Characterization of yeast groupings in the phyllosphere of Sphagnum mosses

Significant differences were revealed in the taxonomic structure of the epiphytic yeast communities formed on Sphagnum mosses and on the leaves of vascular plants. On mosses, low abundance of red yeasts was found (the most typical epiphytes on vascular plant leaves), along with a relatively high content and diversity of nonpigmented dimorphic basidiomycetes related to the order Leucosporidiales. The species composition of epiphytic yeasts from mosses is different from that of both forest and meadow grasses and of the parts of vascular plants submerged in the turf. The specific composition of the Sphagnum mosses yeast community is probably determined by the biochemical characteristics of this environment, rather than by the hydrothermal regime in the turf.     

Field studies of nitrogen fixation of Australian alpine plants and soils

Alpine grassland areas in Victoria and New South Wales have been subjected to summer grazing by cattle and sheep for well over a hundred years. Legumes other than a few species of shrubs, which provide a very small percentage of the vegetation cover in the grasslands, are absent. Other alpine communities include Sphagnum ‘mossbeds’ in the valleys and areas of snowgum woodland and shrubland. Virtually nothing is known of the mineral status of these communities and nothing of their nitrogen economy. On the Bogong High Plains, enclosure of grassland and of Sphagnum mossbeds from grazing and trampling has resulted, in the last few decades, in considerable changes in both cover and composition of the vegetation. A portable gas chromatogram was used to carry out determinations of the capacity of samples of the grassland and Sphagnum to support acetylene reduction to ethylene, by convention equated to a capacity to fix nitrogen. There appears to be a substantial capacity for acetylene reduction associated with the rhizosphere of the grasses (Poa australis agg.). The capacity of the Sphagnum for acetylene reduction is even greater and appears to be due to facultative anaerobes, abundant only in the upper, living part of the Sphagnum. These organisms may depend in part on leakage of photosynthate from the living Sphagnum. Associations of Sphagnum with blue-green algae appear to be unusual in contrast with work on Swedish subarctic mosses, which is discussed. The only non-leguminous Australian alpine plant so far examined for nitrogen fixation is Podocarpus lawrencei. A capacity for acetylene reduction was found for neither the nodules of the roots of this plant nor the associated soils.     

Bryophyte communities in mesotrophic fens in the Netherlands

Seven bryophyte and three vascular plant community types were described from eight small fens in the Vechtplassen area (prov. of Utrecht, the Netherlands). Clear relationships between the species composition of the bryophyte and vascular plant layer were found. The bryophyte species composition shows a gradual change from quaking fens dominated by Calliergon cordifolium to fens dominated by several species of Sphagnum . Fens dominated by C. cordifolium have relatively high pH and conductivity values and are strongly quaking, whereas fens dominated by Sphagnum have relatively low pH and conductivity values and the peat layer is continuous down to the bottom sediment. A comparison of the present-day vegetation with an earlier successional scheme for this vegetation type (Segal 1966) indicates a raise in nutrient levels and a decrease in the amount of seepage water welling up at the sites, both due to human activities. We suggest that in early successional phases bryophytes react faster to these changes, whereas in later phases vascular plants react faster.     

Torfmooskulturen als Ersatzlebensraum

Sphagnum farming In Germany, 99% of the 1.4 Mha of peatlands have been drained for land use. These degraded areas release enormous amounts of greenhouse gases. In contrast, land use on rewetted peatlands (= paludiculture) not only avoids greenhouse gas emissions, but offers numerous additional environmental benefits, while maintaining biomass production. Field studies have demonstrated the additional benefits of peatmoss (Sphagnum) cultivation for plant and animal diversity. After harvesting of the upper moss layer, the biomass is prepared to be used as a substitute for peat in horticultural substrates. Sphagnum farming is a promising and sustainable land use alternative for degraded bog areas.     

