Modelling the Fate of Chromated Copper Arsenate in a sandy Soil

Afforestation of former agricultural land changes soil characteristics such as pH and organic matter content, which may affect heavy metal solubility in the soil. In this study the effects of different tree species on heavy metal solubility were investigated at four 34 years old adjacent stands of beech (Fagus sylvatica L.), grand fir (Abies grandis Lindl.), Norway spruce (Picea abies (L.) Karst.) and oak (Quercus robur L.) planted on former agricultural land at four different sites in Denmark. The sites differ in soil characteristics and represent two texture classes (loamy sand and sandy loam). Soil pH and soil organic matter content was measured in the 16 stands and soil solution was isolated by centrifugation from three depths at four different occasions. Dissolved organic carbon (DOC), pH in the soil solution and the soil solution concentrations (availability) of Cd, Cu, Ni, Pb and Zn were determined. Analysis of variance showed that the tree species affects soil pH and organic matter content in the topsoil, but not in the lower horizons. Norway spruce and grand fir acidify more than beech and oak, and the highest amount of accumulated soil organic matter is in the topsoil under Norway spruce. The effects of tree species on soil solution pH and DOC resemble the effect on soil pH and organic matter content. Grand fir enhances the solubility of Cd and Zn in the topsoil with the lower solubility found under beech and oak and Norway spruce enhances the solubility of Cu, Ni and Pb in the top horizons. The lowest solubility of Ni and Pb is found under beech and oak, whereas the lowest Cu concentrations in the soil solution are found under grand fir. After 34 years of afforestation no effects of tree species on the concentrations of heavy metals in the soil solution from the C-horizons were found. The tree species effect on the concentration of Cd, Cu and Ni in the soil solution depends on the soil characteristics with the higher concentrations found in sandy loam soils, whereas no effect of site on the solution concentration was found for Pb and Zn. It was not possible to find a clear correlation between the soil solution concentrations of heavy metals, pH and DOC concentration.     

Changes in humus properties and collembolan communities following the replanting of beech forests with spruce

Differences of collembolan communities within the organo-mineral A layer were studied in relation to physico-chemical changes in humus at nine sites of beech forests (Fagus sylvatica L.) and first generation spruce stands (Picea abies (L.) Karst.), planted on former beech forest 30 years ago (Central Pyrenees, France). Changes in humus form were caused by the spruce plantation and occurred mainly within the fermentation horizon where acidifying litter accumulation increased the horizon depth. The recent replacement of beech by spruce induced a shift from mull towards moder humus forms, which is explained by the decreasing organic matter turnover rate. A significant decrease in the three exchangeable cations and pH under spruce was also observed. Collembolan species diversity within the A horizon was significantly lower under spruce at this early stage of the silvogenetic cycle. Differences between species composition of Collembola between the two forest stands is related to changes in environmental conditions (e.g. nutrient availability, soil porosity, soil moisture). This study shows how forest management practices are susceptible to modify biological activity within the A horizon under exotic conifer plantations.     

Effects of growing roots of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) on rhizosphere soil solution chemistry

The chemical conditions of the rhizosphere can be very different from that of bulk soil. Up to now, little attention has been given to the problem of spatial heterogeneity and temporal dynamics of rhizosphere soil solution and little is known about the influence of different tree species on rhizosphere chemistry. In the present study, we used micro suction cups to collect soil solution from the rhizosphere of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) seedlings in high spatial resolution and capillary electrophoresis for the determination of major cations and anions. The results indicate, that in a soil with a base saturation of about 20—25% and a pH of 6.5, growing roots of beech and spruce lower the concentrations of nutrient cations and nitrate in the rhizosphere soil solution and decrease significantly the pH. The H⁺ release leads to an enhanced mineral weathering as indicated by an increase of CEC and base saturation and to a mobilization of soluble Al, however, on a very low concentration level. In our experiment rhizosphere effects of spruce have been more pronounced than those of beech, indicating, that with respect to below ground activity young spruce trees have a better competitive power than beech.     

