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Biological nitrogen fixation (BNF) represents the natural pathway by which mosses meet their demands for bioavailable/reactive nitrogen (Nr) in peatlands. However, following intensification of nitrogen fertilizer and fossil fuel use, atmospheric Nr deposition has increased exposing peatlands to Nr loading often above the ecological threshold. As BNF is energy intensive, therefore, it is unclear whether BNF shuts down when Nr availability is no longer a rarity. We studied the response of BNF under a gradient of Nr deposition extending over decades in three peatlands in the U.K., and at a background deposition peatland in Sweden. Experimental nitrogen fertilization plots in the Swedish site were also evaluated for BNF activity. In situ BNF activity of peatlands receiving Nr deposition of 6, 17, and similar to 2 kg N ha(-1) yr(-1) was not shut down but rather suppressed by 54, 69, and 74%, respectively, compared to the rates under background Nr deposition of kg N ha(-1) yr(-1). These findings were corroborated by similar BNF suppression at the fertilization plots in Sweden. Therefore, contribution of BNF in peatlands exposed to chronic Nr deposition needs accounting when modeling peatland's nitrogen pools, given that nitrogen availability exerts a key control on the carbon capture of peatlands, globally.

In order to evaluate the chemical composition of natural background environments of Pur-Taz interfluve (Western Siberia), the mineral components of soils, peats, lichens, and sphagnum mosses have been analyzed. The samples were tested using X-ray fluorescence technology. The average contents of hazardous metals in the soils of the Pur-Taz interfluve are either lower (for Cu, Pb, Zn, Ni, Sr) or equal to (for Hg, Co) the average values of these elements in the Earth's crust. This finding corresponds to the commonly held view that the contents of elements in the soils located in the north of Western Siberia are lower than the world averages. Additionally, in our samples low concentrations of copper and zinc have been observed. Since these microelements are important for soil physiology, this finding indicates unfavorable biochemical conditions in the research area. On the other hand, high concentrations are observed for inactive elements such as Mo, Sn and Zr. The significant differences have been identified in the composition of mineral and organic soil horizons. For instance, the average concentrations of P, Zn and S in organic horizons are 7.1, 8.1 and 18 times greater than in the illuvial mineral horizons, respectively. The intense accumulation of Zn, Cu, Cd, Hg has been recorded, all of them are chalcophiles in the ombrotrophic peat. This means that the chemical composition of soil is largely determined by biological accumulation of chalcophile elements. The content of lithophilic Al, Si, Ti and Zr, coming with dust precipitation from the atmosphere increases in the peat of dwarf shrub-moss-lichen tundras and larch woodlands. The revealed values of the elemental composition of soils can be recommended as background in the course of the environmental monitoring.

This study utilized site-specific peat hydrophysical properties (inverse of air-entry pressure, α; pore size distribution index, n; saturated hydraulic conductivity, Ks; and pore tortuosity, L) as inputs into the HYDRUS 1-D computer model for quantifying moss moisture stresses on Irish peatlands. The site-specific peat hydrophysical properties computed using pedotransfer functions obtained from laboratory measured bulk density (BD) and % organic matter (OM). The peat samples obtained from undrained sites (Scohaboy, Pollagoona and Lough Ghe), three afforested sites (S18, S28 and S44) and rewetted sites (Scohaboy and Pollagoona). The moss moisture stresses quantified using a known ecohydrological threshold of −100 cm. The site-specific peat hydrophysical properties, four initial WTDs (3, 8, 20 and 30 cm) and two distinct precipitation regimes (single and consecutive 4 years having severely dry [SD], extremely dry [ED], near normal [NN], very wet [VW] and extremely wet [EW] periods) were inputs into HYDRUS 1-D model. The modelling results showed that none of the peatland sites ever reached −100 cm threshold in single year simulations at all initial WTDs. However, in the consecutive 4-year simulations, Scohaboy, Pollagoona and Lough Ghe undrained, S28 afforested and Pollagoona rewetted sites first reached −100 cm threshold on 516, 508, 624, 1329 and 517 day, respectively. In the consecutive 4-year simulations, undrained Scohaboy, Pollagoona, Lough Ghe, S28 afforested and Pollagoona rewetted reached −100 cm threshold in ED and SD years. We concluded that moss recolonization is likely to be successfully on peatlands having minimal to no −100 cm threshold days.