Analysis of the bacterial community developing in the course of Sphagnum moss decomposition

Slow degradation of organic matter in acidic Sphagnum peat bogs suggests a limited activity of organotrophic microorganisms. Monitoring of the Sphagnum debris decomposition in a laboratory simulation experiment showed that this process was accompanied by a shift in the water color to brownish due to accumulation of humic substances and by the development of a specific bacterial community with a density of 2.4 x 10(7) cells ml(-1). About half of these organisms are metabolically active and detectable with rRNA-specific oligonucleotide probes. Molecular identification of the components of this microbial community showed the numerical dominance of bacteria affiliated with the phyla Alphaproteobacteria, Actinobacteria, and Phanctomycetes. The population sizes of Firmicutes and Bacteroidetes, which are believed to be the main agents of bacterially-mediated decomposition in eutrophic wetlands, were low. The numbers of planctomycetes increased at the final stage of Sphagnum decomposition. The representative isolates of Alphaproteobacteria were able to utilize galacturonic acid, the only low-molecular-weight organic compound detected in the water samples; the representatives of Planctomycetes were able to decompose some heteropolysaccharides, which points to the possible functional role of these groups of microorganisms in the community under study. Thus, the composition of the bacterial community responsible for Sphagnum decomposition in acidic and low-mineral oligotrophic conditions seems to be fundamentally different from that of the bacterial community which decomposes plant debris in eutrophic ecosystems at neutral pH.     

Decomposition of Carex and Sphagnum litter in two mesotrophic fens differing in dominant plant species

Peatlands can be classified into fens and bogs based on their hydrology. Development of fens to bogs is accompanied by the invasion of Sphagnum species. The purpose of this study was to determine how the decomposition process in fens is influenced by the transition from a vascular plant-dominated system to a Sphagnum -dominated system. We carried out a reciprocal litter bag experiment, using litter of Carex diandra , C. lasiocarpa , Sphagnum papillosum and S. squarrosum in a fen dominated by Sphagnum species and a fen without Sphagnum . Decomposition rate and nitrogen and phosphorus dynamics of the plant litter were measured in a field experiment for two years. Decomposition rate was highest for the Carex litter types and lowest for the Sphagnum litter types. Surprisingly, decomposition rates hardly differed between the two sites. Nutrient dynamics, however, showed a clear site-effect: In the Sphagnum site net mineralization was observed for all litter types whereas in the Carex site net immobilization was observed. These results show that carbon and nutrient cycles were coupled in a different way in a Sphagnum -dominated and a Carex -dominated site, respectively. Nutrient availability and adaptation of the microbial community to nutritional and other environmental conditions may be the main regulators of carbon and nutrient cycles in these peatlands.     

Classification and ordination of the mire vegetation of Stormyra near Tynset, S Norway

The vegetation of Stormyra, a flat fen at Tynset, in Hedmark province, Southern Norway is classified by cluster analyses into seven different plant communities, all of a nonfixed hierarchical, low rank as follows:
(1) Scorpidium scorpioides comm., (2) Campylium stellatum - Drepanocladus revolvers comm., (3) Carex rostrata - Calliergon giganteum comm., (4) Sphagnum papillosum - S. subfulvum comm., (5) Homalothecium nitens - Sphagnum warnstorfii comm., (6) Pinus sylvestris - Sphagnum angustifolium comm. and (7) Empetrum hermaphroditum - Sphagnum fuscum comm.
A DCA-ordination showed that the samples were distributed mainly along a hummock - mud-bottom vegetational gradient, reflecting the local groundwater level. The range of the plant communities in terms of the traditional poor - rich and mire expanse - mire margin vegetational gradients is also dealt with. The vegetation and its relationship to such environmental factors as the ground-water level, and its seasonal fluctuations, the supply or absence of running surface water, the pH and electrical conductivity, are also discussed.     