The Collembola community of a Central European forest: Influence of tree species composition

The present study investigates the response of the Collembola community to replacement of beech by spruce or by mixed stands of beech and spruce in the Solling mountains (Germany). The study was carried out in three beech (Fagus sylvatica), spruce (Picea abies) and mixed stands of beech and spruce arranged in three blocks. The density, diversity and community structure of Collembola as well as microbial and abiotic parameters in the organic layers and mineral soil of the three spruce, three beech and three mixed stands were investigated. Major results are: (i) Collembola communities did not differ strongly between stand types and were dominated by Folsomia quadrioculata and Mesaphorura species, (ii) neither total abundance of Collembola nor densities of the hemiedaphic species F. quadrioculata, Parisotoma notabilis and Isotomiella minor significantly responded to stand type, (iii) in the mixed stands the fungal biomass was increased leading to high densities of fungal feeding Collembola (e.g. Mesaphorura sp.) and high species numbers of Collembola, (iv) the density of the epedaphic and partly herbivorous group Entomobryidae/Tomoceridae in the spruce stands exceeded that in the mixed and beech stands; presumably this was due to the higher diversity of the ground vegetation in the spruce stands. Canonical correspondence analysis (CCA) of the collembolan communities of L/F and H/Ah horizons also indicated that most of the epedaphic species were associated with the spruce stands. Moreover, results of the CCA indicated that soil pH is an important structuring force for collembolan communities. Overall, results suggest that stand type impact collembolan communities, presumably via changes in the amount and quality of food resources, such as fungal biomass and living plant material. However, differences in collembolan community structure between the investigated stand types were moderate supporting earlier findings that Collembola generally respond little to changes in the vegetation structure.     

Microbial biomass and C and N transformations in forest floors under European beech, sessile oak, Norway spruce and Douglas-fir at four temperate forest sites

The purpose of this research was to compare soil chemistry, microbially mediated carbon (C) and nitrogen (N) transformations and microbial biomass in forest floors under European beech (Fagus sylvatica L.), sessile oak (Quercus petraea (Mattuschka) Lieblein), Norway spruce (Picea abies (L.) Karst) and Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) at four study sites. We measured soil chemical characteristics, net N mineralization, potential and relative nitrification, basal respiration, microbial and metabolic quotient and microbial biomass C and N under monoculture stands at all sites (one mixed stand). Tree species affected soil chemistry, microbial activities and biomass, but these effects varied between sites. Our results indicated that the effect of tree species on net N mineralization was likely to be mediated through their effect on soil microbial biomass, reflecting their influence on organic matter content and carbon availability. Differences in potential nitrification and relative nitrification might be related to the presence of ground vegetation through its influence on soil NH₄ and labile C availability. Our findings highlight the need to study the effects of tree species on microbial activities at several sites to elucidate complex N cycle interactions between tree species, ground vegetation, soil characteristics and microbial processes.     

A Comparison of Temporal Patterns in Trace Metal Concentration in Tree Rings of Four Common European Tree Species Adjacent to a Cu-Cd Refinery

Metal processing at a Cu-Cd refinery at Prescot in N.W. England has led to severe contamination of the surrounding soils and vegetation, although Cu and Cd in bulk deposition declined dramatically between 1975 and 1990. Despite high spatial and temporal variability in metal deposition, mean Cd concentrations in annual tree rings of sycamore (Acer pseudoplatanus L.), lime (Tilia europaea L.) and beech (Fagus sylvatica L.) at Prescot were correlated with annual bulk Cd deposition. In contrast, mean Cd concentrations in ash (Fraxinus excelsior L.) were unrelated to Cd deposition and there was no significant relationship between mean Cu concentrations in tree rings and Cu deposition in any species. Mean Pb concentrations in sycamore, lime and beech at Prescot and the reference site also decreased over time. At Prescot however, Cd concentrations in tree rings formed in the mid 1990s were up to 10-fold higher than the reference site despite Cd deposition values during this period that were typical of levels expected for urban areas in the UK. The high Cd concentrations in wood during this period indicate that the majority of Cd in tree rings at Prescot is derived from soil, limiting the usefulness of dendrochemistry for monitoring temporal changes in metal deposition. It appears that trees are not simply passive recorders of metal deposition and other possibilities, in addition to decreasing atmospheric deposition, may explain the patterns of Cd and Pb found in sycamore, lime and beech. More research on the physiology of metal cycling in trees is required before dendrochemical techniques can be applied with confidence in environmental monitoring programs.     

