Subgenome analysis of two southern hemisphere allotriploid species in Sphagnum (Sphagnaceae)

Sphagnum ×australe s.l. and S. ×falcatulum s.l. are both cryptic species complexes of gametophytically allodiploid and allotriploid cytotypes, with the allodiploid cytotype being one parent of the respective allotriploid cytotype. Phylogenetic analyses of S. ×australe s.l. and S. ×falcatulum s.l. were undertaken using sequences from two plastid loci and cloned sequences from three nuclear loci. Subgenomes from three subgenera were detected in allotriploid S. ×australe. The haploid parent of allotriploid S. ×australe was S. fimbriatum (subg. Acutifolia). One of the two subgenomes contributed by allodiploid S. australe was associated with S. strictum (subg. Rigida); the parental species associated with the other subgenome could not be identified, either at the species level or in terms of subgenus association. It may represent an early diverging lineage of subg. Sphagnum or a previously undetected subgenus. Allotriploid S. ×falcatulum has subgenomes from two subgenera. This study confirms prior findings that S. cuspidatum (subg. Cuspidata) was the haploid parent of allotriploid S. ×falcatulum. One of the two subgenomes contributed by allodiploid S. ×falcatulum was associated with subg. Cuspidata (species unidentified) and the second was associated with subg. Subsecunda (species unidentified). Recurrent allopolyploidy appears to have been associated with the complex evolutionary processes (inter-subgeneric hybridization, interploidal hybridization, double allopolyploidy) which resulted in each of these two allotriploids. The highest level of divergence detected among the subgenomes in each of these Sphagnum allotriploids is comparable to the average genetic divergence reported for angiosperm allopolyploids.     

遮阴对两种泥炭藓植物生长及相互作用的影响

以大泥炭藓和喙叶泥炭藓为材料,研究遮阴对其生长及植物相互作用的影响.结果表明:在单种群中,遮阴处理明显促进了大泥炭藓的高生长,但对喙叶泥炭藓的生长以及大泥炭藓生物量和分枝数未产生影响;在混合群中,喙叶泥炭藓抑制了大泥炭藓生物量和分枝数的增长,而大泥炭藓对喙叶泥炭藓的生长无影响.随遮阴胁迫的增加,邻体对喙叶泥炭藓竞争加剧,当胁迫进一步增强,邻体效应有转变为正相互作用的趋势,但邻体对大泥炭藓的效应始终为竞争,未随胁迫增加而变化.     

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.     

The annual growth period of some Sphagnum species on the Silver Flowe National Nature Reserve,south-west Scotland

Abstract

The length of the annual growing season of five Sphagnum species was investigated on the Silver Flowe N.N.R. It ranged from five to six months for S. papillosum and S. magellanicum through approximately seven and ten months for S. capillifolium and S. auriculatum var. inundatum to twleve months for S. cuspidatum A mechanism of hollow and pool enlargement is proposed.     

Mineral nutrient economy in competing species of Sphagnum mosses

Bog vegetation, which is dominated by Sphagnum mosses, depends exclusively on aerial deposition of mineral nutrients. We studied how the main mineral nutrients are distributed between intracellular and extracellular exchangeable fractions and along the vertical physiological gradient of shoot age in seven Sphagnum species occupying contrasting bog microhabitats. While the Sphagnum exchangeable cation content decreased generally in the order Ca²⁺ ≥ K⁺, Na⁺, Mg²⁺ > Al³⁺ > NH₄ ⁺, intracellular element content decreased in the order N > K > Na, Mg, P, Ca, Al. Calcium occurred mainly in the exchangeable form while Mg, Na and particularly K, Al and N occurred inside cells. Hummock species with a higher cation exchange capacity (CEC) accumulated more exchangeable Ca²⁺, while the hollow species with a lower CEC accumulated more exchangeable Na⁺, particularly in dead shoot segments. Intracellular N and P, but not metallic elements, were consistently lower in dead shoot segments, indicating the possibility of N and P reutilization from senescing segments. The greatest variation in tissue nutrient content and distribution was between species from contrasting microhabitats. The greatest variation within microhabitats was between the dissimilar species S. angustifolium and S. magellanicum. The latter species had the intracellular N content about 40% lower than other species, including even this species when grown alone. This indicates unequal competition for N, which can lead to outcompeting of S. magellanicum from mixed patches. We assume that efficient cation exchange enables Sphagnum vegetation to retain immediately the cationic nutrients from rainwater. This may represent an important mechanism of temporal extension of mineral nutrient availability to subsequent slow intracellular nutrient uptake.     

