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Among the many studies devoted to deadwood, very few have considered it in a broader ecosystemic context, especially in relation to the underlying humiferous topsoil. In order to fill this gap, we detail here the concept of lignoforms, humus forms strongly linked to deadwood and mostly ignored by humus forms specialists. After presenting the main characteristics of deadwood, the main actors involved in its life cycle and its important and varied roles in many ecosystems, we explain how to describe and study lignoforms. We also propose new diagnostic horizons for these particular humus forms, as well as a classification system, including an identification key (see Appendix A Identification key for lignoforms). Finally, we discuss some important issues pertinent to continuing to improve knowledge of these common but little studied humus forms.

International audience; This paper presents the specific terms of vocabulary and diagnostic horizons necessary for a field classification of submerged Histic humipedons (peats, moors). It is simply an exposition of definitions placed side by side with photographic samples, with rather practical interest. The knowledge reported here is mandatory for people wanting to use the key of classification of these humipedons presented in Humusica 2, article 10. The paper illustrates with schemes the spatial and functional relationships between diagnostic horizons of different Histic humipedons.

Aim To assess vegetation changes in montane fens and wet meadows and their causes over 38 years. Location Wetlands in the Jura Mountains (Switzerland and France). Methods Plots were inventoried in 1974 and re-located in 2012 (quasi-permanent plots) on the basis of sketches to assess changes in plant communities. The 110 plots belonged to five phytosociological alliances, two in oligotrophic fens (Caricion davallianae, Caricion fuscae) and three in wet meadows (Calthion, Molinion and Filipendulion). Changes between surveys were assessed with NMDS, and changes in species richness, Simpson diversity, species cover and frequency and the causes of these changes were evaluated by comparing ecological indicator values. Results Changes in species composition varied between alliances, with a general trend towards more nutrient-rich flora with less light at the ground level. Species diversity declined, with a marked decreasing trend for the typical species of each alliance. These species were partly replaced by species belonging to nitrophilous and mesophilous grasslands. However, no trend towards drier conditions was detected in these wetlands. The greatest changes, with an important colonization by nitrophilous species, occurred in the Swiss sites, where grazing was banned 25 years ago. As a result of floral shifts, many plots previously belonging to fens or wet mesotrophic meadows shifted to an alliance of the wet meadows, generally Filipendulion. Moreover, communities showed a slight trend towards more thermophilous flora. Conclusions The investigated wetlands in the Jura Mountains have suffered mainly from eutrophication due to land-use abandonment and nitrogen deposition, with a loss of typical species. Areas with constant land use (grazing or mowing) showed less marked changes in species composition. The most important action to conserve these wetlands is to maintain or reintroduce the traditional practices of extensive mowing and livestock grazing in the wetlands, especially in areas where they were abandoned 25 years ago. This previous land-use change was intended to improve fen conservation, but it was obviously the wrong measure for conservation purposes. This article is protected by copyright. All rights reserved.

Humus forms, especially the occurrence and the thickness of the horizon of humified residues (OH), provide valuable information on site conditions. In mountain forest soils, humus forms show a high spatial variability and data on their spatial patterns is often scarce. Our aim was to test the applicability of various vegetation features as proxy for OH thickness. Subalpine coniferous forests dominated by Picea abies (L.) H. Karst. and Larix decidua Mill. were studied in the Province of Trento, Italian Alps, between ca. 900 and 2200 m a.s.l. Braun-Blanquet vegetation releves and OH thickness were recorded at 152 plots. The vegetation parameters, tested for their suitability as indicators of OH thickness, encompassed mean Landolt indicator values of the herb layer (both unweighted and cover-weighted means) as well as parameters of vegetation structure (cover values of plant species groups) calculated from the releves. To our knowledge, the predictive power of Landolt indicator values (LIVs) for humus forms had not been tested before. Correlations between OH thickness and mean LIVs were strongest for the soil reaction value, but indicator values for humus, nutrients, temperature and light were also significantly correlated with OH thickness. Generally, weighting with species cover reduced the indicator quality of mean LIVs for OH thickness. The strongest relationships between OH thickness and vegetation structure existed in the following indicators: the cover of forbs (excluding graminoids and ferns) and the cover of Ericaceae in the herb layer. Regression models predicting OH thickness based on vegetation structure had almost as much predictive power as models based on LIVs. We conclude that LIVs analysis can produce fairly reliable information regarding the thickness of the OH horizon and, thus, the humus form. If no releve data are readily available, a field estimation of the cover values of certain easily distinguishable herb layer species groups is much faster than a vegetation survey with consecutive indicator value analysis, and might be a feasible way of quickly indicating the humus form.

The aim of this study was to map the spatial distribution of enchytraeids and humus forms in a study area in the Italian Alps by means of a knowledge-based modeling approach. The modeled area is located around Val di Sole and Val di Rabbi (Trentino, Italy) and includes the forested parts in the range between 1100 m and 1800 m a.s.l. Elevation and slope exposure are considered as environmental covariates. Models were implemented regarding the spatial distribution of three variables at the landscape scale: 1) enchytraeids indicating mull humus forms, 2) enchytraeids indicating moder/mor humus forms, 3) humus forms showing an OH horizon. All three models reveal a consistent trend of an increasing accumulation of plant residues and humus in organic layers from low to high elevations and from south-facing to north-facing slopes. Validation and uncertainty analysis of input data confirm these trends, although some deviations are to be expected (RMSE values from validation sites range from 26.3 to 36.2% points). Effects of additional potentially influencing variables may lead to uncertainties of the model predictions especially at positions with particular landforms (e.g. gullies and ridges). In the high mountains environmental conditions are often quite heterogeneous due to a highly variable topography, which also affects the species composition of the decomposer community and the occurrence of different humus forms.

Loess of Northern, Central, and Eastern Europe cover large areas and can be of considerable thickness. However, this already well-described loess belt did not reach the Swiss Jura Mountains. Nevertheless, local deflation, transportation, and deposition processes were efficient during the Late Glacial Period. Alpine moraines and outwash deposits on the Swiss foreland worked as deflation sources under the action of winds. Aeolian particles were deposited on the easternmost ridge and summits of the Jura Mountains, forming a thin loessic cover (

International audience; This article is an as simple as possible key of classification of terrestrial (aerobic, not submerged) topsoils (organic and organic-mineral series of soil horizons). Based on the introduction exposed in Humusica 1, article 1, and using vocabulary and definitions listed in article 4, a classification is proposed for better understanding the biological functioning of the soil, partially disclosing the process of litter digestion. Five types of terrestrial topsoils, called terrestrial humus systems, are described and illustrated with the help of photographs. Within each humus system, 3–4 humus forms are also revealed, corresponding to similar series of soil horizons generated in a relatively homogeneous environment whose range of ecological factors is not so large to overstep and cause the genesis of another different humus system. The article ends with a figure that shows the relationship between Tangel and Amphi humus systems, and a dichotomous key of classification that one can easily print and bring in the field for practicing humus classification.

