitivity of trees to drought and winter desiccation, may be at least partially compensated for by concomitant changes in the turgor relations of individual cells. It remains to be established whether interactions between gaseous air pollutants and water stress are a factor contributing to the development of forest decline in central Europe and north eastern America.