Degraded peatlands are often rewetted to prevent oxidation of the peat, which reduces CO2 emission. However, the created anoxic conditions will boost methane (CH4) production and thus emission. Here, we show that submerged Sphagnum peat mosses in rewetted-submerged peatlands can reduce CH4 emission from peatlands with 93%. We were able to mimic the field situation in the laboratory by using a novel mesocosm set-up. By combining these with 16S rRNA gene amplicon sequencing and qPCR analysis of the pmoA and mmoX genes, we showed that submerged Sphagnum mosses act as a niche for CH4 oxidizing bacteria. The tight association between Sphagnum peat mosses and methane oxidizing bacteria (MOB) significantly reduces CH4 emissions by peatlands and can be studied in more detail in the mesocosm setup developed in this study.

From 1992 to 1994, trace metal concentrations of bog water, Sphagnum mosses and peat cores of the bog “Georgenfelder Hochmoor” at Zinnwald-Georgenfeld in the Eastern Ore Mountains (Germany) were investigated. A sampling campaign in September 2019 allows the comparison of the older measurements with today's trace metal concentrations. No changes were found in the bog waters, while the trace metal concentrations of the Sphagnum mosses have decreased significantly. Due to the low growth rate of the peat and despite certain heterogeneity between the peat cores, the investigated elemental data for the peat sampled in the 1990s and in 2019 are in the same concentration range. The maximum concentrations are measured in the upper samples of all peat cores for the analysed elements (except sulphur). Compared to upper crustal data, a different behaviour of the elements is observed: Cr, Sc, Ti, and V, rare earth elements show crustal ratios, while Al and Si are also influenced by crust-air fractionation. Cd, Cu, Ni, Pb, and Zn are additionally enriched by anthropogenic atmospheric inputs from industry and transport. These results confirm the assumption that peat cores record past atmospheric deposition.

The population density and taxonomic structure of micromycetes were monitored for six months in a model experiment with natural and mechanically fragmented (fine and coarse) samples of sphagnum. Sphagnum fragmentation favored an increase in the number of micromycetes only during the first week of the experiment. On the average, the number of micromycetes in fine-fragmented samples was two times greater than that in the coarse-fragmented samples. The diversity of micromycetes increased in the fragmented samples of sphagnum owing to the activation of some species, which remained in the inactive state as spores in the peat before fragmentation.

International audience; Plant community modification may play an important role in peatlands’ carbon balance. We investigated how Molinia caerulea altered CO2 and CH4 fluxes and DOC concentration as well as their sensitivity to water table level, air and soil temperature in Sphagnum-dominated peat mesocosms. The presence of Molinia caerulea significantly increased CO2 and CH4 emissions compared to Sphagnum and decreased the DOC concentration. The rise in temperature exponentially increased DOC as well as CO2 and CH4 emissions. Molinia caerulea decreased the temperature sensitivity of CO2 emissions, suggesting the presence of a more labile substrate (root exudates), while it increased the temperature sensitivity of CH4 emissions, suggesting a possible change in methanogenic communities. Our study highlights a strong impact of vegetation change on C dynamics in peatlands.

Peat is commonly known as a biofuel but it also has other more or less traditional uses, for example in folk medicine, building materials, or preservation of foods. Several studies suggest that the main composers of peat lands, Sphagnum mosses, may also have potential for a variety of other value-added products. Typically, those are related to the antibacterial and other preservative properties of Sphagnum, or to their high water adsorption ability. Molecular level applications, however, are still rarely reported. This might owe to the complex chemistry of Sphagnum and lacking cost-efficient technologies for the isolation of components of interest. In this literature survey, the structural and chemical properties of Sphagnum are reviewed together with their suggested uses. This is expected to facilitate new efforts to find commercially feasible applications for these extraordinary plants.