International audience; The Special Issue Humusica 1 corresponds to a field guide for the classification of terrestrial humus systems and forms. The present first article of the issue defines vocabulary, objects and concepts necessary for: (a) field investigation, (b) understanding the process of classification, (c) assigning ecological significance to the defined morpho-functional units, (d) discussing and exchanging scientific data about humus systems. The article starts with general considerations, as the necessity humans have to classify natural objects for sharing ideas and information on them. Then the article focuses on soil as functional element of every ecosystem. Historical and recently published international definitions of soil are reported and compared to the more biological definition of the authors of the paper. Once the concept “soil” is clarified, the soil profile is shared in three new sub-units, for further specialised investigations. The superficial and organic-rich sub-unit is labelled Humipedon. In the rest of the article, authors explain the different constituents of a general humipedon, introducing even novice soil scientists to field practice and topsoil observation. A general overview of the variety of humipedons that one may expect to find all over planet Earth, classified in humus systems and forms, concludes the article.

Bryophytes dominate northern peatlands. Obtaining reliable measurements of moss-growth and how it may be affected by global changes are therefore important. Several methods have been used to measure moss-growth but it is unclear how comparable they are in different conditions and this uncertainty undermines comparisons among studies. In a field experiment we measured the growth and production of Sphagnum fallax (Sphagnum) and Polytrichum strictum (Polytrichum) using two handling methods, using cut and uncut plants, and three growth-variables, height-growth, length-growth, and mass-growth. We aimed “benchmarking” a combination of six methodological options against exactly the same set of factorial experiments: atmospheric CO2 enrichment and N addition. The two handling methods produced partly different results: in half of the cases, one method revealed a significant treatment effect but the other one did not: significant negative effects on growth were only observed on uncut plants for elevated CO2 and on cut plants for N addition. Furthermore, the correspondence between measurements made with various growth-variables depended on the species and, to a lesser extent, treatments. Sphagnum and Polytrichum growth was inhibited under elevated CO2, and correlated to higher ammonium values. Sphagnum was however less affected than Polytrichum and the height difference between the two species decreased. N addition reduced the P/N ratio and probably induced P-limiting conditions. Sphagnum growth was more inhibited than Polytrichum and the height difference between the two species increased. Our data show that such a problem indeed exists between the cut and uncut handling methods. Not only do the results differ in absolute terms by as much as 82% but also do their comparisons and interpretations depend on the handling method—and thus the interpretation would be biased—in half of the cases. These results call for caution when comparing factorial studies based on different handling methods.

Sources of water use by 10 alluvial trees in various hydrogeological and ecological situations at the Pfyn forest (Wallis canton, Switzerland) were assessed by analysing 18O and 2H isotopes of precipitation, soil water at different depths, surface water, groundwater and xylem sap. The soil water line in a δ18O versus δ2H diagram shows evidence of kinetic fractionation related to evaporation. The tree water line is close to the soil trend; however, an additional enrichment may occur and could be related to xylem–phloem communication under water stress. At sites where the water table was at least 2 m below the ground surface, isotopic temporal variability of soils and trees was strongly linked with seasonal variation of soil water content. When soil water content was low and water table shallow, trees used both soil water and groundwater. When soil water content was high, this source was usually the dominant source for transpiration. In addition, some ecological strategies, reproduction or growth competition, could explain shifts in the utilization of different water sources, for example, from soil water to a mix of soil water and groundwater. At one site where soil water and groundwater were abundant throughout the year (next to the river course), neighbouring trees permanently used distinct water sources. This is consistent with a strategy of competition limitation, which would favour bank colonization. These results provide insight into the ecohydrological functioning of this system and will aid future management responses to both local and climate changes.

In many ecosystems, bioindication is a tool to estimate biodiversity and quality of environment. In soils,invertebrates are generally suitable bioindicators, especially earthworms. In floodplains, young alluvial soils are exposed to sedimentation and erosion, and little is known about soil bioindication. Moreover,a reference state is now needed to evaluate river restoration projects. The aim of our study was thus tom establish an “undisturbed” floodplain reference at the subalpine level based on earthworm communities and to test if they are indicators of fluvial dynamics. Seven plots were chosen along a stretch of the Kander River (BE, Switzerland). At each plot, a soil profile was described (carbonated Fluvisols) and topsoil was analysed. Earthworms were extracted in each plot using standard mustard extraction(3 x 1 m2) and “hand sorting” method (20 x 20 x 20 cm). Eight species were identified, and Lumbricus meliboeus was found for the first time in a carbonated environment. The absence of anecics was considered, at the subalpine level, as a bioindication of the fluvial dynamics (erosion and sedimentation processes). Biomass of epigeics was positively correlated to topsoil texture and organic matter quality,and thus epigeics, sensitive to variations of topsoil composition, are bioindicators of the latest flood event at the subalpine level.

Environmental pollution due to arsenic (As) has been well studied and most investigations have focused on inorganic As coming from industrial areas. However, the natural rock-borne contamination of this metalloid has been underestimated and few studies focusing on annelids have addressed the question of geogenic As distribution in earthworm biogenic structures. Our study concentrated on the earthworm drilosphere and investigated the distribution of As in surface-casts and burrow-linings. In this context, we assumed that the concentration of geogenic As should differ in biogenic structures (faeces, burrow-linings) compared to non-ingested soil. To test our hypothesis, microcosms in controlled conditions were filled with soil containing 157 mg As kg −1 from a geogenic origin. The soil was collected from a meadow in the Jura Mountains. The earthworm Aporrectodea giardi was selected because of its natural presence in the meadow and its anecic behaviour. We found that while earthworm surface-casts were enriched in carbon, nitrogen and available phosphorus compared to non-ingested soil, no enrichment was found for geogenic arsenic. The coarse sand fraction contained 3.5 times more As than silt and clay fractions but no significant difference existed between surface-casts and non-ingested soil. Iron was shown to be the main mineral bearing phase for As and predominated in the coarse sand fraction. No retention effect of organic matter on geogenic arsenic was observed. In conclusion, it appeared that geogenic As did not affect biological components and environmental aspects. These findings are particularly encouraging considering that most of the environments at an altitude of 1330 m in the Jura Mountains have exposed rocks, especially on meadows that are regularly grazed by cattle.

Aquifers provide water, nutrients and energy with various patterns for many aquatic and terrestrial ecosystems. Groundwater-dependent ecosystems (GDEs) are increasingly recognized for their ecological and socio-economic values. The current knowledge of the processes governing the ecohydrological functioning of inland GDEs is reviewed, in order to assess the key drivers constraining their viability. These processes occur both at the watershed and emergence scale. Recharge patterns, geomorphology, internal geometry and geochemistry of aquifers control water availability and nutritive status of groundwater. The interface structure between the groundwater system and the biocenoses may modify the groundwater features by physicochemical or biological processes, for which biocenoses need to adapt. Four major types of aquifer-GDE interface have been described: springs, surface waters, peatlands and terrestrial ecosystems. The ecological roles of groundwater are conditioned by morphological characteristics for spring GDEs, by the hyporheic zone structure for surface waters, by the organic soil structure and volume for peatland GDEs, and by water-table fluctuation and surface floods in terrestrial GDEs. Based on these considerations, an ecohydrological classification system for GDEs is proposed and applied to Central and Western-Central Europe, as a basis for modeling approaches for GDEs and as a tool for groundwater and landscape management.

