Transgenic Bt rice has adverse impacts on CH4 flux and rhizospheric methanogenic archaeal and methanotrophic bacterial communities

Background and Aims

The effect of transgenic insect-resistant crops on soil microorganisms has become an issue of public concern. The goal of this study was to firstly realize the variation of in situ methane (CH₄) emission flux and methanogenic and methanotrophic communities due to planting transgenic Bt rice (Bt) cultivar.

Methods

CH₄ emitted from paddy soil was collected by static closed chamber technique. Denaturing gradient gel electrophoresis and real-time PCR methods were employed to analyze methanogenic archaeal and methanotrophic bacterial community structure and abundance.

Results

Results showed that planting Bt rice cultivar effectively reduced in situ CH₄ emission flux and methanogenic archaeal and methanotrophic bacterial community abundance and diversity. Data analysis showed that in situ CH₄ emission flux increased significantly with the increase of methanogenic archaeal abundance (R ² ?=?0.839, p?<?0.001) and diversity index H′ (R ² ?=?0.729, p?<?0.05), whereas was not obviously related to methanotrophic bacterial community.

Conclusions

Our results suggested that the lower in situ CH₄ emission flux from Bt soil may result from lower methanogenic archaeal community abundance and diversity, lower methanogenic activity and higher methanotrophic activity. Moreover, our results inferred that specific functional microorganisms may be a more sensitive indicator than the total archaeal, bacterial or fungal population to assess the effects of transgenic insect-resistant plants on soil microorganisms.     

Colonization of rice roots with methanogenic archaea controls photosynthesis‐derived methane emission

The methane emitted from rice fields originates to a large part (up to 60%) from plant photosynthesis and is formed on the rice roots by methanogenic archaea. To investigate to which extent root colonization controls methane (CH₄) emission, we pulse‐labeled rice microcosms with ¹³CO₂ to determine the rates of ¹³CH₄ emission exclusively derived from photosynthates. We also measured emission of total CH₄ (¹²⁺¹³CH₄), which was largely produced in the soil. The total abundances of archaea and methanogens on the roots and in the soil were analysed by quantitative polymerase chain reaction of the archaeal 16S rRNA gene and the mcrA gene coding for a subunit of the methyl coenzyme M reductase respectively. The composition of archaeal and methanogenic communities was determined with terminal restriction fragment length polymorphism (T‐RFLP). During the vegetative growth stages, emission rates of ¹³CH₄ linearly increased with the abundance of methanogenic archaea on the roots and then decreased during the last plant growth stage. Rates of ¹³CH₄ emission and the abundance of methanogenic archaea were lower when the rice was grown in quartz‐vermiculite with only 10% rice soil. Rates of total CH₄ emission were not systematically related to the abundance of methanogenic archaea in soil plus roots. The composition of the archaeal communities was similar under all conditions; however, the analysis of mcrA genes indicated that the methanogens differed between the soil and root. Our results support the hypothesis that rates of photosynthesis‐driven CH₄ emission are limited by the abundance of methanogens on the roots.     

Influence of plant species and wastewater strength on constructed wetland methane emissions and associated microbial populations

Wastewater and treatment processes have been regarded as large contributions to sources of methane (CH₄). The flux rate of CH₄ in constructed wetlands (CWs) was evaluated to test the influence of plant species. Methane emission data showed large temporal and spatial variation ranging from 0 to 16.76 g CH₄ m⁻² day⁻¹. The highest CH₄ flux rate was obtained in the Zizania latifolia systems and higher emission was found with higher influent load. The methanogenic and methanotrophic microbial populations were studied to clarify the mechanisms of CH₄ emission. FISH analysis showed highest amounts of methanogens and methanotrophs in the Z. latifolia and Tytha latifolia systems. Linear regression between CH₄ emission and environmental parameters showed that the regression lines were not forced to pass through the origin, and the slopes of the lines of different systems were allowed to vary between vegetation cover.     

