Hummock Species Research Articles

Monthly dynamics of phenolic release and allelopathic effect in hollow and hummock Sphagnum

Monthly variation in accumulation and release of phenolics in bryophytes, and their allelopathic effects are little known despite their ecological significance. We conducted a field transplant experiment to investigate Sphagnum growth and extracellular enzymes that modulate phenolic contents and release along water table level (WTL) gradient. Specifically, we assessed monthly changes in height increment, phenolic release, and allelopathic effect during the growing season, as well as extracellular enzymes at the end of the experiment, for the two Sphagnum species: Sphagnum angustifolium C.E.O. Jensen, 1896, a hollow dwelling species, and Sphagnum magellanicum Bridel, 1798, a hummock species. Both Sphagnum species showed season- and WTL-dependent height increment and released phenolics. Sphagnum angustifolium exhibited negative allelopathy regardless of WTL, while S. magellanicum demonstrated mainly positive allelopathy at high WTL and negative allelopathy at low WTL. The degree of allelopathy was not contingent on phenolic release, but phenolic production was negatively correlated with height growth of the two species at their atypical habitats. Moreover, phenoloxidase or peroxidase did not show high activity at low WTL compared to high WTL. Our findings demonstrate for the first time that the strength and direction of allelopathy in Sphagnum may vary depending on the growing precipitation and temperature, WTL, and inter- and intraspecific trait variability. Longer term experiments may further elucidate the seasonal dynamics and mechanism of Sphagnum allelopathy.

Dry/wet cycling reduces spore germination and viability in six peatland bryophytes.

Dry/wet cycling driven by water level fluctuation in wetlands may strongly influence the destiny of seeds. However, how dry/wet cycling affects spore survival and germinability in peatland bryophytes is poorly understood. Six peatland bryophytes, three hummock- and three hollow-dwelling Sphagnum species, were chosen as study species. We tested the effects of dry (60% air RH)/wet (waterlogging) cycle frequency (once per 12, 8 or 4 days for low, medium or high, respectively) and ratio (3:1, 1:1 or 1:3 dry:wet time per cycle) on spore germinability, viability, dormancy percentage and protonema development. Dry/wet cycling significantly reduced spore germination percentage and viability and slowed protonema development in all Sphagnum species, being more pronounced with higher dry/wet cycling frequencies. The hummock species S. capillifolium and S. fuscum had higher spore germination percentage after the continuous dry treatment, while the hollow species S. angustifolium, S. squarrosum and S. subsecundum showed the opposite response, compared to the continuously wet treatment. Except for S. squarrosum, spore viability was higher after the dry than after the wet treatment. Spore viability and dormancy percentage were higher after a dry/wet ratio of 1:3 than after ratios of 3:1 and 1:1. Our study shows that both germinability and viability of bryophyte spores are reduced by dry/wet cycling (especially when frequent) in peatlands. This emphasizes the need to ensure constant water levels and low frequencies of water level fluctuation, which are relevant in connection with wetland restoration, to promote Sphagnum spore survival and establishment in peatlands after disturbances.

Biochemical components ofSphagnumand persistence in peat soil

The amounts and arrangements of polysaccharides (cellulose and hemicellulose), proteins, phenolic lignin, and pectin that make up plant tissue, in part, determine its decay rate. Lignin-rich and/or nitrogen-poor tissue has been described as biochemically recalcitrant causing a slow decay rate. Although a controversial mechanism for organic matter storage in soils with mineral particles, biochemical recalcitrance is still poorly understood in organic peat soil (Histosols). To investigate the role of Sphagnum in formation of peat soil, we characterize biochemical components for 10 species and examine persistence of the components in soil to 150 cm depth in three peatland ecosystems. We hypothesize that species from hummock microforms have more biochemical structural components and cohesion than species from hollows. Relative proportions of biochemical components changed markedly between plant material and the top 10 cm of peat soil, suggesting that decomposition occurred at the peat soil surface, but thereafter relative proportions of biochemical components did not vary significantly to 150 cm deep. A few differences in biochemical components that distinguished hummock species from hollow species persisted to the deepest depth sampled. Although persistence of the lignin-like component was expected, persistence of soluble and ionically bound pectin compounds was surprising as these biopolymers are thought to be readily decomposable. Our findings indicate that structural components of Sphagnum, specifically polysaccharides and pectin in addition to oft-cited phenolic lignin-like components, persist in peat soil and should not be overlooked in trying to understand carbon dynamics in Sphagnum-dominated ecosystems.