Slash and burn agriculture is a traditional and predominant land use practice in Madagascar and its relevance in the context of forest preservation is significant. At the end of a cycle of culture, the fields become mostly weed covered and the soil fertility starts to drop. As a consequence, these fields are abandoned (they are called “monka”) and the farmers, in the best case, re-use old surfaces where the vegetation has recovered to some extent. Nevertheless, some of the farmers continue to extend part of their cultures into the natural forest. In order to decrease deforestation, the paper focuses on the potential for agricultural re-use of monkas. To do so, we present the soil–vegetation pattern along a slash and burn successional gradient from newly cultivated surfaces to surfaces abandoned for 40 years. Vegetation releves were carried out on 61 plots sampled on yellow and red soils, and soil variables such as loss of ignition, pH, total carbon content and total nitrogen content were measured. Results show that: (1) by the 10th year of abandonment woody species are increasing, and after 21–30 years herbaceous plants become less dominant, (2) the species richness increases with age of abandonment, but flattens out by 40 years, (3) by 20 years of fallow, the loss of ignition, total carbon and total nitrogen show similar values or even higher values than in cultivated surfaces, (4) the yellow soils are related to higher pH more than the red soils and are preferred for cultivation, but the higher pH of yellow soils is not associated with higher species richness. Given these results, we conclude that fields older than 20 years have recovered sufficient fertility to be re-used as agricultural land. This re-use would decrease impacts on natural forests. But beyond the nutrient perspective, critical problems remain, including the growing demand for arable land and the need for cultivation to control invasive weeds.

Summary Soil biota such as earthworms, arbuscular mycorrhizal fungi (AMF) and plant roots are known to play a major role in engineering the belowground part of the terrestrial ecosystems, thus strongly influencing the water budget and quality on earth. However, the effect of soil organisms and their interactions on the numerous soil physical properties to be considered are still poorly understood. Shrinkage analysis allows quantifying a large spectrum of soil properties in a single experiment, with small standard errors. The objectives of the present study were, therefore, to assess the ability of the method to quantify changes in soil properties as induced by single or combined effects of leek roots ( Allium porrum ), AMF ( Glomus intraradices ) and earthworms ( Allolobophora chlorotica ). The study was performed on homogenised soil microcosms and the experiments lasted 35 weeks. The volume of the root network and the external fungal hyphae was measured at the end, and undisturbed soil cores were collected. Shrinkage analysis allowed calculating the changes in soil hydro-structural stability, soil plasma and structural pore volumes, soil bulk density and plant available water, and structural pore size distributions. Data analysis revealed different impacts of the experimented soil biota on the soil physical properties. At any water content, the presence of A. chlorotica resulted in a decrease of the specific bulk volume and the hydro-structural stability around 25%, and in a significant increase in the bulk soil density. These changes went with a decrease of the structural pore volumes at any pore size, a disappearing of the thinnest structural pores, a decrease in plant available water, and a hardening of the plasma. On the contrary, leek roots decreased the bulk soil density up to 1.23 g cm −3 despite an initial bulk density of 1.15 g cm −3 . This increase in volume was accompanied with a enhanced hydro-structural stability, a larger structural pore volume at any pore size, smaller structural pore radii and an increase in plant available water. Interestingly, a synergistic effect of leek roots and AMF in the absence of the earthworms was highlighted, and this synergistic effect was not observed in presence of earthworms. The structural pore volume generated by root and AMF growth was several orders of magnitude larger than the volume of the organisms. Root exudates as well as other AMF secretion have served as carbon source for bacteria that in turn would enhance soil aggregation and porosity, thus supporting the idea of a self-organization of the soil–plant–microbe complex previously described.

Plant and Soil, 319 (1-2), ISSN:0032-079X, ISSN:1573-5036

Earthworms, arbuscular mycorrhiza fungi (AMF) and roots are important components of the belowground part of terrestrial ecosystem. However, their interacting effects on soil properties and plant growth are still poorly understood. A compartmental experimental design was used in a climate chamber in order to investigate, without phosphorus (P) addition, the single and combined effects of earthworms (Allolobophora chlorotica), AMF (Glomus intraradices) and roots (Allium porrum) on soil structure, nutrient concentration and plant growth. In our experimental conditions, plant roots improved soil structure stability (at the level of macroaggregates) whereas earthworms decreased it. AMF had no effect on soil structure stability but increased P transfer from the soil to the plant and significantly increased plant biomass. Earthworms had no direct influence on P uptake or plant biomass, and the N/P ratio measured in the shoots indicated that P was limiting. Interactions between AMF and earthworms were also observed on total C and N content in the soil and on total root biomass. Their effects varied temporally and between the different soil compartments (bulk soil, rhizosphere and drilosphere). After comparison with other similar studies, we suggest that effects of earthworms and AMF on plant production may depend on the limiting factors in the soil, mainly N or P. Our experiment highlights the importance of measuring physical and chemical soil parameters when studying soil organism interactions and their influence on plant performance.Earthworms, arbuscular mycorrhiza fungi (AMF) and roots are important components of the belowground part of terrestrial ecosystem. However, their interacting effects on soil properties and plant growth are still poorly understood. A compartmental experimental design was used in a climate chamber in order to investigate, without phosphorus (P) addition, the single and combined effects of earthworms (Allolobophora chlorotica), AMF (Glomus intraradices) and roots (Allium porrum) on soil structure, nutrient concentration and plant growth. In our experimental conditions, plant roots improved soil structure stability (at the level of macroaggregates) whereas earthworms decreased it. AMF had no effect on soil structure stability but increased P transfer from the soil to the plant and significantly increased plant biomass. Earthworms had no direct influence on P uptake or plant biomass, and the N/P ratio measured in the shoots indicated that P was limiting. Interactions between AMF and earthworms were also observed on total C and N content in the soil and on total root biomass. Their effects varied temporally and between the different soil compartments (bulk soil, rhizosphere and drilosphere). After comparison with other similar studies, we suggest that effects of earthworms and AMF on plant production may depend on the limiting factors in the soil, mainly N or P. Our experiment highlights the importance of measuring physical and chemical soil parameters when studying soil organism interactions and their influence on plant performance.

