EFFECTS OF ELEVATED CO2, O-3 AND K DEFICIENCY ON NORWAY SPRUCE (PICEA-ABIES) - NUTRIENT SUPPLY, CONTENT AND LEACHING

Two clones of 5-yr-old Norway spruce (Picea abies [L.] Karst.) were ex posed to two atmospheric concentrations of CO2 (350 and 750 mu mol mol (-1)) and of O-3 (20 and 75 nmol mol(-1)) in a phytotron at the GSF-Fo rschungszentrum (Munich) over the course of a single season (April-Oct ober). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian forest, and trees were grown in 401 containers of soil (pH 3.5) fertilized to achieve two levels of potassium nutrition; well fertilized and K-defi cient. Foliar nutrient analyses performed at the beginning of the expo sure indicated that the fertilization programmes achieved their goal w ithout significantly altering the levels of other nutrients or the soi l pH. At the beginning of the fumigation, foIiar K concentrations were 7-9 mg g(-1) d. wt for well fertilized trees and 4-5 mg g(-1) d. wt f or trees receiving no supplemental K. Over the course of the season, d ifferences between K treatments intensified so that by the end of the experiment there was a five to sixfold difference between foliar K con centrations. This was associated with slight, but significant (P < 0.0 5), decreases in S and Zn (and of Cu in the 1989 needle year age class ) and higher levels of C, N and Mg in K-deficient trees. Foliar N conc entrations were low for all trees (9-15 mg g(-1) needle d. wt) but wer e similar to levels found in the field. Elevated O-3 was found to decr ease significantly the C (P < 0.05) and N (P < 0.001) content of both current-year (1989) and previous-pear (1988) needles independent of CO 2 concentration, but apart from some minor changes in the concentratio ns of Cu and Mn in the current-year needles no other effects of the po llutant on plant nutrient status were found. In contrast, CO2 enrichme nt resulted in significantly (P < 0.01) lower concentrations of K and P (effects on Mg were also on the borderlines of statistical significa nce) in current-year needles, but there was no influence on the nutrie nt composition of the previous-year needles (although effects on N wer e on the borderlines of statistical significance). CO2 enrichment also increased (P < 0.05) the C:N ratio of both current-year and previous- year needles. One factor contributing to the decline in foIiar K at el evated CO2 appeared to be a marked increase (25-30%) in the rate at wh ich cations were leached from the canopy by repeated simulated acid mi st (pH 4.0) events, and this effect occurred independently of the O-2 concentration. The information presented will aid the interpretation o f parallel studies examining the effects of elevated CO2 and/or O-2 on seasonal changes in photosynthesis, non-structural carbohydrate conte nt, antioxidants, tree growth and water use efficiency, and sheds furt her light on the growing scepticism concerning the role of O-2 in the development of Mg and K-deficiency symptoms characteristic of certain types of forest decline in central Europe.