The Response of Spore Germination of Sphagnum Mosses to Single and Combined Fire-Related Cues.

Plants in flammable ecosystems have different response strategies to fire, such as increasing germination after exposure to smoke and break of dormancy through heat shock. Peatlands are ecosystems that are more likely to be disturbed by fire with increasing temperatures, but it is not clear how fire affects spore germination of Sphagnum, the dominant plants in peatlands. Here, we hypothesize that Sphagnum spores respond positively to single and combined treatments of moderate heat and smoke (by increased germinability), while spore germinability decreases in response to high temperature. We exposed the Sphagnum spores of four selected species (S. angustifolium, S. fuscum, S. magellanicum and S. squarrosum) collected from peatlands in the Changbai Mountains to heat (40, 60 and 100 °C), on its own and combined with smoke-water treatments. Our results showed that a heat of 100 °C inhibited the spore germination or even killed spores of all species, while spore germination of three (Sphagnum angustifolium, S. fuscum and S. squarrosum) of the four species was promoted by 40 and 60 °C heat compared to the control (20 °C). Hollow species (S. angustifolium and S. squarrosum) showed a stronger positive responsive to heat than hummock species (S. fuscum and S. magellanicum). Sphagnum fuscum spores responded positively to the combined heat and smoke treatment while the other species did not. For the first time, we demonstrate the positive effects of heat on its own and in combination with smoke on spore germination in wetland mosses, which may be important for the establishment and persistence of peatmoss populations after fire.

Accelerated vegetation succession but no hydrological change in a boreal fen during 20years of recent climate change.

Northern mires (fens and bogs) have significant climate feedbacks and contribute to biodiversity, providing habitats to specialized biota. Many studies have found drying and degradation of bogs in response to climate change, while northern fens have received less attention. Rich fens are particularly important to biodiversity, but subject to global climate change, fen ecosystems may change via direct response of vegetation or indirectly by hydrological changes. With repeated sampling over the past 20 years, we aim to reveal trends in hydrology and vegetation in a pristine boreal fen with gradient from rich to poor fen and bog vegetation. We resampled 203 semi‐permanent plots and compared water‐table depth (WTD), pH, concentrations of mineral elements, and dissolved organic carbon (DOC), plant species occurrences, community structure, and vegetation types between 1998 and 2018. In the study area, the annual mean temperature rose by 1.0°C and precipitation by 46 mm, in 20‐year periods prior to sampling occasions. We found that wet fen vegetation decreased, while bog and poor fen vegetation increased significantly. This reflected a trend of increasing abundance of common, generalist hummock species at the expense of fen specialist species. Changes were the most pronounced in high pH plots, where Sphagnum mosses had significantly increased in plot frequency, cover, and species richness. Changes of water chemistry were mainly insignificant in concentration levels and spatial patterns. Although indications toward drier conditions were found in vegetation, WTD had not consistently increased, instead, our results revealed complex dynamics of WTD as depending on vegetation changes. Overall, we found significant trend in vegetation, conforming to common succession pattern from rich to poor fen and bog vegetation. Our results suggest that responses intrinsic to vegetation, such as increased productivity or altered species interactions, may be more significant than indirect effects via local hydrology to the ecosystem response to climate warming.

The effect of different treatments of moss layer transfer technique on plant functional types' biomass in revegetated milled peatlands

The number and the area of former milled peatlands under restoration have increased rapidly in the Northern Hemisphere in recent decades with the primary aim of promoting peat accumulation. However, the application of similar restoration techniques across different sites does not always lead to desired results, and some site‐specific modifications may be needed. This study aimed to evaluate the response of aboveground plant biomass on three experimental sites in northern Estonia to different restoration techniques in degraded peatlands. The sites were restored using the moss layer transfer technique, which was modified with different plant spreading rates and species composition of spread material, fertilization, and creating variations in microtopography. The strongest effect of manipulations was found for bryophyte biomass responses to treatments. The creation of a microtopographic relief during the site preparation phase favored the development of Sphagnum biomass in depressions rather than in positive microforms. The species composition of the spreading material had some effect on bryophyte biomass: Sphagnum biomass was higher where hummock species had been spread. We did not find any statistical difference in the ratio of Sphagnum reintroduction tested ranging from 1:10 to 1:15.

