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Nitrogen (N) isotope systematics were investigated at two high-elevation ombrotrophic peat bogs polluted by farming and heavy industry. Our objective was to identify N sources and sinks for isotope mass balance considerations. For the first time, we present a time-series of delta super(15)I values of atmospheric input at the same locations as delta super(15)I values of living Sphagnum and peat. The mean delta super(15)I values systematically increased in the order: input NH sub(4) super(+) (-10.0ppt) < input NO sub(3) super(-) (-7.9ppt) < peat porewater (-5.6ppt) < Sphagnum (-5.0ppt) < shallow peat (-4.2ppt) < deep peat (-2.2ppt) < runoff (-1.4ppt) < porewater N sub(2)O (1.4ppt). Surprisingly, N of Sphagnum was isotopically heavier than N of the atmospheric input (P < 0.001). If partial incorporation of reactive N from the atmosphere into Sphagnum was isotopically selective, the residual N would have to be isotopically extremely light. Such N, however, was not identified anywhere in the ecosystem. Alternatively, Sphagnum may have contained an admixture of isotopically heavier N. Ambient air contains such N in the form of N sub(2) ( delta super(15)I sub(N2) = 0ppt). Because high energy is required to break the triple bond, microbial N fixation is likely to proceed only under limited availability of pollutant N. Also for the first time, a delta super(15)I comparison is presented between anoxic deeper peat and porewater N sub(2)O. Isotopically light N is removed from anoxic substrate by denitrification, whose final product, N sub(2), escapes into the atmosphere. Porewater N sub(2)O is an isotopically heavy residuum following partial N sub(2)O reduction to N sub(2).

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 CO sub(2) 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.

Questions Does the facilitation of herbaceous species seedling establishment by tussock-forming species collapse in an extreme drought year? Do different germination phenologies, between the seedling species, influence the variation in facilitation? Location A post-mined S phagnum peatland at S arobetsu mire, H okkaido, northern J apan. Methods The effects of tussock-forming species, as potential facilitators, on seedling emergence and survival of five perennial herbs were examined during a 4-yr seedling monitoring, which included an extreme drought. The general effects of tussocks on each seedling species during annual variations were simultaneously assessed using hierarchical Bayesian analysis. To examine the stress limiting seedling establishment, which was ameliorated by the tussocks, micro-environments (i.e. light, temperature, water content and erosion) altered by morphological traits of the tussocks with litter cover were compared to those in open areas. Results In general, tussocks facilitated seedling establishment of all species through a positive effect on emergence and no effect on survival; however, the facilitative effect declined for several species in an extreme drought year. Peat erosion was the limiting stress on seedling establishment in normal years, however, peat water content also limited seedling establishment in a drought year. During the drought year, the positive effect of tussocks on seedling emergence for species that germinated before or during the drought was weakened for one species, and a negative effect on seedling survival emerged in another species. In contrast, species that germinated after the drought did not exhibit annual variation in the effects of tussocks on seedling emergence and survival. Conclusions Our results illustrate that collapse of facilitation arises under extremely severe conditions through addition of infrequently occurring stress (drought) on frequently occurring stress (peat erosion). Variation in seedling emergence and survival of the five study species in response to severe drought suggests that species-specific traits must be considered when assessing how facilitation varies temporally. Further, these findings suggest that facilitation in temporally varying environments can drive plant community composition and dynamics. We tested the facilitation effect of tussock-forming species on seedling establishment of perennial herbaceous species in a post-mined Sphagnum peatland. Our results showed that the facilitation effect collapsed in an extreme drought year and its effect varied among seedling species having different germination phenologies. These suggest that variation in facilitation effects by early colonizers can drive plant community composition.

