Transition of sulfur nutrition from excessive supply to potential deficiency in spruce forest ecosystems in Central Europe

1970-90年代大气硫沉降对北欧和中欧森林生态系统产生了明显的负面影响。因此，S在森林营养中的作用主要被看作是一种过剩的养分，甚至是污染物，从而假设森林生长有长期充足的S供应。然而，最近来自欧洲森林监测的结果显示，森林土壤中的S储量显著减少，不同树种的叶片S含量明显减少，尤其是挪威云杉。这些效应与大气中S沉降的显著减少和从前高S沉降的逐渐恢复有关。因此，森林生态系统的S营养状况越来越依赖于内部S循环（矿化）和矿物来源的S供应。此外，部分与气候变化有关的其他环境因素（即大气二氧化碳水平和温度升高）可能引起森林营养的变化，特别是在植物和土壤的营养化学计量方面。因此，拟议的项目侧重于了解森林中S营养从过度供应到潜在不足的转变。这还将考虑与其他生物地球化学循环（碳、氮、磷）的相互联系以及可能出现的营养不平衡。我们将结合分析方法（经典元素分析，SEM/EDX， IRMS）对不同的生态系统区室（针叶，树木年轮木材，矿物土壤，o层）使用存档的旧样本和新样本。试验场包括德国的挪威云杉林，在数量、时间变化和大气/岩石成因方面具有不同的S供应。根据浓度和元素比（“生态化学计量学”），将追溯S供应随时间的变化。这将有助于根据可能出现的不足和不平衡来评估生态系统营养。

Atmospheric sulfur (S) deposition during the 1970-90s caused distinct negative effects in forest ecosystems of North and Central Europe. Therefore, the role of S in forest nutrition was mainly seen as a surplus nutrient, or even pollutant, resulting in the assumption of a long-term sufficient S supply for forest growth. Nonetheless, recent results from European forest monitoring have revealed a considerable decrease of S stocks in forest soils and clearly reduced foliar S contents in different tree species, especially Norway spruce. These effects are related to the marked decrease of atmospheric S deposition and gradual recovery from formerly high S deposition. Consequently, the S nutritional status in forest ecosystems is increasingly relying on internal S cycling (from mineralization) and S supply from mineral sources. In addition, other environmental factors, partly related to climate change (i.e. increased levels of atmospheric CO2 and temperature) may induce changes in forest nutrition, especially with regard to nutrient stoichiometry in plant and soil. Thus, the proposed project focusses on the understanding of the transition of S nutrition in forests from excessive supply to the point of potential deficiency. This will also consider interconnections with other biogeochemical cycles (C, N, P) and potentially emerging nutrient imbalances. We will apply a combination of analytical approaches (classical element analysis, SEM/EDX, IRMS) on various ecosystem compartments (needles, tree ring wood, mineral soil, O-layer) using archived old as well as newly taken samples. The test sites comprise Norway spruce forests in Germany with contrasting S supply in terms of quantity, temporal changes and atmospheric/lithogenic sources. Based on concentrations and elemental ratios ('ecological stoichiometry') changes in S supply over time will be retraced. This will allow to assess ecosystem S nutrition in terms of potentially emerging deficiency and imbalances.