Responses of aerobic microbial communities and soil respiration to water-level drawdown in a northern boreal fen

Labile carbon-induced soil organic matter turnover in a subtropical forest under different redox conditions

Labile organic carbon (LOC) input strongly affects soil organic matter (SOM) dynamics, including gains and losses. However, it is unclear how redox fluctuations regulate these processes of SOM decomposition and formation induced by LOC input. The objective of this study was to explore the impacts of LOC input on SOM turnover under different redox conditions. Soil samples were collected in a subtropical forest. A single pulse of 13C-labeled glucose (i.e., LOC) was applied to the soil. Soil samples were incubated for 40 days under three redox treatments, including aerobic, anoxic, and 10-day aerobic followed by 10-day anoxic conditions. Results showed that LOC input affected soil priming and 13C-SOM accumulation differently under distinct redox conditions by altering the activities of various microorganisms. 13C-PLFAs (phospholipid fatty acids) were analyzed to determine the role of microbial groups in SOM turnover. Increased activities of fungi and gram-positive bacteria (i.e., the K-strategists) by LOC input could ingest metabolites or residues of the r-strategists (e.g., gram-negative bacteria) to result in positive priming. Fungi could use gram-negative bacteria to stimulate priming intensity via microbial turnover in aerobic conditions first. Reduced activities of K-strategists as a result of the aerobic to anoxic transition decreased priming intensity. The difference in LOC retention in SOM under different redox conditions was mainly attributable to 13C-particulate organic carbon (13C-POC) accumulation. Under aerobic conditions, fungi and gram-positive bacteria used derivatives from gram-negative bacteria to reduce newly formed POC. However, anoxic conditions were not conducive to the uptake of gram-negative bacteria by fungi and gram-positive bacteria, favoring SOM retention. This work indicated that redox-regulated microbial activities can control SOM decomposition and formation induced by LOC input. It is extremely valuable for understanding the contribution of soil affected by redox fluctuations to the carbon cycle.

Responses of soil microbes and enzymes to long-term warming incubation in different depths of permafrost peatland soil

Soil microbes and enzymes mediate soil carbon-climate feedback, and their responses to increasing temperature partly affect soil carbon stability subjected to the effects of climate change. We performed a 50-month incubation experiment to determine the effect of long-term warming on soil microbes and enzymes involved in carbon cycling along permafrost peatland profile (0-150 cm) and investigated their response to water flooding in the active soil layer. Soil bacteria, fungi, and most enzymes were observed to be sensitive to changes in temperature and water in the permafrost peatland. Bacterial and fungal abundance decreased in the active layer soil but increased in the deepest permafrost layer under warming. The highest decrease in the ratio of soil bacteria to fungi was observed in the deepest permafrost layer under warming. These results indicated that long-term warming promotes recalcitrant carbon loss in permafrost because fungi are more efficient in decomposing high-molecular-weight compounds. Soil microbial catabolic activity measured using Biolog Ecoplates indicated a greater degree of average well color development at 15 °C than at 5 °C. The highest levels of microbial catabolic activity, functional diversity, and carbon substrate utilization were found in the permafrost boundary layer (60-80 cm). Soil polyphenol oxidase that degrades recalcitrant carbon was more sensitive to increases in temperature than β-glucosidase, N-acetyl-β-glucosaminidase, and acid phosphatase, which degrade labile carbon. Increasing temperature and water flooding exerted a synergistic effect on the bacterial and fungal abundance and β-glucosidase, acid phosphatase, and RubisCO activity in the topsoil. Structural equation modeling analysis indicated that soil enzyme activity significantly correlated with ratio of soil bacteria to fungi and microbial catabolic activity. Our results provide valuable insights into the linkage response of soil microorganisms, enzymes to climate change and their feedback to permafrost carbon loss.

