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William W Mohn - One of the best experts on this subject based on the ideXlab platform.
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unexpectedly high bacterial diversity in arctic Tundra relative to boreal forest Soils revealed by serial analysis of ribosomal sequence tags
Applied and Environmental Microbiology, 2005Co-Authors: Josh D Neufeld, William W MohnAbstract:Arctic Tundra and boreal forest Soils have globally relevant functions that affect atmospheric chemistry and climate, yet the bacterial composition and diversity of these Soils have received little study. Serial analysis of ribosomal sequence tags (SARST) and denaturing gradient gel electrophoresis (DGGE) were used to compare composite Soil samples taken from boreal and arctic biomes. This study comprises an extensive comparison of geographically distant Soil bacterial communities, involving the analysis of 12,850 ribosomal sequence tags from six composite Soil samples. Bacterial diversity estimates were greater for undisturbed arctic Tundra Soil samples than for boreal forest Soil samples, with the highest diversity associated with a sample from an extreme northern location (82oN). The lowest diversity estimate was obtained from an arctic Soil sample that was disturbed by compaction and sampled from a greater depth. Since samples from the two biomes did not form distinct clusters on the basis of SARST data and DGGE fingerprints, factors other than latitude likely influenced the phylogenetic compositions of these communities. The high number of ribosomal sequences analyzed enabled the identification of possible cosmopolitan and endemic bacterial distributions in particular Soils.
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unexpectedly high bacterial diversity in arctic Tundra relative to boreal forest Soils revealed by serial analysis of ribosomal sequence tags
Applied and Environmental Microbiology, 2005Co-Authors: Josh D Neufeld, William W MohnAbstract:Arctic and boreal environments cover 22% of the terrestrial surface of the planet and are sensitive to climate change, and changes in their productivity have substantial impacts on the global climate (7). Considering the critical role that the microbial components of these Soils play, it is surprising how little is known about their composition and distribution. In particular, arctic Tundra Soil is poorly studied, and its microbial communities are commonly assumed to be species poor (15, 17). In fact, the application of genomic research in polar biology is considered a “test bed” for extrapolation to more complex ecosystems (28). However, recent results have suggested that polar environments may contain substantial microbial diversity. Schadt et al. (32) used biomass measurements and fungal sequence libraries to describe unexpectedly high fungal diversity and activity in snow-covered Tundra Soils. Furthermore, DNA reassociation analysis from a variety of Soils indicated that genetic diversity in high arctic Tundra was similar to that in temperate Soils (31). Previously, only one study investigated Tundra bacterial diversity by examining a 16S rRNA gene clone library. Zhou et al. (39) screened 43 clones from a Siberian Tundra by using restriction fragment length polymorphism. They demonstrated maximum possible diversity, because all clones had unique restriction fragment length polymorphism patterns. Similar high diversity was observed for Wisconsin agricultural Soil (4) and a tropical forest Soil (5). However, all these studies involved small clone libraries, which preclude relative comparisons of diversity. Prior to this study, there was no published evidence suggesting that bacterial diversity in arctic Tundra was higher or lower than that in different geographical regions. Cloning and sequencing of PCR-amplified 16S rRNA genes are commonly used methods for profiling microbial community composition (14). However, labor and cost limitations have precluded sample sizes of greater than a few hundred sequences. These sample sizes are too small to adequately describe and compare multiple microbial communities containing thousands of species (19), such as those found in pristine Soil and sediment samples (21, 36). Toward overcoming these limitations, serial analysis of ribosomal sequence tags (SARST) was developed for amplification of a highly variable region of the 16S rRNA gene and ligation of these fragments into concatemers that are cloned and sequenced (22, 29, 30). The power of this method is that variable regions from many different organisms are obtained from each sequencing reaction. In this study, SARST and denaturing gradient gel electrophoresis (DGGE) were used to examine the relative abundance and diversity of bacteria in composite Soil samples from five undisturbed sites in the boreal forest and arctic Tundra biomes. A sample from a disturbed arctic site was also characterized, in which the Soil was compacted during construction of a pad supporting a fuel storage tank. Analysis of between 1,487 and 2,659 ribosomal sequence tags (RSTs) from each sample, with a total of 12,850 RSTs, provided the basis for robust estimates of phylotype richness and composition. RST library analysis indicated a positive correlation between diversity and latitude, contrary to the latitudinal biodiversity gradient observed for most biodiversity on earth (38). Similarity analysis of SARST and DGGE data determined that samples did not form discrete biome-specific clusters, indicating that factors other than those represented by latitude governed the microbial community compositions of these geographically distant Soils. The large collection of RSTs from each sample provided evidence for potentially endemic and cosmopolitan distributions of bacteria within these Soil environments.