Mechanisms behind species-specific water economy responses to water level drawdown in peat mosses.

Background and AimsThe ecosystem engineers Sphagnum (peat mosses) are responsible for sequestering a large proportion of carbon in northern peatlands. Species may respond differently to hydrological changes, and water level changes may lead to vegetation shifts in peatlands, causing them to revert from sinks to sources of carbon. We aimed to compare species-specific responses to water level drawdown within Sphagnum, and investigate which traits affect water economy in this genus.MethodsIn a mesocosm experiment, we investigated how water level drawdown affected water content (WC) in the photosynthetically active apex of the moss and maximum quantum yield of photosystem II (i.e. Fv/Fm) of 13 Sphagnum species. Structural traits were measured, and eight anatomical traits were quantified from scanning electron microscopy micrographs.Key ResultsMixed-effects models indicated that at high water level, large leaves were the most influential predictor of high WC, and at low water level WC was higher in species growing drier in the field, with larger hyaline cell pore sizes and total pore areas associated with higher WC. Higher stem and peat bulk density increased WC, while capitulum mass per area and numerical shoot density did not. We observed a clear positive relationship between Fv/Fm and WC in wet-growing species.ConclusionsWhile we found that most hummock species had a relatively high water loss resistance, we propose that some species are able to maintain a high WC at drawdown by storing large amounts of water at a high water level. Our result showing that leaf traits are important warrants further research using advanced morphometric methods. As climate change may lead to more frequent droughts and thereby water level drawdowns in peatlands, a mechanistic understanding of species-specific traits and responses is crucial for predicting future changes in these systems.

Resource competition and allelopathy in two peat mosses: implication for niche differentiation

Separating the effect of resource competition from allelopathy in plants is challenging and it has never been attempted in closely related co-occurring bryophytes. In peatlands, peat mosses (Sphagnum spp.) show niche differentiation along water table level (WTL) gradient. Our aim was to evaluate whether the hummock species, S. magellanicum would be a winner at low WTL due to its allelopathic advantage and the hollow species, S. angustifolium would win by virtue of its superior competitive ability but not of allelopathy at high WTL due to dilution of its allelochemicals. We used a nested, field experimental design, with two WTL treatments—low WTL (hummock habitat) and high WTL (hollow habitat)—and three different inter-specific interactions: 1) monoculture; 2) mixed culture without activated charcoal; and 3) mixed culture with activated charcoal added to the neighbor. We measured growth and biochemical traits of the two species and compared the index of relative neighbor effect on each other. We discovered a trade-off between biomass production (competitive outcome) and phenolic content (allelopathy) in these species. At low WTL, allelopathy of the hummock species is the main mechanism to suppress the hollow species, whereas at high WTL, competition is the main driver to suppress the hummock species. Competitive advantage in Sphagnum is mediated by both resource competition and allelopathy of the co-occurring species through niche differentiation along a WTL gradient. Unlike vascular plants, Sphagnum mosses can serve as excellent model organisms in studying allelopathic interaction since they bypass the complexity of plant-soil interactions.

Production and decomposition rates of different fen species as targets for restoration

There is an increasing interest in considering ecosystem processes after fen restoration, and not solely species composition. To evaluate the success of ecological restoration, comparisons with targets from reference ecosystems are required. We documented net primary production (NPP) and decomposition of the main vegetation components in order to describe a reference data set for ecological restoration of moderately rich to rich minerotrophic peatlands (fens) in southeastern Canada. Data collection included three growing seasons for herbs and shrubs and two growing seasons for belowground biomass, trees and bryophytes. Average NPP for above and belowground biomass of three selected natural basin fens were 450 g m−2 yr−1. Belowground NPP represented 45% of the total NPP. Sphagnum warnstorfii was the most productive bryophyte (140 g m−2 yr−1) and the slowest plant species to decompose (exponential decomposition constant k = 0.07 yr−1). The brown mosses Tomenthypnum nitens, Campylium stellatum and Scorpidium cossonii had a NPP of 79, 69 and 92 g m−2 yr−1, respectively, and decomposed at the same rate (identical k values of 0.14 yr−1). Trees covered a large surface area in the fens, with an average NPP of 73 g m−2 yr−1. S. warnstorfii contributed to hummocks having a higher peat accumulation potential than lawn vegetation. The graminoid Trichophorum cespitosum significantly increased NPP in lawns and should be targeted in restoration plans for fens. To restore peat accumulating processes (production and decomposition) in fens, bryophytes should be the primary focus for re-introduction, specifically species that are adapted to living in drier conditions, such as hummock species. The range of variability for NPP and decomposition established by this study should be considered as a decision tool in restoration projects to monitor restored ecosystems trajectories and successes.