Short-term responses of the soil microbiome and its environment indicate an uncertain future of restored peatland forests

Restoring peatland ecosystems involves significant uncertainty due to complex ecological and socio-economic feedbacks as well as alternative stable ecological states. The primary aim of this study was to investigate to what extent the natural functioning of drainage-affected peat soils can be restored, and to examine role of soil microbiota in this recovery process. To address these questions, a large-scale before-after-control-impact (BACI) experiment was conducted in drained peatland forests in Estonia. The restoration treatments included ditch closure and partial tree cutting to raise the water table and restore stand structure. Soil samples and environmental data were collected before and 3-4 years after the treatments; the samples were subjected to metabarcoding to assess fungal and bacterial communities and analysed for their chemical properties. The study revealed some indicators of a shift toward the reference state (natural mixotrophic bog-forests): the spatial heterogeneity in soil fungi and bacteria increased, as well as the relative abundance of saprotrophic fungi; while nitrogen content in the soil decreased significantly. However, a general stability of other physico-chemical properties (including pH remaining elevated by ca. one unit) and annual fluctuations in the microbiome suggested that soil recovery will remain incomplete and patchy for decades. The main implication is the necessity to manage hydrologically restored peatland forests while explicitly considering an uncertain future and diverse outcomes. This includes their continuous monitoring and the adoption of a precautionary approach to prevent further damage both to these ecosystems and to surrounding intact peatlands.

Peat loss collocates with a threshold in plant-mycorrhizal associations in drained peatlands encroached by trees

Drainage-induced encroachment by trees may have major effects on the carbon balance of northern peatlands, and responses of microbial communities are likely to play a central mechanistic role. We profiled the soil fungal community and estimated its genetic potential for the decay of lignin and phenolics (class II peroxidase potential) along peatland drainage gradients stretching from interior locations (undrained, open) to ditched locations (drained, forested). Mycorrhizal fungi dominated the community across the gradients. When moving towards ditches, the dominant type of mycorrhizal association abruptly shifted from ericoid mycorrhiza to ectomycorrhiza at c. 120 m from the ditches. This distance corresponded with increased peat loss, from which more than half may be attributed to oxidation. The ectomycorrhizal genus Cortinarius dominated at the drained end of the gradients and its relatively higher genetic potential to produce class II peroxidases (together with Mycena) was positively associated with peat humification and negatively with carbon-to-nitrogen ratio. Our study is consistent with a plant-soil feedback mechanism, driven by a shift in the mycorrhizal type of vegetation, that potentially mediates changes in aerobic decomposition during postdrainage succession. Such feedback may have long-term legacy effects upon postdrainage restoration efforts and implication for tree encroachment onto carbon-rich soils globally.

Degradation Reduces Microbial Richness and Alters Microbial Functions in an Australian Peatland

Peatland ecosystems cover only 3% of the world's land area; however, they store one-third of the global soil carbon (C). Microbial communities are the main drivers of C decomposition in peatlands, yet we have limited knowledge of their structure and function. While the microbial communities in the Northern Hemisphere peatlands are well documented, we have limited understanding of microbial community composition and function in the Southern Hemisphere peatlands, especially in Australia. We investigated the vertical stratification of prokaryote and fungal communities from Wellington Plains peatland in the Australian Alps. Within the peatland complex, bog peat was sampled from the intact peatland and dried peat from the degraded peatland along a vertical soil depth gradient (i.e., acrotelm, mesotelm, and catotelm). We analyzed the prokaryote and fungal community structure, predicted functional profiles of prokaryotes using PICRUSt, and assigned soil fungal guilds using FUNGuild. We found that the structure and function of prokaryotes were vertically stratified in the intact bog. Soil carbon, manganese, nitrogen, lead, and sodium content best explained the prokaryote composition. Prokaryote richness was significantly higher in the intact bog acrotelm compared to degraded bog acrotelm. Fungal composition remained similar across the soil depth gradient; however, there was a considerable increase in saprotroph abundance and decrease in endophyte abundance along the vertical soil depth gradient. The abundance of saprotrophs and plant pathogens was two-fold higher in the degraded bog acrotelm. Soil manganese and nitrogen content, electrical conductivity, and water table level (cm) best explained the fungal composition. Our results demonstrate that both fungal and prokaryote communities are shaped by soil abiotic factors and that peatland degradation reduces microbial richness and alters microbial functions. Thus, current and future changes to the environmental conditions in these peatlands may lead to altered microbial community structures and associated functions which may have implications for broader ecosystem function changes in peatlands.