Background and aims Sphagnum mosses are ecosystem engineers that create and maintain boreal peatlands. With unique biochemistry, waterlogging and acidifying capacities, they build up meters-thick layers of peat, reducing competition and impeding decomposition. We quantify within-genus differences in biochemical composition to make inferences about decay rates, related to hummock–hollow and fen–bog gradients and to phylogeny. Methods We sampled litter from 15 Sphagnum species, abundant over the whole northern hemisphere. We used regression and Principal Components Analysis (PCA) to evaluate general relationships between litter quality parameters and decay rates measured under laboratory and field conditions. Results Both concentrations of the polysaccharide sphagnan and the soluble phenolics were positively correlated with intrinsic decay resistance, however, so were the previously understudied lignin-like phenolics. More resistant litter had more of all the important metabolites; consequently, PC1 scores were related to lab mass loss (R2 = 0.57). There was no such relationship with field mass loss, which is also affected by the environment. PCA also revealed that metabolites clearly group Sphagnum sections (subgenera). Conclusions We suggest that the commonly stated growth-decomposition trade-off is largely due to litter quality. We show a strong phylogenetic control on Sphagnum metabolites, but their effects on decay are affected by nutrient availability in the habitat.

Sphagnum mosses mediate long-term carbon accumulation in peatlands. Given their functional role as keystone species, it is important to consider their responses to ecological gradients and environmental changes through the production of phenolics. We compared the extent to which Sphagnum phenolic production was dependent on species, microhabitats and season, and how surrounding dwarf shrubs responded to Sphagnum phenolics. We evaluated the phenolic profiles of aqueous extracts of Sphagnum fallax and Sphagnum magellanicum over a 6-month period in two microhabitats (wet lawns versus dry hummocks) in a French peatland. Phenolic profiles of water-soluble extracts were measured by UHPLC-QTOF-MS. Andromeda polifolia mycorrhizal colonization was quantified by assessing the intensity of global root cortex colonization. Phenolic profiles of both Sphagnum mosses were species-, season- and microhabitat- dependant. Sphagnum-derived acids were the phenolics mostly recovered; relative quantities were 2.5-fold higher in S. fallax than in S. magellanicum. Microtopography and vascular plant cover strongly influenced phenolic profiles, especially for minor metabolites present in low abundance. Higher mycorrhizal colonization of A. polifolia was found in lawns as compared to hummocks. Mycorrhizal abundance, in contrast to environmental parameters, was correlated with production of minor phenolics in S. fallax. Our results highlight the close interaction between mycorrhizae such as those colonizing A. polifolia and the release of Sphagnum phenolic metabolites and suggest that Sphagnum-derived acids and minor phenolics play different roles in this interaction. This work provides new insight into the ecological role of Sphagnum phenolics by proposing a strong association with mycorrhizal colonization of shrubs.

Pristine bogs, peatlands in which vegetation is exclusively fed by rainwater (ombrotrophic), typically have a low atmospheric deposition of reactive nitrogen (N) (Here, we studied the effects of 11 years of experimentally increased deposition (32 versus 8 kg N ha(-1) y(-1)) of either NH4+ or NO3- on N accumulation in three moss and one lichen species (Sphagnum capillifolium, S. papillosum, Pleurozium schreberi and Cladonia portentosa), N-2 fixation rates of their symbionts, and potential N losses to peat soil and atmosphere, in a bog in Scotland.Increased input of both N forms led to 15-90% increase in N content for all moss species, without affecting their cover. The keystone species S. capillifolium showed 4 times higher N allocation into free amino acids, indicating N stress, but only in response to increased NH4+. In contrast, NO3- addition resulted in enhanced peat N mineralization linked to microbial NO(3)(-)reduction, increasing soil pH, N concentrations and N losses via denitrification. Unexpectedly, increased deposition from 8 to 32 kg ha(-1) y(-1) in both N forms did not affect N-2 fixation rates for any of the moss species and corresponded to an additional input of 5 kg N ha(-1) y(-1) with a 100% S. capillifolium cover. Since both N forms clearly show differential effects on living Sphagnum and biogeochemical processes in the underlying peat, N form should be included in the assessment of the effects of N pollution on peatlands. (C) 2017 Elsevier B.V. All rights reserved.