Plants are generally assumed to influence the surrounding soil microflora through rhizodeposition. However, the role of rhizodeposits, and especially organic acids, in structuring the bacterial communities is still poorly understood. In this study, we asked the question whether plants differing in organic acid secretion have a different impact on the soil bacterial communities, and if this is the case, to which extent this impact is due to different organic acid concentrations in the rhizosphere. To investigate this question, we compared white lupin and wheat. The former is a high organic acid-secreting species, while the latter secretes only low amounts of carboxylates. We grew the plants in large microcosms including root-free control compartments for one year (replanted every second month) and analyzed the spatio-temporal changes in soil ATP concentrations, as well as in diversity and structure of bacterial communities (using DNA- and RNA-based DGGE) along a root-soil gradient after two, six and twelve month's cultivation. Our results showed: i) that white lupin and wheat differed in their impact on soil ATP concentrations and on the structure of root bacterial communities; ii) that cultivation time was a key factor in explaining the observed differences in all the parameters studied; and iii) that the amounts of organic acids accounted for a significant proportion (15%) of the variability within root active communities. These results indicate that plants influence their associated bacterial communities in a species-specific way and that for communities living in the direct vicinity of roots (rhizoplane-endorhizosphere), a significant part of this influence can be attributed to root-secreted organic acids.

Purpose Urban soils and soils of river valleys are constituted of heterogeneous materials that have been manipulated, disturbed or transported at different spatial and temporal scales. Despite these similarities, little is known about soil evolution in urban soils and their comparison with natural soils remains therefore highly useful. We hypothesized that, according to their degree of perturbation, urban soils and natural soils of river valleys have similar soil processes related to their structure, physical and chemical characteristics. Materials and methods Using a synchronic approach, we compared two soil gradients, one located in the natural reserve of the Allondon River (canton of Geneva, Switzerland) and the other in and around the city of Neuchâtel, Switzerland. A total of five alluvial and 18 urban soil profiles were described according to vegetation type and alluvial terraces formed at different distances from the river for the river valley ecosystem and to soil age for the urban ecosystem. Correlations between soil gradients and classical physical (soil depth, particle-size distribution, coarse fraction) and chemical (Corg, pHH2O, Ptot, Ntot, CaCO3, CEC and C/N ratio) parameters of soils were first tested in order to identify similarities and differences among soil gradients. Data of soil properties were then clustered hierarchically in order to identify soil group classification. Results and discussion Our results showed similarities and differences between soil gradients. In the urban context, soil thickness was positively correlated to soil age, while the coarse fraction, sand content and C/N were negatively correlated to soil age gradient. In soils of the river valley, most of the chemical variables were either negatively (pHH2O and CaCO3) or positively (CEC, Corg and Ntot) correlated to soil distance from the river. These differences between gradients can be mainly explained by parent material, depositional conditions and land use which can influence soil processes. However, alluvial soils were well clustered with two identified urban soil groups according to soil maturity. Evolved alluvial soils far from the river were grouped with natural and near natural urban soils. Conversely, “young” perturbed alluvial soils were most clustered with human-made soils. Conclusions From the two selected soil gradients, soils on alluvial sediments are similar to urban soils in some characteristics. However, parent material, depositional conditions and soil and vegetation interactions on soil processes (e.g. matter cycle, energy flux) still need more investigation. This study contributes to the development of a natural soil reference for urban soils.

Saxifraga hirculus is a postglacial relict in Central Europe, whose populations suffered a dramatic decrease in the 19th and 20th centuries. However, few researchers have been interested in its ecological requirements in Central Europe. This article synthesizes previous knowledge supplemented by original data from the last large population (Switzerland). S. hirculus is a weak competitor which needs precise ecological conditions. It grows on bryophyte carpets in neutral to slightly acid wetlands, with stable water table close to the soil surface (optimum between 8 and 14 cm) but does not stand long flooding. However, it requires a good oxygen supply, with roots 2–3 cm under the soil surface, generally not reached by water, with running, cold water through loose, fibric peat. Its optimal conditions are in spring fens, but it grows in other types of wetlands as well. However, overgrowing by shrubs, sedges or Sphagnum in natural successions may threaten the species with extinction, as did drainage and peat extraction previously. Now, its survival in Central Europe depends on an adequate management of the ecosystems. Moderate grazing (cattle or sheep) or mowing help to limit competition with taller Carex species. Reintroduction of disappeared populations or creation of new ones from cultivation in botanical garden is possible, but appropriate sites are rare. In some cases, substrate management could improve the conditions in somewhat inadequate situations. This management in four directions can be flexibly applied in different situations to progress to optimal conditions for the conservation of this valuable species.

Cattle influences gap dynamics in pastures in two ways: (1) by creating gaps and (2) by affecting the colonization process. This effect of cattle activity on gap revegetation can be subdivided in three main factors: herbage removal, trampling and dung and urine deposition. The objective of this study was to assess how these three effects moderate the plant succession following gap creation. In an exclosure, four controlled treatments simulating cattle activity (repeated mowing, trampling, manuring and untreated control) were applied on plots of 2 × 2 m. In the centre of each plot, one artificial gap of 60 × 60 cm was created. During three years, vegetation changes were monitored in spring and in autumn, with a square grid of 100 cells of 0.01 m2 centred on the gap. Our experiment confirmed that fine-scale gap creation may have a high impact on relative abundances of species in the community. The gap environment acts on species as a filter and this filtering was described in terms of regenerative attributes. Colonizers were species with small seeds, unspecialized seed dispersal, persistent seed bank and high vegetation spread. However, the role of dung deposition, herbage removal or trampling by cattle did not seem to be of primary importance in the revegetation process, but could moderate vegetation response. Therefore, the different cattle effects act as secondary filters that selectively favoured or disadvantaged different species from the gap-regenerating community. These complex interactions are probably keys to understand plant coexistence in perennial grasslands.

A cell-grid method was used to survey seasonal changes in four herbaceous communities of a wooded pasture. Permanent plots consisted in 1-m3 grids subdivided into 100 cells of 1 dm2. In each cell of each plot and every month from May to September, we estimated dominance, and grazing occurrence of all species. Plant communities included an eutrophic grazed meadow, a temporary refused meadow, an underwood herb community and an oligotrophic lawn. Our results showed that seasonal changes in species composition were very strong and scale-dependent. Changes at plot scale were mainly driven by a seasonal shift. Changes at cell scale suggested high small-scale dynamics of species. Despite high changes at cell scale, the structure of the community did not change and local species richness did not show any trend. We found no correlation between the turnover at cell scale and cattle activity. We conclude that dynamics and internal species turnover of the community at fine scale and short time seem more driven by internal characteristics of the community than by disturbances induced by cattle. Furthermore, at seasonal scale, plant communities may be stable in their structure despite fluctuations in their texture. © Akademiai Kiado, Budapest.

