The effect of temperature on growth and competition between <Emphasis Type="Italic">Sphagnum</Emphasis> species

Peat bogs play a large role in the global sequestration of C, and are often dominated by different Sphagnum species. Therefore, it is crucial to understand how Sphagnum vegetation in peat bogs will respond to global warming. We performed a greenhouse experiment to study the effect of four temperature treatments (11.2, 14.7, 18.0 and 21.4°C) on the growth of four Sphagnum species: S. fuscum and S. balticum from a site in northern Sweden and S. magellanicum and S. cuspidatum from a site in southern Sweden. In addition, three combinations of these species were made to study the effect of temperature on competition. We found that all species increased their height increment and biomass production with an increase in temperature, while bulk densities were lower at higher temperatures. The hollow species S. cuspidatum was the least responsive species, whereas the hummock species S. fuscum increased biomass production 13-fold from the lowest to the highest temperature treatment in monocultures. Nutrient concentrations were higher at higher temperatures, especially N concentrations of S. fuscum and S. balticum increased compared to field values. Competition between S. cuspidatum and S. magellanicum was not influenced by temperature. The mixtures of S. balticum with S. fuscum and S. balticum with S. magellanicum showed that S. balticum was the stronger competitor, but it lost competitive advantage in the highest temperature treatment. These findings suggest that species abundances will shift in response to global warming, particularly at northern sites where hollow species will lose competitive strength relative to hummock species and southern species.     

Response of <Emphasis Type="Italic">Sphagnum</Emphasis> species mixtures to increased temperature and nitrogen availability

To predict the role of ombrotrophic bogs as carbon sinks in the future, it is crucial to understand how Sphagnum vegetation in bogs will respond to global change. We performed a greenhouse experiment to study the effects of two temperature treatments (17.5 and 21.7°C) and two N addition treatments (0 and 4 g N m⁻² year⁻¹) on the growth of four Sphagnum species from three geographically interspersed regions: S. fuscum, S. balticum (northern and central Sweden), S. magellanicum and S. cuspidatum (southern Sweden). We studied the growth and cover change in four combinations of these Sphagnum species during two growing seasons. Sphagnum height increment and production were affected negatively by high temperature and high N addition. However, the northern species were more affected by temperature, while the southern species were more affected by N addition. High temperature depressed the cover of the ‘wet’ species, S. balticum and S. cuspidatum. Nitrogen concentrations increased with high N addition. N:P and N:K ratios indicated P-limited growth in all treatments and co-limitation of P and K in the high N treatments. In the second year of the experiment, several containers suffered from a severe fungal infection, particularly affecting the ‘wet’ species and the high N treatment. Our findings suggest that global change can have negative consequences for the production of Sphagnum species in bogs, with important implications for the carbon sequestration in these ecosystems.     

Population structure and interspecific differentiation of the peat moss sister speciesSphagnum rubellum andS. capillifolium (Sphagnaceae) in northern Europe

Isozyme electrophoresis was used to study the morphologically similar sister speciesSphagnum rubellum andS. capillifolium from a sample of 1313 plants representing 37 populations from Scandinavia, Great Britain and S Germany. The mean pairwise genetic identities (I) among conspecific populations were 0.976 forS. rubellum and 0.969 forS. capillifolium, versus 0.627 between populations of the two species. Interspecific gene flow was indicated by the observation of occasional plants in sympatric populations with alleles otherwise unique to the other species. Populations of bisexualS. capillifolium were significantly more variable than populations of unisexualS. rubellum. Alpine populations ofS. rubellum andS. capillifolium were dominated by few genotypes, and differentiation among populations was pronounced, indicating a low level of sexual recombination. InS. rubellum, maximum variability was found in western areas with high annual precipitation. Distribution of alleles inS. rubellum indicated restricted gene flow between Great Britain and Scandinavia. Postglacial migration from separate refugia may explain large-scale variation inS. rubellum.     