Interferences between Sphagnum and vascular plants: effects on plant community structure and peat formation

The interference between vascular plants and peat mosses with respect to nitrogen and phosphorus was studied in a fertilization experiment and with respect to competition for light in a removal experiment in poor fens with either soligenous or topogenous hydrology using Narthecium ossifragum (L.) Huds. and three species of Sphagnum sect. Sphagnum as targets. Adding fertilizer either on the moss surface or below it confirmed the hypotheses of an asymmetric competition for nutrients, viz. that the Sphagnum mosses relied on the atmospheric supply while Narthecium depended on mineralization in the peat. The results of the removal experiments and the negatively correlated growth of Narthecium and Sphagnum mosses demonstrated a symmetric competition for light. The intensity of the competition for light increased as the availability of N and P increased. The nutrient resources in the total biomass decreased with decreasing standing crop of Narthecium . Only with a considerable amount of mineral nutrients in the biomass has Narthecium the capacity to grow ahead of Sphagnum, because the asymmetric competition for N and P gives Sphagnum the capacity to reduce the performance of vascular plants. The mosses are more efficient in their use of nutrients and produce a decay-resistant litter inducing low mineralization and increasing the peat accumulation rate, and that withdraws N and P from the rhizosphere. The Sphagnum mosses thus act as ecological engineers structuring the plant community and determining the carbon balance of the system. The development of ombrotrophic conditions through peat accumulation seems less probable on soligenous than on topogenous mires owing to the higher mineralization rate there supporting the growth of the vascular plants. Correspondingly, disturbances of the Sphagnum cover, such as through airborne pollutants, increase the productivity of the vascular plants and decrease the capacity for carbon accumulation.     

Do bryophyte shoot systems function like vascular plant leaves or canopies? Functional trait relationships in Sphagnum mosses (Sphagnaceae)

Vascular plant leaf traits that influence photosynthetic function form the basis of mechanistic models of carbon exchange. Given their unique tissue organization, bryophytes may not express similar patterns. We investigated relationships among tissue, shoot, and canopy traits, and their associations with photosynthetic characteristics in 10 Sphagnum species. Trait relationships were organized around a primary dimension accounting for 43% of variation in 12 traits. There was no significant relationship between nitrogen content of shoot systems and maximum photosynthesis expressed on mass (A(mass)) or area (A(area)) bases due to nitrogen sequestration and storage within the canopy interior. This pattern differs from the distribution of nitrogen in vascular plant canopies. Thus, nitrogen and its relationship to carbon uptake in Sphagnum shoots does not conform to patterns of either vascular plant leaves or canopies. Species that concentrate biomass and nitrogen in the capitulum have enhanced rates of A(mass) and A(area). Consequently, A(area) was positively associated with N(area) of the capitulum only. Overall, water content and carotenoid concentration were the strongest predictors of both A(mass) and A(area) and these were expressed as inverse relationships. The relationships of plant traits in Sphagnum defines a principal trade-off between species that tolerate environmental stress and those that maximize carbon assimilation.     

Maternal transmission of cytoplasmic DNA in interspecific hybrids of peat mosses, Sphagnum (Bryophyta)

The progeny of spontaneous interspecific hybrid sporophytes of Sphagnum were used to analyse the inheritance of cytoplasmic DNA. The analysis showed that only the female parent donated chloroplasts and mitochondria in Sphagnum hybrids. Thus, this is the first study demonstrating maternal cytoplasmic inheritance in a nonvascular land plant. This finding has important implications for phylogenetic reconstructions utilizing chloroplast and mitochondrial DNA sequences as well as for the evolution of cytoplasmic inheritance in relation to the life cycle of land plants.     

The bryophyte genus Sphagnum is a reservoir for powerful and extraordinary antagonists and potentially facultative human pathogens

Sphagnum plants grow in natural, species-poor carpets at low pH but without any known substantial fungal disease. To investigate this phenomenon, we analysed bacterial populations associated with two Sphagnum species with different ecological behaviour, namely S. magellanicum and S. fallax, from three sites in Germany and three in Norway, with a special focus on the functional group of antagonists. The screening of 493 bacterial isolates for antagonistic activity against fungal pathogens resulted in 237 (48%) active isolates. We found a higher proportion of antagonists for S. magellanicum (24%) than we did for S. fallax (19%) in general. The majority of the antagonists belonged to the genera Serratia (15%), Burkholderia (13.5%), Staphylococcus (13.5%), and Pseudomonas (10%). In contrast to the high moss specificity found for antagonistic bacteria, Burkholderia as well as Serratia isolates with highly similar molecular fingerprints as ascertained by BOX-PCR for both Sphagnum species were found. Interestingly, a high proportion of antagonists, for example Staphylococcus, Hafnia, Yersinia, and Pantoea, were identified as strains that are known as facultative pathogens of humans. Sphagnum plants represent an ecological niche not only for diverse and extraordinary microbial populations with a high potential for biological control of plant pathogens but also for opportunistic human pathogens.     