Nitrogen Deposition and Nitrate Leaching at Forest Edges Exposed to High Ammonia Emissions in Southern Bavaria

The atmospheric deposition of air pollutants was studied by means of monitoring canopy throughfall at six forest stands. The investigation was carried out in Norway spruce (Picea abies L. Karst.) forests in Southern Bavaria with high ambient ammonia concentrations due to either adjacent intensive agriculture or poultry housing. Five monitoring plots transected the forest edges and forest interior from the edge, at 50, 150, about 400 m and about 800m to the interior. Additionally, nutrient concentration in soil solution was sampled with suction cups at each plot, and C/N ratio of the humus layer was also determined. The variation of ambient ammonia concentration between three of the six investigated sites was estimated using diffusive samplers. In order to compare the effects of atmospheric deposition on European beech (Fagus sylvatica L.) and Norway spruce additional monitoring plotswere installed under each of these species in a mixed beech and spruce stand. Bulk deposition and soil water samples were analysed for major ions (NO₃ ^-, NH₄ ⁺, SO₄ ^2-, Cl^-, Na⁺, K⁺, Mg²⁺, Ca^2+M).The results show a substantial increase of deposition towards the forest edges for all ions. This so called 'edge effect' continued in most cases until a distance from 50 to 150 m from edge. For both ambient ammonia concentrations and nitrogen deposition, it can be concluded that increased dry deposition is the main reason for the edge effect. Over 76% of the nitrogen ratios in throughfall deposition between the edge and 50 m distance into the spruce forest exceed 1.0. Except for potassium, beech generally showed lower ratios than spruce.Due to high nitrogen deposition the forest floor, C/N ratios were lower at stand edges when compared to their interior. In contrast to the increase of nitrogen deposition at the edge, nitrate export below the main rooting zone was lower at the edge. Nitrate export was generally lower under beech than spruce. Nitrogen budgets of some plots were negative, indicating a reduction of total ecosystem nitrogen stock.The results show that forest edges, especially in areas with high air pollution, receive much more atmospheric deposition than the interior parts of closed forest stands. As many deposition studies in forests were conducted at field stations in the central parts of forests the estimated deposition for the whole forest may be underestimated. This may be important to consider in geo-statistical studies and models aiming to estimate spatial critical deposition values, especially with an increasing fragmentation of the forest cover.     

Carbon dioxide emissions of soils under pure and mixed stands of beech and spruce, affected by decomposing foliage litter mixtures

Soil respiration is the largest terrestrial source of CO₂ to the atmosphere. In forests, roughly half of the soil respiration is autotrophic (mainly root respiration) while the remainder is heterotrophic, originating from decomposition of soil organic matter. Decomposition is an important process for cycling of nutrients in forest ecosystems. Hence, tree species induced changes may have a great impact on atmospheric CO₂ concentrations. Since studies on the combined effects of beech-spruce mixtures are very rare, we firstly measured CO₂ emission rates in three adjacent stands of pure spruce (Picea abies), mixed spruce-beech and pure beech (Fagus sylvatica) on three base-rich sites (Flysch) and three base-poor sites (Molasse; yielding a total of 18 stands) during two summer periods using the closed chamber method. CO₂ emissions were higher on the well-aerated sandy soils on Molasse than on the clayey soils on Flysch, characterized by frequent water logging. Mean CO₂ effluxes increased from spruce (41) over the mixed (55) to the beech (59) stands on Molasse, while tree species effects were lower on Flysch (30-35, mixed > beech = spruce; all data in mg CO₂-C m⁻² h⁻¹). Secondly, we studied decomposition after fourfold litter manipulations at the 6 mixed species stands: the O_i - and O_e horizons were removed and replaced by additions of beech -, spruce - and mixed litter of the adjacent pure stands of known chemical quality and one zero addition (blank) in open rings (20 cm inner diameter), which were covered with meshes to exclude fresh litter fall. Mass loss within two years amounted to 61-68% on Flysch and 36-44% on Molasse, indicating non-additive mixed species effects (mixed litter showed highest mass loss). However, base cation release showed a linear response, increasing from the spruce - over the mixed - to the beech litter. The differences in N release (immobilization) resulted in a characteristic converging trend in C/N ratios for all litter compositions on both bedrocks during decomposition. In the summers 2006 and 2007 we measured CO₂ efflux from these manipulated areas (a closed chamber fits exactly over such a ring) as field indicator of the microbial activity. Net fluxes (subtracting the so-called blank values) are considered an indicator of litter induced changes only and increased on both bedrocks from the spruce - over the mixed - to the beech litter. According to these measurements, decomposing litter contributed between 22-32% (Flysch) and 11-28% (Molasse) to total soil respiration, strengthening its role within the global carbon cycle.     