Linear growth and production of Sphagnum mosses in the middle taiga zone of West Siberia

Приведены данные линейного прироста 3 видов мхов в средней тайге Западной Сибири, полученные за последние 3 года. Линейные приросты S. fuscum и S. magellanicum, растущих на повышенных элементах болотного микрорельефа, имеют сходную динамику, как по годам, так и по ключевым участкам, и зависят от годовой и летней суммы осадков. Средняя скорость прироста этих видов варьировала от 0.05 до 0.25 мм/день в зависимости от года исследования и ключевого участка. Прирост мочажинного вида S. balticum на 30% больше, чем линейный прирост мхов повышенных элементов микрорельефа, и имеет 2 пика – весенний и летний. Максимальная скорость прироста S. balticum приходится на летний период и составляет 0.55 мм/день, при средней скорости – 0.23 мм в день. Первичная продукция S. fuscum была выше продукции S. magellanicum, при этом продукция обоих видов различалась по годам и между ключевыми участками. Продукция S. magellanicum была наибольшей на западе региона, постепенно снижаясь к востоку.

Hydrogen isotope ratios of moss cellulose and source water in wetlands of Lake Superior, United States reveal their potential for quantitative paleoclimatic reconstructions

The hydrogen isotopic composition of organic substrates provides valuable information on past hydrological changes. To explore whether quantitative information can be obtained from this proxy, we measured D/H ratios of cellulose extracted from mosses inhabiting both hollow and hummock sites in three swales located near Lake Superior, United States. These isotope ratios were compared to those of potential water sources, namely swale, moss, and ground water, to evaluate whether cellulose D/H ratios reflect those of its water sources. For that evaluation, we relied on a better mechanistic understanding of the isotopic fractionation occurring during cellulose synthesis in plants as well as the relative simplicity of moss physiology in regard to water use strategies and a dataset that combines published D/H ratios for modern moss cellulose. We found that moss cellulose δD values for hollow species (−118.1±8.5‰) were significantly depleted (p=0.016) in D by 8‰ in relation to those for hummock species (−110.1±8.1‰), possibly due to an averaging effect taking place in hollow species. In addition, we found that 40% of the hydrogen in cellulose from hollow species probably experienced isotopic exchange with the surrounding cell water, and this percentage is not statistically different from that (42%) obtained from an analysis of published data on modern moss cellulose. This analysis also reveals that the fraction of hydrogen in modern moss cellulose that is subjected to isotope exchange falls within a relatively narrow range (±3%). Using this range and a mechanistic model, we were able to estimate source water δD values using those measured for moss cellulose, and these estimates were statistically indistinguishable from the measured δD values of moss and swale water. Further, the ratios of δD/δ18O of moss cellulose of hollow species yielded values that are similar to those reported for the local meteoric water line, thus adding a potential source of paleo-hydrological reconstructions from moss cellulose. Consequently, our combined results suggest not only that moss cellulose D/H ratios reflect those of source water, but that the latter values can be estimated fairly precisely from cellulose D/H ratios using a relatively simple mechanistic model. However, the accuracy of this model hinges on assumptions that need to be tested further to corroborate its widespread applicability.

