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Climate warming and projected increase in summer droughts puts northern peatlands under pressure by subjecting them to a combination of gradual drying and extreme weather events. The combined effect of those on peatland functions is poorly known. Here, we studied the impact of long‐term water level drawdown (WLD) and contrasting weather conditions on leaf phenology and biomass production of ground level vegetation in boreal peatlands. Data were collected during two contrasting growing seasons from a WLD experiment including a rich and a poor fen and an ombrotrophic bog. Results showed that WLD had a strong effect on both leaf area development and biomass production, and these responses differed between peatland types. In the poor fen and the bog, WLD increased plant growth, while in the rich fen, WLD reduced the growth of ground level vegetation. Plant groups differed in their response, as WLD reduced the growth of graminoids, while shrubs and tree seedlings benefited from it. In addition, the vegetation adjusted to the lower WTs, was more responsive to short‐term climatic variations. The warmer summer resulted in a greater maximum and earlier peaking of leaf area index, and greater biomass production by vascular plants and Sphagnum mosses at WLD sites. In particular, graminoids benefitted from the warmer conditions. The change towards greater production in the WLD sites in general and during the warmer weather in particular, was related to the observed transition in plant functional type composition towards arboreal vegetation. [ABSTRACT FROM AUTHOR]

Aim: Boreal peatlands are very sensitive to nitrogen (N) enrichment due to the low soil N availability. Our aim was to reveal how increased N availability altered plant composition in boreal permafrost peatlands with dense vascular plants (>50%). Location: Greater Khingan Mountains, Northeast China. Methods: A nitrogen addition experiment with four N addition levels (0, 3, 6, and 12 g N m-2 year-1) was conducted in a poor fen in the continuous permafrost zone with vascular plant coverage above 60%. Plant diversity, community composition, and above-ground biomass were investigated after four, six, and eight years of N addition. Results: Nitrogen addition decreased species richness and diversity but enhanced total above-ground biomass. Plant height determined the plants' responses to N addition, and the magnitudes increased with N addition level and experimental duration. The relative coverage of high-stature (>50 cm) species increased, but the relative coverage of low-stature (<50 cm) species decreased with elevating N addition levels. When N addition proceeded, the relative coverage and above-ground biomass of tall deciduous shrubs and nitrophilous grasses increased, whereas the relative coverage and above-ground biomass of dwarf evergreen shrubs, mosses, and lichens declined. Regardless of N addition levels, cryptogams (i.e., mosses and lichens) and a dwarf evergreen shrub (Chamaedaphne calyculata) disappeared after eight-year N addition. Conclusions: Cryptogams and dwarf evergreen shrubs are highly vulnerable to increased N availability, and N enrichment-induced biodiversity loss, especially the disappearance of cryptogams, will deteriorate ecosystem structure and function in boreal permafrost peatlands. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Questions: Climate warming has been demonstrated to shift peatland plant community composition from Sphagnum mosses to vascular plants in Sphagnum‐dominated peatlands. However, fewer studies have determined how increasing temperature affects vegetation patterns in Carex‐dominated peatlands. As plants are important determinants of carbon storage potential in peatlands, we aim to determine how climate warming alters plant community composition in peatlands of two different vegetation types. Location: Boreal peatlands in north–central Ontario, Canada. Methods: In a Sphagnum‐ and a Carex‐dominated peatland over two growing seasons, we instigated passive warming using clear open‐topped chambers, providing a modest increase (1–2°C) in temperature. In replicated plots we examined shifts in plant community composition using the point intercept method, and total above‐ground biomass using Leaf Area Index (LAI) against non‐warmed control plots. Results: While there was no difference in species diversity between control and warmed plots in either fen site, warming significantly increased above‐ground biomass in the Carex‐dominated fen and decreased moss abundance in the Sphagnum‐dominated fen. Both fens also displayed significantly different plant community composition between warming and control plots, and increased heterogeneity under warming. Conclusion: Peatlands are important global carbon stores and the plant community contributes to their carbon storage; Sphagnum mosses, in particular, are linked to high peatland carbon storage potential. Previous studies in Sphagnum‐dominated peatlands have shown concomitant declines in Sphagnum biomass and increases in vascular plant biomass, and in the short term, we show only a decline in Sphagnum. At both sites the increase in plant community heterogeneity suggests that climate warming effects on plant community composition in boreal peatlands may be more unpredictable than the literature suggests. Furthermore, this study demonstrates that plant community shifts occur even under modest warming scenarios. [ABSTRACT FROM AUTHOR]

