B. Ulrich

Chemical changes due to acid precipitation in a loess-derived soil in central Europe.

In a stand of Fagus silvatica in the Solling highlands, Federal Republic of Germany, we followed the effect of acid precipitation on chemical soil state and the ion fluxes in the ecosystem between 1966 and 1979. As indicated by increasing aluminum concentration in the soil solution and an increase in organic matter storage in the forest floor, for example, the soil shifted during the measuring period from one state toward another one. During this transition, the acid precipitation has induced soil internal H+ ion production, partly by accumulation of organic matter poor in nitrogen, and partly by a probable change in the type of nitrogen nutrition. Two-thirds of the H+ ion buffering is due to the dissolution of polymeric hydroxoaluminum, resulting in the formation of solid AlOHSO4 and the leaching of Al ions. There are indications that the Al concentration in soil solution reaches toxic levels for the stand. The findings may have serious consequences for forestry in central Europe.

Eine ökosystemare Hypothese über die Ursachen des Tannensterbens (Abies alba Mill.)

ZusammenfassungEs wird folgende Hypothese über das Tannensterben aufgestell: In kühl-feuchten Jahren häufen sich im Wurzelraum N-reiche, leicht mineralisierbare Rückstände aus der Wurzelzersetzung an. Werden diese Vorräte in warm-trockenen Jahren mineralisiert, so lösen sie einen Versauerungsschub aus. Führt die Versauerung zum Auftreten von Al-Ionen in der Bodenlösung, so kann es durch Al-Toxicität zu Wurzelschäden kommen. Der ab 1950 großräumig auftretende Saure Niederschlag hat die Bodenversauerung so weit fortschreiten lassen, daß Wurzelschäden immer häufiger auftreten. Die geschädigten Wurzeln stellen die Eingangspforten für die den Naßkern auslösenden Bakterien dar. Der Naßkern führt über Verringerung der Transpiration zur Kronentrocknis. Einmalige bodenchemische Untersuchungen an Schadflächen führen zu Hypothesen über die vom Zustand des Ökosystems abhängige Prozeßkette, die zum Tannensterben führt.SummaryThe following hypothesis concerning fir-dieback is postulated: In cool-humid years residues from root decomposition which are rich in nitrogen and decompose easily are accumulated. If these stores are mineralised in warm-dry years, an acidification pulse in the soil is started. If soil acidification leads to the appearence of aluminum ions in the soil solution, Al-toxicity may cause root damage. The acid precipitation, being a widespread phenomenon since 1950, has increased soil acidity so much that root damage occurs increasingly. The damaged roots allow the entrance of bacteria which cause the wetwood. The wetwood, through the decrease of transpiration, leads to crown desiccation. Soil-chemical investigations on samples collected once on damaged plots lead to hypotheses concerning the chain of events leading to fir-dieback and its dependence on the condition of the ecosystem.

Die Rolle der Bodenversauerung beim Waldsterben: Langfristige Konsequenzen und forstliche Möglichkeiten

ZusammenfassungDie Ursachen der Bodenversauerung werden diskutiert. Die auf allen Standorttypen mit Ausnahme kalkskeletthaltiger Kalkverwitterungsböden und Geschiebemergel in Fallstudien angetroffene starke tiefgründige Versauerung wird auf die saure Deposition zurückgeführt. Die forstlichen Möglichkeiten zur Verringerung der ökosysteminternen Säureproduktion, zur Behebung akuter versauerungsbedingter Ernährungsstörungen, zur Vertiefung des potentiellen Wurzelraums und zur Begründung von Waldökosystemen, die ohne saure Deposition stabil mit hoher Elastizität sein können, werden diskutiert.SummaryThe causes of soil acidification are discussed. The strong and deep reaching acidification which has been found in case studies on all sites (with the exception of soils containing limestone or marl) is traced back to acid deposition. The possibilities of forest management to reduce ecosystem-internal acid production, to eliminate acute malnutrition, to increase deep rooting, and to establish forest ecosystems which can be stable with high elasticity without acid deposition, are discussed.

Parameters for describing soil acidification and their relevance to the stability of forest ecosystems

Abstract A theoretical description of the soil processes involved in the buffering of protons has been used as the basis for a grouping of forest soil into various buffering ranges. Such a grouping provides a framework for studying the response of the system to acidification. This response is described in terms of the elasticity (resilience) of the system to the generation and buffering of protons. A number of soil, humus and root parameters are suggested as measures of the ‘elasticity’ of soils. The soil chemical parameters include the proportion of calcium in the exchange complex, the effective cation exchange capacity (CECe), H + Fe as fractions of the CECe and the molar ratios of base cations/acid cations in the solution phase. The Ca/Al ratio in both the humus layer (OH horizon) and the fine roots are suggested as other measures of the elasticity of the soil system. A number of recommendations to forest managers are provided concerning the application of major plant nutrients and lime to acid forest soils of Central Europe. Liming is discussed in relation to: (a) growing forest stands — to compensate for the incoming acidity and (b) application at the time of establishment as a part of the ameliorative measures to improve the chemical status of forest soils.