Diversity and Distribution Characteristics of Soil Microbes across Forest-Peatland Ecotones in the Permafrost Regions

Permafrost peatlands are a huge carbon pool that is uniquely sensitive to global warming. However, despite the importance of peatlands in global carbon sequestration and biogeochemical cycles, few studies have characterized the distribution characteristics and drivers of soil microbial community structure in forest-peatland ecotones. Here, we investigated the vertical distribution patterns of soil microbial communities in three typical peatlands along an environmental gradient using Illumina high-throughput sequencing. Our findings indicated that bacterial richness and diversity decreased with increasing soil depth in coniferous swamp (LT) and thicket swamp (HT), whereas the opposite trend was observed in a tussock swamp (NT). Additionally, these parameters decreased at 0-20 and 20-40 cm and increased at 40-60 cm along the environmental gradient (LT to NT). Principal coordinate analysis (PCoA) indicated that the soil microbial community structure was more significantly affected by peatland type than soil depth. Actinomycetota, Proteobacteria, Firmicutes, Chloroflexota, Acidobacteriota, and Bacteroidota were the predominant bacterial phyla across all soil samples. Moreover, there were no significant differences in the functional pathways between the three peatlands at each depth, except for amino acid metabolism, membrane transport, cell motility, and signal transduction. Redundancy analysis (RDA) revealed that pH and soil water content were the primary environmental factors influencing the bacterial community structure. Therefore, this study is crucial to accurately forecast potential changes in peatland ecosystems and improve our understanding of the role of peat microbes as carbon pumps in the process of permafrost degradation.

Land Cover and Land Use Change Decreases Net Ecosystem Production in Tropical Peatlands of West Kalimantan, Indonesia

Deforested and converted tropical peat swamp forests are susceptible to fires and are a major source of greenhouse gas (GHG) emissions. However, information on the influence of land-use change (LUC) on the carbon dynamics in these disturbed peat forests is limited. This study aimed to quantify soil respiration (heterotrophic and autotrophic), net primary production (NPP), and net ecosystem production (NEP) in peat swamp forests, partially logged forests, early seral grasslands (deforested peat), and smallholder-oil palm estates (converted peat). Peat swamp forests (PSF) showed similar soil respiration with logged forests (LPSF) and oil palm (OP) estates (37.7 Mg CO2 ha−1 yr−1, 40.7 Mg CO2 ha−1 yr−1, and 38.7 Mg CO2 ha−1 yr−1, respectively), but higher than early seral (ES) grassland sites (30.7 Mg CO2 ha−1 yr−1). NPP of intact peat forests (13.2 Mg C ha−1 yr−1) was significantly greater than LPSF (11.1 Mg C ha−1 yr−1), ES (10.8 Mg C ha−1 yr−1), and OP (3.7 Mg C ha−1 yr−1). Peat swamp forests and seral grasslands were net carbon sinks (10.8 Mg CO2 ha−1 yr−1 and 9.1 CO2 ha−1 yr−1, respectively). In contrast, logged forests and oil palm estates were net carbon sources; they had negative mean Net Ecosystem Production (NEP) values (−0.1 Mg CO2 ha−1 yr−1 and −25.1 Mg CO2 ha−1 yr−1, respectively). The shift from carbon sinks to sources associated with land-use change was principally due to a decreased Net Primary Production (NPP) rather than increased soil respiration. Conservation of the remaining peat swamp forests and rehabilitation of deforested peatlands are crucial in GHG emission reduction programs.

The Rhizosphere Responds: Rich Fen Peat and Root Microbial Ecology after Long-Term Water Table Manipulation

