Mountain soils under a changing climate and land-use

Mountain ecosystems are currently experiencing the strongest climatic warming and the largest changes in land-use during the last millennia. The impacts of these changes on soils and their roles in the cycling of carbon and nutrients are, however, largely unknown. Here, we define mountain soils as soils from mountainous areas with cool summers and cold winters and thus, soils from ecosystems that are influenced by snow and ice and where biogeochemical processes are limited by temperature. Because climatic conditions, soil properties, plant species and productivity vary at a small scale in mountains, they provide a unique natural but a seldom used laboratory to study soil processes. In this special issue, we compile different studies on soils from European mountains, reaching from the functioning of mountain soils along natural climatic gradients to responses of greenhouse gas fluxes from mountain soils to experimental warming, soil frost and changes in precipitatio

Decomposition pathways of 13C-depleted leaf litter in forest soils of the Swiss Jura

Decomposition of leaf litter and its incorporation into the mineral soil are key components of the C cycle in forest soils. In a 13C tracer experiment, we quantified the pathways of C from decomposing leaf litter in calcareous soils of a mixed beech forest in the Swiss Jura. Moreover, we assessed how important the cold season is for the decomposition of freshly fallen leaves. The annual C loss from the litter layer of 69-77% resulted mainly from the C mineralization (29-34% of the initial litter C) and from the transfer of litter material to the deeper mineral soil (>4cm) by soil fauna (30%). Although only 4-5% of the initial litter C was leached as dissolved organic carbon (DOC), this pathway could be important for the C sequestration in soils in the long term: The DOC leached from the litter layer was mostly retained (95%) in the first 5cm of the mineral soil by both physico-chemical sorption and biodegradation and, thus, it might have contributed significantly to the litter-derived C recovered in the heavy fraction (>1.6gcm−3) at 0-4cm depth (4% of the initial litter C). About 80% of the annual DOC leaching from the litter layer occurred during the cold season (Nov-April) due to an initial DOC flush of water-soluble substances. In contrast, the litter mineralization in winter accounted for only 25% of the annual C losses through CO2 release from the labelled litter. Nevertheless, the highest contributions (45-60%) of litter decay to the heterotrophic soil respiration were observed on warm winter days when the mineral soil was still cold and the labile litter pool only partly mineralized. Our 13C tracing also revealed that: (1) the fresh litter C only marginally primed the mineralization of older SOM (>1year); and (2) non-litter C, such as throughfall DOC, contributed significantly to the C fluxes from the litter layer since the microbial biomass and the DOC leached from the litter layer contained 20-30% and up to 60% of unlabelled C, respectively. In summary, our study shows that significant amounts of recent leaf litter C (<1year) are incorporated into mineral soils and that the cold season is clearly less important for the litter turnover than the warm season in this beech forest ecosyste

Retention and Leaching of Elevated N Deposition in a Forest Ecosystem with Gleysols

The responses of nitrogen transformations and nitrate (NO_3 -) leaching to experimentally increased N deposition were studied in forested sub-catchments (1500 m2) with Gleysols in Central Switzerland. The aim was toinvestigate whether the increase in NO3 - leaching,due to elevated N deposition, was hydrologically driven orresulted from N saturation of the forest ecosystem.Three years of continuous N addition at a rate of 30 kgNH4NO3-N ha-1 yr-1 had no effects on bulksoil N, on microbial biomass N, on K2SO4-extractableN concentrations in the soil, and on net nitrification rates.In contrast, N losses from the ecosystem through denitrification and NO3 - leaching increased significantly. Nitrate leaching was 4 kg N ha-1yr-1at an ambient N deposition of 18 kg N ha-1 yr-1.Leaching of NO3 - at elevated N deposition was 8 kg Nha-1 yr-1. Highest NO3 - leaching occurredduring snowmelt. Ammonium was effectively retained within theuppermost centimetres of the soil as shown by the absence ofNH4 + in the soil solution collected with microsuction cups. Quantifying the N fluxes indicated that 80% ofthe added N were retained in the forest ecosystem.Discharge and NO3 - concentrations of the outflow from the sub-catchments responded to rainfall within 30 min. The water chemistry of the sub-catchment outflow showed thatduring storms, a large part of the runoff from this Gleysol derived from precipitation and from water which had interactedonly with the topsoil. This suggests a dominance of near-surface flow and/or preferential transport through this soil. The contact time of the water with the soil matrix wassufficient to retain NH4 +, but insufficient for a complete retention of NO3 -. At this site with soilsclose to water saturation, the increase in NO3 - leaching by 4 kg N ha-1 yr-1 through elevated N inputsappeared to be due to the bypassing of the soil and the rootsystem rather than to a soil-internal N surplu