Methanotrophic Activity,Abundance, and Diversity in Forested Swamp Pools: Spatiotemporal Dynamics and Influences on Methane Fluxes

Methane oxidation (methanotrophy) in the water column and sediments of forested swamp pools likely control seasonal and annual emission of CH₄ from these systems, but the methanotrophic microbial communities, their activities, locations, and overall impact, is poorly understood. Several techniques including ¹⁴CH₄ oxidation assays, culture-based most probable number (MPN) estimates of methane-oxidizing bacteria (MOB) and protozoan abundance, MOB strain isolation and characterization, and PCR techniques were used to investigate methanotrophy at a forested swamp near Ithaca, New York. The greatest methanotrophic activity and largest numbers of MOB occurred predominantly at the low oxygen sediment/water interface in the water column. Seasonally, methanotrophic activity was very dynamic, ranging from 0.1 to 61.9 μ moles CH₄ d^?1 g^?1 dry sediment, and correlated most strongly with dissolved inorganic carbon (r = 0.896). Incorporation of methanotrophic variables (abundance and activity) into existing CH₄ flux regression models improved model fit, particularly during mid summer when CH₄ fluxes were most dynamic. Annually integrated methane flux and methanotrophic activity measurements indicate that differences in methanotrophic activity at the sediment/water interface likely accounted for differences in the annual CH₄ emission from the field site. Direct isolations of MOB resulted in the repeated isolation of organisms most closely related to Methylomonas methanica S1. A single acidophilic, type II MOB related to Methylocella palustris K was also isolated. Using a PCR-based MPN method and 16S rRNA genome copy number from isolates and control strains, type I and type II MOB were enumerated and revealed type I dominance of the sediment-associated MOB community.     

Methane oxidation and methane driven redox process during sequential reduction of a flooded soil ecosystem

A laboratory incubation study conducted to assess the temporal variation of CH₄ oxidation during soil reduction processes in a flooded soil ecosystem. A classical sequence of microbial terminal electron accepting process observed following NO₃ ^? reduction, Fe³⁺ reduction, SO₄ ^2? reduction and CH₄ production in flooded soil incubated under initial aerobic and helium-flushed anaerobic conditions. CH₄ oxidation in the slurries was influenced by microbial redox process during slurry reduction. Under aerobic headspace condition, CH₄ oxidation rate (k) was stimulated by 29 % during 5 days (NO₃ ^? reduction) and 32 % during both 10 days (Fe³⁺) and 20 days (early SO₄ ^2? reduction) over unreduced slurry. CH₄ oxidation was inhibited at the later methanogenic period. Contrastingly, CH₄ oxidation activity in anaerobic incubated slurries was characterized with prolonged lag phase and lower CH₄ oxidation. Higher CH₄ oxidation rate in aerobically incubated flooded soil was related to high abundance of methanotrophs (r?=?0.994, p?<?0.01) and ammonium oxidizers population (r?=?0.184, p?<?0.05). Effect of electron donors NH₄ ⁺, Fe^2+, S^2? on CH₄ oxidation assayed to define the interaction between reduced inorganic species and methane oxidation. The electron donors stimulated CH₄ oxidation as well as increased the abundance of methanotrophic microbial population except S^2? which inhibited the methanotrophic activity by affecting methane oxidizing bacterial population. Our result confirmed the complex interaction between methane-oxidizing microbial groups and redox species during sequential reduction processes of a flooded soil ecosystem.     

Activity, distribution, and abundance of methane-oxidizing bacteria in the near surface soils of onshore oil and gas fields

Methane-oxidizing bacteria (MOB) have long been used as an important biological indicator for oil and gas prospecting, but the ecological characteristics of MOB in hydrocarbon microseep systems are still poorly understood. In this study, the activity, distribution, and abundance of aerobic methanotrophic communities in the surface soils underlying an oil and gas field were investigated using biogeochemical and molecular ecological techniques. Measurements of potential methane oxidation rates and pmoA gene copy numbers showed that soils inside an oil and gas field are hot spots of methane oxidation and MOB abundance. Correspondingly, terminal restriction fragment length polymorphism analyses in combination with cloning and sequencing of pmoA genes also revealed considerable differences in the methanotrophic community composition between oil and gas fields and the surrounding soils. Principal component analysis ordination furthermore indicated a coincidence between elevated CH₄ oxidation activity and the methanotrophic community structure with type I methanotrophic Methylococcus and Methylobacter, in particular, as indicator species of oil and gas fields. Collectively, our results show that trace methane migrated from oil and gas reservoirs can considerably influence not only the quantity but also the structure of the methanotrophic community.     