Summer warming and increased winter snow cover affect Sphagnum fuscum growth, structure and production in a sub-arctic bog

Sphagnum mosses form a major component of northern peatlands, which are expected to experience substantially higher increases in temperature and winter precipitation than the global average. Sphagnum may play an important role in the responses of the global carbon cycle to climate change. We investigated the responses of summer length growth, carpet structure and production in Sphagnum fuscum to experimentally induced changes in climate in a sub‐arctic bog. Thereto, we used open‐top chambers (OTCs) to create six climate scenarios including changes in summer temperatures, and changes in winter snow cover and spring temperatures. In winter, the OTCs doubled the snow thickness, resulting in 0.5–2.8°C higher average air temperatures. Spring air temperatures in OTCs increased by 1.0°C. Summer warming had a maximum effect of 0.9°C, while vapor pressure deficit was not affected. The climate manipulations had strong effects on S. fuscum. Summer warming enhanced the length increment by 42–62%, whereas bulk density decreased. This resulted in a trend (P<0.10) of enhanced biomass production. Winter snow addition enhanced dry matter production by 33%, despite the fact that the length growth and bulk density did not change significantly. The addition of spring warming to snow addition alone did not significantly enhance this effect, but we may have missed part of the early spring growth. There were no interactions between the manipulations in summer and those in winter/spring, indicating that the effects were additive. Summer warming may in the long term negatively affect productivity through the adverse effects of changes in Sphagnum structure on moisture holding and transporting capacity. Moreover, the strong length growth enhancement may affect interactions with other mosses and vascular plants. Because winter snow addition enhanced the production of S. fuscum without affecting its structure, it may increase the carbon balance of northern peatlands.     

Field Simulation of Global Change: Transplanting Northern Bog Mesocosms Southward

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.     

Response of Sphagnum fuscum to water levels and CO2 concentration

Abstract

Sphagnum fuscum samples collected from an ombrotrophic bog were grown in a greenhouse at six water levels (0, 5, 10, 15, 25 and 30 cm) below the capitulum level and in four concentrations of CO₂ (350, 700, 1000 and 2000 ppm). The cores of S. fuscum were treated for 87 days and length increment was measured by the plastic strip method and by innate time markers. Water content of the shoot, dry mass of the capitulum, dry mass per unit length of stem and production of dry mass were measured at the end of the experiment.

The water content, capitulum dry mass, dry mass per unit length of stem, length increment and dry mass production differed markedly for S. fuscum grown in different water levels. With lower water levels, the water content of the shoot decreased and the dry mass of both the capitulum and unit length of stem increased. The total length increment was highest when the water level was at or near the capitulum level (0–10 cm). No clear trend in dry mass production on an areal basis could be found due to uncoupled responses in length increment and stem dry mass at the experimental water levels.

Neither capitulum dry mass nor dry mass per unit length of stem showed distinct trends in S. fuscum grown at different ambient CO₂ concentrations. Some increase in length increment and in dry mass production was detected at CO₂ concentrations above 350 ppm, but this effect appeared only at high water levels. It is suggested that the low response in length increment and production to CO₂ concentration resulted in part from insufficient moisture for photosynthesis at the lower water levels. Also, the possibility of increased nonstructural production is discussed.     

Nutrient dynamics of 12 Sphagnum species during establishment on a rewetted bog

• Peatland degradation through drainage and peat extraction have detrimental environmental and societal consequences. Rewetting is an option to restore lost ecosystem functions, such as carbon storage, biodiversity and nutrient sequestration. Peat mosses (Sphagnum) are the most important peat-forming species in bogs. Most Sphagnum species occur in nutrient-poor habitats; however, high growth rates have been reported in artificial nutrient-rich conditions with optimal water supply.
• Here, we demonstrate the differences in nutrient dynamics of 12 Sphagnum species during their establishment in a 1-year field experiment at a Sphagnum paludiculture area in Germany. The 12 species are categorized into three groups (slower-, medium- and fast-growing). Establishment of peat mosses is facilitated by constant supply of nutrient-rich, low pH, and low alkalinity surface water.
• Our study shows that slower-growing species (S. papillosum, S. magellancium, S. fuscum, S. rubellum, S. austinii; often forming hummocks) displayed signs of nutrient imbalance. These species accumulated higher amounts of N, P, K and Ca in their capitula, and had an elevated stem N:K quotient (>3). Additionally, this group sequestered less C and K per m² than the fast and medium-growing species (S. denticulatum, S. fallax, S. riparium, S. fimbriatum, S. squarrosum, S. palustre, S. centrale). Lower lawn thickness may have amplified negative effects of flooding in the slower-growing species.
• We conclude that nutrient dynamics and carbon/nutrient sequestration rates are species-specific. For bog restoration, generating ecosystem services or choosing suitable donor material for Sphagnum paludiculture, it is crucial to consider their compatibility with prevailing environmental conditions.