Can small‐scale experiments predict ecosystem responses? An example from peatlands

Oligotrophic, Sphagnum -dominated peatlands have been regarded as long-term stable ecosystems that function as carbon sinks. As a result of environmental perturbations, particularly anthropogenic N deposition, this view is now increasingly questioned. We examined whether small-scale field experiments can predict the direction and magnitude of ecosystem responses to increased N supply. We, therefore, compared data from a 10-year field experiment (involving deposition of 2, 15 and 30 kg N ha⁻¹ year⁻¹) with data from a gradient associated with increased N deposition (2, 8 and 12 kg N ha⁻¹ year⁻¹). We chose to compare: (1) the physiological response of Sphagnum balticum , measured in the form of N accumulation as free amino acids (N_AA); and (2) changes in the total Sphagnum cover, the cover of S. balticum , and vascular plant cover. In all cases we found a highly significant correlation between the two data sets. We attribute the high correspondence between the two data sets to the key function of the dominant group of organisms, the Sphagna, that monopolize N availability and control the water balance, creating an environment hostile to vascular plants. Thus the key role of Sphagna as ecosystem engineers seems to supersede the role of other, scale-dependent processes. We also conclude that N_AA is a sensitive indicator that can be used to signal the slow and gradual shift from Sphagnum to vascular plant dominance.     

Polytrichum strictum as a Nurse-Plant in Peatland Restoration

Polytrichum strictum is a pioneer plant frequently found on bare peat substrate after perturbations (fire, peat extraction). Can this moss facilitate the return of Sphagnum species or other boreal plants after disturbances? Field surveys of abandoned peatlands after peat extraction revealed that Sphagnum was always found in association with P. strictum carpets. We conducted field experiments in abandoned peatlands and showed that P. strictum carpets were able to keep Sphagnum fragments more humid than bare peat but only when the P. strictum carpets were not totally bone dry. In general, daytime temperatures beneath P. strictum carpets and fragments were reduced during the day and increased during the night compared to bare peat. Polytrichum strictum carpets acted as a seed trap, retaining more artificial seeds than bare peat. Polytrichum strictum can be a nurse‐plant: after 16 months, vascular plants transplanted in the P. strictum carpet were healthier than the ones planted on bare peat. The use of P. strictum as a nurse‐plant in boreal forest or peatland restoration is recommended for sites prone to frost heaving and with harsh microclimatic conditions.     

Microsite and regional variation in the potential decay rate of Sphagnum magellanicum in south Swedish raised bogs

In southern Sweden there are regional gradients in the rate of atmospheric deposition of nitrogen, and the rate of N deposition has increased in recent decades This may have caused a shift in the growth-limiting nutrient of Sphagnum growth from nitrogen to phosphorus In this study, the influence of N and P concentrations on the decay of litter peat formed by Sphagnum magellanicum was examined A total of 90 litter peat samples formed by this species was collected from 15 raised bogs (3 sites per bog, 2 microsites per site) Total N and P of samples were determined and the rate of decomposition (C0₂ release) was measured under aerated, laboratory conditions at 18°C Differences in decomposition rates, N and P concentrations were most pronounced among microsites within sites, whereas no significant differences were observed among bogs The results indicate that decomposition of 5 magellanicum litter peat is influenced more by P than by N Thus, it appears that the recent increase in atmospheric N deposition has not had a large direct effect on peat decomposition rates It is suggested that the efficient uptake of N and P by the Sphagnum plant may lead to a positive feedback mechanism, whereby more slowly growing Sphagnum produces more nutrient-enriched litter peat with a more rapid decay Such a mechanism could promote the development of microtopography (hummocks and hollows) on bogs     

The interaction between epiphytic algae, a parasitic fungus and Sphagnum as affected by N and P