International audience; In a bog site in way of paludification, a pine stand is declining, which presently is an infrequent phenomenon on the Swiss Jura scale. A transect was positioned in the bog, from the external and driest part (pine-spruce stand) towards the central and wettest part (pine stand). Water table, tree structure, tree age structure and pine radial growth were analysed with spatial and temporal references. The ground water level is very shallow and the hydrologic gradient is obvious during dry periods. Tree structure (height and diameter) is strongly linked to the hydrologic gradient. Two cohorts have invaded the bog with a 70-year-time period between them. The first one concerned the whole transect; it started around 1840 and could be related to a clear cutting on the fringe of the bog. After a quick initial radial growth, the pines reduced their radial growth abruptly (1870-1885), more quickly and strongly in the centre of the bog, where an important mortality was observed over the last 10 years. Bog pine can thus survive over decades with a very reduced growth and in very wet environment. We think that the edge of raised bogs probably constituted the bog pines' survival niche during paludification in the Jura bogs.; Réactions spatio-temporelles du pin à crochets (Pinus uncinata var. rotundata) à l'interface d'une ceinture d'épicéas (Picea abies) sur la marge d'un haut-marais de la chaîne jurassienne, Suisse. Dans un site de haut-marais en voie de paludification, un peuplement de pins dépérit, ce qui est actuellement peu fréquent à l'échelle du Jura suisse. Un transect a été établi dans la tourbière de la partie externe et sèche (peuplement mixte pin-épicéa) vers la partie centrale et très humide (peuplement de pins). La nappe phréatique, la structure des arbres, la structure d'âge des arbres et la croissance radiale des pins ont été analysées avec références spatiale et temporelle. La nappe est très superficielle et le gradient hydrique est évident lors de périodes sèches. La structure des arbres (hauteur, diamètre) est nettement liée au gradient hydrique. Deux cohortes ont envahi le marais à 70 ans d'intervalle. La première, sur l'ensemble du transect, a débuté vers 1840 et pourrait être en relation avec un déboisement à la périphérie de la tourbière. Après une croissance radiale initiale rapide, les pins ont réduit brusquement leur croissance radiale (1870-1885), plus rapidement et plus fortement au centre du marais où une forte mortalité fut observée depuis 10 ans. Les pins à crochets peuvent donc survivre durant des décennies avec une croissance très réduite en milieu très humide et nous pensons que le bord des tourbières fut probablement leur niche de survie durant la paludification des marais jurassiens.

1 Significant areas of temperate bogs have been damaged by peat harvesting but may regenerate. These secondary mires, if well managed, may act as strong C sinks, regulate hydrology and buffer regional climate. 2 The potential effects of bog regeneration will, however, depend on the successful establishment of the principal peat formers –Sphagnum mosses. The influence of hydrology and microclimate on Sphagnum re-growth is well studied but effects of elevated CO2 and N deposition are not known. 3 We carried out two in-situ experiments in a cutover bog during three growing seasons in which we raised either CO2 (to 560 p.p.m.) or N (by adding NH4NO3, 3 g m−2 year−1). The two treatments had contrasting effects on competition between the initial coloniser Polytrichum strictum (favoured by high N) and the later coloniser Sphagnum fallax (favoured by high CO2). 4 Such changes may have important consequences for bog regeneration and hence for carbon sequestration in cutover bogs, with potential feedback on regional hydrological and climatic processes.

Les zones alluviales constituent un objet environnemental complexe, très révélateur des enjeux sécuritaires, culturels, économiques et écologiques à l'œuvre dans la gestion actuelle des cours d'eau. Cet article, construit sur les résultats d'une recherche interdisciplinaire récente, interroge, à travers trois études de cas, sur la transformation des modes de gestion des cours d'eau en Suisse. Articulant dorénavant les principes de sécurité et de conservation de la biodiversité, cette transformation prend en compte les contraintes écologiques, hydrologiques et socioculturelles qui délimitent l'action publique dans le domaine de la gestion des cours d'eau. L'émergence des nouvelles procédures de communication, de médiation et de négociation est au cœur d'un processus d'apprentissage social collectif qui devrait, à terme, produire un changement des valeurs, des représentations sociales de la nature et des risques, ainsi que des principes qui orientent l'action. Floodplains are a complex environmental "object" which reveal the cultural, economic and ecological as well as safety stakes nowadays to be taken into account in river management. This paper is based on the results of a recent interdisciplinary research involving scientists in sociology, hydrology and soil ecology. Taking three case studies it examines the changes in the river management paradigm in Switzerland. This new paradigm pays growing attention to environmental protection issues and complementarily articulates safety and biodiversity conservation principles. Its application is nevertheless faced with various ecological, hydrological and socio-cultural constraints that limit public action. Floodplains represent a multidimensional ecosystem whose natural dynamic is crucial for maintaining the richness of its biodiversity. In this perspective, the new paradigm aims to reconcile ecological concerns with modern hydrological techniques and public acceptance. Complex social negotiations govern the implementation of the new revitalization measures. Public and private actors are the main pivots of these processes. New communication, collaboration and mediation procedures are enabling a process of social collective training. This process could facilitate in the future a deeper change in the values, the social representations of nature and risks, and the principles of value-based action.

Stratigraphy, radiocarbon dating and analyses of pollen, plant macrofossils and testate amoebae were used to reconstruct the development and ecology of a small raised bog in a karst-dominated landscape in the Swiss Jura Mountains. Special focus was on past vegetation and on the history of Pinus rotundata in relation to anthropogenic and climatic influences. Testate amoebae were used to reconstruc-t past local soil pH and water-table depth. The inferred development of the Praz-Rodet bog typifies a classic hydroseral tefrestrialization of a small basin. Two features are specific for this site. First, the bog was much wetter than today for a long period; according to our hypothesis, this only changed as a consequence of human activities. Second, two hiatuses are present at the coring location (Younger Dryas--early Preboreal, and 4700-2800 cal. yr BP), the former probably caused by low lake productivity due to cold temperatures and the latter by the erosional activity of the adjacent small river. The date of 2800 cal. yr BP for renewed peat accumulation may be related to climatic change (Subboreal-Subatlantic transition). Pollen indicators failed to show one hiatus: an apparently complete pollen sequence is therefore no guarantee of an uninterrupted sediment accumulation. Evidence of early minor human impact on the vegetation in the Joux Valley dates back to c. 6850 calendar years, congruous with the early Neolithic in the Jura Mountains. The history of Pinuis rotindata appears to be more complex than previously believed. Human activity is clearly responsible for the present abundance of this species, but the tree was naturally present on the bog long before the first evidence of important human disturbance of the site (1500 cal. yr BP). It is suggested that, in karst-dominated landscapes, dense forests growing on mineral soils around raised bogs may significantly reduce summer evapotranspiration by acting as windbreaks. Forest clearance results in increased evapotranspiration, causing a lowering of the water table on the bog and a modification of the vegetation cover. This hypothesis has implications for the management of similar small raised bogs in karst-dominated landscape.