     

Interactive effects of water table and precipitation on net CO2 assimilation of three co-occurring Sphagnum mosses differing in distribution above the water table

Sphagnum cuspidatum , S. magellanicum and S. rubellum are 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 CO₂ assimilation 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, CO₂ assimilation of all species gradually increased over time, irrespective of the precipitation. At low water table, net CO₂ assimilation of all species declined over time, with the earliest onset and highest rate of decline for S. 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 the Sphagnum vegetation and so did net CO₂ assimilation. CO₂ assimilation rate showed species-specific relationships with capitulum water content, with narrow but contrasting optima for S. cuspidatum and S. rubellum . Assimilation by S. magellanicum was 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.     

Sphagnum establishment on bare peat: The importance of climatic variability and Sphagnum species richness

Question: What is the relative ability of four species of Sphagnum (S. fuscum, S. rubellum, S. magellanicum and S. angustifolium) to establish on bare peat substratum in the field when re‐introduced as single or multi‐species re‐introductions and in relation to interannual variations in climate? Location: Continental southeastern Canada. Methods: Diaspores (fragments) of four Sphagnum species alone or in combination were re‐introduced onto residual peat surfaces and were monitored to follow the development of the moss carpet over four growing seasons. In order to compare results under a variety of climatic conditions, this whole experimental setting was repeated four times (trials), with a four‐year follow‐up for each trial. Conclusions: The establishment rate of the moss carpet varied among years, in response to climatic variations between growing seasons. The relative success of different moss species and combinations of species, however, did not vary within or between trials. Thus, the species and combinations of species resulting in the highest short‐term or long‐term establishment rates remained the same for all trials, independent of the climatic conditions at the time of re‐introduction. Our results showed no link between the number of species in the diaspore mixture and successful establishment of the moss carpet. Yet successful regeneration was clearly influenced by the identity of species chosen for re‐introduction. S. fuscum, alone or in combination, was the species found to lead to the most extensive development of the moss carpet under the current test conditions.     

Mechanisms involved in the re-establishment of Sphagnum-dominated vegetation in rewetted bog remnants

Restoration of peat bog vegetation inhighly degraded peatlands is generallyattempted by improving the hydrology ofthese areas. The present paper discussesand explains various restoration strategiesrelating to peat quality, water chemistryand hydrology. In some cases, (shallow)inundation of bog remnants leads to a rapidredevelopment of (floating) Sphagnumvegetation, usually when poorly humifiedSphagnum peat is still present. Afterinundation, the peat either swells up tothe newly created water table or becomesbuoyant, in both cases creating a favorablesubstrate for Sphagnum mosses. Bulkdensity and methane production rate play animportant role in the buoyancy of floatingpeat, methane providing buoyancy to thesubstrates. The presence of (slightly)calcareous groundwater in the peat base mayenhance the development of floating raftsby stimulating decomposition processes.Alternatively, the growth of submerged Sphagnum species can also lead to thedevelopment of floating rafts. This dependson the penetration of light into the waterlayer and the availability of carbondioxide in the water layer.Many bog remnants, however, only havestrongly humified peat, which does notfavor the redevelopment of Sphagnumcarpets after deep inundation. On the otherhand, most peat moss species appear to dovery well on surface soaked black peat,which is why shallow inundation (< 0.3 m)is to be preferred in such cases.Compartmentalization of the terrain willprobably be necessary to ensure a more orless constant water table.An important prerequisite for thesuccessful restoration of bog remnants isthe development of a hydrologicallyself-regulating acrotelm. Key speciesinvolved in this development are Sphagnum magellanicum, Sphagnumpapillosum and Sphagnum rubellum.These typical hummock and lawn species areusually very slow colonizers compared tohollow species such as Sphagnumcuspidatum and Sphagnum fallax.Introduction of key species in carpetsdominated by hollow species or on baresubstrates appears to be very successful,indicating that the main constraint iscolonization.     