Methanotrophic community structure and activity under warming and grazing of alpine meadow on the Tibetan Plateau

Knowledge about methanotrophs and their activities is important to understand the microbial mediation of the greenhouse gas CH₄ under climate change and human activities in terrestrial ecosystems. The effects of simulated warming and sheep grazing on methanotrophic abundance, community composition, and activity were studied in an alpine meadow soil on the Tibetan Plateau. There was high abundance of methanotrophs (1.2–3.4 × 10⁸ pmoA gene copies per gram of dry weight soil) assessed by real-time PCR, and warming significantly increased the abundance regardless of grazing. A total of 64 methanotrophic operational taxonomic units (OTUs) were obtained from 1,439 clone sequences, of these OTUs; 63 OTUs (98.4%) belonged to type I methanotrophs, and only one OTU was Methylocystis of type II methanotrophs. The methanotroph community composition and diversity were not apparently affected by the treatments. Warming and grazing significantly enhanced the potential CH₄ oxidation activity. There were significantly negative correlations between methanotrophic abundance and soil moisture and between methanotrophic abundance and NH₄–N content. The study suggests that type I methanotrophs, as the dominance, may play a key role in CH₄ oxidation, and the alpine meadow has great potential to consume more CH₄ under future warmer and grazing conditions on the Tibetan Plateau.     

Linking activity,composition and seasonal dynamics of atmospheric methane oxidizers in a meadow soil

Microbial oxidation is the only biological sink for atmospheric methane. We assessed seasonal changes in atmospheric methane oxidation and the underlying methanotrophic communities in grassland near Giessen (Germany), along a soil moisture gradient. Soil samples were taken from the surface layer (0–10 cm) of three sites in August 2007, November 2007, February 2008 and May 2008. The sites showed seasonal differences in hydrological parameters. Net uptake rates varied seasonally between 0 and 70 μg CH₄ m⁻² h⁻¹. Greatest uptake rates coincided with lowest soil moisture in spring and summer. Over all sites and seasons, the methanotrophic communities were dominated by uncultivated methanotrophs. These formed a monophyletic cluster defined by the RA14, MHP and JR1 clades, referred to as upland soil cluster alphaproteobacteria (USCα)-like group. The copy numbers of pmoA genes ranged between 3.8 × 10⁵–1.9 × 10⁶ copies g⁻¹ of soil. Temperature was positively correlated with CH₄ uptake rates (P<0.001), but had no effect on methanotrophic population dynamics. The soil moisture was negatively correlated with CH₄ uptake rates (P<0.001), but showed a positive correlation with changes in USCα-like diversity (P<0.001) and pmoA gene abundance (P<0.05). These were greatest at low net CH₄ uptake rates during winter times and coincided with an overall increase in bacterial 16S rRNA gene abundances (P<0.05). Taken together, soil moisture had a significant but opposed effect on CH₄ uptake rates and methanotrophic population dynamics, the latter being increasingly stimulated by soil moisture contents >50 vol% and primarily related to members of the MHP clade.     