The spatial and temporal variability of net ecosystem exchange (NEE) of CO sub(2) and evapotranspiration (ET) of a karst-hole sphagnum peat mire situated at the boundary between broad-leaved and forest-steppe zones in the central part of European Russia in the Tula region was described using results from field measurements. NEE and ET were measured using a portable measuring system consisting of a transparent ventilated chamber combined with an infrared CO sub(2)/H sub(2)O analyzer, LI-840A (Li-Cor, USA) along a transect from the southern peripheral part of the mire to its center under sunny clear-sky weather conditions in the period from May to September of 2012 and in May 2013. The results of the field measurements showed significant spatial and temporal variability of NEE and ET that was mainly influenced by incoming solar radiation and ground water level. The seasonal patterns of NEE and ET within the mire were quite different. During the entire growing season the central part of the mire was a sink of CO sub(2) for the atmosphere. NEE reached maximal values in June-July (-6.8 + or - 4.2 mu mol m super(-2) s super(-1)). The southern peripheral part of the mire, due to strong shading by the surrounding forest, was a sink of CO sub(2) for the atmosphere in June-July only. ET reached maximal values in the well-lighted central parts of the mire in May (0.34 + or - 0.20 mm h super(-1)) mainly because of high air and surface temperatures and the very wet upper peat horizon and sphagnum moss. Herbaceous species made the maximum contribution to the total gross primary production (GPP) in both the central and the peripheral parts of the mire. The contribution of sphagnum to the total GPP of these plant communities was relatively small and ranged on sunny days of July-August from -1.1 + or - 1.1 mgC g super(-1) of dry weight (DW) per hour in the peripheral zone of the mire to -0.6 + or - 0.2 mgC g super(-1) DW h super(-1) at the mire center. The sphagnum layer made the maximum contribution to total ET at the mire center (0.25 + or - 0.10 mm h super(-1)) and the herbaceous species on the peripheral part of the mire (0.03 + or - 0.03 mm h super(-1)).

Sphagnum mosses are keystone components of peatland ecosystems. They facilitate the accumulation of carbon in peat deposits, but climate change is predicted to expose peatland ecosystem to sustained and unprecedented warming leading to a significant release of carbon to the atmosphere. Sphagnum responses to climate change, and their interaction with other components of the ecosystem, will determine the future trajectory of carbon fluxes in peatlands. We measured the growth and productivity of Sphagnum in an ombrotrophic bog in northern Minnesota, where ten 12.8‐m‐diameter plots were exposed to a range of whole‐ecosystem (air and soil) warming treatments (+0 to +9°C) in ambient or elevated (+500 ppm) CO2. The experiment is unique in its spatial and temporal scale, a focus on response surface analysis encompassing the range of elevated temperature predicted to occur this century, and consideration of an effect of co‐occurring CO2 altering the temperature response surface. In the second year of warming, dry matter increment of Sphagnum increased with modest warming to a maximum at 5°C above ambient and decreased with additional warming. Sphagnum cover declined from close to 100% of the ground area to <50% in the warmest enclosures. After three years of warming, annual Sphagnum productivity declined linearly with increasing temperature (13–29 g C/m2 per °C warming) due to widespread desiccation and loss of Sphagnum. Productivity was less in elevated CO2 enclosures, which we attribute to increased shading by shrubs. Sphagnum desiccation and growth responses were associated with the effects of warming on hydrology. The rapid decline of the Sphagnum community with sustained warming, which appears to be irreversible, can be expected to have many follow‐on consequences to the structure and function of this and similar ecosystems, with significant feedbacks to the global carbon cycle and climate change. The responses of Sphagnum to climate change are critical to the future trajectory of peatland ecosystems and their important role in the global carbon cycle. We test three hypotheses related to the response of Sphagnum growth and community composition to experimental warming and CO2 enrichment. The decline of the Sphagnum community with sustained warming that we document can be expected to have many follow‐on consequences to the structure and function of this and similar ecosystems, with significant feedbacks to the global carbon cycle and climate change.