泥炭地苔藓植物孢子生活力的快速检测

适量的烟气能够促进有性繁殖体萌发,但迄今尚无辅助烟气处理探究孢子生活力快速检测方法的研究报道。该文选择毛缘泥炭藓（Sphagnum fimbriatum）、中位泥炭藓（S.magellanicum）和粗叶泥炭藓（S.squarrosum）作为材料,分别使用亚甲基蓝染色法、四唑（TTC）染色法、碘-碘化钾（I₂-KI）染色法和红墨水染色法对泥炭藓孢子进行染色,并比照营养液、烟溶液+营养液培养的孢子萌发试验,对比研究泥炭地苔藓植物孢子生活力快速检测的最佳方法。结果表明：亚甲基蓝染色法的染色效果最为明显,TTC和I₂-KI均未能使泥炭藓孢子着色,孢子对红墨水虽有着色反应但不清晰;与营养液培养相比,添加烟溶液使毛缘泥炭藓、中位泥炭藓和粗叶泥炭藓孢子萌发率分别提高5%、5%和18%;使用亚甲基蓝染色的孢子染色率与经烟溶液处理过的孢子萌发率最为接近。综上认为,亚甲基蓝染色法能快速检测泥炭藓孢子的生活力。     

Sphagnum production and decomposition in a restored cutover peatland

Natural peatlands represent a long-termsink of atmospheric carbon dioxide(CO₂), however, drained and extractedpeatlands can represent a source ofatmospheric CO₂. The restoration ofSphagnum mosses on abandoned milledpeatlands has the potential to sequesteratmospheric CO₂ thereby returning thepeatland to a peat accumulating system.Micrometeorological and chambermeasurements of net ecosystem CO₂exchange are proven methods forinvestigating production and decompositionprocesses in both natural, extracted, andrestored peatlands. However, this approachis relatively expensive because ofinfrastructure and human resources that notonly limits potential use for ecologicalmanagers but it limits the number of sitesthat can be monitored due to high spatialvariability. Here we present crank wire anddestructive sampling productionmeasurements, litter bag decompositionmeasurements and measurements of netecosystem CO₂ exchange made in arestored peatland and natural peatlandsites nearby. The objectives were to assessproduction and decomposition rates in thetwo systems as well as to compare thedifferent measurements techniques.Estimates of Sphagnum fuscumproduction at a restored peatland, usingthe different methods, followed the trend:crank wire < destructive sampling < gasexchange, with the two last methodsproviding comparable estimates. Productionestimates using crank wires in cutover peatsurfaces with a thin newly formed Sphagnum mat were shown unreliable due topeat subsidence. Results using thedestructive sampling method suggest thatSphagnum production varies betweenspecies (S. fuscum > S.capillifolium) according to their abilityto withstand harsh conditions on restoredpeat surfaces. Decomposition rate was alsosignificantly greater (p<0.05) for S. capillifolium than S. fuscum,resulting in an overall plant accumulationgreater for S. fuscum. Although therestored surfaces were fairly young,production rates estimated on cutoversurfaces that were fully covered with athin Sphagnum mat compared withproduction rates observed in natural sitesnearby.     

Response to heat stress of populations of two Sphagnum species from alpine bogs at different altitudes

Sphagnum mosses are a fundamental component of bog vegetation in northern regions, where these plants play a major role in controlling important ecosystem processes. As heat waves are expected to become increasingly intense and frequent, especially in cold territories, it is important to improve our knowledge of heat resistance in Sphagnum species. We investigated the response to heat stress of S. fuscum and S. magellanicum. Three populations of the two species collected at different altitudes (1090 m, 1870 m and 2100 m) were grown at three daytime temperature levels: 25 °C (AT); 36 °C (MT); 43 °C (HT). The HT treatment decreased concentrations of chlorophyll and nitrogen in the plant tissues, which resulted in lower net CO₂ exchange rates and quantum yield of PS_II. The plants recovered significantly within six days, probably because temperature in the living tissue did not reach lethal thresholds because of the high water content in the plant tissues. Contrary to our main hypothesis, that S. magellanicum had greater resistance to high temperatures because of its more southern distribution, the two species showed much the same response patterns to heat stress. Supporting our second hypothesis, populations of both species originating from the highest site suffered somewhat stronger, although still reversible, damage when grown at HT. Heat stress brought about by heat waves will unlikely have differential effects on these two Sphagnum species. We also conclude that heat waves are unlikely to exert irreversible damage to the Sphagnum layer in bog ecosystems if high temperatures are not coupled with drought.     