Wildfire as a key determinant of peatland microtopography

Microtopography is a common attribute of wetlands, particularly boreal bog and fen peatlands. This self-organized patterning is primarily an autogenic process; however, the role of allogenic forces such as disturbance in the maintenance of microtopography is poorly understood. In this study, we quantify the effect of fire on the distribution of the microtopographic gradient in boreal bogs using a before–after wildfire natural experiment. We also quantify the change in spatial abundance of microforms in boreal treed peatlands over a 100-year successional chronosequence. Wildfire nearly doubled the range of the microtopographic gradient, increasing the relative abundance of low-elevation microforms (hollows), although the distribution of elevations was influenced by peatland ontogeny at the time of wildfire. Through succession, raised microforms (hummocks) became more abundant, presumably due to autogenic surface drying facilitating hummock species expansion into adjacent hollows. Although autogenic processes may be responsible for the development of self-organized spatial patterning in wetlands, disturbances such as wildfire are necessary for maintaining boreal peatland microtopography over extended time scales. Because of the tight linkage between microtopography, species diversity, and ecosystem function, these feedbacks between wildfire and microtopography are critical for understanding peatland dynamics and the potential impact of a changing environment.

Desiccation tolerance of Sphagnum revisited: a puzzle resolved.

As ecosystem engineers, Sphagnum mosses control their surroundings through water retention, acidification and peat accumulation. Because water retention avoids desiccation, sphagna are generally intolerant to drought; however, the literature on Sphagnum desiccation tolerance (DT) provides puzzling results, indicating the inducible nature of their DT. To test this, various Sphagnum species and other mesic bryophytes were hardened to drought by (i) slow drying; (ii) ABA application and (iii) chilling or frost. DT tolerance was assessed as recovery of chlorophyll fluorescence parameters after severe desiccation. We monitored the seasonal course of DT in bog bryophytes. Under laboratory conditions, following initial de-hardening, untreated Sphagnum shoots lacked DT; however, DT was induced by all hardening treatments except chilling, notably by slow drying, and in Sphagnum species of the section Cuspidata. In the field, sphagna in hollows and lawns developed DT several times during the growing season, responding to reduced precipitation and a lowered water table. Hummock and aquatic species developed DT only in late autumn, probably as a response to frost. Sphagnum protonemata failed to develop DT; hence, desiccation may limit Sphagnum establishment in drier habitats with suitable substrate chemistry. Desiccation avoiders among sphagna form compact hummocks or live submerged; thus, they do not develop DT in the field, lacking the initial desiccation experience, which is frequent in hollow and lawn habitats. We confirmed the morpho-physiological trade-off: in contrast to typical hollow sphagna, hummock species invest more resources in water retention (desiccation avoidance), while they have a lower ability to develop physiological DT.

Facilitation vs. competition: Does interspecific interaction affect drought responses in Sphagnum?

The stress-gradient hypothesis (SGH) predicts that the relative importance of competition decreases and facilitation increases with an increase in abiotic stress. In peatlands, Sphagnum faces the threat of drought and differentiates into hummock species (drought-tolerant) and hollow species. Whether interspecific interaction affects the influence of drought on bryophyte composition in peatlands is unknown. We established an experiment by simulating drought and building bryophyte communities with two hummock species (S. palustre and S. capillifolium) and one hollow species (S. fallax). In all three species, drought decreased biomass production, height increment and side-shoot production. Sphagnum stores water in the hyaline cells, and leaf hyaline cell percentage (HCP) in the two hummock species increased with drought while no effect was found in S. fallax, suggesting that adjusting HCP is not an effective response to drought for the hollow species. Morphological traits and carbon and nitrogen contents in hummock species responded more to drought than in the hollow species, indicating a rapid response in phenotypic plasticity is an important strategy to resist drought in the hummock species. The presence of neighboring Sphagnum species, rather than drought, decreased carbon content for all three species. All three bryophytes showed interaction between drought and neighbor in two or more plant traits. Our study, however, did not support SGH, and there were no changes from competition under wet to facilitation under dry treatments in any of the six species combinations. On the contrary, when S. fallax was the target species, a change from facilitation under wet to competition under dry treatments was observed. The results suggest that hummock species can facilitate hollow species in wet environments but they could suppress hollow species under drought conditions by competing for water resources. Both drought and strong competition are the probable reasons why hollow species rarely grow in hummocks.