Influence of tree species on acidification and mineral pools in deciduous forest soils of South Sweden

The influence of tree species on chemical properties of the soil profile (0 to 70 cm), especially acidity and cation pools, was studied below canopies of 100 to 150 yr old individuals of Fagus sylvatica L., Quercus robur L., Carpinus betulus L., Tilia cordata Mill, and Acer platanoides L., in three mixed deciduous forests. The pH(H₂O) range in the topsoil (0 to 5 cm) was 4.2 to 5.3 at the different sites and increased for all species by about 0.2 pH units to the upper C-horizon (50 to 70 cm). Carpinus had higher pH and base saturation, and the total exchangeable store of Ca (0 to 70 cm) at the ‘poorest’ site was ca 1.5 times greater than for Fagus and Quercus. Soils were less acid under crowns of Quercus than under Fagus and Carpinus in the upper 20 cm of the soil profile in the ‘richest’ site, but more acid at the deeper levels. The total exchangeable pools (0 to 70 cm) of K and Zn were 2 and 1.6 times greater under Quercus at the ‘richest’ site. Tilia had 10 to 20% units higher base saturation values and twice as much exchangeable Ca and Mg than the other species. It was concluded that out of all tree species studied, Tilia acidified the soil the least. The current annual total proton load (TPL) on the soil was 1.3 to 3.0 kEq ha^?1 yr^?1. The annual acid load due to cation excess accumulation in biomass was 30 to 50% of TPL. The remainder originated from atmospheric deposition. Quercus had the highest annual TPL at all sites, mainly because of greater input of atmospherically derived acidity, but also by a greater cation excess accumulation in biomass. Carpinus, compared to Fagus and Quercus, tended to have the lowest TPL at all sites, and Tilia had the lowest TPL at the intermediate site.     

Changes in the earthworm community of an acidophilous lowland beech forest during a stand rotation

The study examines humus profile development during a chronosequence consisting of four beech forest growth stages, and particularly the role of some components of soil fauna (lumbricid oligochaetes) on humus morphogenesis. An experimental site was set up in a lowland beech forest (Fougères state forest, eastern Brittany, France) to carry out a chronosequence analysis. This lowland beech forest is acidophilous, managed as an even-aged beech stand. The dominant tree species is beech (Fagus sylvatica L.). Samples were taken twice a year, from autumn 1997 to spring 2000 inclusive. Earthworms were caught after watering with formalin solutions. Only five species were found: three epigeic (litter-dwellers): Dendrobaena octaedra, D. rubida tenuis, Eisenia eiseni; one epi-anecic (litter/soil-dweller): Lumbricus rubellus; one endogeic (soil-dweller): Allolobophora caliginosa. D. octaedra is dominant in the four plots at densities ranging from 41 ind·m^–2 (88 % of total earthworm population) to 12.4 ind·m^–2 (99 % of total). Species richness and abundance are low in accordance with a moder humus form typical of acid soil conditions. Results are discussed according to plot heterogeneity, stand age, seasonal variations and functional diversity.     

Effects of tree identity dominate over tree diversity on the soil microbial community structure

This study investigated the possible effects of tree species diversity and identity on the soil microbial community in a species-rich temperate broad-leaved forest. For the first time, we separated the effects of tree identity and tree species diversity on the link between above and belowground communities in a near-natural forest. We established 100 tree clusters consisting of each three tree individuals represented by beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.), hornbeam (Carpinus betulus L.), maple (Acer pseudoplatanus L.), or lime (Tilia spec.) at two different sites in the Hainich National Park (Thuringia, Germany). The tree clusters included one, two or three species forming a diversity gradient. We investigated the microbial community structure, using phospholipid fatty acid (PLFA) profiles, in mineral soil samples (0–10 cm) collected in the centre of each cluster.The lowest total PLFA amounts were found in the pure beech clusters (79.0 ± 23.5 nmol g⁻¹ soil dw), the highest PLFA amounts existed in the pure ash clusters (287.3 ± 211.3 nmol g⁻¹ soil dw). Using principle components analyses (PCA) and redundancy analyses (RDA), we found only for the variables ‘relative proportion of beech trees’ and ‘living lime fine root tips associated with ectomycorrhiza’ a significant effect on the PLFA composition. The microbial community structure was mainly determined by abiotic environmental parameters such as soil pH or clay content. The different species richness levels in the clusters did not significantly differ in their total PLFA amounts and their PLFA composition. We observed a tendency that the PLFA profiles of the microbial communities in more tree species-rich clusters were less influenced by individual PLFAs (more homogenous) than those from species-poor clusters.We concluded that tree species identity and site conditions were more important factors determining the soil microbial community structure than tree species diversity per se.     