Effects of fertilization on the fluxes of chemical elements through different forest ecosystems

SummaryThe effects of N−K fertilization and of liming on the fluxes of chemical elements within forest ecosystems were followed in a beech and a spruce stand in the German Solling region.No effect on the chemistry of throughfall was obvious except for K (beech). N added in form of nitrate to the humus layer was transferred rapidly into the mineral soil and was nearly totally lost from the soil of the spruce stand while the beech stand took up considerable amounts of nitrate. No nitrification of the NH4−N added occurred within the humus layer of both stands. The input of K and NH4 caused a strong acidification push within the mineral soil due to the exchange of Al-ions and led to heavy losses mainly of Al and Mn with seepage water.Liming caused increased rates of NO3−N losses under both stands but was followed by a significant reduction of the output of Al, Mn and SO4 under the spruce stand as compared to the unfertilized stand. Only a slight reduction was found under beech.The ratio of Ca/Al in the soil solution was substantially raised after liming.

Acidity of precipitation as influenced by the filtering of atmospheric sulphur and nitrogen compounds — its role in the element balance and effect on soil

Acidity of throughfall precipitation is increased by the filtering of S and N from the atmosphere by trees. An element balance for a beech forest is given. As a consequence of acidification the soil chemical conditions are changed in a way that plants rooting close to the soil surface are affected. Losses of nutrients may pose a problem in forest plant nutrition in the near future in Central European forests on light or medium textured acid soils.

Effects of fertilization and liming on the chemical soil conditions and element distribution in forest soils

SummaryThe distribution and storage of major elements in acid soils from a spruce and a beech forest was investigated after fertilization of NH4NO3 and KCl followed by Ca and Mg fertilization by 2 liming applications. All fertilizers were applied on top of the soil without mixing. Most of the added Ca and Mg was detected in the humus layer, a significant part of it still in carbonatic form. The effect of liming on mineral soil pH is very low, and was only observed in the 0–10 cm layer. However, base saturation of the mineral soil increased. The storage of C and N of the humus layer was not affected. N fertilization increased the N storage of the soil only under beech, but was followed by heavy NO3-losses with seepage water under spruce. High leaching rates for K were also found in the spruce stand. The amount of K that was not leached increased the pool of exchangeable K in the deeper soil layer.

Input, Output und Interner Umsatz von Chemischen Elementen bei einem Buchen- und einem Fichtenbestand

The element flux balance measured over a period of 4 years in a beech and a spruce stand is given. By the use of measured data two element fluxes are calculated: the leaching of salts and metabolic substances from the canopy by precipitation (part of the internal turnover), and filtering of atmospheric substances by impaction with the forest canopy (atmospheric input). With these data the flux balance for the forest ecosystem is complete, element uptake by roots included.

Die Bedeutung von rodung und Feuer für die Boden- und Vegetationsentwicklung in Mitteleuropa

Anhand ausgewählter Böden wird gezeigt, daß der Humus- und Stickstoffvorrat in den vom Menschen unberührten Böden mit zunehmender Höhenlage stark zugenommen hat. Als Folge einer Rodung, die wahrscheinlich meist mit dem Einsatz von Feuer verknüpft war, treten mit steigendem Stickstoffvorrat steigende Stickstoffverluste auf. Die mit der Überschuß-Nitrifikation verknüpfte H+-Ionen-Produktion wird rechnerisch abgeschätzt. Aus dem Vergleich der wahrscheinlichen H+-Ionen-Produktionsrate mit den möglichen Pufferraten wird auf Versauerungsphasen geschlossen, die sich u. U. über Jahrzehnte erstreckt haben. Als ökologische Folgen lang anhaltender Versauerungsphasen werdens Verminderungen der Rate der Biomasse-Produktion, Änderungen in der Artenzusammensetzung des Sekundärwalds und Zunahme von Vernässungsmerkmalen im Boden diskutiert. Using selected soils it is demonstrated that the storage of organic matter and nitrogen in soils untouched by man increased strongly with increasing sea level. As consequence of soil cultivation, which was probably often combined with the use of fire for clearing the soil surface, nitrogen losses occur. The losses increase with increasing nitrogen storage. The production of H+ ions occuring as consequence of surplus nitrification is calculated. Comparing the estimated rate of H+ ion production with the buffer rates possible it is followed that long lasting acidification periods, up to decades, occured. As consequences of such long lasting acidification periods are discussed: depression of the rate of biomass production, changes in the species composition of the secondary forest, increase in soil wetness.

Die Umweltbeeinflussung des Nährstoffhaushaltes eines bodensauren Buchenwalds

Data are presented concerning the rain input, the filtering action of the forest in respect to air impurities, the percolation output, the uptake and the changes in soil stores. The hydrogen ion balance shows the acidification pressure exerted on the soil and the contribution of SO2 (75%) and litter decomposation (25%). 85% of the hydrogen ion input is buffered by the mineral soil, as a consequence losses of Al, Mn, Ca, Mg and Na occur. The annual losses correspond to 0.1% of the clay and feldspar content of the uppermost 20 cm soil layer. There are indications that due to the losses Mg will become a growth limiting factor in the next decades. It is assumed that the features indications Aeh-and Ahe-horizons developed during the last decades as a consequence of acid rain. The nitrogen input from air covers 40% of the uptake and is of high ecological significance. From this input 50% are stored in the increment of the stand, 25% in the soil. Liming is recommended in order to compensate the soil acidification.