Ecdysteroids and oocyte development in the black fly Simulium vittatum

BACKGROUND: Oocyte development was studied in the autogenous black fly, Simulium vittatum (Diptera, Nematocera), a vector of Onchocerca volvulus, the causative agent of onchocerciasis. RESULTS: Oocyte growth was nearly linear between adult eclosion and was complete by 72 hours at 21°C. The oocyte became opaque at 14 hours after eclosion indicating the initiation of protein yolk deposition. The accumulation of vitellogenin was measured using SDS-PAGE. The density of the yolk protein bands at about 200 and 65 kDa increased during the first and second days after eclosion. The amount of protein in the 200 kDa band of vitellogenin, determined using densitometry, rapidly increased between 12 and 25 hours after eclosion. Ecdysteroid levels were measured using a competitive ELISA. Ecdysteroid levels increased rapidly and subsequently declined during the first day after eclosion. CONCLUSION: These data show a correlation between the appearance of vitellogenin in the oocyte, and the rise in ecdysteroids. A possible relationship to molting of the nematode, Onchocerca volvulus, is discussed

Experimental summer drought reduces soil CO2 effluxes and DOC leaching in Swiss grassland soils along an elevational gradient

Soil moisture affects belowground activity in grasslands, but the effects of summer drought on different soil C fluxes is uncertain. Soil respiration (SR), dissolved organic carbon (DOC) leaching and their components may all respond differently and drought effects will interact with other factors such as temperature, making a priori predictions of soil C balances difficult. In this study, we used rain shelters to simulate summer droughts by reducing annual precipitation by around 30% in three managed grassland sites at 400, 1,000 and 2,000m a.s.l. in Switzerland covering a gradient in mean annual temperatures of 7.5°C. During the growing season, we quantified the impacts of drought on SR, DOC leaching, litter decomposition and the contribution of 13C-depleted litter to DOC fluxes. Along the elevational gradient, SR rates did not decrease with increasing altitude. Thus, SR was higher at a given temperature at higher altitudes, which probably reflects more labile soil C and hence greater substrate availability in a colder climate. Fluxes of DOC at 5cm depth were a magnitude smaller than SR and did not show a pattern with elevation. At all altitudes, the experimental summer drought significantly reduced SR rates by 25-57% and DOC leaching by 80-100%, with a declining contribution of 13C-depleted litter-DOC. The remaining litter mass after drought was two to seven times larger as compared to the control. We did not observe a strong C release upon rewetting and hence, there was no compensation for the reduced soil C fluxes during drought. The more sensitive drought response in the litter layer than in the deeper soil and the declining DOC fluxes indicate an altered soil C balance with a C preservation in the topsoil, but ongoing losses of probably ‘older' C in subsoils under drought

Performance of germinating tree seedlings below and above treeline in the Swiss Alps