Roots from beech (Fagus sylvatica L.) and ash (Fraxinus excelsior L.) differentially affect soil microorganisms and carbon dynamics

Knowledge about the influence of living roots on decomposition processes in soil is scarce but is needed to understand carbon dynamics in soil. We investigated the effect of dominant deciduous tree species of the Central European forest vegetation, European beech (Fagus sylvatica L.) and European ash (Fraxinus excelsior L.), on soil biota and carbon dynamics differentiating between root- and leaf litter-mediated effects. The influence of beech and ash seedlings on carbon and nitrogen flow was investigated using leaf litter enriched in ¹³C and ¹⁵N in double split-root rhizotrons planted with beech and ash seedlings as well as a mixture of both tree species and a control without plants. Stable isotope and compound-specific fatty acid analysis (¹³C-PLFA) were used to follow the incorporation of stable isotopes into microorganisms, soil animals and plants. Further, the bacterial community composition was analyzed using pyrosequencing of 16S rRNA gene amplicons. Although beech root biomass was significantly lower than that of ash only beech significantly decreased soil carbon and nitrogen concentrations after 475 days of incubation. In addition, beech significantly decreased microbial carbon use efficiency as indicated by higher specific respiration. Low soil pH probably increased specific respiration of bacteria suggesting that rhizodeposits of beech roots induced increased microbial respiration and therefore carbon loss from soil. Compared to beech δ¹³C and δ¹⁵N signatures of gamasid mites in ash rhizotrons were significantly higher indicating higher amounts of litter-derived carbon and nitrogen to reach higher trophic levels. Similar δ¹³C signatures of bacteria and fine roots indicate that mainly bacteria incorporated root-derived carbon in beech rhizotrons. The results suggest that beech and ash differentially impact soil processes with beech more strongly affecting the belowground system via root exudates and associated changes in rhizosphere microorganisms and carbon dynamics than ash.     

What Characteristics of Soil Fertility Can Improve in Mixed Stands of Scots Pine and European Beech Compared with Monospecific Stands?

According to the current trends in forest management, endeavors are made to adjust the species composition to the site conditions and to increase the biodiversity. Changes in the species composition of forest stands lead to modifications of soil properties and nutrients cycle. The objective of the study was to evaluate the effect of monocultures (beech and pine) and mixed-species stands (pine-beech) on soil properties, particularly accumulation of soil organic carbon. We aim to demonstrate how different vegetation types influence soil properties in surface horizons of soil. The study sites are located in Germany and Poland under different tree stands Pinus sylvestris L., Fagus sylvatica L., and mixed-species stand. Contents of organic carbon and nitrogen, pH, and soil texture were analyzed. The studies conducted confirmed the positive effect of beech and mixed-species stands on acidification of surface soil horizons. We ordered the stands tested according to acidification effect on soils: pine stand > mixed stand > beech stand, which is consistent with previous studies. The most beneficial impact on the accumulation of organic carbon was observed in mixed-species stands in which beech and pine were found. Lower carbon-to-nitrogen (C/N) ratios confirm the high rate of organic matter decomposition and lower C/N ratio was reported in soil under beech stand in comparison to pine stands.     