Methane production potential and methanogenic archaea community dynamics along the Spartina alterniflora invasion chronosequence in a coastal salt marsh

Invasion by the exotic species Spartina alterniflora, which has high net primary productivity and superior reproductive capacity compared with native plants, has led to rapid organic carbon accumulation and increased methane (CH₄) emission in the coastal salt marsh of China. To elucidate the mechanisms underlying this effect, the methanogen community structure and CH₄ production potential as well as soil organic carbon (SOC), dissolved organic carbon, dissolved organic acids, methylated amines, aboveground biomass, and litter mass were measured during the invasion chronosequence (0–16 years). The CH₄ production potential in the S. alterniflora marsh (range, 2.94–3.95 μg kg^?1 day^?1) was significantly higher than that in the bare tidal mudflat. CH₄ production potential correlated significantly with SOC, acetate, and trimethylamine concentrations in the 0–20 cm soil layer. The abundance of methanogenic archaea also correlated significantly with SOC, and the dominant species clearly varied with S. alterniflora-driven SOC accumulation. The acetotrophic Methanosaetaceae family members comprised a substantial proportion of the methanogenic archaea in the bare tidal mudflat while Methanosarcinaceae family members utilized methylated amines as substrates in the S. alterniflora marsh. Ordination analysis indicated that trimethylamine concentration was the primary factor inducing the shift in the methanogenic archaea composition, and regressive analysis indicated that the facultative family Methanosarcinaceae increased linearly with trimethylamine concentration in the increasingly sulfate-rich salt marsh. Our results indicate that increased CH₄ production during the S. alterniflora invasion chronosequence was due to increased levels of the non-competitive substrate trimethylamine and a shift in the methanogenic archaea community.     

Effect of Temperature on Carbon and Electron Flow and on the Archaeal Community in Methanogenic Rice Field Soil

Temperature is an important factor controlling CH₄ production in anoxic rice soils. Soil slurries, prepared from Italian rice field soil, were incubated anaerobically in the dark at six temperatures of between 10 to 37°C or in a temperature gradient block covering the same temperature range at intervals of 1°C. Methane production reached quasi-steady state after 60 to 90 days. Steady-state CH₄ production rates increased with temperature, with an apparent activation energy of 61 kJ mol⁻¹. Steady-state partial pressures of the methanogenic precursor H₂ also increased with increasing temperature from <0.5 to 3.5 Pa, so that the Gibbs free energy change of H₂ plus CO₂-dependent methanogenesis was kept at −20 to −25 kJ mol of CH₄⁻¹ over the whole temperature range. Steady-state concentrations of the methanogenic precursor acetate, on the other hand, increased with decreasing temperature from <5 to 50 μM. Simultaneously, the relative contribution of H₂ as methanogenic precursor decreased, as determined by the conversion of radioactive bicarbonate to ¹⁴CH₄, so that the carbon and electron flow to CH₄ was increasingly dominated by acetate, indicating that psychrotolerant homoacetogenesis was important. The relative composition of the archaeal community was determined by terminal restriction fragment length polymorphism (T-RFLP) analysis of the 16S rRNA genes (16S rDNA). T-RFLP analysis differentiated the archaeal Methanobacteriaceae, Methanomicrobiaceae, Methanosaetaceae, Methanosarcinaceae, and Rice clusters I, III, IV, V, and VI, which were all present in the rice field soil incubated at different temperatures. The 16S rRNA genes of Rice cluster I and Methanosaetaceae were the most frequent methanogenic groups. The relative abundance of Rice cluster I decreased with temperature. The substrates used by this microbial cluster, and thus its function in the microbial community, are unknown. The relative abundance of acetoclastic methanogens, on the other hand, was consistent with their physiology and the acetate concentrations observed at the different temperatures, i.e., the high-acetate-requiring Methanosarcinaceae decreased and the more modest Methanosaetaceae increased with increasing temperature. Our results demonstrate that temperature not only affected the activity but also changed the structure and the function (carbon and electron flow) of a complex methanogenic system.     