Hydrologic shifts due to climate change will affect the cycling of carbon (C) stored in boreal peatlands. Carbon cycling in these systems is carried out by microorganisms and plants in close association. This study investigated the effects of experimentally manipulated water tables (lowered and raised) and plant functional groups on the peat and root microbiomes in a boreal rich fen. All samples were sequenced and processed for bacterial, archaeal (16S DNA genes; V4), and fungal (internal transcribed spacer 2 [ITS2]) DNA. Depth had a strong effect on microbial and fungal communities across all water table treatments. Bacterial and archaeal communities were most sensitive to the water table treatments, particularly at the 10- to 20-cm depth; this area coincides with the rhizosphere or rooting zone. Iron cyclers, particularly members of the family Geobacteraceae, were enriched around the roots of sedges, horsetails, and grasses. The fungal community was affected largely by plant functional group, especially cinquefoils. Fungal endophytes (particularly Acephala spp.) were enriched in sedge and grass roots, which may have underappreciated implications for organic matter breakdown and cycling. Fungal lignocellulose degraders were enriched in the lowered water table treatment. Our results were indicative of two main methanogen communities, a rooting zone community dominated by the archaeal family Methanobacteriaceae and a deep peat community dominated by the family Methanomicrobiaceae. IMPORTANCE This study demonstrated that roots and the rooting zone in boreal fens support organisms likely capable of methanogenesis, iron cycling, and fungal endophytic association and are directly or indirectly affecting carbon cycling in these ecosystems. These taxa, which react to changes in the water table and associate with roots and, particularly, graminoids, may gain greater biogeochemical influence, as projected higher precipitation rates could lead to an increased abundance of sedges and grasses in boreal fens.

Site fertility and soil water-table level affect fungal biomass production and community composition in boreal peatland forests

A substantial amount of below-ground carbon (C) is suggested to be associated with fungi, which may significantly affect the soil C balance in forested ecosystems. Ergosterol from in-growth mesh bags and litterbags was used to estimate fungal biomass production and community composition in drained peatland forests with differing fertility. Extramatrical mycelia (EMM) biomass production was generally higher in the nutrient-poor site, increased with deeper water table level and decreased along the length of the recovery time. EMM biomass production was of the same magnitude as in mineral-soil forests. Saprotrophic fungal biomass production was higher in the nutrient-rich site. Both ectomycorrhizal (ECM) and saprotrophic fungal community composition changed according to site fertility and water table level. ECM fungal community composition with different exploration types may explain the differences in fungal biomass production between peatland forests. Melanin-rich Hyaloscypha may indicate decreased turnover of biomass in nutrient-rich young peatland forest. Genera Lactarius and Laccaria may be important in nutrient rich and Piloderma in the nutrient-poor conditions, respectively. Furthermore, Paxillus involutus and Cortinarius sp. may be important generalists in all sites and responsible for EMM biomass production during the first summer months. Saprotrophs showed a functionally more diverse fungal community in the nutrient-rich site.

Experimental nitrogen addition alters structure and function of a boreal poor fen: Implications for critical loads

Bogs and fens cover 6 and 21%, respectively, of the 140,329 km² Oil Sands Administrative Area in northern Alberta. Regional background atmospheric N deposition is low (<2 kg N ha^-1 yr^-1), but oil sands development has led to increasing N deposition (as high as 17 kg N ha^-1 yr^-1). To examine responses to N deposition, over five years, we experimentally applied N (as NH₄NO₃) to a poor fen near Mariana Lake, Alberta, unaffected by oil sands activities, at rates of 0, 5, 10, 15, 20, and 25 kg N ha^-1 yr^-1, plus controls (no water or N addition). At Mariana Lake Poor Fen (MLPF), increasing N addition: 1) progressively inhibited N₂-fixation; 2) had no effect on net primary production (NPP) of Sphagnum fuscum or S. angustifolium, while stimulating S. magellanicum NPP; 3) led to decreased abundance of S. fuscum and increased abundance of S. angustifolium, S. magellanicum, Andromeda polifolia, Vaccinium oxycoccos, and of vascular plants in general; 4) led to an increase in stem N concentrations in S. angustifolium and S. magellanicum, and an increase in leaf N concentrations in Chamaedaphne calyculata, Andromeda polifolia, and Vaccinium oxycoccos; 5) stimulated root biomass and production; 6) stimulated decomposition of cellulose, but not of Sphagnum or vascular plant litter; and 7) had no or minimal effects on net N mineralization in surface peat, NH₄⁺-N, NO₃^--N or DON concentrations in surface porewater, or peat microbial composition. Increasing N addition led to a switch from new N inputs being taken up primarily by Sphagnum to being taken up primarily by shrubs. MLPF responses to increasing N addition did not exhibit threshold triggers, but rather began as soon as N additions increased. Considering all responses to N addition, we recommend a critical load for poor fens in Alberta of 3 kg N ha^-1 yr^-1.