Spatial variability of photosynthetically active radiation in European beech and Norway spruce

The vertical and horizontal variability of solar radiation within a mature European beech (Fagus sylvatica L.)-Norway spruce (Picea abies [L.] Karst) mixed stand in Southern Germany is investigated. A large dataset with more than one million spectral measurements of photon fluence rates at six vertical levels within the stand is analyzed with respect to tree species, meteorological sky conditions, and the influence of solar elevation angle on canopy penetration. Irradiance probability density functions of the photosynthetically active waveband are used to describe the three-dimensional radiation field. For a quantification of umbra, penumbra, and sunfleck frequencies, in-canopy fractions of photon fluence rates within the photosynthetically active waveband are investigated. Different phenological stages of beech and their effects on the in-canopy light climate are compared. The results show that during overcast conditions (OVC) fractions of photosynthetically active radiation (PAR) are higher at all canopy levels than during clear sky (CS) conditions due to their exclusively diffuse character. The lowest median PAR level of less than 1% of above-canopy PAR can be observed in the shade crown of beech and at ground level. More PAR can penetrate the canopy at a higher solar elevation under CS conditions. This effect is more pronounced for spruce than for beech due to the conical crown shape of the conifers that allows photons from higher angles to enter the gaps inbetween trees in contrast to the more homogeneously closed beech canopy. Solar elevation is not an important factor at uniformly overcast conditions. Differences in the vertical distribution of umbra and penumbra can be detected when comparing species or different sky conditions. The frequency of sunflecks differs more by species and by the vertical position within the canopy than by sky condition.     

To What Extent Can Silviculture Enhance Sustainability of Forest Sites under the Immission Regime in Central Europe?

Stand structure and tree species composition influence not only the volume flux of soil water but also the concentration of dissolved minerals in the soil solution. We found much higher element fluxes under spruce than under beech stands. This is mainly caused by different activities of nitrate in the soil solution and by different deposition rates of nitrogen and acids from the atmosphere which were ±60% lower in beech stands than in spruce stands. In old spruce stands, the acid output with the seepage water was more or less equal to the input, whereas in beech stands most of the acid deposition was buffered. The nitrogen balance in beech stands was characterized by a net uptake of about 60% to 75% of the input. In spruce stands only 40% of the nitrogen input was incorporated. In a clear-cut, a high mobilization rate of nitrate was found in the first 5 years, resulting in nitrate concentrations above the threshold for drinking water quality. The cutting of even a single tree in a spruce stand caused heavy mineralization and nitrification for at least 2 years, which indicates that the system is near nitrogen saturation.     

Seasons differently impact the structure of mineral weathering bacterial communities in beech and spruce stands

Bacterial communities play an essential role in the sustainability of forest ecosystems by releasing from soil minerals the nutritive cations required not only for their own nutrition but also for that of trees. If it is admitted that the nutritional needs of trees vary during seasons, the seasonal dynamics of the mineral weathering bacterial communities colonizing the tree rhizosphere remain unknown. In this study, we characterized the mineral weathering efficacy of bacterial strains, from the rhizosphere and the adjacent bulk soil at four different seasons under two different tree species, the evergreen spruce and the deciduous beech, using a microplate assay that measures the quantity of iron released from biotite. We showed that the functional and taxonomic structures of the mineral weathering bacterial communities varied significantly with the tree species as well as with the season. Notably, the Burkholderia strains from the beech stand appeared more efficient to weather biotite that the one from the spruce stand. The mineral weathering efficacy of the bulk soil isolates did not vary during seasons under the beech stand whereas it was significantly higher for the spring and summer isolates from the spruce stand. The weathering efficacy of the rhizosphere isolates was significantly higher for the autumn isolates compared to the isolates sampled in the other seasons under the beech stand and in summer compared to the other seasons under spruce. These results suggest that seasonal differences do occur in forest soil bacterial communities and that evergreen and deciduous trees do not follow the same dynamic.     

Variability of CO2 and N2O emissions during freeze‐thaw cycles: results of model experiments on undisturbed forest‐soil cores