Species-specific Effects of Vascular Plants on Carbon Turnover and Methane Emissions from Wetlands

Species composition affects the carbon turnover and the formation and emission of the greenhouse gas methane (CH₄) in wetlands. Here we investigate the individual effects of vascular plant species on the carbon cycling in a wetland ecosystem. We used a novel combination of laboratory methods and controlled environment facilities and studied three different vascular plant species (Eriophorum vaginatum, Carex rostrata and Juncus effusus) collected from the same wetland in southern Sweden. We found distinct differences in the functioning of these wetland sedges in terms of their effects on carbon dioxide (CO₂) and CH₄ fluxes, bubble emission of CH₄, decomposition of ¹⁴C-labelled acetate into ¹⁴CH₄ and ¹⁴CO₂, rhizospheric oxidation of CH₄ to CO₂ and stimulation of methanogenesis through root exudation of substrate (e.g., acetate). The results show that the emission of CH₄ from peat–plant monoliths was highest when the vegetation was dominated by Carex (6.76 mg CH₄ m⁻² h⁻¹) than when it was dominated by Eriophorum (2.38 mg CH₄ m⁻² h⁻¹) or Juncus (2.68 mg CH₄ m⁻² h⁻¹). Furthermore, the CH₄ emission seemed controlled primarily by the degree of rhizospheric CH₄ oxidation which was between 20 and 40% for Carex but >90% for both the other species. Our results point toward a direct and very important linkage between the plant species composition and the functioning of wetland ecosystems and indicate that changes in the species composition may alter important processes relating to controls of and interactions between greenhouse gas fluxes with significant implications for feedback mechanisms in a changing climate as a result.     

Substrate Specificity of Methanogenic Communities from Lake Baikal Bottom Sediments Associated with Hydrocarbon Gas Discharge

Methane production by microbial communities from Lake Baikal bottom sediments with different chemical composition of pore water was studied. Methane production was more active in the media supplemented with H₂: CO₂ and H₂ + CH₃COONa, rather than on media with acetate as the sole source of carbon and energy. Addition of methanol stimulated methane production only in the case of microbial communities from upper silts. Ability of the communities to produce methane correlated reliably with the concentrations of the NO^3–, SO₄^2?, Cl^–, and CH₃COO^– ions in the pore water of the relevant sediments. Cultivation of communities from the mud volcano sediments resulted in development of methanogenic archaea of the family Methanocellaсеае in the media supplemented with H₂: CO₂ and H₂ + CH₃COONa, while methanogenic archaea in the communities cultivated without additional substrates belonged to the genera Methanoregula, Methanobacterium, and Methanosaeta.     

Effects of nonmethane volatile organic compounds on microbial community of methanotrophic biofilter

Effects of nonmethane volatile organic compounds (NMVOCs) on methanotrophic biofilter were investigated. Laboratory-scale biofilters packed with pumice and granular-activated carbon (10:1, w/w) were operated with CH₄ and NMVOCs including dimethyl sulfide (DMS) and benzene/toluene (B/T). DMS alone exhibited a positive effect on the methanotrophic performance; however, the coexistence of B/T removed this effect. B/T alone exerted no effect on the performance. Pyrosequencing and quantitative PCR revealed that the NMVOCs strongly influenced the bacterial and methanotrophic communities but not the population density of methanotrophs. DMS alone diversified and changed both bacterial and methantrophic communities, but its effects were nullified by the presence of B/T. Canonical correspondence analysis revealed significant correlations between the NMVOCs and community composition and significant interaction between DMS and B/T. DMS did not affect the distribution of types I/II methanotrophs (60/40), while B/T increased the abundance of type I to 82 %. DMS and B/T favored the growth of the methanotrophic bacteria Methylosarcina and Methylomonas, respectively. These results suggest that NMVOCs can be a significant abiotic factor influencing methane biofiltration.     