Ethnopharmacological relevance Sphagnum mosses and peat could have been utilized as wound dressings for centuries, however reliable data on this subject are ambiguous; sometimes even no distinction between peat moss (Sphagnum spp.) and peat is made or these terms become confused. The first scientific account on surgical use of peat comes from 1882: a peat digger who successfully, by himself and in the way unknown to the then medicine, cured an open fracture of his forearm with peat. The peat, and very soon the peat moss itself (which is the major constituent of peat) drew attention of the 19th-century surgeons. Aims of the work We search for reliable information on: (1) inspirations for Sphagnum usage for medical purposes and its beginnings in the 19th century, (2) substances or products named sphagnol and their connections with (1); (3) on the origin of this name, (4) and on the occurrence of this name in medical sources. Materials and methods We have identified and studied published sources on the uses of peat-based and Sphagnum-based preparations and products of any processing level (including herbal stock, distillate, isolated pure or impure active principle, or a mixture of such) in surgery, pharmacy or cosmetics. A special attention was paid to the name sphagnol, which appeared many a time, in more than one context since 1899. Source publications were critically analysed from the taxonomical, pharmacognostical and ethnopharmacological points of view. Gathered data were cross-checked with the modern knowledge of the biologically active principles of Sphagnum and the prospects of their medical use. Results The application of peat in surgery started 1882. The use of peat moss as dressings was developed in the 1880's. It returned to surgical practice during WW1. The name sphagnol has two meanings: (1) A chemical substance isolated from the cell walls of Sphagnum mosses in 1899. A post-1950 research showed it to be a mixture of phenols dominated by sphagnum acid. (2) A product of dry distillation of peat contains solid and liquid fractions and was applied in skin diseases due to antiseptic properties. It was added to ointments and medicated soaps manufactured up to the late 1960's. Today none of these two sphagnols is in use. Conclusions Surgical application of peat had an ethnopharmacological origin: a case of wound treatment with peat as a remedy rather than a dressing (1880, published 1882) shortly shifted the surgeons' attention to peat moss as an absorptive dressing. The 1880's tests of antiseptic properties of peat and peat moss failed, the sterilization methods overrode the physiological effects of Sphagnum dressings. Sphagnan, a polysaccharide from Sphagnum cell walls, discovered 1983, inhibits microbial growth, tans the collagen and removes ammonia from microbial environments. Portions of raw peat could be sterile. The isolation of sphagnol (1899) from Sphagnum cell walls was not inspired by old surgery. Main component of sphagnol, the sphagnic acid, was used clinically during WW2, but was proved a weak antimicrobial agent. A homonymous name sphagnol appeared independently for a product of dry distillation of peat, introduced commercially probably about 1899, too, which gave rise to confusions: a) the commercial, “distilled” sphagnol was not the crystalline principle of Sphagnum cell walls. 2) the “distilled” sphagnol was hardly defined technologically or pharmacologically, never standardized in terms of the substrate (a variety of peat rather than Sphagnum herb) and the production process. This sphagnol, resembling pitch or tar, was an additive to medicated soaps and ointments for skin treatment and care. It must have been a low-scale product although advertised worldwide. Neither sphagnum acid nor sphagnan are used medicinally today.

Summary Northern peatlands represent a large global carbon store that can potentially be destabilized by summer water table drawdown. Precipitation can moderate the negative impacts of water table drawdown by rewetting peatmoss (Sphagnum spp.), the ecosystem's key species. Yet, the frequency of such rewetting required for it to be effective remains unknown. We experimentally assessed the importance of precipitation frequency for Sphagnum water supply and carbon uptake during a stepwise decrease in water tables in a growth chamber. CO2 exchange and the water balance were measured for intact cores of three peatmoss species (Sphagnum majus, Sphagnum balticum and Sphagnum fuscum) representative of three hydrologically distinct peatland microhabitats (hollow, lawn and hummock) and expected to differ in their water table–precipitation relationships. Precipitation contributed significantly to peatmoss water supply when the water table was deep, demonstrating the importance of precipitation during drought. The ability to exploit transient resources was species-specific; S. fuscum carbon uptake increased linearly with precipitation frequency for deep water tables, whereas carbon uptake by S. balticum and S. majus was depressed at intermediate precipitation frequencies. Our results highlight an important role for precipitation in carbon uptake by peatmosses. Yet, the potential to moderate the impact of drought is species-specific and dependent on the temporal distribution of precipitation.