Microbial diversity along a gradient in peatlands treating mining-affected waters

Peatlands are used for the purification of mining-affected waters in Northern Finland. In Northern climate, microorganisms in treatment peatlands (TPs) are affected by long and cold winters, but studies about those microorganisms are scarce. Thus, the bacterial, archaeal and fungal communities along gradients of mine water influence in two TPs were investigated. The TPs receive waters rich in contaminants, including arsenic (As), sulfate (SO42-) and nitrate (NO3-). Microbial diversity was high in both TPs, and microbial community composition differed between the studied TPs. Bacterial communities were dominated by Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria, archaeal communities were dominated by Methanomicrobia and the Candidate phylum Bathyarchaeota, and fungal communities were dominated by Ascomycota (Leotiomycetes, Dothideomycetes, Sordariomycetes). The functional potential of the bacterial and archaeal communities in TPs was predicted using PICRUSt. Sampling points affected by high concentrations of As showed higher relative abundance of predicted functions related to As resistance. Functions potentially involved in nitrogen and SO42- turnover in TPs were predicted for both TPs. The results obtained in this study indicate that (i) diverse microbial communities exist in Northern TPs, (ii) the functional potential of the peatland microorganisms is beneficial for contaminant removal in TPs and (iii) microorganisms in TPs are likely well-adapted to high contaminant concentrations as well as to the Northern climate.

Effects of forest regeneration practices on the flux of soil CO2 after clear-cutting in subtropical China

Reforestation after clear-cutting is used to facilitate rapid establishment of new stands. However, reforestation may cause additional soil disturbance by affecting soil temperature and moisture, thus potentially influencing soil respiration. Our aim was to compare the effects of different reforestation methods on soil CO₂ flux after clear-cutting in a Chinese fir plantation in subtropical China: uncut (UC), clear-cut followed by coppicing regeneration without soil preparation (CC), clear-cut followed by coppicing regeneration and reforestation with soil preparation, tending in pits and replanting (CCR_P), and clear-cut followed by coppicing regeneration and reforestation with overall soil preparation, tending and replanting (CCR_O). Clear-cutting significantly increased the mean soil temperature and decreased the mean soil moisture. Compared to UC, CO₂ fluxes were 19.19, 37.49 and 55.93 mg m^-2 h^-1 higher in CC, CCR_P and CCR_O, respectively (P < 0.05). Differences in CO₂ fluxes were mainly attributed to changes in soil temperature, litter mass and the mixing of organic matter with mineral soil. The results suggest that, when compared to coppicing regeneration, reforestation practices result in additional CO₂ released, and that regarding the CO₂ emissions, soil preparation and tending in pits is a better choice than overall soil preparation and tending.

Patterns and drivers of fungal community depth stratification in Sphagnum peat

Peatlands store an immense pool of soil carbon vulnerable to microbial oxidation due to drought and intentional draining. We used amplicon sequencing and quantitative PCR to (i) examine how fungi are influenced by depth in the peat profile, water table and plant functional group at the onset of a multiyear mesocosm experiment, and (ii) test if fungi are correlated with abiotic variables of peat and pore water. We hypothesized that each factor influenced fungi, but that depth would have the strongest effect early in the experiment. We found that (i) communities were strongly depth stratified; fungi were four times more abundant in the upper (10-20 cm) than the lower (30-40 cm) depth, and dominance shifted from ericoid mycorrhizal fungi to saprotrophs and endophytes with increasing depth; (ii) the influence of plant functional group was depth dependent, with Ericaceae structuring the community in the upper peat only; (iii) water table had minor influences; and (iv) communities strongly covaried with abiotic variables, including indices of peat and pore water carbon quality. Our results highlight the importance of vertical stratification to peatland fungi, and the depth dependency of plant functional group effects, which must be considered when elucidating the role of fungi in peatland carbon dynamics.