Biomass, productivity and relative rate of photosynthesis of Sphagnum at different water levels on a South Swedish peat bog

The distribution pattern of Sphagnum species on bogs follows a hummock-hollow gradient. S . Sect. Acutifolia (that is in this study S. fuscum and S. rubellum combined) dominates hummock tops, ca 20 cm above the maximum water level with a green biomass of 50 g m⁻², S. magellancium dominates at a lower level, about 5 cm above the water level with a green biomass of 75 g m⁻² and S. cuspidatum dominates in the wettest hollows with a green biomass of about 50 g m⁻².
In situ measurements of length growth of S . Sect. Acutifolia and S. magellanicum using a ¹⁴CO₂-labelling technique during three consecutive years, revealed an unexpectedly high between-year variation in length growth of 7-23 mm yr⁻¹, and 16-22 mm yr⁻¹, respectively. Consequently the dominating producer in the transition between hummock and hollow changes from year to year, probably depending on climatic conditions.
In vitro experiments on the effects of different water levels of 2, 5, 10 and 20 cm below the moss surface, on photosynthetic activity of S . Sect. Acutifolia and S. magellanicum , measured by a second ¹⁴CO₂-technique, indicate optimal conditions for S. magellanicum at 10 cm above water level, and for S . Sect, Acutifolia at 20 cm above water level.
Differences in capillary water transport capability between the species are more important than the sensitivity of photosynthesis to water stress in explaining field patterns of productivity and distribution.     

Isozyme evidence of relationships withinSphagnum sect.Acutifolia (Sphagnaceae,Bryophyta)

Ten enzyme systems coding for 13 putative loci were studied in 12 European species ofSphagnum sect.Acutifolia (peat mosses). On average seven plants from each of 73 collections made throughout N Europe were analysed. Despite complex morphological variation, all species expressed unique allele combinations. Principal components and cluster analyses based on allele frequencies showed that sect.Acutifolia can be divided into two major groups; one comprisingSphagnum fimbriatum, S. girgensohnii andS. molle; the second comprisingS. capillifolium, S. angermanicum, S. fuscum, S. quinquefarium, S. rubellum, S. subfulvum, S. subnitens andS. warnstorfii. These groups are linked byS. russowii, which is shown to be an allopolyploid, with fixed heterozygosity at 6 to 8 of the loci. The presumed progenitors ofS. russowii areS. girgensohnii andS. rubellum. Allelic data also indicate thatS. teres from sect.Squarrosa is related toS. girgensohnii andS. fimbriatum. The bisexual species tend to be less variable than the unisexual species.     

The effect of increased temperature and nitrogen deposition on decomposition in bogs

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.     

Regeneration of Three <Emphasis Type="Italic">Sphagnum</Emphasis> species

Sphagnum capillifolium var. tenellum, S. magellanicum, and S. recurvum var. brevifolium were regenerated from stem pieces grown in containers to assess their potential for use in peatland restoration projects. The effect of two water levels; peat, peat/sand or peat/clay substrates; and peat decomposition level on the species’ regeneration was evaluated. S. magellanicum attained the greatest cover on the peat or peat/sand mixture using decomposed peat when the growing surface was occasionally inundated. S. recurvum attained the greatest cover grown on the peat or peat/sand mixture using undecomposed peat when the water level was kept below the surface. S. capillifolium showed an affinity for the peat/clay mixture, and overall attained a greater total cover than the other species when grown under the lower water level on all substrate types, with total cover approximately three to five times that of the others. When developing management plans for restoration of mined peatlands, species-specific responses to water level, type and extent of mineral soil mixed with the peat surface, and peat decomposition level should be considered.     

