ISOTOPE RATIOS AND CONCENTRATIONS OF SULFUR AND NITROGEN IN NEEDLES AND SOILS OF PICEA-ABIES STANDS AS INFLUENCED BY ATMOSPHERIC DEPOSITIONOF SULFUR AND NITROGEN-COMPOUNDS

Concentrations and natural isotope abundance of total sulfur and nitro gen as well as sulfate and nitrate concentrations were measured in nee dles of different age classes and in soil samples of different horizon s from a healthy and a declining Norway spruce (Picea abies (L.) Karat .) forest in the Fichtelgebirge (NE Bavaria, Germany), in order to stu dy the fate of atmospheric depositions of sulfur and nitrogen compound s. The mean delta(15)N of the needles ranged between -3.7 and -2.1 par ts per thousand and for delta(34)S a range between -0.4 and +0.9 parts per thousand was observed. delta(34)S and sulfur concentrations in th e needles of both stands increased continuously with needle age and th us, were closely correlated. The delta(15)N values of the needles show ed an initial decrease followed by an increase with needle age. The he althy stand showed more negative 6'5N values in old needles than the d eclining stand. Nitrogen concentrations decreased with needle age. For soil samples at both sites the mean delta(15)N and delta(34)S values increased from -3 parts per thousand (delta(15)N) or +0.9 parts per th ousand (delta(34)S) in the uppermost organic layer to about +4 parts p er thousand (delta(15)N) or +4.5 parts per thousand (delta(34)S) in th e mineral soil. This depth-dependent increase in abundance of N-15 and S-34 was accompanied by a decrease in total nitrogen and sulfur conce ntrations in the soil. delta(15)N values and nitrogen concentrations w ere closely correlated (slope -0.0061 parts per thousand delta(15)N pe r mu mol eq N g(dw)(-1)), and delta(34)S values were linearly correlat ed with sulfur concentrations (slope -0.0576 parts per thousand delta( 34)S per mu mol eq S g(dw)(-1)). It follows that in the same soil samp les sulfur concentrations were linearly correlated with the nitrogen c oncentrations (slope 0.0527), and delta(34)S values were linearly corr elated with delta(15)N values (slope 0.459). A correlation of the sulf ur and nitrogen isotope abundances on a Delta basis (which considers t he different relative frequencies of N-15 and S-34), however, revealed an isotope fractionation that was higher by a factor of 5 for sulfur than for nitrogen (slope 5.292). These correlations indicate a long te rm synchronous mineralization of organic nitrogen and sulfur compounds in the soil accompanied by element-specific isotope fractionations. B ased on different sulfur isotope abundance of the soil (delta(34)S = 0 .9 parts per thousand for total sulfur of the organic layer was assume d to be equivalent to about -1.0 parts per thousand for soil sulfate) and of the atmospheric SO2 deposition (delta(34)S = 2.0 parts per thou sand at the healthy site and 2.3 parts per thousand at the declining s ite) the contribution of atmospheric SO2 to total sulfur of the needle s was estimated. This contribution increased from about 20 % in curren t-year needles to more than 50 % in 3-year-old needles. The proportion of sulfur from atmospheric deposition was equivalent to the age depen dent sulfate accumulation in the needles. In contrast to the accumulat ion of atmospheric sulfur compounds nitrogen compounds from atmospheri c deposition were metabolized and were used for growth. The implicatio ns of both responses to atmospheric deposition are discussed.