A description of bog pine stands (Pinus uncinata Ramond var. rotundata (Link) Antoine) on uncut oligotrophic mires affected by drainage and nearby peat cuttings at three sites of the Jura Mountains (Switzerland) is given. In all sites, three situations were chosen: (i) central parts of the bogs, (ii) surfaces near cutting walls and bog margins, and (iii) intermediate situations. Population structures were characteristic for each situation. In the open and wet central parts of the bogs, trees were scattered, small, and uneven aged. In the intermediate situations, tree density was higher, and the stand was multilayered with taller and uneven-aged individuals. Near the edges of the bogs or close to the peat cutting walls, the trees were tall, even-aged, and younger with a high growth rate. The nonsynchronous colonization of the bog pine trees on the three sites indicates that local factors such as drainage and peat cuttings in the vicinity of the uncut surfaces were more influential than climate factors. Radial growth patterns, very similar between the sites and the various pinewood stands, and the numerous common pointer years reflect local and regional climate fluctuations. The pinewood development on uncut bogs in the Jura Mountains thus represents a recent dynamics, which is strongly linked to human activities.

A description of bog pine stands (Pinus uncinata Ramond var. rotundata (Link) Antoine) on uncut oligotrophic mires affected by drainage and nearby peat cuttings at three sites of the Jura Mountains (Switzerland) is given. In all sites, three situations were chosen: (i) central parts of the bogs, (ii) surfaces near cutting walls and bog margins, and (iii) intermediate situations. Population structures were characteristic for each situation. In the open and wet central parts of the bogs, trees were scattered, small, and uneven aged. In the intermediate situations, tree density was higher, and the stand was multilayered with taller and uneven-aged individuals. Near the edges of the bogs or close to the peat cutting walls, the trees were tall, even-aged, and younger with a high growth rate. The nonsynchronous colonization of the bog pine trees on the three sites indicates that local factors such as drainage and peat cuttings in the vicinity of the uncut surfaces were more influential than climate factors. Radial growth patterns, very similar between the sites and the various pinewood stands, and the numerous common pointer years reflect local and regional climate fluctuations. The pinewood development on uncut bogs in the Jura Mountains thus represents a recent dynamics, which is strongly linked to human activities.

The relationships between several diversity indices and tree cover in subalpine wooded pastures with Larix de-cidua were analysed at two spatial scales: phytocoenoses (2500-m2 plots) and herbaceous synusia (1-m2 quadrats). Diversity indices have a non-linear relationship to Larix cover; the best fit was obtained with Gaussian regressions. Species richness was influenced by Larix cover more than evenness. At the phytocoenosis level, the optimum for species and synusial richness in the herb layer was near 25 % tree cover. At the synusia level, species richness of the herb layer showed an optimum when mean distance to the four nearest Larix trees was ca. 30 m, or when the potential number of sunshine hours between April and September was close to 1250 h. Canonical Correspondence Analysis confirmed the influence of Larix cover on the composition of phytocoenoses and herbaceous synusiae, but included also the role of altitude, slope and aspect.

Testate amoebae (Protozoa) living in Sphagnum peatlands are important environmental and paleoecological indicators. The distribution of these animals is closely related to soil moisture variables. This study examines the ecology of sphagnicolous testate amoebae near the southern limit of bogs in Europe. A total of 64 samples were collected for analysis of testate amoebae from six peatlands in the Jura region of Switzerland and France. Eleven site-specific ecological variables, six of which were soil-moisture related variables, were measured at each site. The data were subjected to weighted averaging, jack-knifing, cluster analysis, canonical correspondence analysis, and the indicator value method to model relationships between testate amoebae distributions and environmental variables. Testate amoebae abundance showed a direct relationship with pear pH and depth to water table. Strong relationships were with sites that had a water table less than 41 cm deep. In drier sites with water table depth greater than 41 cm, other factors such as soil porosity and water holding capacity were more important compared to the wetter sites. Though there was a strong relationship between restate amoebae faunas and soil moisture content and porosity, these two variables could not be confidently predicted. Testate amoebae in peatlands in this region appear to be sensitive to peat pH and water tables. Further work is needed to explore relationships between restate amoebae, soil moisture, and porosity.

Background and aims: Uptake of 90Sr and 137Cs in plants varies widely between soil types and between plant species. It is now recognized that the radionuclide uptake in plants is more influenced by site-specific and plant-specific parameters rather than the bulk radionuclide concentration in soil. We hypothesized that the stress which Alpine plants experience because of the short growing season may enhance the phylogenetic effect on the 137Cs and 90Sr transfer factors as well as the dependency of the uptake by plant to the concentrations of exchangeable Ca and K of soils. Methods: We carried out a field study on the 90Sr and 137Cs uptake by 11 species of Alpine plants growing on 6 undisturbed and geochemically different soils in the Alpine valley of Piora, Switzerland. Results: Results show that a strong correlation exists between the log TF and the log of exchangeable Ca or K of the soils. Conclusions: Cs uptake by Phleum rhaeticum (Poales) and Alchemilla xanthochlora (Rosales) is more sensitive to the amount of exchangeable K in the soil than the corresponding uptake by other orders. Moreover, the 90Sr results indicate a phylogenetic effect between Non-Eudicot and Eudicots: the order Poales (Phleum rhaeticum) concentrating much less 90Sr than Eudicots do

Peatlands represent massive global C pools and sinks. Carbon accumulation depends on the ratio between net primary production and decomposition, both of which can change under projected increases of atmospheric CO2 and N deposition. The decomposition of litter is influenced by 1) the quality of the litter, and 2) the microenvironmental conditions in which the litter decomposes. This study aims at experimentally testing the effects of these two drivers in the context of global change. We studied the in situ litter decomposition from three common peatland species (Eriophorum vaginatum, Polytrichum strictum and Sphagnum fallax) collected after one year of litter production under pre-treatment conditions (elevated CO2: 560 ppm or enhanced N: 3 g m(-2) y(-1) NH4NO3) and decomposed the following year under treatment conditions (same as pre-treatment). By considering the cross-effects between pre-treatments and treatments, we distinguished between the effects on mass loss of 1) the pre-treatment-induced litter quality and 2) the treatment conditions under which the litters were decomposing. The combination between CO2 pre-treatment and CO2 treatment reduced Polytrichum decomposition by 24% and this can be explained by litter quality-driven decomposition changes brought by the pre-treatment. CO2 pre-treatment reduced Eriophorum litter quality, although this was not sufficient to predict decomposition. The N addition pretreatment reduced the decomposition of Eriophorum, due to enhanced lignin and soluble phenols concentrations in the initial litter, and reduced litter-driven losses of starch and enhanced litter-driven losses of soluble phenols. While decomposition indices based on initial litter quality provide a broad explanation of quantitative and qualitative decomposition, they can only be taken as first approximations. Indeed, the microbial ATP activity, the litter N loss and resulting litter quality, were strongly altered irrespective of the compounds' initial concentration and by means of processes that occurred independently of the initial litter-qualitative changes. The experimental design was valuable to assess litter- and ecosystem-driven decomposition pathways simultaneously or independently. The ability to separate these two drivers makes it possible to attest the presence of litter-qualitative changes even without any litter biochemical determinations, and shows the screening potential of this approach for future experiments dealing with multiple plant species. (C) 2010 Elsevier Ltd. All rights reserved.