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apparent contradiction psychrotolerant bacteria from hydrocarbon contaminated arctic Tundra Soils that degrade diterpenoids synthesized by trees
Applied and Environmental Microbiology, 2000Co-Authors: Gordon R Stewart, William W MohnAbstract:Resin acids are tricyclic terpenoids occurring naturally in trees. We investigated the occurrence of resin acid-degrading bacteria on the Arctic Tundra near the northern coast of Ellesmere Island (82 degrees N, 62 degrees W). According to most-probable-number assays, resin acid degraders were abundant (10(3) to 10(4) propagules/g of Soil) in hydrocarbon-contaminated Soils, but they were undetectable (<3 propagules/g of Soil) in pristine Soils from the nearby Tundra. Plate counts indicated that the contaminated and the pristine Soils had similar populations of heterotrophs (10(6) to 10(7) propagules/g of Soil). Eleven resin acid-degrading bacteria belonging to four phylogenetically distinct groups were enriched and isolated from the contaminated Soils, and representative isolates of each group were further characterized. Strains DhA-91, IpA-92, and IpA-93 are members of the genus Pseudomonas. Strain DhA-95 is a member of the genus Sphingomonas. All four strains are psychrotolerant, with growth temperature ranges of 4 degrees C to 30 degrees C (DhA-91 and DhA-95) or 4 degrees C to 22 degrees C (IpA-92 and IpA-93) and with optimum temperatures of 15 to 22 degrees C. Strains DhA-91 and DhA-95 grew on the abietanes, dehydroabietic and abietic acids, but not on the pimaranes, isopimaric and pimaric acids. Strains IpA-92 and IpA-93 grew on the pimaranes but not the abietanes. All four strains grew on either aliphatic or aromatic hydrocarbons, which is unusual for described resin acid degraders. Eleven mesophilic resin acid degraders did not use hydrocarbons, with the exception of two Mycobacterium sp. strains that used aliphatic hydrocarbons. We conclude that hydrocarbon contamination in Arctic Tundra Soil indirectly selected for resin acid degraders, selecting for hydrocarbon degraders that coincidentally use resin acids. Psychrotolerant resin acid degraders are likely important in the global carbon cycle and may have applications in biotreatment of pulp and paper mill effluents.
Josh D Neufeld - One of the best experts on this subject based on the ideXlab platform.
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ORIGINAL ARTICLE Targeted recovery of novel phylogenetic diversity from next-generation sequence data
2016Co-Authors: Michael Dj Lynch, Andrea K Bartram, Josh D NeufeldAbstract:Next-generation sequencing technologies have led to recognition of a so-called ‘rare biosphere’. These microbial operational taxonomic units (OTUs) are defined by low relative abundance and may be specifically adapted to maintaining low population sizes. We hypothesized that mining of low-abundance next-generation 16S ribosomal RNA (rRNA) gene data would lead to the discovery of novel phylogenetic diversity, reflecting microorganisms not yet discovered by previous sampling efforts. Here, we test this hypothesis by combining molecular and bioinformatic approaches for targeted retrieval of phylogenetic novelty within rare biosphere OTUs. We combined BLASTN network analysis, phylogenetics and targeted primer design to amplify 16S rRNA gene sequences from unique potential bacterial lineages, comprising part of the rare biosphere from a multi-million sequence data set from an Arctic Tundra Soil sample. Demonstrating the feasibility of the protocol developed here, three of seven recovered phylogenetic lineages represented extremely divergent taxonomic entities. These divergent target sequences correspond to (a) a previously unknown lineage within the BRC1 candidate phylum, (b) a sister group to the early diverging and currently recognized monospecific Cyanobacteria Gloeobacter, a genus containing multiple plesiomorphic traits and (c) a highly divergent lineage phylogenetically resolved within mitochondria. A comparison to twelve next-generation data sets from additional Soils suggested persistent low-abundance distributions of these novel 16S rRNA genes. The results demonstrate this sequence analysis and retrieval pipeline as applicable for exploring underrepresented phylogenetic novelty and recovering taxa that may represent significant steps in bacterial evolution
