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

20世纪70 - 90年代大气硫沉降对北欧和中欧的森林生态系统造成了明显的负面影响。因此，S在森林营养中的作用主要被视为剩余养分，甚至是污染物，导致森林生长假设长期充足的S供应。尽管如此，最近的欧洲森林监测结果显示，森林土壤中的S库存量大幅下降，不同树种，特别是挪威云杉叶片中的S含量明显降低。这些效应与大气S沉降量的显著减少和从高S沉降量逐渐恢复有关。因此，森林生态系统中的硫营养状况越来越依赖于内部的S循环（来自矿化）和来自矿物源的S供应。此外，部分与气候变化有关的其他环境因素（即大气CO2和温度水平的增加）可能引起森林营养的变化，特别是在植物和土壤的养分化学计量方面。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缺乏点的过渡。这也将考虑与其他生物地球化学循环（C，N，P）和潜在的新兴营养失衡的相互联系。我们将应用分析方法（经典元素分析，SEM/EDX，IRMS）的组合在各种生态系统分区（针叶，树木年轮木材，矿物土壤，O-层）使用存档的旧的以及新采取的样品。测试地点包括挪威云杉林在德国对比S供应量，时间变化和大气/成岩源。基于浓度和元素比（“生态化学计量”）的变化，在S供应随着时间的推移将追溯。这将允许评估生态系统S营养方面的潜在出现的不足和不平衡。

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.