Peatland ecosystems are globally important carbon and terrestrial surface water stores that have formed over millennia. These ecosystems have likely optimized their ecohydrological function over the long-term development of their soil hydraulic properties. The optimization of peat hydraulic properties is examined to determine which of the following conditions peatland ecosystems target during this development: (i) maximize carbon accumulation, (ii) maximize water storage, or (iii) balance carbon profit across hydrological disturbances. To identify this control, the short-term hydrological response of a 0.5-m-deep peat profile was simulated during a 50-day rain-free period. A total of 5000 Monte-Carlo model realizations were conducted, with peat hydraulic properties differing between each realization (values derived from known probability distributions). Saturated hydraulic conductivity ( Ks) and empirical van Genuchten water retention parameter α were shown to provide a first order control on simulated water tensions. For hypothetical combinations of Ks and α, the probability that water tension exceeds the ecologically important threshold of 100 mb within 24 h showed a bimodal distribution. A peak at high probabilities was associated with profiles of high Ks and low α. Such a profile is optimized for water storage. A peak at low probabilities is associated with low Ks, high α, and is optimized for carbon accumulation. Actual hydraulic properties from five northern peatlands fall between this binominal distribution, balancing the competing demands of carbon accumulation and water storage. We argue that peat hydraulic properties are thus optimized to maximize water use efficiency and that this optimization occurs over a centennial to millennial timescale. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Bog ecosystems fulfil important functions in Earth's carbon and water turnover. While plant communities and their keystone species Sphagnum have been well studied, less is known about the microbial communities associated with them. To study our hypothesis that bog plants share an essential core of their microbiome despite their different phylogenetic origins, we analysed four plant community plots with 24 bryophytes, vascular plants and lichen species in two Alpine bogs in Austria by 16S rDNA amplicon sequencing followed by bioinformatic analyses. The overall bog microbiome was classified into 32 microbial phyla, while Proteobacteria (30.8%), Verrucomicrobia (20.3%) and Planctomycetes (15.1%) belonged to the most abundant groups. Interestingly, the archaeal phylum Euryarcheota represented 7.2% of total microbial abundance. However, a high portion of micro-organisms remained unassigned at phylum and class level, respectively. The core microbiome of the bog vegetation contained 177 operational taxonomic units ( OTUs) (150 526 seq.) and contributed to 49.5% of the total microbial abundance. Only a minor portion of associated core micro-organisms was host specific for examined plant groups (5.9-11.6%). Using our new approach to analyse plant-microbial communities in an integral framework of ecosystem, vegetation and microbiome, we demonstrated that bog vegetation harboured a core microbiome that is shared between plants and lichens over the whole ecosystem and formed a transkingdom metacommunity. All micro- and macro-organisms are connected to keystone Sphagnum mosses via set of microbial species, for example Burkholderia bryophila which was found associated with a wide spectrum of host plants and is known for a beneficial plant-microbe interaction. [ABSTRACT FROM AUTHOR]

Fen bryophytes are an important component of natural fens and should be included in fen restoration projects. The goal of this study was to examine the regeneration capabilities of nine bryophytes common to moderate-rich and poor fens in North America. A greenhouse experiment was carried out to examine the limitations and optima for the regeneration of fen bryophytes under different light and water regimes. A field experiment tested these same bryophytes in the presence of three potential nurse-plants. In the greenhouse experiment, the presence of shade increased regeneration success for eight out of nine species. A high water level was ideal for the regeneration of the majority of species tested. In the field experiment, Sphagnum species had the highest regeneration, and all species had higher regeneration under a dense canopy of herbaceous plants. Fen bryophytes show good potential for use in restoration projects because the tested bryophytes regenerated well from fragments. [ABSTRACT FROM AUTHOR]