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generation of multimillion sequence 16s rrna gene libraries from complex microbial communities by assembling paired end illumina reads
Applied and Environmental Microbiology, 2011Co-Authors: Andrea K Bartram, Michael D Lynch, Jennifer C Stearns, Gabriel Morenohagelsieb, Josh D NeufeldAbstract:Microbial communities host unparalleled taxonomic diversity. Adequate characterization of environmental and host-associated samples remains a challenge for microbiologists, despite the advent of 16S rRNA gene sequencing. In order to increase the depth of sampling for diverse bacterial communities, we developed a method for sequencing and assembling millions of paired-end reads from the 16S rRNA gene (spanning the V3 region; ∼200 nucleotides) by using an Illumina genome analyzer. To confirm reproducibility and to identify a suitable computational pipeline for data analysis, sequence libraries were prepared in duplicate for both a defined mixture of DNAs from known cultured bacterial isolates (>1 million postassembly sequences) and an Arctic Tundra Soil sample (>6 million postassembly sequences). The Illumina 16S rRNA gene libraries represent a substantial increase in number of sequences over all extant next-generation sequencing approaches (e.g., 454 pyrosequencing), while the assembly of paired-end 125-base reads offers a methodological advantage by incorporating an initial quality control step for each 16S rRNA gene sequence. This method incorporates indexed primers to enable the characterization of multiple microbial communities in a single flow cell lane, may be modified readily to target other variable regions or genes, and demonstrates unprecedented and economical access to DNAs from organisms that exist at low relative abundances.
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unexpectedly high bacterial diversity in arctic Tundra relative to boreal forest Soils revealed by serial analysis of ribosomal sequence tags
Applied and Environmental Microbiology, 2005Co-Authors: Josh D Neufeld, William W MohnAbstract:Arctic Tundra and boreal forest Soils have globally relevant functions that affect atmospheric chemistry and climate, yet the bacterial composition and diversity of these Soils have received little study. Serial analysis of ribosomal sequence tags (SARST) and denaturing gradient gel electrophoresis (DGGE) were used to compare composite Soil samples taken from boreal and arctic biomes. This study comprises an extensive comparison of geographically distant Soil bacterial communities, involving the analysis of 12,850 ribosomal sequence tags from six composite Soil samples. Bacterial diversity estimates were greater for undisturbed arctic Tundra Soil samples than for boreal forest Soil samples, with the highest diversity associated with a sample from an extreme northern location (82oN). The lowest diversity estimate was obtained from an arctic Soil sample that was disturbed by compaction and sampled from a greater depth. Since samples from the two biomes did not form distinct clusters on the basis of SARST data and DGGE fingerprints, factors other than latitude likely influenced the phylogenetic compositions of these communities. The high number of ribosomal sequences analyzed enabled the identification of possible cosmopolitan and endemic bacterial distributions in particular Soils.