We report the effects of fertilisation with N and P on the infection of Sphagnum by its fungal parasite Lyophyllum palustre, the expansion of epiphytic algae and the interaction between the latter two from 1998 to 2001. We added 40 kg N ha⁻¹ yr⁻¹ or 3 kg P ha⁻¹ yr⁻¹ in a full factorial design at 4 field sites. In a greenhouse experiment we reinoculated Sphagnum to verify the identity of the fungus and its necrotic effect on Sphagnum .
Lyophyllum palustre was responsible for the necrosis of Sphagnum in our experiments. Adding N induced complete necrosis of Sphagnum cuspidatum by L. palustre , whereas adding P decreased the area of necrotic tissue. Disease severity was related to the N concentration in the Sphagnum capitula. In Sphagnum magellanicum and S. papillosum , infection with L. palustre resulted in defoliation of stem sections. Adding N stimulated the expansion of algae at all sites, reducing the volume of photosynthetic tissue in Sphagnum. The density of the film of algae in the treatments receiving N was a function of the frequency of defoliated Sphagnum stems.
We conclude that infection with parasitic fungi and, in humid environments, the expansion of epiphytic algae, may aggravate the impact of increased N deposition or of other ecosystem disturbances that affect nutrient availability.     

A

A valley mire was sampled on the flanks of Swampy Hill, east Otago, New Zealand. It formed in a narrow valley, apparently originally comprising two basins. The end of the mire nearest the outlet contained species typical of fens (i.e., rheotrophic mires). At the head of the valley there was a section of the mire with mixed vegetation cover comprising the tussock grass Chionochloa rubra, Sphagnum species, and cushion/herb/shrub cover. Ombrotrophic status of this section was indicated by a slightly raised profile, greater acidity, lower exchangeable Na and K, and lower substrate cation exchange capacity, identifying it as a bog. Total Ca:Mg molar ratios were generally above 1.0, but this rule-of-thumb for ombrotrophic status may be inapplicable here. It is not known whether New Zealand Sphagnum species are as efficient at lowering the pH as those investigated elsewhere. Macrofosssil evidence indicates that some components of the bog, such as Sphagnum and epacridaceous subshrubs, have remained constant, almost since the inception of the bog. However, Empodisma minus, currently absent from the bog and rare in the region, was present at one stage. The change from cover with Empodisma and Dracophyllum as significant components, to the present Chionochloa/Sphagnum/cushion composition, occurred a few hundred years ago, probably initiated by fire. Comparison with preliminary information for other bogs suggests that those in the eastern part of the South Island vary considerably in species composition, with individualistic assemblages of species. The site is seen as having high conservation values. To protect these values the bog needs protection from invasive exotic weeds, and from damage by wild pigs.     

Interactions among fungal community structure, litter decomposition and depth of water table in a cutover peatland

Peatlands are important reservoirs of carbon (C) but our understanding of C cycling on cutover peatlands is limited. We investigated the decomposition over 18 months of five types of plant litter (Calluna vulgaris, Eriophorum angustifolium, Eriophorum vaginatum, Picea sitchensis and Sphagnum auriculatum) at a cutover peatland in Scotland, at three water tables. We measured changes in C, nitrogen (N) and phosphorus (P) in the litter and used denaturing gradient gel electrophoresis to investigate changes in fungal community composition. The C content of S. auriculatum litter did not change throughout the incubation period whereas vascular plant litters lost 30-40% of their initial C. There were no differences in C losses between low and medium water tables, but losses were always significantly less at the high water table. Most litters accumulated N and E. angustifolium accumulated significant quantities of P. C, N and P were significant explanatory variables in determining changes in fungal community composition but explained <25% of the variation. Litter type was always a stronger factor than water table in determining either fungal community composition or turnover of C, N and P in litter. The results have implications for the ways restoration programmes and global climate change may impact upon nutrient cycling in cutover peatlands.     