Anthropogenic nitrogen (N) loading has the potential to affect plant community structure and function, and the carbon dioxide (CO sub(2)) sink of peatlands. Our aim is to study how vegetation changes, induced by nutrient input, affect the CO sub(2) exchange of a nutrient-limited bog. We conducted 9- and 4-year fertilization experiments at Mer Bleue bog, where we applied N addition levels of 1.6, 3.2, and 6.4gNm super(-2) super(-1), upon a background deposition of about 0.8gNm super(-2)a super(-1), with or without phosphorus and potassium (PK). Only the treatments 3.2 and 6.4gNm super(-2)a super(-1) with PK significantly affected CO sub(2) fluxes. These treatments shifted the Sphagnum moss and dwarf shrub community to taller dwarf shrub thickets without moss, and the CO sub(2) responses depended on the phase of vegetation transition. Overall, compared to the large observed changes in the vegetation, the changes in CO sub(2) fluxes were small. Following Sphagnum loss after 5years, maximum ecosystem photosynthesis (Pg sub(max)) and net CO sub(2) exchange (NEE sub(max)) were lowered (-19 and -46%, respectively) in the highest NPK treatment. In the following years, while shrub height increased, the vascular foliar biomass did not fully compensate for the loss of moss biomass; yet, by year 8 there were no significant differences in Pg sub(max) and NEE sub(max) between the nutrient and the control treatments. At the same time, an increase (24-32%) in ecosystem respiration (ER) became evident. Trends in the N-only experiment resembled those in the older NPK experiment by the fourth year. The increasing ER with increasing vascular plant and decreasing Sphagnum moss biomass across the experimental plots suggest that high N deposition may lessen the CO sub(2) sink of a bog.

Experimental warming of an ombrotrophic bog in northern Minnesota has caused a rapid decline in the productivity and areal cover of Sphagnum mosses, affecting whole‐ecosystem carbon balance and biogeochemistry. Direct effects of elevated temperature and the attendant drying are most likely the primary cause of the effects on Sphagnum, but there may also be responses to the increased shading from shrubs, which increased with increasing temperature. To evaluate the independent effects of reduction in light availability and deposition of shrub litter on Sphagnum productivity, small plots with shrubs removed were laid out adjacent to the warming experiment on hummocks and hollows in three blocks and with five levels of shading. Four plots were covered with neutral density shade cloth to simulate shading from shrubs of 30%–90% reduction in light; one plot was left open. Growth of Sphagnum angustifolium/fallax and S. divinum declined linearly with increasing shade in hollows, but there was no response to shade on hummocks, where higher irradiance in the open plots may have been inhibitory. Shading caused etiolation of Sphagnum—they were thin and spindly under the deepest shade. A dense mat of shrub litter, corresponding to the amount of shrub litter produced in response to warming, did not inhibit Sphagnum growth or cause increases in potentially toxic base cations. CO2 exchange and chlorophyll‐a fluorescence of S. angustifolium/fallax from the 30% and 90% shade cloth plots were measured in the laboratory. Light response curves indicate that maximal light saturated photosynthesis was 42% greater for S. angustifolium/fallax grown under 30% shade cloth relative to plants grown under 90% shade cloth. The response of Sphagnum growth in response to increasing shade is consistent with the hypothesis that increased shade resulting from shrub expansion in response to experimental warming contributed to reduced Sphagnum growth. Sphagnum was maintained under shade cloth of different densities to simulate the effect of shading from shrubs in SPRUCE enclosures. Sphagnum production declined with increasing shade, supporting the hypothesis that Sphagnum decline in response to warming was due in part to increased shade from shrubs.