Eriophorum vaginatum is a characteristic species of northern peatlands and a keystone plant for cutover bog restoration. Understanding the factors affecting E. vaginatum seedling establishment (i.e. growth dynamics and allocation) under global change has practical implications for the management of abandoned mined bogs and restoration of their C-sequestration function. We studied the responses of leaf dynamics, above- and belowground biomass production of establishing seedlings to elevated CO(2) and N. We hypothesised that nutrient factors such as limitation shifts or dilutions would modulate growth stimulation. Elevated CO(2) did not affect biomass, but increased the number of young leaves in spring (+400 %), and the plant vitality (i.e. number of green leaves/total number of leaves) (+3 %), both of which were negatively correlated to [K(+)] in surface porewater, suggesting a K-limited production of young leaves. Nutrient ratios in green leaves indicated either N and K co-limitation or K limitation. N addition enhanced the number of tillers (+38 %), green leaves (+18 %), aboveground and belowground biomass (+99, +61 %), leaf mass-to-length ratio (+28 %), and reduced the leaf turnover (-32 %). N addition enhanced N availability and decreased [K(+)] in spring surface porewater. Increased tiller and leaf production in July were associated with a doubling in [K(+)] in surface porewater suggesting that under enhanced N production is K driven. Both experiments illustrate the importance of tradeoffs in E. vaginatum growth between: (1) producing tillers and generating new leaves, (2) maintaining adult leaves and initiating new ones, and (3) investing in basal parts (corms) for storage or in root growth for greater K uptake. The K concentration in surface porewater is thus the single most important factor controlling the growth of E. vaginatum seedlings in the regeneration of selected cutover bogs.

This study examines the role of abiotic (texture, calcium carbonates or iron) and biotic parameters (earthworm and enchytraeid activities) on the initial phases of soil aggregation. Our research focused on humus forms in alluvial soils, which are considered as young and heterogeneous environments. We hypothesized that the soil structure formation is determined by both the nature of the recent alluvial deposits and the soil fauna. For this purpose, six sites were chosen throughout two types of softwood forests (willow and alder forest) representing two stages of vegetation succession. Evidence of soil texture influence on aggregate stability was observed. A dominance of a coarse sand fraction caused a quick colonization of enchytraeids and epigeic earthworms while a silty texture favoured the presence of anecic earthworms, thus increasing the aggregate stabilisation. Iron forms, acting as cementing agents, were observed in the coarse silt, while calcium carbonates were equally distributed among the textural fractions. Active calcium carbonate fraction, binding organic matter with mineral components, was not found in the coarse sand fraction. In conclusion, the tree age cannot alone be used as an indicator of the humus form evolution but biological and physicochemical parameters also influence the initial steps of soil structuration.

Plant and Soil, 283 (1-2), ISSN:0032-079X, ISSN:1573-5036

Management-oriented models of cattle habitat use often treat grazing pressure as a single variable summarizing all cattle activities. This paper addresses the following questions: How does the spatial pattern of cattle effects vary between cattle activities in a highly heterogeneous landscape? Do these patterns change over the grazing season as forage availability decreases? What are the respective roles of natural and management-introduced structures? We estimated the intensity of herbage removal, dung deposition and trampling after each of three grazing periods on a grid of 25 m × 25 m cells covering an entire paddock in the Swiss Jura Mountains. We found no significant positive correlations between cattle effects. Spatial patterns weakened through the season for grazing and trampling, whereas dunging patterns changed little between grazing periods. Redundancy analysis showed that different cattle effects were correlated with different environmental variables and that the importance of management-introduced variables was highest for herbage removal. Autocorrelograms and partial redundancy analyses using principal coordinates of neighbour matrices suggested that dunging patterns were more coarse-grained than the others. Systematic differences in the spatial and seasonal patterns of cattle effects may result in complex interactions with vegetation involving feedback effects through nutrient shift, with strong implications for ecosystem management. In heterogeneous environments, such as pasture-woodland landscapes, spatially explicit models of vegetation dynamics need to model cattle effects separately.

Cattle influences gap dynamics in pastures in two ways: (1) by creating gaps and (2) by affecting the colonization process. This effect of cattle activity on gap revegetation can be subdivided in three main factors: herbage removal, trampling and dung and urine deposition. The objective of this study was to assess how these three effects moderate the plant succession following gap creation. In an exclosure, four controlled treatments simulating cattle activity (repeated mowing, trampling, manuring and untreated control) were applied on plots of 2 X 2 in. In the centre of each plot, one artificial gap of 60 X 60 cm was created. During three years, vegetation changes were monitored in spring and in autumn, with 2 a square grid of 100 cells of 0.01 m(2) centred on the gap. Our experiment confirmed that fine-scale gap creation may have a high impact on relative abundances of species in the community. The gap environment acts on species as a filter and this filtering was described in terms of regenerative attributes. Colonizers were species with small seeds, unspecialized seed dispersal, persistent seed bank and high vegetation spread. However, the role of dung deposition, herbage removal or trampling by cattle did not seem to be of primary importance in the revegetation process, but could moderate vegetation response. Therefore, the different cattle effects act as secondary filters that selectively favoured or disadvantaged different species from the gap-regenerating community. These complex interactions are probably keys to understand plant coexistence in perennial grasslands.

International audience; The effect of cattle activity on pastures can be subdivided into three categories of disturbances: herbage removal, dunging and trampling. The objective of this study was to assess separately or in combination the effect of these factors on the potential activities of soil microbial communities and to compare these effects with those of soil properties and plant composition or biomass. Controlled treatments simulating the three factors were applied in a fenced area including a light gradient (sunny and shady situation): (i) repeated mowing; (ii) trampling; (iii) fertilizing with a liquid mixture of dung and urine. In the third year of the experiment, community level physiological profiles (CLPP) (Biolog Ecoplates (TM)) were measured for each plots. Furthermore soil chemical properties (pH, total organic carbon, total nitrogen and total phosphorus), plant species composition and plant biomass were also assessed. Despite differences in plant communities and soil properties, the metabolic potential of the microbial community in the sunny and in the shady situations were similar. Effects of treatments on microbial communities were more pronounced in the sunny than in the shady situation. In both cases, repeated mowing was the first factor retained for explaining functional variations. In contrast, fertilizing was not a significant factor. The vegetation explained a high proportion of variation of the microbial community descriptors in the sunny situation, while no significant variation appeared under shady condition. The three components of cattle activities influenced differently the soil microbial communities and this depended on the light conditions within the wooded pasture. Cattle activities may also change spatially at a fine scale and short-term and induce changes in the microbial community structure. Thus, the shifting mosaic that has been described for the vegetation of pastures may also apply for below-ground microbial communities.