Rockin' in rhythm,growth dynamics of the peat moss Sphagnum

The genus Sphagnum is an essential component in the formation and maintenance of high latitude peatlands, bogs and mires. The species grows in dense, extended mats of agglomerated shoots that allow it to retain water necessary for its growth. These mats are partly responsible for maintaining the right conditions for other species in these wetlands to thrive. In this issue of Physiologia Plantarum, Mironov et al. (2020) monitored the growth of Sphagnum riparium for a period of 4 years and revealed three distinct growth rhythms: a seasonal temperature dependent, a circalunar and a third one, synchronized with the circalunar. This synchronised nature of Sphagnum growth could contribute to its position as a key species in the maintenance of peatlands.     

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 CO₂ 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 CO₂ 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 effects of winter stress on Sphagnum species with contrasting macro- and microdistributions

Introduction. Sphagnum L. forms much of the ground cover in northern peatlands. Different species show affinities for bioclimatic regions in Europe (oceanic/continental; northern/southern) and species-specific tolerance of winter conditions can be a factor explaining their distribution.

Methods. We focussed on low temperature in a series of experiments and tested (1) the innate ability of a selection of Sphagnum species to tolerate low temperature in relation to their micro-topographic (wetness) and geographical (climate) distribution; (2) the rate of cold tolerance acquisition; and (3) the ability of species to survive a range of low temperature once cold hardened.

Key results. Our experiments showed that maximal PSII efficiency (F_v/F_m, chlorophyll fluorescence), growth rates and survival were all negatively affected by sub-zero temperatures. Environmental conditions associated with the onset of winter (colder nights and shorter days) triggered the acquisition of cold tolerance in Sphagnum.

Conclusions. The results were not unequivocal, but species associated with colder climates were generally more tolerant of sub-zero conditions. Species associated with the wettest and driest ends of the wetness gradient were more consistent in their responses than those in between, with wetter-dwelling species being less sensitive to sub-zero temperature than species found in drier microhabitats. Overall, our results suggest that adaptation to winter conditions contribute to the current distribution patterns of Sphagnum species.     

Microcosm tests of the effects of temperature and microbial species number on the decomposition of Carex aquatilis and Sphagnum fuscum litter from southern boreal peatlands

Increased decomposition rates in boreal peatlands with global warming might increase the release of atmospheric greenhouse gases, thereby producing a positive feedback to global warming. How temperature influences microbial decomposers is unclear. We measured in vitro rates of decomposition of senesced sedge leaves and rhizomes (Carex aquatilis), from a fen, and peat moss (Sphagnum fuscum), from a bog, at 14 and 20 degrees C by the three most frequently isolated fungi and bacteria from these materials. Decomposition rates of the bog litter decreased (5- to 17-fold) with elevated temperatures, and decomposition of the sedge litters was either enhanced (2- to 30-fold) or remained unaffected by elevated temperatures. The increased temperature regime always favoured fungal over bacterial decomposition rates (2- to 3-fold). Different physiological characteristics of these microbes suggest that fungi using polyphenolic polymers as a carbon source cause greater mass losses of these litters. Litter quality exerted a stronger influence on decomposition at elevated temperatures, as litter rich in nutrients decomposed more quickly than litter poorer in nutrients at higher temperatures (8.0%-25.7% for the sedge litters vs. 0.2% for the bryophyte litter). We conclude that not all peatlands may provide a positive feedback to global warming. Cautious extrapolation of our data to the ecosystem level suggests that decomposition rates in fens may increase and those in bogs may decrease under a global warming scenario.     

Plant species composition and vegetation structure of Sphagnum cultivation sites

Aims

The cultivation of Sphagnum mosses in paludiculture has high potential for the use of formerly drained peatlands under wet conditions. The aim of this study was to evaluate the plant species composition and vegetation structure of Sphagnum cultivation sites in comparison with near-natural donor sites and rewetted sites without Sphagnum introduction.