Bogs are globally important sinks of atmospheric carbon (C) due to the accumulation of partially decomposed litter that forms peat. Because bogs receive their nutrients from the atmosphere, the world-wide increase of nitrogen (N) deposition is expected to affect litter decomposition and, ultimately, the rate of C accumulation. However, the mechanism of such biogeochemical alteration remains unclear and quantification of the effect of N addition on litter accumulation has yet to be done. Here, we show that 7 similar to years of N addition to a bog decreased the C similar to N ratio, increased the bacterial biomass and stimulated the activity of hydrolytic and oxidative enzymes in surface peat. Furthermore, N addition modified nutrient limitation of microbes during litter decomposition so that phosphorus became a primary limiting nutrient. Alteration of N release from decomposing litter affected bog water chemistry and the competitive balance between peat-forming mosses and vascular plants. We estimate that deposition of about 4 g similar to N similar to m-2 similar to yr-1 will cause a mean annual reduction of fresh litter C accumulation of about 40 similar to g similar to m-2 primarily as a consequence of decreased litter production from peat-forming mosses. Our findings show that N deposition interacts with both above and below ground components of biodiversity to threaten the ability of bogs to act as N-sinks, which may offset the positive effects of N on C accumulation seen in other ecosystems.

High demand for horticultural peat has increased peatland drainage and peat extraction in Canada. The hydrology and carbon cycling of these cutover peatlands is greatly altered, necessitating active restoration efforts to permit the regeneration of Sphagnum mosses and the re-establishment of natural peatland function. The effect of peatland extraction and restoration on the export of dissolved organic carbon (DOC) was examined for three successive seasons (May to October, 1999 to 2001) at two different sites (cutover and restored) in eastern Quebec. A shift towards higher DOC concentrations was observed following peatland extraction (maximum: 182·6 mg L−1) and concentrations remained high post-restoration (maximum: 191·0 mg L−1). The cutover site exported more DOC than the restored site in all three study seasons. The highest exports occurred during the wettest year (1999), with cutover and restored site export of 10·3 and 4·8 g m−2, respectively. In 2000, 8·5 g C m−2 was released from the cutover site, while the restored site released less than half that amount (3·4 g C m−2). In 2001, the restored site released about the same amount of DOC as in the previous year (3·5 g C m−2), while the cutover site load dropped to 6·2 g C m−2. Both sites were net exporters of DOC in all years. Copyright © 2007 John Wiley & Sons, Ltd.

Despite their low primary production, ombrotrophic peatlands have a considerable potential to store atmospheric carbon as a result of their extremely low litter decomposition rates. Projected changes in temperature and nitrogen (N) deposition may increase decomposition rates by their positive effects on microbial activity and litter quality, which can be expected to result in enhanced mass loss and N release from Sphagnum and vascular plant litter. This is the first study that examines the combined effects of increased temperature and N deposition on decomposition in bogs. We investigated mass loss and N release at four bog sites along a gradient from north Sweden to northeast Germany in which both temperature and N deposition increased from north to south. We performed two litterbag experiments: one reciprocal experiment with Eriophorum vaginatum litter and one experiment using recalcitrant (Sphagnum fuscum) and more degradable (Sphagnum balticum) Sphagnum litter collected from the most northern site. We measured mass loss and N release during two (Sphagnum) and three (E. vaginatum) years. The N concentration and decomposability of the E. vaginatum litter did not differ between the sites. Mass loss from E. vaginatum litter increased over the gradient from north to south, but there was no such effect on Sphagnum litter. N loss of all litter types was affected by collection site, incubation site and time and all interactions between these factors. N release in Sphagnum was positively related to N concentration. We conclude that decomposition of vascular plants and Sphagnum litter is influenced by different environmental drivers, with enhanced temperatures stimulating mass loss of vascular plant litter, but not of Sphagnum. Enhanced N deposition increases Sphagnum litter N loss. As long-term consequences of climate change will presumably entail a higher vascular plant production, overall litter decomposition rates are likely to increase, especially in combination with increased temperature.

