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

1970-90年代的大气硫(S)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一种过剩的养分，甚至是污染物，从而假设S为森林生长提供了长期充足的供应。尽管如此，欧洲森林监测的最新结果显示，森林土壤中的S蓄积量大幅下降，不同树种，特别是挪威云杉的叶片S含量明显下降。这些影响与大气S沉降量明显减少和S沉降量逐渐回升有关。因此，S在森林生态系统中的营养状况越来越依赖于S的内部循环(从矿化)和S的矿源供应。此外，部分与气候变化有关的其他环境因素(即大气中二氧化碳和温度的升高)可能会引起森林营养的变化，特别是植物和土壤中的营养化学计量比的变化。因此，拟议的项目重点是了解S在森林中的营养从过度供应到潜在缺陷点的转变。这还将考虑与其他生物地球化学循环(C、N、P)的相互联系以及可能出现的营养失衡。我们将结合各种分析方法(经典元素分析、扫描电子显微镜/能谱分析、红外光谱分析)对不同的生态系统隔层(针叶、树木年轮木材、矿物土壤、O层)进行分析，使用存档的旧样品和新采集的样品。这些试验点包括德国的挪威云杉林，与S在数量、时间变化和大气/岩石成因方面的供应进行了对比。基于浓度和元素比例(生态化学计量学)，S供应的变化将被追溯到一段时间。这将允许评估生态系统S的营养潜在地出现的缺陷和失衡。

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.