Derivation of threshold values for the sulfur nutritional status of European silver fir from a cumulative concentration distribution

For European silver fir (Abies alba (Mill)), reliable threshold values for the sulfur nutritional status are not available. Because European silver fir is an important coniferous tree species in Central Europe and due to the fact that by reduced S emissions, S is becoming a more and more critical nutrient this knowledge gap should be closed. From the interpretation of the cumulative distribution of sulfur concentrations in first-year needles, the respective threshold values for the range of normal nutrition as well as the threshold for deficiency could be derived. When knowing these thresholds also the range of harmonic nutrition, which is the range for the optimal relation of two nutrients, could be calculated. As compared to the very few literature data available and compared to the respective values of the two most important European conifers Norway spruce (Picea abies) and Scots pine (Pinus sylvestris), the values derived for S nutrition of European silver fir are very reasonable. With respect to the S nutritional thresholds, European silver fir is very close to the values of the other two conifers, whereas the harmonic range of S in relation to N is a bit shifted to higher values indicating that European silver fir has a slightly higher demand for S (in relation to N). There is a certain time lag between the reduction of SO₂ emissions in Europe and the reduction of S concentrations in needles, suggesting that S stored in the soil during periods of high emissions is relevant for S nutrition of trees for a longer period of time.