• Sphagnum farming can substitute peat with renewable biomass and thus help mitigate climate change. Large volumes of the required founder material can only be supplied sustainably by axenic cultivation in bioreactors. • We established axenic in vitro cultures from sporophytes of 19 Sphagnum species collected in Austria, Germany, Latvia, the Netherlands, Russia, and Sweden: S. angustifolium, S. balticum, S. capillifolium, S. centrale, S. compactum, S. cuspidatum, S. fallax, S. fimbriatum, S. fuscum, S. lindbergii, S. medium/divinum, S. palustre, S. papillosum, S. rubellum, S. russowii, S. squarrosum, S. subnitens, S. subfulvum and S.warnstorfii. These species cover five of the six European Sphagnum subgenera; namely, Acutifolia, Cuspidata, Rigida, Sphagnum and Squarrosa. • Their growth was measured in suspension cultures, whereas their ploidy was determined by flow cytometry and compared with the genome size of Physcomitrella patens. We identified haploid and diploid Sphagnum species, found that their cells are predominantly arrested in the G1 phase of the cell cycle, and did not find a correlation between plant productivity and ploidy. DNA barcoding was achieved by sequencing introns of the BRK1 genes. • With this collection, high-quality founder material for diverse large-scale applications, but also for basic Sphagnum research, is available from the International Moss Stock Center.

Although recent studies have recognized Northern Eurasian ecosystems as an important carbon reservoir, little is known about the forest--peatland interactions in a boreal environment induced by ongoing climatic changes. This study focuses on the evaluation of both the long-term and contemporary trends of land-cover changes and rates of lateral extension of peat-accumulating wetlands toward the adjacent forests, estimated at the southern climatic range of the Sphagnum-dominated mires in Western Siberia. We used the radiocarbon dates and stratigraphy of peat sediments from seven peat cores, analyzed at two types of forest--peatland ecotones, which are located close to each other but differ by topography and composition of their plant communities. The rate of lateral extension was found in a wide range varying from 2.3 to 791.7 cm yr-1. It was observed to be rapid during the initial stage of mire development, but to have slowed down over the last 2000--3000 yr. Our results, therefore, strongly contradict the concept of progressive peat accumulation throughout the late Holocene and contribute to our knowledge about ongoing land-cover change in the natural ecosystems of the Northern hemisphere.

Field‐scale experiments have shown the Natural Flood Management (NFM) potential of peatland restoration. The likelihoods of effectiveness are yet unknown at scales and storms large enough to impact human lives. Using GMD‐TOPMODEL, we upscale a rare Before‐After‐Control‐Intervention empirical data set to a 25 km2 catchment with >600 properties at flood‐risk, and test storms of up to a 1,000‐year return period (RP). Under these scales/storms, we find that it is not necessary (nor feasible) to delay the outlet flow‐peak to meaningfully attenuate it. Enhancing catchment “kinematic” storage, for example, through restoration, can be sufficient to reduce flow magnitudes without detectable changes to peak‐flow timing. NFM benefit increases exponentially with restoration area size under smaller storms, but linearly under larger storms. At RP ≤ 100 years, longer‐lasting frontal‐type storms are more challenging to defend against via NFM, but at RP > 100 years shorter‐duration convectional‐type events become more challenging. In the order of 1,000–10 years storms: (a) revegetating the bare‐peat areas in 15% of the catchment is 31%–61% likely to reduce peak‐flows by >5%; (b) revegetating & damming the erosion gullies in ∼20% of the catchment is 42%–71% likely to reduce peak‐flows by >5%; (c) Growth of Sphagnum in the dammed gullies of ∼20% and ∼40% of the catchment increase the likelihoods of >5% peak reductions to 65%–86% and 90%–98%, respectively. The numerical evidence of significant NFM benefit due to Sphagnum re‐establishment is an important finding, because it shows that meaningful flood‐risk mitigation in headwater catchments under scales/storms relevant to communities at risk can be delivered alongside other ecosystem benefits of Sphagnum re‐establishment. Key Points At catchment scale, it is not necessary (nor feasible) to delay the flood‐wave to meaningfully attenuate it at the outlet Deferring only a portion of the flood volume to the receding limb can be sufficient for meaningful flood risk mitigation at catchment scale Through Sphagnum re‐establishment, significant Natural Flood Management + ecosystem benefits can be delivered at scales/storms relevant to communities at risk