Direct and interaction-mediated effects of environmental changes on peatland bryophytes

Ecosystem processes of northern peatlands are largely governed by the vitality and species composition in the bryophyte layer, and may be affected by global warming and eutrophication. In a factorial experiment in northeast China, we tested the effects of raised levels of nitrogen (0, 1 and 2 g m⁻² year⁻¹), phosphorus (0, 0.1 and 0.2 g m⁻² year⁻¹) and temperature (ambient and +3°C) on Polytrichum strictum, Sphagnum magellanicum and S. palustre, to see if the effects could be altered by inter-specific interactions. In all species, growth declined with nitrogen addition and increased with phosphorus addition, but only P. strictum responded to raised temperature with increased production of side-shoots (branching). In Sphagnum, growth and branching changed in the same direction, but in Polytrichum, the two responses were uncoupled: with nitrogen addition there was a decrease in growth (smaller than in Sphagnum) but an increase in branching; with phosphorus addition growth increased but branching was unaffected. There were no two-way interactions among the P, N and T treatments. With increasing temperature, our results indicate that S. palustre should decrease relative to P. strictum (Polytrichum increased its branching and had a negative neighbor effect on S. palustre). With a slight increase in phosphorus availability, the increase in length growth and production of side-shoots in P. strictum and S. magellanicum may give them a competitive superiority over S. palustre. The negative response in Sphagnum to nitrogen could favor the expansion of vascular plants, but P. strictum may endure thanks to its increased branching.     

Effects of elevated CO2 and vascular plants on evapotranspiration in bog vegetation

We determined evapotranspiration in three experiments designed to study the effects of elevated CO₂ and increased N deposition on ombrotrophic bog vegetation. Two experiments used peat monoliths with intact bog vegetation in containers, with one experiment outdoors and the other in a greenhouse. A third experiment involved monocultures and mixtures of Sphagnum magellanicum and Eriophorum angustifolium in containers in the same greenhouse. To determine water use of the bog vegetation in July–August for each experiment and each year we measured water inputs and outputs from the containers. We studied the effects of elevated CO₂ and N supply on evapotranspiration in relation to vascular plant biomass and exposure of the moss surface (measured as height of the moss surface relative to the container edge). Elevated CO₂ reduced water use of the bog vegetation in all three experiments, but the CO₂ effect on evapotranspiration interacted with vascular plant biomass and exposure of the moss surface. Evapotranspiration in the outdoor experiment was largely determined by evaporation from the Sphagnum moss surface (as affected by exposure to wind) and less so by vascular plant transpiration. Nevertheless, elevated CO₂ significantly reduced evapotranspiration by 9–10% in the outdoor experiment. Vascular plants reduced evapotranspiration in the outdoor experiment, but increased water use in the greenhouse experiments. The relation between vascular plant abundance and evapotranspiration appears to depend on wind conditions; suggesting that vascular plants reduce water losses mainly by reducing wind speed at the moss surface. Sphagnum growth is very sensitive to changes in water level; low water availability can have deleterious effects. As a consequence, reduced evapotranspiration in summer, whether caused by elevated CO₂ or by small increases in vascular plant cover, is expected to favour Sphagnum growth in ombrotrophic bog vegetation.     

Sphagnum growth under N saturation: interactive effects of water level and P or K fertilization

• Sphagnum biomass is a promising material that could be used as a substitute for peat in growing media and can be sustainably produced by converting existing drainage‐based peatland agriculture into wet, climate‐friendly agriculture (paludiculture). Our study focuses on yield maximization of Sphagnum as a crop.
• We tested the effects of three water level regimes and of phosphorus or potassium fertilization on the growth of four Sphagnum species (S. papillosum, S. palustre, S. fimbriatum, S. fallax). To simulate field conditions in Central and Western Europe we carried out a glasshouse experiment under nitrogen‐saturated conditions.
• A constant high water table (remaining at 2 cm below capitulum during growth) led to highest productivity for all tested species. Water table fluctuations between 2 and 9 cm below capitulum during growth and a water level 2 cm below capitulum at the start but falling relatively during plant growth led to significantly lower productivity. Fertilization had no effect on Sphagnum growth under conditions with high atmospheric deposition such as in NW Germany (38 kg N, 0.3 kg P, 7.6 kg K·ha^?1·year^?1).
• Large‐scale maximization of Sphagnum yields requires precise water management, with water tables just below the capitula and rising with Sphagnum growth. The nutrient load in large areas of Central and Western Europe from atmospheric deposition and irrigation water is high but, with an optimal water supply, does not hamper Sphagnum growth, at least not of regional provenances of Sphagnum.