ASSESSING THE IMPACT OF ELEVATED O-3 AND CO2 ON GAS-EXCHANGE CHARACTERISTICS OF DIFFERENTLY K SUPPLIED CLONAL NORWAY SPRUCE-TREES DURING EXPOSURE AND THE FOLLOWING SEASON

Well-supplied and K-deficient 4-year-old clonal Norway spruce trees we re exposed to combinations of two levels of ozone (20 and 80 nl 1(-1) O-3) and carbon dioxide (350 and 750 mu 1 1(-1) CO2) to study the effe cts of possible future climate factors on gas exchange characteristics . The fumigation was performed in environmental chambers for a complet e growing season. After the exposure, plants were cultivated outdoors to investigate possible recovery and delayed effects. During the expos ure 1-year-old needles responded to the 80 nl 1(-1) O-3 treatment by a sharp but transient decrease of both apparent carboxylation efficienc y (CE) and maximum photosynthetic capacity (A(2500)). Elevated CO2 als o reduced CE and A(2500). The effect became stronger in the course of the exposure and was accompanied by decreases of N and P as well as ch lorophyll contents. In case of K deficiency, the acclimation response of current-year needles was even more pronounced reflecting lower sink capacities for carbon metabolites. The joint application of elevated O-3 and CO2 resulted in the lowest values of gas exchange parameters a nd chlorophyll contents. At the beginning of the growing season after the exposure and under outdoor conditions, all these treatment effects disappeared in the needles which had developed during the fumigation. In the course of the development of the new flush, however, the well- supplied 1-year-old needles which had been treated with 80 nl 1(-1) O- 3 and 350 mu 1 1(-1) CO2 in the year before, exhibited a sharp decline of CE and A(2500). Simultaneously, chlorotic mottle and bands develop ed. These delayed symptoms are discussed in the context of the previou sly published ''memory'' effect for O-3 (Sandermann et al. 1989). Addi tionally, evidence is presented that shoot development is altered in p lants which had been exposed to elevated O-3.