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unexpectedly high bacterial diversity in arctic Tundra relative to boreal forest Soils revealed by serial analysis of ribosomal sequence tags
Applied and Environmental Microbiology, 2005Co-Authors: Josh D Neufeld, William W MohnAbstract:Arctic and boreal environments cover 22% of the terrestrial surface of the planet and are sensitive to climate change, and changes in their productivity have substantial impacts on the global climate (7). Considering the critical role that the microbial components of these Soils play, it is surprising how little is known about their composition and distribution. In particular, arctic Tundra Soil is poorly studied, and its microbial communities are commonly assumed to be species poor (15, 17). In fact, the application of genomic research in polar biology is considered a “test bed” for extrapolation to more complex ecosystems (28). However, recent results have suggested that polar environments may contain substantial microbial diversity. Schadt et al. (32) used biomass measurements and fungal sequence libraries to describe unexpectedly high fungal diversity and activity in snow-covered Tundra Soils. Furthermore, DNA reassociation analysis from a variety of Soils indicated that genetic diversity in high arctic Tundra was similar to that in temperate Soils (31). Previously, only one study investigated Tundra bacterial diversity by examining a 16S rRNA gene clone library. Zhou et al. (39) screened 43 clones from a Siberian Tundra by using restriction fragment length polymorphism. They demonstrated maximum possible diversity, because all clones had unique restriction fragment length polymorphism patterns. Similar high diversity was observed for Wisconsin agricultural Soil (4) and a tropical forest Soil (5). However, all these studies involved small clone libraries, which preclude relative comparisons of diversity. Prior to this study, there was no published evidence suggesting that bacterial diversity in arctic Tundra was higher or lower than that in different geographical regions. Cloning and sequencing of PCR-amplified 16S rRNA genes are commonly used methods for profiling microbial community composition (14). However, labor and cost limitations have precluded sample sizes of greater than a few hundred sequences. These sample sizes are too small to adequately describe and compare multiple microbial communities containing thousands of species (19), such as those found in pristine Soil and sediment samples (21, 36). Toward overcoming these limitations, serial analysis of ribosomal sequence tags (SARST) was developed for amplification of a highly variable region of the 16S rRNA gene and ligation of these fragments into concatemers that are cloned and sequenced (22, 29, 30). The power of this method is that variable regions from many different organisms are obtained from each sequencing reaction. In this study, SARST and denaturing gradient gel electrophoresis (DGGE) were used to examine the relative abundance and diversity of bacteria in composite Soil samples from five undisturbed sites in the boreal forest and arctic Tundra biomes. A sample from a disturbed arctic site was also characterized, in which the Soil was compacted during construction of a pad supporting a fuel storage tank. Analysis of between 1,487 and 2,659 ribosomal sequence tags (RSTs) from each sample, with a total of 12,850 RSTs, provided the basis for robust estimates of phylotype richness and composition. RST library analysis indicated a positive correlation between diversity and latitude, contrary to the latitudinal biodiversity gradient observed for most biodiversity on earth (38). Similarity analysis of SARST and DGGE data determined that samples did not form discrete biome-specific clusters, indicating that factors other than those represented by latitude governed the microbial community compositions of these geographically distant Soils. The large collection of RSTs from each sample provided evidence for potentially endemic and cosmopolitan distributions of bacteria within these Soil environments.
Max M. Häggblom - One of the best experts on this subject based on the ideXlab platform.
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granulicella arctica sp nov granulicella mallensis sp nov granulicella tundricola sp nov and granulicella sapmiensis sp nov novel acidobacteria from Tundra Soil
International Journal of Systematic and Evolutionary Microbiology, 2012Co-Authors: Minna K. Männistö, Suman R. Rawat, Valentin Starovoytov, Max M. HäggblomAbstract:Four aerobic bacteria, designated MP5ACTX2(T), MP5ACTX8(T), MP5ACTX9(T) and S6CTX5A(T), were isolated from Tundra Soil of north-western Finland (69° 03' N 20° 50' E). Cells of all isolates were Gram-negative, non-motile rods. Phylogenetic analysis indicated that they belonged to the genus Granulicella of subdivision 1 of the phylum Acidobacteriahttp://dx.doi.org/10.1601/nm.7918. 16S rRNA gene sequence similarity between the new isolates and the type strains of Granulicella aggregans, Granulicella paludicola, Granulicella pectinivorans and Granulicella rosea ranged from 94 to 99 %. Analysis of the RNA polymerase beta subunit (rpoB) gene sequence indicated that the isolates represented novel species of the genus Granulicella (<92 % rpoB sequence similarity between the isolates and members of the genus Granulicella). This was also confirmed by low DNA-DNA relatedness (31 %) between strain S6CTX5A(T) and the type strain of G. pectinivorans, which exhibited 99.1 % 16S rRNA gene sequence similarity and 91.7 % rpoB gene sequence similarity. The isolates grew at pH 3.5-6.5 and at 4-26 °C. Sugars were the preferred growth substrates. The major cellular fatty acids were iso-C(15 : 0), C(16 : 1)ω7c and C(16 : 0) and the major isoprenoid quinone was MK-8. The DNA G+C content was 56-60 mol%. On the basis of phylogenetic analysis and chemotaxonomic and physiological data, the isolates represent four novel species of the genus Granulicella, for which the names Granulicella arctica MP5ACTX2(T) (= ATCC BAA-1858(T) = DSM 23128(T)), Granulicella mallensis MP5ACTX8(T) (= ATCC BAA-1857(T) = DSM 23137(T)), Granulicella tundricola MP5ACTX9(T) (ATCC BAA-1859(T) = DSM 23138(T)) and Granulicella sapmiensis S6CTX5A(T) (= LMG 26174(T) = DSM 23136(T)) are proposed. An emended description of the genus Granulicella is also presented.