International audience; In Jura bogs, on deep and nutrient-poor peat, the ecotone between bog pine forest and Norway spruce forest is sharp and, in a few disturbed situations, no succession pine forest-spruce forest occurs. The bog Les Saignolis lies at the top of an anticline, on thin and oligotrophic peat. Several documents attest some anthropic disturbances (clear cut and drainage). Beside these historical data and with the aim of reconstructing vegetation dynamics and tree growth, we realised synusial phytosociological relevés and, in a mixed pine-spruce stand, we studied tree radial growth. Following the clear cut, the bog pine, the pubescent birch, and the Norway spruce settled simultaneously. The birch disappeared rapidly. The present cohort of pine settled and grew rapidly, and then declined because of the competition by spruce. Spruce settled progressively and increased its growth regularly except when pine settled and grew. Interspecific competition between pines and spruces and intraspecific competition between dominant and sub-dominant spruces were put into evidence by radial growth analysis.; Succession pinède-pessière en relation avec les facteurs anthropiques dans la tourbière des Saignolis, chaîne jurassienne, Suisse. Dans les hauts marais jurassiens, sur tourbe épaisse et oligotrophe, la limite entre la pinède et la ceinture d'épicéas est très nette et il n'y a pas de succession pinède-pessière en situations peu perturbées. Le marais des Saignolis est situé au sommet d'un anticlinal, sur tourbe mince et oligotrophe. Plusieurs documents témoignent de perturbations anthropiques (coupe rase et drainage). En complément aux données historiques et dans le but de reconstruire la dynamique de la végétation et de la croissance des arbres, nous avons effectué des relevés phytosociologiques synusiaux et, dans un peuplement mixte pin-épicéa, nous avons étudié la croissance radiale des arbres. Après l'éclaircie, le pin, le bouleau pubescent et l'épicéa se sont installés simultanément. Le bouleau a rapidement disparu. La cohorte actuelle du pin s'est installée et a grandi rapidement, puis a dépéri, concurrencée par l'épicéa. L'épicéa s'est installé progressivement et a régulièrement augmenté sa croissance, sauf au moment de l'installation et de la croissance des pins. La compétition interspécifique entre pins et épicéas et la compétition intraspécifique entre épicéas dominants et sub-dominants ont été mises en évidence par l'analyse de la croissance radiale.

To monitor global change, large scale long term studies are needed. Such studies often focus on vegetation, but most plant species have limited distribution areas. Micro-organisms by contrast are mostly cosmopolitan in their distributions. To study the relationships between organisation groups, we analysed the testate amoebae (Protozoa), vegetation, and water chemistry of five Sphagnum peatlands across Europe. Inter-site differences were more pronounced for the vegetation than for testate amoebae species assemblage. Testate amoebae represent a useful tool in multi-site studies and environmental monitoring of peatlands because: 1) the number of species is much higher than for plants, 2) most species are cosmopolitan and are therefore less affected by biogeographical distribution patterns than plants; thus differences in testate amoebae assemblages can be interpreted primarily in terms of ecology, 3) testate amoebae can be used to analyse and monitor small scale (cm) gradients that play a major role in the functioning of peatland ecosystems. We further studied the effect of elevated CO2 on microbial communities in the same peatlands. Elevated CO2 increased the biomass of heterotrophic bacteria and decreased the biomass of medium size protozoa (mostly small testate amoebae). These effects suggest changes in community functioning that may have feedback effects on other components of the ecosystem.

In the Swiss Jura mountains most of the remaining ombrotrophic peat bogs have been exploited to some extent for peat. In these sites, natural regeneration processes are taking place. The dominant process is paludification, where a cut over drained surface is colonised by key species, usually either Polytrichum strictum or Eriophortum vaginatum. These early colonisers of bare peat surfaces create microclimatic conditions that enable the re-colonisation of Sphagnum mosses, usually S.fallax. In later stages of the succession S. fallax grows to form a continuous carpet and the key species gradually suffer from competition for light availability. We studied the effect of elevated CO2 (560 ppm) and nitrogen deposition (30 kg ha -1 year -1) on the competition between Sphagnum fallax and Polytrichum strictum year in a three years field experiment (EU project BERI — Bog Ecosystem Research Initiative) using miniFACE systems (small size Free Air Carbon dioxide Enrichment). The cover and growth in length of the two species was monitored. The height difference between the emerging Polytrichum and the top of the Sphagnum mosses was also recorded at regular intervals. Effect Of CO2: Sphagnum cover increased in the first year but this trend was not confirmed subsequently, whereas Polytrichum cover was not affected by elevated CO2 Both Sphagnum and Polytrichum had a reduced growth in length under elevated CO2. However, the growth of Sphagnum was less reduced than that of Polytrichum and therefore the height difference between Sphagnum and Polytrichum decreased. Effect of N: Sphagnum cover declined and Polytrichum cover doubled over the three years period in the high N plots. Sphagnum growth in length was not significant affected by N, but Polytrichum grew more in the high N plots. As a results the height difference between Sphagnum and Polytrichum increased. These results suggest that elevated CO2 and nitrogen deposition may have contrasting effects on bog regeneration. The positive effect of elevated CO2 on Sphagnum mosses may be counterbalanced by higher N deposition levels.

A brief overview of an attempt to link the effect of elevated CO2 and nitrogen deposition on litter quality and decomposition in a Sphagnum peat bog is given. Litter of three common species (Eriophorum vaginatum, Polytrichum strictum and Sphagnum fallax) was collected from field plots after two years of pre-treatment in two parallel experiments: a) Elevated atmospheric CO2 experiment, b) mineral nitrogen fertilisation experiment. The litters were put into litterbags, leached and inserted into field plots for 3 months, where they decomposed under specific treatment. Distinction between effects of initial litter quality and decomposition on mass loss in the bioleaching and/or in field decomposition process could be tested using a particular set-up in which cross-effects of pre-treatment and treatment were considered.

In many terrestrial ecosystems, soil parameters usually regulate the distribution of earthworm communities. In alluvial ecosystems, few studies have investigated the impact of periodic floods and alluvium deposition on soil fauna. In this context, we assumed that earthworm communities may vary depending on altitude (alpine, subalpine, mountain and hill levels), forest successional stage (post-pioneer to mature forests) and some soil parameters. Our results demonstrated that the composition of earthworm communities differed depending on altitudinal gradients. No earthworm was found at the alpine level while maximum density and biomass were observed at the hill level mainly due to the contribution of anecic species. A total of 27 species and subspecies were found over the three sampling sites, and Lumbricus moliboeus was discovered for the first time in carbonated soils. Soil texture had a major effect on epigeics that were often associated with coarse sandy texture in contrast to anecics which preferred deep soils and mature forest stages, which in combination provided the highest carbon content and the finest soil texture. In our study, carbonated fluviosols (Fluvisols according to the World Reference Base) were recorded; fluviosols typiques with well-structured A layers were generally found in mature or intermediate forest stages while most of fluviosols juveniles with heterogeneous texture were observed principally in post-pioneer forests. We conclude that in alluvial ecosystems, earthworm communities were highly dependent first on soil parameters, then altitude and to a lesser extent forest successional stages. Changes in earthworm communities tend to reflect a gradient of alluvial dynamics thus reinforcing the potential role of earthworms as bioindicators in natural and/or semi natural alluvial ecosystems.