Ecohydrology of Sphagnum moss hummocks: mechanisms of capitula water supply and simulated effects of evaporation

ABSTRACTMaintaining sufficiently high surface (capitula) soil‐water pressures to avoid the draining of hyaline cells (desiccation) is paramount to hummock‐forming Sphagnum species' survival; however, the mechanisms of capitula water supply are poorly understood. This study investigates how the hydraulic characteristics of different Sphagnum species (Sphagnum fuscum, Sphagnum rubellum and Sphagnum magellanicum) contribute to desiccation avoidance, on the basis of numerical simulations parameterized with measured soil hydraulic characteristics for each species. Although having similar unsaturated hydraulic conductivity values, the upper 5 cm of S. magellanicum retains ~20% less moisture under tension than S. fuscum and S. rubellum; in fact, S. rubellum on average retained slightly more water than S. fuscum. Hydrus‐1D was used to simulate daytime and nighttime conditions over a 7‐day period, where daily potential evaporation was 4 mm, to explore the governing mechanisms controlling water supply to the capitula. The simulations showed that S. fuscum and S. rubellum were able to retain sufficiently high moisture content under the prevailing simulated water demand to sustain surface soil‐water pressure heads (greater than −100 cm), whereas S. magellanicum could not prevent depressurization and the concomitant desiccation of its surface layer. A similar number of the same size pores were observed in all species; however, there was lower pore connectivity in S. magellanicum leading to the desiccation of the capitula. Contrary to previous studies, the results of this study indicate that it is not only soil‐water retention but also pore connectivity that allows hummock species to thrive above the water table. Copyright © 2012 John Wiley & Sons, Ltd.

Sphagnum growth and ecophysiology during mire succession

Sphagnum mosses are widespread in areas where mires exist and constitute a globally important carbon sink. Their ecophysiology is known to be related to the water level, but very little is currently known about the successional trend in Sphagnum. We hypothesized that moss species follow the known vascular plant growth strategy along the successional gradient (i.e., decrease in production and maximal photosynthesis while succession proceeds). To address this hypothesis, we studied links between the growth and related ecophysiological processes of Sphagnum mosses from a time-since-initiation chronosequence of five wetlands. We quantified the rates of increase in biomass and length of different Sphagnum species in relation to their CO(2) assimilation rates, their photosynthetic light reaction efficiencies, and their physiological states, as measured by the chlorophyll fluorescence method. In agreement with our hypothesis, increase in biomass and CO(2) exchange rate of Sphagnum mosses decreased along the successional gradient, following the tactics of more intensely studied vascular plants. Mosses at the young and old ends of the chronosequence showed indications of downregulation, measured as a low ratio between variable and maximum fluorescence (F(v)/F(m)). Our study divided the species into three groups; pioneer species, hollow species, and ombrotrophic hummock formers. The pioneer species S. fimbriatum is a ruderal plant that occurred at the first sites along the chronosequence, which were characterized by low stress but high disturbance. Hollow species are competitive plants that occurred at sites with low stress and low disturbance (i.e., in the wet depressions in the middle and at the old end of the chronosequence). Ombrotrophic hummock species are stress-tolerant plants that occurred at sites with high stress and low disturbance (i.e., at the old end of the chronosequence). The three groups along the mire successional gradient appeared to be somewhat analogous to the three primary strategies suggested by Grime.

The response of carbon dioxide exchange to manipulations of Sphagnum water content in an ombrotrophic bog

AbstractSphagnum mosses contribute to the long‐term carbon sequestration of many northern peatlands. Variability in both Sphagnum and peatland CO2 exchange is strongly influenced by water availability, but there is limited work examining the links between these relationships, particularly in a field setting. In this study, the effects of varying moss water content (WC), through precipitation exclusion (PE) and water addition (WA) treatments, on net ecosystem CO2 exchange (NEE) and component fluxes were assessed during a single growing season at Mer Bleue bog, a temperate ombrotrophic peatland. CO2 exchange by Sphagnum, vascular plants, and the total ecosystem were measured in situ using chambers. On average, the hummock species of Sphagnum dominant at the site maintained WCs within the optimal range for photosynthesis in all treatments and no treatment effect on CO2 exchange was observed. However, in a few samples associated with below optimal WCs, Sphagnum photosynthesis was reduced. Water table (WT) depth and direct precipitation were both important controls on Sphagnum WC, suggesting that frequent small rain events may be important in maintaining Sphagnum WC. This study only explored one variable associated with drought conditions (i.e. water availability through intercepted precipitation). Consequently, further study is necessary to assess the relative importance of deep WT positions and high temperatures on moss WC. Nevertheless, the results of this study suggest that decreased Sphagnum photosynthesis has the potential to influence peatland CO2 uptake at Mer Bleue in drought years, but only if moss WC is reduced below the optimal range. Copyright © 2010 John Wiley & Sons, Ltd.