Termite mounds contain soil-derived methanotroph communities kinetically adapted to elevated methane concentrations

Termite mounds have recently been confirmed to mitigate approximately half of termite methane (CH₄) emissions, but the aerobic CH₄ oxidising bacteria (methanotrophs) responsible for this consumption have not been resolved. Here, we describe the abundance, composition and CH₄ oxidation kinetics of the methanotroph communities in the mounds of three distinct termite species sampled from Northern Australia. Results from three independent methods employed show that methanotrophs are rare members of microbial communities in termite mounds, with a comparable abundance but distinct composition to those of adjoining soil samples. Across all mounds, the most abundant and prevalent methane monooxygenase sequences were affiliated with upland soil cluster α (USCα), with sequences homologous to Methylocystis and tropical upland soil cluster (TUSC) also detected. The reconstruction of a metagenome-assembled genome of a mound USCα representative highlighted the metabolic capabilities of this group of methanotrophs. The apparent Michaelis–Menten kinetics of CH₄ oxidation in mounds were estimated from in situ reaction rates. Methane affinities of the communities were in the low micromolar range, which is one to two orders of magnitude higher than those of upland soils, but significantly lower than those measured in soils with a large CH₄ source such as landfill cover soils. The rate constant of CH₄ oxidation, as well as the porosity of the mound material, were significantly positively correlated with the abundance of methanotroph communities of termite mounds. We conclude that termite-derived CH₄ emissions have selected for distinct methanotroph communities that are kinetically adapted to elevated CH₄ concentrations. However, factors other than substrate concentration appear to limit methanotroph abundance and hence these bacteria only partially mitigate termite-derived CH₄ emissions. Our results also highlight the predominant role of USCα in an environment with elevated CH₄ concentrations and suggest a higher functional diversity within this group than previously recognised.Subject terms: Soil microbiology, Biogeochemistry     

Plants,microorganisms, and soil temperatures contribute to a decrease in methane fluxes on a drained Arctic floodplain

As surface temperatures are expected to rise in the future, ice‐rich permafrost may thaw, altering soil topography and hydrology and creating a mosaic of wet and dry soil surfaces in the Arctic. Arctic wetlands are large sources of CH₄, and investigating effects of soil hydrology on CH₄ fluxes is of great importance for predicting ecosystem feedback in response to climate change. In this study, we investigate how a decade‐long drying manipulation on an Arctic floodplain influences CH₄‐associated microorganisms, soil thermal regimes, and plant communities. Moreover, we examine how these drainage‐induced changes may then modify CH₄ fluxes in the growing and nongrowing seasons. This study shows that drainage substantially lowered the abundance of methanogens along with methanotrophic bacteria, which may have reduced CH₄ cycling. Soil temperatures of the drained areas were lower in deep, anoxic soil layers (below 30 cm), but higher in oxic topsoil layers (0–15 cm) compared to the control wet areas. This pattern of soil temperatures may have reduced the rates of methanogenesis while elevating those of CH₄ oxidation, thereby decreasing net CH₄ fluxes. The abundance of Eriophorum angustifolium, an aerenchymatous plant species, diminished significantly in the drained areas. Due to this decrease, a higher fraction of CH₄ was alternatively emitted to the atmosphere by diffusion, possibly increasing the potential for CH₄ oxidation and leading to a decrease in net CH₄ fluxes compared to a control site. Drainage lowered CH₄ fluxes by a factor of 20 during the growing season, with postdrainage changes in microbial communities, soil temperatures, and plant communities also contributing to this reduction. In contrast, we observed CH₄ emissions increased by 10% in the drained areas during the nongrowing season, although this difference was insignificant given the small magnitudes of fluxes. This study showed that long‐term drainage considerably reduced CH₄ fluxes through modified ecosystem properties.     

