Daniele Pezzotta

Das Programm «Langfristige Waldökosystem-Forschung» in der Schweiz liefert detaillierte Ergebnisse zu den Auswirkungen von Luftverschmutzung und Klimaänderung auf die Waldböden und Baumernährung. Seit den 1980er-Jahren sind die Emissionen von Schwefeldioxid und Stickoxiden in Mitteleuropa signifikant zurückgegangen. Diese Trends können auch für die Immissionen in der Schweiz bestätigt werden. Die Monitoringdaten zeigen, dass die Auswaschung von Sulfat aus dem Bodenprofil zurückgegangen ist. Auch die Stickstoffauswaschung nahm grösstenteils ab, jedoch nicht an Standorten mit weiterhin hohen Stickstoffeinträgen, wo sogar ansteigende Trends beobachtet wurden. Daher bleibt die Stickstoffbelastung trotz der insgesamt positiven Entwicklungen ein Problem. Ein weiterer kritischer Befund ist die fortschreitende Bodenversauerung, die sich in abnehmenden pH-Werten und niedrigen Verhältnissen von basischen Kationen zu Aluminium zeigt. Die Böden puffern die sauren Depositionen durch die Auswaschung von Nährstoffen und die Freisetzung von Aluminium. Diese Veränderungen in der Bodenlösungschemie können lange anhalten und die Nährstoffverfügbarkeit für die Bäume beeinträchtigen. Dies ist einer der Faktoren, die zu einem signifikanten Rückgang wichtiger Nährstoffe wie Stickstoff, Phosphor und Schwefel in den Blättern geführt haben. Dies weist auf eine Verschlechterung der Baumernährung hin. Zusammengefasst zeigen die Ergebnisse, dass trotz des Rückgangs saurer Depositionen die langfristigen Auswirkungen auf die Waldböden und die Baumernährung bestehen bleiben, was sich auf die Gesundheit und Vitalität der Schweizer Wälder auswirken kann.

Trends in atmospheric deposition and effects on soil water quality and tree nutrition
Long-term forest ecosystem research (LWF) in Switzerland provides detailed results on the impacts of air pollution and climate change on forest soils and tree nutrition. Since the 1980s, sulphur dioxide and nitrogen oxides emissions have significantly decreased in Central Europe. These trends can also be confirmed for emissions in Switzerland. Monitoring data show that sulphate leaching from the soil profile has decreased. Nitrogen leaching has also mostly declined, but not at sites with persistently high nitrogen inputs, where even increasing trends have been observed. Therefore, nitrogen deposition remains a problem despite the overall positive developments. Another critical finding is the ongoing soil acidification, reflected in decreasing pH values and low ratios of base cations to aluminium. The soils buffer the acidic deposition through nutrient leaching and aluminium release. These changes in soil solution chemistry can persist for a long time and impair nutrient availability for trees. This is one of the factors contributing to a significant decline in key nutrients such as nitrogen, phosphorus, and sulphur in the leaves. In summary, the results show that despite the reduction in acidic deposition, the long-term impacts on forest soils and tree nutrition persist, potentially affecting the health and vitality of Swiss forests.

δ¹³C In carbonate-containing soils a reliable determination of organic C requires a method that effectively separates organic and inorganic C without altering the organic matter. This study was conducted to determine whether HCl vapor completely removes carbonates even in dolomiterich soils and to what extent a widely used acid-fumigation method has to be modified for humus-rich soils. Furthermore, it was tested whether HCl fumigation alters organic-C content. Since C and N parameters are often analyzed simultaneously we also tested the influence of acid-vapor treatment on N content and on δ¹³C of soil organic matter. We applied fumigation with 37% HCl for 8 and 32 h using 9 carbonate-containing soil samples. Inorganic C ranged from 7 to 124 and organic C from 9 to 267 g kg^–1. The maximum contents of dolomite and calcite were 940 and 640 g kg^–1, respectively. A time of 8 h was enough to completely remove all carbonates. Neither the content nor the δ¹³C of organic C were significantly affected by fumigation. In contrast, N contents were altered by acid treatment. Based on these results and on our experience in analyzing more than 1000 soil samples, a recommended procedure for acid fumigation of carbonate-containing soils with a wide range of organic- and inorganic-C contents was derived. Samples pretreated in this way can be analyzed reliably for their organic-C content and δ¹³C. Furthermore, N and inorganic-C contents can be determined with a quality sufficient for many purposes.

Communities of young spruce (Picea abies K a r s t.) and beech (Fagus sylvatica L.) trees were grown for 4 years under two atmospheric CO₂ concentrations (370 vs. 570 μmol mol^-1) and two levels of nitrogen deposition (0.5-0.7 vs. 5-7 g N m^-2 a^-1) on two different native forest soils, i.e. a fertile calcareous sand and a low fertility acidic brown earth. 'Final' community biomass was 42% larger on the calcareous than on the acidic soil. Enhanced N deposition stimulated community biomass on the acidic soil (+34%) but not on the calcareous soil. In contrast, CO₂ enrichment had a significant biomass effect on the calcareous soil (+30%) but not on the acidic soil. Elevated CO₂ increased final spruce biomass by 44% on the calcareous and by 20% on the acidic soil. Beech also responded positively to CO₂ on the calcareous soil (+18%) but showed a negative response on the acidic soil (-18% for the aboveground biomass: virtually no change in the belowground biomass).
The effect of elevated CO₂ was generally a decrease in the concentrations of important nutrients, but plant response was strongly dependent on soil type and species. Elevated CO₂ significantly increased P and Zn concentrations in beech leaves and those of Zn in spruce needles on the calcareous soil. Enhanced N deposition also led to a dilution of nutrients and increased N contents. A discriminant analysis revealed more pronounced shifts in nutrient concentrations in the foliage of spruce and beech saplings by enhanced N deposition than by elevated CO₂, except in beech on the calcareous soil. Interactions between both treatments were rare.
Our results provide evidence for the conclusion that the responsiveness to CO₂ enrichment depends on the resource status of the system. Growth responses and nutrient availability are not linearly correlated, but differ from species to species. Further, nutrient concentrations in the foliage of spruce and beech are controlled by growth processes.