Sphagnum re-introduction in degraded peatlands: The effects of aggregation, species identity and water table

In European peatlands which have been drained and cut-over in the past, re-vegetation often stagnates after the return of a species-poor Sphagnum community. Re-introduction of currently absent species may be a useful tool to restore a typical, and more diverse, Sphagnum vegetation and may ultimately improve the functioning of peatland ecosystems, regarding atmospheric carbon sequestration. Yet, the factors controlling the success of re-introduction are unclear. In Ireland and Estonia, we transplanted small and large aggregates of three Sphagnum species into existing vegetation. We recorded changes in cover over a 3-year period, at two water levels (?5 and ?20 cm). Performance of transplanted aggregates of Sphagnum was highly species specific. Hummock species profited at low water tables, whereas hollow species profited at high water tables. But our results indicate that performance and establishment of species was also promoted by increased aggregate size. This mechanism (positive self-association) has earlier been seen in other ecosystems, but our results are the first to show this mechanism in peatlands. Our results do not agree with present management, which is aimed at retaining water on the surface of peat remnants in order to restore a functional and diverse Sphagnum community. More than the water table, aggregate size of the reintroduced species is crucial for species performance, and ultimately for successful peatland restoration.

Interactive effects of water table and precipitation on net CO2assimilation of three co‐occurringSphagnummosses differing in distribution above the water table

AbstractSphagnum cuspidatum,S. magellanicumandS. rubellumare three co‐occurring peat mosses, which naturally have a different distribution along the microtopographical gradient of the surface of peatlands. We set out an experiment to assess the interactive effects of water table (low: −10 cm and high: −1 cm) and precipitation (present or absent) on the CO2assimilation and evaporation of these species over a 23‐day period. Additionally, we measured which sections of the moss layer were responsible for light absorption and bulk carbon uptake. Thereafter, we investigated how water content affected carbon uptake by the mosses. Our results show that at high water table, CO2assimilation of all species gradually increased over time, irrespective of the precipitation. At low water table, net CO2assimilation of all species declined over time, with the earliest onset and highest rate of decline forS. cuspidatum. Precipitation compensated for reduced water tables and positively affected the carbon uptake of all species. Almost all light absorption occurred in the first centimeter of theSphagnumvegetation and so did net CO2assimilation. CO2assimilation rate showed species‐specific relationships with capitulum water content, with narrow but contrasting optima forS. cuspidatumandS. rubellum. Assimilation byS. magellanicumwas constant at a relatively low rate over a broad range of capitulum water contents. Our study indicates that prolonged drought may alter the competitive balance between species, favoring hummock species over hollow species. Moreover, this study shows that precipitation is at least equally important as water table drawdown and should be taken into account in predictions about the fate of peatlands with respect to climate change.

Ecophysiological adjustment of two Sphagnum species in response to anthropogenic nitrogen deposition

Here, it was investigated whether Sphagnum species have adjusted their nitrogen (N) uptake in response to the anthropogenic N deposition that has drastically altered N-limited ecosystems, including peatlands, worldwide. A lawn species, Sphagnum balticum, and a hummock species, Sphagnum fuscum, were collected from three peatlands along a gradient of N deposition (2, 8 and 12 kg N ha(-1) yr(-1)). The mosses were subjected to solutions containing a mixture of four N forms. In each solution one of these N forms was labeled with (15)N (namely (15)NH(+)(4), (15)NO(-)(3) and the amino acids [(15)N]alanine (Ala) and [(15)N]glutamic acid (Glu)). It was found that for both species most of the N taken up was from , followed by Ala, Glu, and very small amounts from NO(-)(3). At the highest N deposition site N uptake was reduced, but this did not prevent N accumulation as free amino acids in the Sphagnum tissues. The reduced N uptake may have been genetically selected for under the relatively short period with elevated N exposure from anthropogenic sources, or may have been the result of plasticity in the Sphagnum physiological response. The negligible Sphagnum NO(-)(3) uptake may make any NO(-)(3) deposited readily available to co-occurring vascular plants.