Boreal peatlands store large amounts of carbon, reflecting their important role in the global carbon cycle. The short-term exchange and the long-term storage of atmospheric carbon dioxide (CO2 ) in these ecosystems are closely associated with the permanently wet surface conditions and are susceptible to drought. Especially, the single most important peat forming plant genus, Sphagnum, depends heavily on surface wetness for its primary production. Changes in rainfall patterns are expected to affect surface wetness, but how this transient rewetting affects net ecosystem exchange of CO2 (NEE) remains unknown. This study explores how the timing and characteristics of rain events during photosynthetic active periods, that is daytime, affect peatland NEE and whether rain event associated changes in environmental conditions modify this response (e.g. water table, radiation, vapour pressure deficit, temperature). We analysed an 11-year time series of half-hourly eddy covariance and meteorological measurements from Degerö Stormyr, a boreal peatland in northern Sweden. Our results show that daytime rain events systematically decreased the sink strength of peatlands for atmospheric CO2 . The decrease was best explained by rain associated reduction in light, rather than by rain characteristics or drought length. An average daytime growing season rain event reduced net ecosystem CO2 uptake by 0.23-0.54 gC m(-2) . On an annual basis, this reduction of net CO2 uptake corresponds to 24% of the annual net CO2 uptake (NEE) of the study site, equivalent to a 4.4% reduction of gross primary production (GPP) during the growing season. We conclude that reduced light availability associated with rain events is more important in explaining the NEE response to rain events than rain characteristics and changes in water availability. This suggests that peatland CO2 uptake is highly sensitive to changes in cloud cover formation and to altered rainfall regimes, a process hitherto largely ignored.

Sphagnum mosses have been observed for the first time in the Alpes-de-Haute-Provence French department. The four species discovered are confined to Annot sandstone siliceous bedrock formations scattered amongst dominating calcareous bedrock in the area. Both Sphagnum nemoreum and Sphagnum teres are quite frequent in the French Alps while Sphagnum flexuosum and Sphagnum angustifolium on the contrary are rare peat mosses in this chain. Local edaphic and climatic conditions might be responsible for the reduced number of sites discovered. All Sphagnum sites are briefly described. One of them a true peatland is of particular interest and deserves protection.

During the last two years the Urbino University and the Padua ICTIMA CNR collaborated on a special radioecological program having the aim to study the Pu and Am retention behaviour in Sphagnum peat in the Alps region (northern Italy). 239,240 Pu, 238 Pu and 241 Am were separated and determined by extraction chromatography, electroplating and alpha spectrometry; 242 Pu and 243 Am were used as the yield tracers. The paper summarizes the results dealing with the vertical profiles of the radionuclides in Sphagnum compactum and S. nemoreum . Several 1–2 cm high sections were obtained and dated by 210 Pb determination. Typical concentration peaks for Pu and Am were found at a depth corresponding to the early 1960s which is the period characterized by the maximum nuclear weapon tests.

Moss-dominated peat bogs store approximately 30% of global soil carbon. A climate induced-shift from current moss-dominated conditions to tree-dominated states is expected to strongly affect their functioning and carbon sequestration capacity. Consequently, unravelling the mechanisms that may explain successful tree seedling establishment in these ecosystems is highly relevant. To assess the role of drought on early tree seedling establishment and the relative importance of plant traits in tree seedling survival, we conducted a factorial glasshouse experiment with seven conifer species. Our results show that drought inhibits moss growth, thereby increasing survival of tree seedlings. Survival success was higher in Pinus than in Picea species, ranking Pinus banksiana > Pinus sylvestris > Pinus nigra > Picea mariana > Picea glauca, Picea sitchensis > Picea rubens. We found that those species most successful under dry and wet conditions combined a fast shoot growth with high seed mass. We conclude that plant traits contribute to explaining successful early tree seedling establishment in bogs. © 2013 The Authors. Functional Ecology © 2013 British Ecological Society.

Raised bogs have accumulated more atmospheric carbon than any other terrestrial ecosystem on Earth. Climate-induced expansion of trees and shrubs may turn these ecosystems from net carbon sinks into sources when associated with reduced water tables. Increasing water loss through tree evapotranspiration could potentially deepen water tables, thus stimulating peat decomposition and carbon release. Bridging the gap between modelling and field studies, we conducted a three-year mesocosm experiment subjecting natural bog vegetation to three birch tree densities, and studied the changes in subsurface temperature, water balance components, leaf area index and vegetation composition. We found the deepest water table in mesocosms with low tree density. Mesocosms with high tree density remained wettest (i.e. highest water tables) whereas the control treatment without trees had intermediate water tables. These differences are attributed mostly to differences in evapotranspiration. Although our mesocosm results cannot be directly scaled up to ecosystem level, the systematic effect of tree density suggests that as bogs become colonized by trees, the effect of trees on ecosystem water loss changes with time, with tree transpiration effects of drying becoming increasingly offset by shading effects during the later phases of tree encroachment. These density-dependent effects of trees on water loss have important implications for the structure and functioning of peatbogs.