The germination and early survival of tree seedlings is a critical process for the understanding of treeline dynamics with ongoing climate change. Here we analyzed the performance of 0-4year-old seedlings of seven tree species at three sites above and below the current altitudinal treeline in the Swiss Central Alps near Davos. Starting from sown seeds, we monitored the seedling performance as proportions of living seedlings, seedling shoot height growth, and biomass allocation over 4years to examine changes along an elevational gradient. We evaluated the relative importance of the environmental factors soil temperature, light conditions, water use efficiency, and nitrogen availability on seedling performance. During the 4years, the proportions of living seedlings differed only slightly along the elevational gradient even in species currently occurring at lower elevations. Microsite-specific soil temperature and light availability had only little effect on the proportion of living seedlings and seedling biomass across the elevational gradient. Conversely, seedling biomass and biomass allocation correlated well with the foliar stable nitrogen isotope abundance (δ 15N) that was used as an indicator for nitrogen availability. Collectively, our results suggested that the early establishment of seedlings of a variety of tree species in the treeline ecotone was not limited by current climatic conditions even beyond the species' actual upper distribution limit. Nitrogen dynamics appeared to be an important environmental co-driver for biomass production and allocation in very young tree seedling

Promoting the multifunctionality of agriculture, forestry, and rural areas - design and implementation of public policies in Germany

The multiple roles and functions of agriculture and forestry beyond those of supplying food and fibre, such as the provision of environmental benefits and the contribution to the socio-economic viability of rural areas, account for a growing recognition in both scientific debates and political decision making. In order to foster further research in the field of multifunctionality of agriculture, forestry, and rural areas, this report provides an overview of the scientific work that has been done with respect to the different ways and goals of setting up and management of public policies with multifunctional purpose. It particularly focuses on policies that have been implemented in Germany since 1992. Initially, a description of traditional policies for multifunctionality that have been initiated at EU, national, Laender, regional, and local level is provided. This includes, among other things, the EU Rural Development Regulations, the LEADER initiatives, the Flora-Fauna-Habitats Directive and Federal State and Laender legislation on protected areas. For each policy presented, apart from their content, important characteristics with regard to their setting up and implementation, such as responsibilities for and processes of goal determination, policy and measure design, and administrative implementation are presented. Subsequently, policies are introduced that particularly aim at creating new markets and services. Furthermore, innovative approaches are presented which involve new institutional arrangements for the provision of goods and services. Based on this presentation, the scientific debate on the design and implementation of policies with multifunctional purpose is sketched out. Five major strands of debates dealing with issues of setting up and management of those policies are highlighted: First, scientific literature is reflected that discusses issues regarding the allocation of property rights and the related question of applying standards, such as GFP, or incentive based policies. Second, light is shed on the scientific debate on the appropriate degree of centralisation and decentralisation, respectively. Third, directions of the discussion on policy and scheme design are considered. Fourth, the closely related issues of acceptance and demand of policies are highlighted. Fifth, questions of monitoring and enforcement are addressed. Finally, the main research gaps are highlighted. Outstanding and promising issues include the research on optimal institutional arrangements of property rights and matching forms of governance as well as interdisciplinary work on policies other than agri-environmental schemes

Feedback between erosion and active deformation: geomorphic constraints from the frontal Jura fold-and-thrust belt (eastern France)

A regional tectono-geomorphic analysis indicates a Pliocene to recent rock uplift of the outermost segment of the Jura fold-and-thrust belt, which spatially coincides with the intra-continental Rhine-Bresse Transfer Zone. Elevated remnants of the partly eroded Middle Pliocene Sundgau-Forêt de Chaux Gravels identified by heavy mineral analyses allow for a paleo-topographic reconstruction that yields minimum regional Latest Pliocene to recent rock uplift rates of 0.05±0.02mm/year. This uplift also affected the Pleistocene evolution of the Ognon and Doubs drainage basins and is interpreted as being tectonically controlled. While the Ognon River was deflected from the uplifted region the Doubs deeply incised into it. Focused incision of the Doubs possibly sustained ongoing deformation along anticlines which were initiated during the Neogene evolution of the thin-skinned Jura fold-and-thrust belt. At present, this erosion-related active deformation is taking place synchronously with thick-skinned tectonics, controlling the inversion of the Rhine-Bresse Transfer Zone. This suggests local decoupling between seismogenic basement faulting and erosion-related deformation of the Mesozoic cover sequence