Location

Central Europe, northwest Germany close to the Dutch–German border.

Methods

The treatments (rewetting with and without Sphagnum introduction) and a near-natural donor as a reference were each studied at three different sites. At each site, bryophyte and vascular plant species composition as well as parameters of vegetation structure were sampled in 40 randomly positioned plots of 25 cm × 25 cm.

Results

In addition to the highly frequent Sphagnum, several further plant species typical of bogs were introduced. At two cultivation sites, the species composition showed a high degree of similarity to the near-natural donor sites, whereas the third site was more similar to the rewetted sites without the introduction of Sphagnum biomass. Rewetted sites were species-poor in comparison with all other sites. Apart from a high cover of Sphagnum, the vegetation structure at the cultivation sites differed significantly from the near-natural donor sites.

Conclusions

Sphagnum cultivation sites can be used to grow donor material for peatland restoration and contribute to species conservation by providing substitute habitat for bog-typical and threatened plant species.     

Responses of Sphagnum species to atmospheric nitrogen and sulphur deposition

The responses of Sphagnum species to atmospheric pollution by sulphur and nitrogen oxides are reviewed. An explanation of the tolerance of sulphur dioxide in Sphagnum cuspidatum is provided. This involves an exclusion mechanism by the oxidation of bisulphite ions to less toxic sulphate ions catalysed by the presence of iron and possibly other metals on the cell wall cation-exchange sites. Tolerance is influenced by changing the iron content of the plants. A similar mechanism may account for sulphur dioxide tolerance in Sphagnum recurvum.
Evidence for a close coupling of nitrate assimilation with the atmospheric nitrogen supply in ombrotrophic Sphagnum species in unpolluted regions is reviewed, and this coupling is shown to be lost in polluted environments with high atmospheric nitrogen supply. The potential effects of a supra-optimal atmospheric nitrogen supply to Sphagnum species on the ecology of mires is discussed.
The effects of nitrogen and sulphur pollutants on Sphagnum species are used to make broad generalizations as to how other bryophyte species might respond to these pollutants and to explain known effects of atmospheric pollution on bryophyte communities.     

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.     

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.     

The taxonomy and distribution of Azolla species in southern Africa

The three Azolla species which occur in southern Africa, A. pinnata var. pinnata, A. nilotica and A. filiculoides are identified and their distributions illustrated. The endosymbiotic cyanobacterium Anabaena azollae occurred in dorsal leaf lobe cavities of all three species. The first two species are indigenous to southern Africa, whilst the third, A. filiculoides , is an introduced species from North America. Possible means whereby this species could have been introduced are discussed.     

The vegetation of the moor house national nature reserve in the northern Pennines,England

Summary The vegetation of a 40 km² area in northern England, ranging in altitude from 300 to 850 m, is described. Sheep graze the whole area and influence the composition of most vegetation types. Trees are absent. Blanket bog poor in species predominates and grassy communities on acidic ill-drained soils have considerable extent. There are also limestone outcrops which give rise to Agrosto-Festucetum on mineral soils and a variety of species-rich bryophytic and herbaceous cummunities in eutrophic flushes. An attempt has been made to relate the vegetation units to the classifications used in central Europe.

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Zusammenfassung Die Vegetation von einem 40 km² großen Gebiet in Nordengland, auf Höhen von 300 bis 850 m, wird beschrieben. Schafe grasen auf dem ganzen Gebiet und bestimmen die Zusammensetzung der meisten Vegetationstypen. Bäume sind nicht vorhanden. Artenarmes Hochmoor prädominiert und Gras-Gesellschaften auf saurem, schlecht-entwässertem Boden kommen in beträchtlichem Ausmaß vor. Es gibt auch an die Oberfläche tretenden Kalkstein, der das Entstehen von Agrosto-Festucetum auf Mineralboden veranlasst und eine Mannigfaltigkeit von Moos- und Krautgesellschaften, die darin auf eutrophem Torfboden vielerlei Arten haben. Ein Versuch ist gemacht worden, die Vegetationseinheiten in die in Mitteleuropa gebräuchlichen Klassifikationen einzuordnen.