• Peat bogs have accumulated more atmospheric carbon (C) than any other terrestrial ecosystem today. Most of this C is associated with peat moss (Sphagnum) litter. Atmospheric nitrogen (N) deposition can decrease Sphagnum production, compromising the C sequestration capacity of peat bogs. The mechanisms underlying the reduced production are uncertain, necessitating multifactorial experiments. • We investigated whether glasshouse experiments are reliable proxies for field experiments for assessing interactions between N deposition and environment as controls on Sphagnum N concentration and production. We performed a meta-analysis over 115 glasshouse experiments and 107 field experiments. • We found that glasshouse and field experiments gave similar qualitative and quantitative estimates of changes in Sphagnum N concentration in response to N application. However, glasshouse-based estimates of changes in production - even qualitative assessments - diverged from field experiments owing to a stronger N effect on production response in absence of vascular plants in the glasshouse, and a weaker N effect on production response in presence of vascular plants compared to field experiments. • Thus, although we need glasshouse experiments to study how interacting environmental factors affect the response of Sphagnum to increased N deposition, we need field experiments to properly quantify these effects. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.

A large proportion of northern peatlands consists of Sphagnum-dominated ombrotrophic bogs. In these bogs, peat mosses (Sphagnum) and vascular plants occur in an apparent stable equilibrium, thereby sustaining the carbon sink function of the bog ecosystem. How global warming and increased nitrogen (N) deposition will affect the species composition in bog vegetation is still unclear. We performed a transplantation experiment in which mesocosms with intact vegetation were transplanted southward from north Sweden to north-east Germany along a transect of four bog sites, in which both temperature and N deposition increased. In addition, we monitored undisturbed vegetation in control plots at the four sites of the latitudinal gradient. Four growing seasons after transplantation, ericaceous dwarf shrubs had become much more abundant when transplanted to the warmest site which also had highest N deposition. As a result ericoid aboveground biomass in the transplanted mesocosms increased most at the southernmost site, this site also had highest ericoid biomass in the undisturbed vegetation. The two dominant Sphagnum species showed opposing responses when transplanted southward; Sphagnum balticum height increment decreased, whereas S. fuscum height increment increased when transplanted southward. Sphagnum production did not differ significantly among the transplanted mesocosms, but was lowest in the southernmost control plots. The dwarf shrub expansion and increased N concentrations in plant tissues we observed, point in the direction of a positive feedback toward vascular plant-dominance suppressing peat-forming Sphagnum in the long term. However, our data also indicate that precipitation and phosphorus availability influence the competitive balance between Sphagnum, dwarf shrubs and graminoids.

Climate change can be expected to increase the frequency of summer droughts and associated low water tables in ombrotrophic peatlands. We studied the effects of periodic water table drawdown in a mesocosm experiment. Mesocosms were collected in Southern Sweden, and subsequently brought to an experimental field in the Netherlands. Two water table treatments were applied: one with constant water tables at 5 cm below the moss surface, and one in which the water table was allowed to drop, resulting in water tables fluctuating between 5 and 21 cm below the moss surface. Sphagnum growth, as well as Sphagnum and vascular plant abundance, were assessed for 2 1 2 years. Our results show that the abundance of graminoid species increased most in the constant water table treatment. In contrast, ericoid species cover increased when water tables were allowed to fluctuate. Furthermore, Sphagnum cuspidatum production decreased with fluctuating summer water tables, while Sphagnum magellanicum responded oppositely. From these results we conclude that increased occurrence of periods with low water tables may bring about a shift in dominant Sphagnum species as well as a shift from graminoid to ericoid vascular plant cover, resembling the shift from hollow to lawn or hummock vegetation. The difference in response within functional groups (vascular plants, Sphagnum) may add to the resilience of the ecosystem.