Competition between Sphagnum magellanicum and Eriophorum angustifolium as affected by raised CO2 and increased N deposition

The competition between peat mosses ( Sphagnum ) and vascular plants as affected by raised CO₂ and increased N deposition was studied in a glasshouse experiment by exposing peat monoliths with monocultures and mixtures of Sphagnum magellanicum and Eriophorum angustifolium to ambient (350 ppmv) or raised (560 ppmv) atmospheric CO₂ concentrations, combined with low (no N addition) or high (5 g m⁻² yr⁻¹ added) N deposition. Growth of the two species was monitored for three growing seasons.
The presence of Eriophorum did not affect Sphagnum biomass, because Eriophorum density did not become high enough to severely shade the moss surface. In contrast, Sphagnum had a negative effect on Eriophorum biomass, particularly on the number of flowering stems. Possibly, the presence of a living Sphagnum layer decreased nutrient availability to Eriophorum by immobilising nutrients mineralised from the peat.
Raised CO₂ and/or increased N deposition did not change these competitive relationships between Sphagnum and Eriophorum , but had independent effects. Raised CO₂ had a positive effect both on Sphagnum and Eriophorum biomass, though on Eriophorum the effect was transient, probably because of P limitation. Nitrogen addition had a direct negative effect on Sphagnum height growth in the first growing season, but by the third year an increased shoot density had cancelled this out, so no N effect on Sphagnum biomass was present at the end of the experiment. The response of Eriophorum to N addition was small; N availability appeared not to limit its growth.     

Bryophyte and vascular plant responses to base-richness and water level gradients in Western Carpathian<Emphasis Type="Italic">Sphagnum</Emphasis>-rich mires

We investigated the importance of water chemistry and water regime for vascular plant and bryophyte species distribution in Western Carpathian mires dominated bySphagnum. Seventy-seven small circle plots distributed across a wide geographical area, a wide range of mineral richness and all possible microtopographical features were sampled in terms of species composition, physical-chemical water properties and water regime during one growing season. Both water chemistry and water regime were found to be important factors for vegetation composition. Bryophytes reflected only one clear gradient, connected to base-richness (pH, conductivity) and maximal water-level, whereas three different environmental gradients determined the occurrence of vascular plants: water-level amplitude, base-richness and an indistinct gradient presumably connected to peat layer thickness. When the entire data set was subjected to DCA ordination, the first resulting axis was governed by the bryophyte subset, whereas the second one was governed by the vascular plant subset. The species density of vascular plants was positively correlated with pH and conductivity. On the contrary, bryophyte species density showed no relationship to environmental factors. We further compared the pH values measured in groundwater and in water squeezed from bryophytes from the same plot; these plots were distributed along the base-richness gradient. Only in the acidic mires did the use of squeezed-water chemistry in the analyses give results similar to the use of groundwater pH. Further, we found thatSphagnum species with a similar response to the base-richness gradient had differentiated niches with respect to the water level gradient and vice versa.Sphagnum contortum andS. warnstorfii exhibiting the same demands for groundwater pH were segregated along the gradient of maximum water level. An analogous pattern was detected for acidophilous speciesSphagnum magellanicum andS. papillosum.     

Nitrogen fertilization reduces Sphagnum production in bog communities

The effects of increased nitrogen influx on Sphagnum growth and on interspecific competition between Sphagnum species were studied in a 3-yr experiment in mires situated in two areas with different rates of airborne N deposition. Sphagnum growth was recorded after various supplementary N influxes (0, 1, 3, 5 and 10 g m ⁻² yr⁻¹) in hummocks and lawn communities. Sphagnum biomass production decreased with increasing N influx in both areas. After the first season at the low-deposition site, Sphagnum showed an increased growth in length with the intermediate N treatment, but in the second and third seasons the control treatment had the highest growth in length. Capitulum dry mass increased with increasing N influx. Sphagnum N concentration and N/P quotient were higher at the high- than at the low-deposition site. The low quotient at the low-deposition site, together with the initial growth increase with intermediate N supplements, indicates that growth was N-limited at this site, but our lowest N supplement was sufficient to reduce growth. The N treatments had no effect on interspecific competition between the Sphagnum species. This indicates that the species have similar responses to N. The species studied all occur naturally on ombrotrophic, N-poor sites and show low tolerances to increased N influx. Reduced Sphagnum production may affect the carbon balance, changing the mires from C sinks to sources.