The amounts of N₂O released in periods of alternate freezing and thawing depend on site and freezing conditions, and contribute considerably to the annual N₂O emissions. However, quantitative information on the N₂O emission level of forest soils in freeze‐thaw cycles is scarce, especially with regard to the direct and indirect effect of tree species and the duration of freezing. Our objectives were (i) to quantify the CO₂ and N₂O emissions of three soils under beech which differed in their texture, C and N contents, and humus types in freeze‐thaw cycles, and (ii) to study the effects of the tree species (beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.)) for silty soils from two adjacent sites and the duration of freezing (three and eleven days) on the emissions. Soils were adjusted to a matric potential of –0.5 kPa, and emissions were measured in 3‐hr intervals for 33 days. CO₂ emissions of all soils were similar in the two freeze‐thaw cycles, and followed the temperature course. In contrast, the N₂O emissions during thawing differed considerably. Large N₂O emissions were found on the loamy soil under beech (Loam‐beech) with a maximum N₂O emission of 1200 μg N m^–2 h^–1 and a cumulative emission of 0.15 g N m^–2 in the two thawing periods. However, the sandy soil under beech (Sand‐beech) emitted only 1 mg N₂O‐N m^–2 in the two thawing periods probably because of a low water‐filled pore space of 44 %. The N₂O emissions of the silty soil under beech (Silt‐beech) were small (9 mg N m^–2 in the two thawing periods) with a maximum emission of 150 μg N m^–2 h^–1 while insignificant N₂O emissions were found on the silty soil under spruce (0.2 mg N m^–2 in the two thawing periods). The cumulative N₂O emissions of the short freeze‐thaw cycles were 17 % (Sand‐beech) or 22 % (Loam‐beech, Silt‐beech) less than those of the long freeze‐thaw cycles, but the differences between the emissions of the two periods were not significant (P ≤ 0.05). The results of the study show that the amounts of N₂O emitted in freeze‐thaw cycles vary markedly among different forest soils and that the tree species influence the N₂O thawing emissions in forests considerably due to direct and indirect impacts on soil physical and chemical properties, soil structure, and properties of the humus layer.     

Die horizontale Verteilung von Radiocäsium im Waldboden unter Fichte und Buche

Horizontal distribution of radiocesium in forest soils under spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) The horizontal distribution of radiocesium in the soil under the canopy of several beeches and spruces was examined. At the base of spruces mean ¹³⁷Cs activities are about twice, and under beeches 5 to 15 times as high as under more distant parts of the canopy. Between 80 and 95% of the ¹³⁷Cs activity can be attributed to the Chernobyl fallout, the rest to the global fallout from weapons testing in the 1950s and 1960s. While the ¹³⁷Cs accumulation at the base of spruces can be explained by litter fall and remains of bark, the up to 30 times increased values at the base of beeches are explained by stemflow. Mean activity of radiocesium in the bark of spruce (0,62 Bq/g dry weight) is about twice as high as in the bark of a beech. This can be explained by considering that in contrast to beeches the ¹³⁷Cs activity in the soil under spruces is corresponding to some extend with the main rooting zone. Thus, we expect an increased uptake by the roots of this species and a subsequent transfer to the bark.     

Are Indicators for Critical Load Exceedance Related to Forest Condition?

The aim of this study was to evaluate the suitability of the (Ca?+?Mg?+?K)/Al and the Ca/Al ratios in soil solution as chemical criteria for forest condition in critical load calculations for forest ecosystems. The tree species Norway spruce, Sitka spruce and beech were studied in an area with high deposition of sea salt and nitrogen in the south-western part of Jutland, Denmark. Throughfall and soil water were collected monthly and analysed for pH, NO₃-N, NH₄-N, K, Ca, Mg, DOC and Al_tot. Organic Al was estimated using DOC concentrations. Increment and defoliation were determined annually, and foliar element concentrations were determined every other year. The throughfall deposition was highest in the Sitka spruce stand (maximum of 40 kg N ha^?1yr^?1) and lowest in the beech stand (maximum of 11 kg N ha^?1yr^?1). The Sitka spruce stand leached on average 12 kg N ha^?1yr^?1 during the period 1988–1997 and leaching increased throughout the period. Only small amounts of N were leached from the Norway spruce stand whereas almost no N was leached from the beech stand. For all tree species, both (Ca?+?Mg?+?K)/Al and Ca/Al ratios decreased in soil solution at 90 cm depth between 1989 and 1999, which was mainly caused by a decrease in concentrations of base cations. The toxic inorganic Al species were by far the most abundant Al species at 90 cm depth. At the end of the measurement period, the (Ca?+?Mg?+?K)/Al ratio was approximately 1 for all species while the Ca/Al ratio was approximately 0.2. The lack of a trend in the increment rates, a decrease in defoliation as well as sufficient levels of Mg and Ca in foliage suggested an unchanged or even slightly improved health condition, despite the decreasing and very low (Ca?+?Mg?+?K)/Al and Ca/Al ratios. The suitability of these soil solution element ratios is questioned as the chemical criteria for soil acidification under field conditions in areas with elevated deposition rates of sea salts, in particular Mg.