Titanium concentrations and Ti inventories (total Ti in the sample) in living Sphagnum mosses from the surfaces of eight ombrotrophic peat bogs of five different regions of Germany and Belgium were studied over a period of two years (1995–7). Six to ten peat moss samples with a given surface area (100 cm2) and length (5 cm) were collected at different sites in the peat bogs studied several times (every six weeks to three months) during a year. Variability of Ti concentrations and inventories were determined within each peat bog for the species S. magellanicum, S. rubellum, S. papillosum, and S. cuspidatum, for the microhabitats 'lawn', 'slope' and 'hollow', as well as for the studied peat bogs of different regions and for each season. Likewise, Ti concentration values were determined for the moss plant segments: ‘capitulum’, ‘living green’ and ‘dead brown’. Ti concentrations and inventories were found to be highly variable, even in one species of the same peat bog and at the same time. Moreover, median Ti concentrations and inventories of different species and microhabitats were quite similar to one another. As a result, we suggest that more productive species might be able to accumulate more Ti onto their bigger surface areas than the less productive ones. Besides, Ti particles might be transported downwards with the water and accumulated by the mosses over a longer time period than only one year. To reliably specify the variations in the geochemistry of peat mosses on the peat bog surface the annual production of each collected Sphagnum sample has to be exactly known and samples of equal ages and time periods they were exposed to atmospheric deposition have to be studied.

The normal processes of decomposition start soon after death and, under normal circumstances, it may be only a matter of days before a human body loses recognisable form. However, in a few instances human bodies have retained a recognisable appearance for hundreds, or even thousands, of years by preservation due to natural circumstances. Rapid desiccation produced by burial in dry sand produces preservation by reducing the water content of the body below a point where microorganisms will thrive. Alternatively, the presence of large quantities of salts, e.g. the use of natron by the ancient Egyptians, can produce preservation (1). Extreme cold can halt the deterioration of animal flesh is well known from our domestic freezers, but as soon as temperatures return to normal, biodeterioration sets in. However, natural freeze-drying can occur to bodies in cold regions when water vapour from ice in bodies is removed by sublimation into cold air currents resulting in preservation by desiccation. The majority of examples of body preservation in northern Europe occur due to accidental or intentional burial in peat bogs. Skin and hair are often preserved but internal organs less frequently. There are over 120 recorded sites where human remains have been discovered in bogs in Great Britain and Ireland (1). The conditions are often quoted to be anaerobic, acidic and wet, and until recently these conditions were considered to be those necessary for the preservation of skin. However, Painter (2) suggests that bodies are preserved in sphagnum peat bogs because they are tanned by spagnan, a pectin-like polysaccharide from the cell walls of sphagnum mosses. Additionally, sphagnan aids preservation by reacting with the digestive enzymes secreted by putrefactive bacteria and immobilising them on the surface of the peat.

Sphagnum fuscum decreased initially in the hollows but recovered and showed a highly variable result after a decade, with an increase in area in many cases. It was not extinguished by the hollow species in any one case. These long-term results do not support the hypothesis that it is excluded from the hollows by competition, but the treatments did not include the wettest parts of the hollows. Among the hollow species S. balticum seemed to have a competitive advantage, but the trend was reversed in one year when S. tenellum regained area. This result stresses the importance of long-term experiments. There were also other instances when the conclusions drawn from the long-term monitoring differed from those reached after 4-5 years. The results suggest that these closely related species were on average rather similar in competitive ability in the hollows, but results varied considerably between nominal replicates. Competition also varied seasonally: S. balticum often lost area to S. fuscum and won area from S. tenellum in the autumn, with a compensation for these changes earlier in the summer. Variation in water level within habitat could not be shown to affect the outcome of competition between species.

Peatlands are important sinks for atmospheric carbon (C), yet the role of plant functional types (PFTs) for C sequestration under climatic perturbations is still unclear. A plant-removal experiment was used to study the importance of vascular PFTs for the net ecosystem CO2 exchange (NEE) during (i.e., resistance) and after (i.e., recovery) an experimental drought. The removal of PFTs caused a decrease of NEE, but the rate differed between microhabitats (i.e., hummocks and lawns) and the type of PFTs. Ericoid removal had a large effect on NEE in hummocks, while the graminoids played a major role in the lawns. The removal of PFTs did not affect the resistance or the recovery after the experimental drought. We argue that the response of Sphagnum mosses (the only PFT present in all treatments) to drought is dominant over that of coexisting PFTs. However, we observed that the moment in time when the system switched from C sink to C source during the drought was controlled by the vascular PFTs. In the light of climate change, the shifts in species composition or even the loss of certain PFTs are expected to strongly affect the future C dynamics in response to environmental stress.