Subtle shifts in microbial communities occur alongside the release of carbon induced by drought and rewetting in contrasting peatland ecosystems

Peat represents a globally significant pool of sequestered carbon. However, peatland carbon stocks are highly threatened by anthropogenic climate change, including drought, which leads to a large release of carbon dioxide. Although the enzymatic mechanisms underlying drought-driven carbon release are well documented, the effect of drought on peatland microbial communities has been little studied. Here, we carried out a replicated and controlled drought manipulation using intact peat ‘mesocosm cores’ taken from bog and fen habitats, and used a combination of community fingerprinting and sequencing of marker genes to identify community changes associated with drought. Community composition varied with habitat and depth. Moreover, community differences between mesocosm cores were stronger than the effect of the drought treatment, emphasising the importance of replication in microbial marker gene studies. While the effect of drought on the overall composition of prokaryotic and eukaryotic communities was weak, a subset of the microbial community did change in relative abundance, especially in the fen habitat at 5 cm depth. ‘Drought-responsive’ OTUs were disproportionately drawn from the phyla Bacteroidetes and Proteobacteria. Collectively, the data provide insights into the microbial community changes occurring alongside drought-driven carbon release from peatlands, and suggest a number of novel avenues for future research.

Experimental Climate Change Modifies Degradative Succession in Boreal Peatland Fungal Communities

Peatlands play an important role in global climate change through sequestration of atmospheric CO₂. Climate-driven changes in the structure of fungal communities in boreal peatlands that favor saprotrophic fungi can substantially impact carbon dynamics and nutrient cycling in these crucial ecosystems. In a mesocosm study using a full factorial design, 100 intact peat monoliths, complete with living Sphagnum and above-ground vascular vegetation, were subjected to three climate change variables (increased temperature, reduced water table, and elevated CO₂ concentrations). Peat litterbags were placed in mesocosms, and fungal communities in litterbags were monitored over 12 months to assess the impacts of climate change variables on peat-inhabiting fungi. Changes in fungal richness, diversity, and community composition were assessed using Illumina MiSeq sequencing of ribosomal DNA (rDNA). While general fungal richness reduced under warming conditions, Ascomycota exhibited higher diversity under increased temperature treatments over the course of the experiment. Both increased temperature and lowered water table position drove shifts in fungal community composition with a strong positive effect on endophytic and mycorrhizal fungi (including one operational taxonomic unit (OTU) tentatively identified as Barrenia panicia) and different groups of saprotrophs identified as Mortierella, Galerina, and Mycena. These shifts were observed during a predicted degradative succession in the decomposer community as different carbon substrates became available. Since fungi play a central role in peatland communities, increased abundances of saprotrophic fungi under warming conditions, at the expense of reduced fungal richness overall, may increase decomposition rates under future climate scenarios and could potentially aggravate the impacts of climate change.

Time-scales of hydrological forcing on the geochemistry and bacterial community structure of temperate peat soils

Peatlands are an important global carbon reservoir. The continued accumulation of carbon in peatlands depends on the persistence of anoxic conditions, in part induced by water saturation, which prevents oxidation of organic matter, and slows down decomposition. Here we investigate how and over what time scales the hydrological regime impacts the geochemistry and the bacterial community structure of temperate peat soils. Peat cores from two sites having contrasting groundwater budgets were subjected to four controlled drought-rewetting cycles. Pore water geochemistry and metagenomic profiling of bacterial communities showed that frequent water table drawdown induced lower concentrations of dissolved carbon, higher concentrations of sulfate and iron and reduced bacterial richness and diversity in the peat soil and water. Short-term drought cycles (3-9 day frequency) resulted in different communities from continuously saturated environments. Furthermore, the site that has more frequently experienced water table drawdown during the last two decades presented the most striking shifts in bacterial community structure, altering biogeochemical functioning of peat soils. Our results suggest that the increase in frequency and duration of drought conditions under changing climatic conditions or water resource use can induce profound changes in bacterial communities, with potentially severe consequences for carbon storage in temperate peatlands.

Effect of Dursban 480 EC (chlorpyrifos) and Talstar 10 EC (bifenthrin) on the physiological and genetic diversity of microorganisms in soil