Changes in Microbial Biofilm Communities during Colonization of Sewer Systems

The coexistence of sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) in anaerobic biofilms developed in sewer inner pipe surfaces favors the accumulation of sulfide (H₂S) and methane (CH₄) as metabolic end products, causing severe impacts on sewerage systems. In this study, we investigated the time course of H₂S and CH₄ production and emission rates during different stages of biofilm development in relation to changes in the composition of microbial biofilm communities. The study was carried out in a laboratory sewer pilot plant that mimics a full-scale anaerobic rising sewer using a combination of process data and molecular techniques (e.g., quantitative PCR [qPCR], denaturing gradient gel electrophoresis [DGGE], and 16S rRNA gene pyrotag sequencing). After 2 weeks of biofilm growth, H₂S emission was notably high (290.7 ± 72.3 mg S-H₂S liter⁻¹ day⁻¹), whereas emissions of CH₄ remained low (17.9 ± 15.9 mg COD-CH₄ liter⁻¹ day⁻¹). This contrasting trend coincided with a stable SRB community and an archaeal community composed solely of methanogens derived from the human gut (i.e., Methanobrevibacter and Methanosphaera). In turn, CH₄ emissions increased after 1 year of biofilm growth (327.6 ± 16.6 mg COD-CH₄ liter⁻¹ day⁻¹), coinciding with the replacement of methanogenic colonizers by species more adapted to sewer conditions (i.e., Methanosaeta spp.). Our study provides data that confirm the capacity of our laboratory experimental system to mimic the functioning of full-scale sewers both microbiologically and operationally in terms of sulfide and methane production, gaining insight into the complex dynamics of key microbial groups during biofilm development.     

Methane dynamics across wetland plant species

We examined patterns of methane flux, plant biomass, and microbial methanogenic populations in nine wetland plant species. Methane dynamics varied across plant functional groupings, with patterns distinctive among forbs, clonal dominants, and tussock/clump-forming graminoids. Carex stricta and Scirpus atrovirens showed the highest emissions (31.7 and 20.6 mg CH₄-C m⁻² h⁻¹), followed by other tussock- or clump-forming graminoids that averaged 11.0 mg CH₄-C m⁻² h⁻¹ (Scirpus cyperinus, Glyceria striata, and Juncus effusus). The clonal dominants (Phalaris arundinacea and Typha angustifolia) had the lowest methane emissions (1.3 and 3.4 mg CH₄-C m⁻² h⁻¹) of all seven graminoid species, and the forbs (Mimulus ringens and Verbena hastata) emitted no detectable methane flux from their leaves. In general, methane emissions decreased with greater plant biomass. Terminal restriction fragment analysis (T-RFLP) of archaeal 16S rRNA revealed that the structure of the soil methanogen communities isolated from plant rhizospheres had no effect on methane flux. The relative proportions of the different terminal fragments were not correlated with either methane emissions or plant biomass. Methanogen populations from J. effusus soils were dominated by acetoclastic archaea of the Methanosarcinaceae and Methanosaetaceae families, while all other graminoid soils were colonized primarily by hydrogenotrophic archaea of the Methanobacteriaceae family. The results indicate that plant functional groups and plant biomass are useful in predicting methane flux differences across plant species, while soil methanogen community structure showed no distinguishable patterns.     

Vegetation-Environment Relationships in Peatlands Dominated by Sphagnum fallax in Western Poland

We investigated species composition and relative abundance of Sphagnum fallax dominated peatlands in relation to measured environmental variables on the basis of 26 sites in the Wielkopolska region. Most studied plots were characterized by soft waters, poor in Ca²⁺ but rich in nutrients, especially N-NH₄ ⁺ and P-PO₄ ^3-, with high electrolytic conductivity and high DOC (dissolved organic carbon) concentration. Six of the 19 measured variables of surface water chemistry (DOC, pH, SO₄ ^2-, P-PO₄ ^3-, Na⁺ and Ca²⁺) significantly explained 23% of the variation in floristic composition. In 65 vegetation plots, 107 species were observed. Cluster analysis revealed four types of vegetation in the studied mires. Sphagnum fallax was the most abundant species and formed plant communities in a wide range of habitats: in floating mats, with the plants usually adjoining the mineral basin edge (e.g. E. vaginatum, Andromeda polifolia and Ledum palustre) as well as it occupied central parts of Sphagnum lawn (e.g. Eriophorum angustifolium) and rich fen habitats (e.g. Carex rostrata or Phragmites australis). In Wielkopolska terrestrializating peatlands, four variables determine the poor-rich gradient: conductivity, DOC, SiO₂ dissolved, Ca²⁺ and alkalinity. This study provides new data on the ecology and typology of Sphagnum peatlands in western Poland.