Afforestation with Norway spruce on a subalpine pasture alters carbon dynamics but only moderately affects soil carbon storage

There is a strong trend toward reforestation of abandoned grasslands in alpine regions which may impact the carbon balance of alpine ecosystems. Here, we studied the effects of afforestation with Norway spruce (Picea abies L.) on an extensively grazed subalpine pasture in Switzerland on soil organic carbon (SOC) cycling and storage. Along a 120-year long chronosequence with spruce stands of 25, 30, 40, 45, and >120years and adjacent pastures, we measured tree biomass, SOC stocks down to the bedrock, natural 13C abundances, and litter quality. To unravel controls on SOC cycling, we have monitored microclimatic conditions and quantified SOC decomposability under standardized conditions as well as soil respiration in situ. Stocks of SOC were only moderately affected by the afforestation: in the mineral soil, SOC stocks transiently decreased after tree establishment, reaching a minimum 40-45years after afforestation (−25%) and increased thereafter. Soils of the mature spruce forest stored the largest amount of SOC, 13% more than the pasture soils, mainly due to the accumulation of an organic layer (23tCha−1). By comparison, C accumulated in the tree biomass exceeded the SOC pool by a factor of three in the old forest. In contrast to the small impact on C storage, afforestation strongly influenced the composition and quality of the soil organic matter (SOM). With increasing stand age, δ13C values of the SOM became consistently more positive, which can be interpreted as a gradual replacement of grass- by spruce-derived C. Fine roots of spruce were enriched in 13C, in lignin and had a higher C/N ratio in comparison to grass roots. As a consequence, SOM quality as indicated by the lower fraction of readily decomposable (labile) SOM and higher C:N ratios declined after the land-use change. Furthermore, spruce plantation induced a less favorable microclimate for microbial activity with the average soil temperature during the growing season being 5°C lower in the spruce stands than in the pasture. In situ soil respiration was approximately 50% lower after the land use conversion, which we primarily attribute to the colder conditions and the lower SOM quality, but also to drier soils (−25%) and to a decreased fine root biomass (−40%). In summary, afforestation on subalpine pastures only moderately affected SOC storage as compared to the large C sink in tree biomass. In contrast, SOC cycling rates strongly decreased as a result of a less favorable microclimate for decomposition of SOM, a lower C input by roots, and a lower litter qualit

Effects of Land-Use Change on Carbon Stocks in Switzerland

We assessed how consequences of future land-use change may affect size and spatial shifts of C stocks under three potential trends in policy—(a) business-as-usual: continuation of land-use trends observed during the past 15years; (b) extensification: full extensification of open-land; and (c) liberalization: full reforestation potential. The build-up times for the three scenarios are estimated at 30, 80 and 100years, respectively. Potential C-stock change rates are derived from the literature. Whereas the business-as-usual scenario would cause marginal changes of 0.5%, liberalization would provoke a 13% increase in C stocks (+62MtC). Gains of 24% would be expected for forests (+95MtC), whereas open-land C stock would decrease 27% (−33MtC). Extensification would lead to a C stock decrease of 3% (−12MtC). Whereas forest C is expected to increase 12% (+36.5MtC) at high elevations, stocks of open-land C would decline 38.5% (−48.5MtC). Most affected are unfavorable grasslands, which increase in area (+59%) but contribute only 14.5% to the C stocks. C sinks would amount to 0.6MtCy−1 assuming a build-up time of 100years for the liberalization scenario. C stocks on the current forest area are increasing by 1MtCy−1. The maximal total C sink of 1.6MtC might thus suffice to compensate for agricultural greenhouse gases (2004: 1.4Mt CO2-C equivalents), but corresponds only to 11-13% of the anthropogenic greenhouse gas emission in Switzerland. Thus, even the largest of the expected terrestrial C stocks under liberalization will be small in comparison with current emissions of anthropogenic greenhouse gase