This investigation was undertaken to determine the impact of the insecticides Dursban 480 EC (with organophosphate compound chlorpyrifos as the active ingredient) and Talstar 10 EC (with pyrethroid bifenthrin as the active ingredient) on the respiration activity and microbial diversity in a sandy loam luvisol soil. The insecticides were applied in two doses: the maximum recommended dose for field application (15 mg kg(-1) for Dursban 480 EC and 6 mg kg(-1) for Talstar 10 EC) and a 100-fold higher dose for extrapolation of their effect. Bacterial and fungal genetic diversity was analysed in soil samples using PCR DGGE and the functional diversity (catabolic potential) was studied using BIOLOG EcoPlates at 1, 3, 7, 14, 28, 56 and 112 days after insecticide application. Five bacterial groups (α, β, γ proteobacteria, firmibacteria and actinomycetes) and five groups of fungi or fungus-like microorganisms (Ascomycota, Basidiomycota, Chytridiomycota, Oomycota and Zygomycota) were analysed using specific primer sets. This approach provides high resolution of the analysis covering majority of microorganisms in the soil. Only the high-dose Dursban 480 EC significantly changed the community of microorganisms. We observed its negative effect on α- and γ-proteobacteria, as the number of OTUs (operational taxonomic units) decreased until the end of incubation. In the β-proteobacteria group, initial increase of OTUs was followed by strong decrease. Diversity in the firmibacteria, actinomycetes and Zygomycota groups was minimally disturbed by the insecticide application. Dursban 480 EC, however, both positively and negatively affected certain species. Among negatively affected species Sphingomonas, Flavobacterium or Penicillium were detected, but Achromobacter, Luteibacter or Aspergillus were supported by applied insecticide. The analysis of BIOLOG plates using AWCD values indicated a significant increase in metabolic potential of microorganisms in the soil after the high-dose Dursban application. Analysis of respiration demonstrated high microbial activity after insecticide treatments; thus, microbial degradation was relatively fast. The half-life of the active insecticide compounds were estimated within the range of 25 to 27 days for Talstar and 6 to 11 days for Dursban and higher doses stimulated degradation. The recommended dose levels of both insecticides can be considered as safe for microbial community in the soil.

The effects of salinization on aerobic and anaerobic decomposition and mineralization in peat meadows: the roles of peat type and land use

Peat soils comprise a large part of the western and northern Netherlands. Drainage for agriculture has caused increased soil aeration which has stimulated decomposition and, hence, soil subsidence, currently amounting to 1-2 cm/yr. River water is supplied to these peat areas in summer to prevent drying out of the peat soils. Saltwater intrusion and evaporation make this surface water slightly brackish during drought periods. In addition, brackish seepage can surface more easily during such dry periods. We performed an incubation experiment in which the effects of salinization on aerobic decomposition and mineralization of shallow peat samples and anaerobic decomposition and mineralization of deep peat samples were studied. We considered four different types of peat samples: peat sampled in agricultural peat meadows and in nature reserves, originally formed under either eutrophic or oligotrophic conditions. The aerobic decomposition was approximately reduced by 50% after salinization, whereas the anaerobic decomposition rates remained unchanged. Remarkably, the response to salinization did not differ between the peat types and land uses. Ammonium concentrations increased while nitrate concentrations decreased after salinization, probably as a result of reduced nitrification. Especially in the oligotrophic peat, ammonium concentrations increased substantially. Phosphate concentrations increased, possibly caused by changes in desorption and adsorption processes due to higher ion concentrations. DOC concentrations decreased in the brackish samples due to precipitation. Furthermore, the eutrophic peat samples showed increasing sulfate concentrations, both in oxic and anoxic incubations, which was attributed to pyrite oxidation. Independently of salinization, nitrification rates were higher in the agricultural, fertilized, peat soils. In conclusion, while salinization might reduce subsidence rates, it will have adverse effects on water quality.

Degradation and structure change of humic acids corresponding to water decline in Zoige peatland, Qinghai-Tibet Plateau

As the largest plateau-type wetland in the world and the largest peat storage in China, Zoige wetland faces severe water decline, and consequently accelerated peat degradation and carbon emission. Here, a variety of characterization approaches, including elemental analysis, UV-vis spectra, FT-IR spectra, and solid state (13)C NMR spectra were used to investigate the degradation and the structural shift of humic acids (HAs) in correspondence with serious water loss in Zoige peatland. Water loss derived from both natural slope and artificial drainage caused a substantial degradation of organic matter and HAs. Compared with the blocks immersed by free surface water, HAs extracted from the drier blocks had more pronounced signals of carboxyl and carbonyl groups, but carried lower content of methoxyl, carbohydrate, alcohol and ether groups. The total aliphatic carbon in HAs from natural-slope drier site decreased almost one half, but in the artificial-drained site, only slightly decreased. Correspondingly, the HA aromaticity substantially increased in the site undergoing the longer time of aerobic oxidation, whereas varied little in the site impacted by extensive water leaching.

Detrital floc and surface soil microbial biomarker responses to active management of the nutrient impacted Florida everglades

Alterations in microbial community composition, biomass, and function in the Florida Everglades impacted by cultural eutrophication reflect a new physicochemical environment associated with monotypic stands of Typha domingensis. Phospholipid fatty acid (PLFA) biomarkers were used to quantify microbial responses in detritus and surface soils in an active management experiment in the eutrophic Everglades. Creation of open plots through removal of Typha altered the physical and chemical characteristics of the region. Mass of PLFA biomarkers increased in open plots, but magnitude of changes differed among microbial groups. Biomarkers indicative of Gram-negative bacteria and fungi were significantly greater in open plots, reflective of the improved oxic environment. Reduction in the proportion of cyclopropyl lipids and the ratio of Gram-positive to Gram-negative bacteria in open plots further suggested an altered oxygen environment and conditions for the rapid growth of Gram-negative bacteria. Changes in the PLFA composition were greater in floc relative to soils, reflective of rapid inputs of new organic matter and direct interaction with the new physicochemical environment. Created open plot microbial mass and composition were significantly different from the oligotrophic Everglades due to differences in phosphorus availability, plant community structure, and a shift to organic peat from marl-peat soils. PLFA analysis also captured the dynamic inter-annual hydrologic variability, notably in PLFA concentrations, but to a lesser degree content. Recently, use of concentration has been advocated over content in studies of soil biogeochemistry, and our results highlight the differential response of these two quantitative measures to similar pressures.

Tricholoma matsutake dominates diverse microbial communities in different forest soils

Fungal and actinobacterial communities were analyzed together with soil chemistry and enzyme activities in order to profile the microbial diversity associated with the economically important mushroom Tricholoma matsutake. Samples of mycelium-soil aggregation (shiro) were collected from three experimental sites where sporocarps naturally formed. PCR was used to confirm the presence and absence of matsutake in soil samples. PCR-denaturing gradient gel electrophoresis (DGGE) fingerprinting and direct sequencing were used to identify fungi and actinobacteria in the mineral and organic soil layers separately. Soil enzyme activities and hemicellulotic carbohydrates were analyzed in a productive experimental site. Soil chemistry was investigated in both organic and mineral soil layers at all three experimental sites. Matsutake dominated in the shiro but also coexisted with a high diversity of fungi and actinobacteria. Tomentollopsis sp. in the organic layer above the shiro and Piloderma sp. in the shiro correlated positively with the presence of T. matsutake in all experimental sites. A Thermomonosporaceae bacterium and Nocardia sp. correlated positively with the presence of T. matsutake, and Streptomyces sp. was a common cohabitant in the shiro, although these operational taxonomic units (OTUs) did not occur at all sites. Significantly higher enzyme activity levels were detected in shiro soil. These enzymes are involved in the mobilization of carbon from organic matter decomposition. Matsutake was not associated with a particular soil chemistry compared to that of nearby sites where the fungus does not occur. The presence of a significant hemicellulose pool and the enzymes to degrade it indicates the potential for obtaining carbon from the soil rather than tree roots.

Quantitative PCR of pmoA using a novel reverse primer correlates with potential methane oxidation in Finnish fen

We report a new reverse primer (A621r) for use with A189f in PCR amplification of pmoA alleles in type II methanotrophs. The new primer combination was used to successfully amplify pmoA in peat monolith samples of various depths taken from fen-type peatlands in Finland. In quantitative PCR, pmoA amplicons produced from two sets of three replicate monoliths showed a significant Pearson correlation coefficient (r=0.77 and 0.61) with methane oxidation potential. The maximum methane oxidation potential and number of pmoA amplicons ranged between 8.8-40.5 micromol g (dry weight)(-1) d(-1) and 5.5 x 10(7)-18.7 x 10(7) g (wet weight)(-1), respectively, occurring in depths between 10 and 30 cm beneath the surface in the seven individual monoliths used in this study.