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Comparative genomic and physiological analysis provides insights into the role of Acidobacteria in organic carbon utilization in Arctic Tundra Soils.
FEMS microbiology ecology, 2012Co-Authors: Suman R. Rawat, Minna K. Männistö, Yana Bromberg, Max M. HäggblomAbstract:Acidobacteria are among the most abundant bacterial phyla found in terrestrial ecosystems, but relatively little is known about their diversity, distribution and most critically, their function. Understanding the functional activities encoded in their genomes will provide insights into their ecological roles. Here we describe the genomes of three novel cold-adapted strains of subdivision 1 Acidobacteria. The genomes consist of a circular chromosome of 6.2 Mbp for Granulicella mallensis MP5ACTX8, 4.3 Mbp for Granulicella tundricola MP5ACTX9, and 5.0 Mbp for Terriglobus saanensis SP1PR4. In addition, G. tundricola has five mega plasmids for a total genome size of 5.5 Mbp. The three genomes showed an abundance of genes assigned to metabolism and transport of carbohydrates. In comparison to three mesophilic Acidobacteria, namely Acidobacterium capsulatum ATCC 51196, ‘Candidatus Koribacter versatilis’ Ellin345, and ‘Candidatus Solibacter usitatus’ Ellin6076, the genomes of the three Tundra Soil strains contained an abundance of conserved genes/gene clusters encoding for modules of the carbohydrate-active enzyme (CAZyme) family. Furthermore, a large number of glycoside hydrolases and glycosyl transferases were prevalent. We infer that gene content and biochemical mechanisms encoded in the genomes of three Arctic Tundra Soil Acidobacteria strains are shaped to allow for breakdown, utilization, and biosynthesis of diverse structural and storage polysaccharides and resilience to fluctuating temperatures and nutrient-deficient conditions in Arctic Tundra Soils.
Steven K Schmidt - One of the best experts on this subject based on the ideXlab platform.
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the effects of chronic nitrogen fertilization on alpine Tundra Soil microbial communities implications for carbon and nitrogen cycling
Environmental Microbiology, 2008Co-Authors: Diana R Nemergut, William D. Bowman, Christopher W Schadt, Jason C. Neff, Alan R Townsend, Sarah R Sattin, Kristen R Freeman, Noah Fierer, Michael N Weintraub, Steven K SchmidtAbstract:Summary Many studies have shown that changes in nitrogen (N) availability affect primary productivity in a variety of terrestrial systems, but less is known about the effects of the changing N cycle on Soil organic matter (SOM) decomposition. We used a variety of techniques to examine the effects of chronic N amendments on SOM chemistry and microbial community structure and function in an alpine Tundra Soil. We collected surface Soil (0–5 cm) samples from five control and five long-term N-amended plots established and maintained at the Niwot Ridge Longterm Ecological Research (LTER) site. Samples were bulked by treatment and all analyses were conducted on composite samples. The fungal community shifted in response to N amendments, with a decrease in the relative abundance of basidiomycetes. Bacterial community composition also shifted in the fertilized Soil, with increases in the relative abundance of sequences related to the Bacteroidetes and Gemmatimonadetes, and decreases in the relative abundance of the Verrucomicrobia. We did not uncover any bacterial sequences that were closely related to known nitrifiers in either Soil, but sequences related to archaeal nitrifiers were found in control Soils. The ratio of fungi to bacteria did not change in the N-amended Soils, but the ratio of archaea to bacteria dropped from 20% to less than 1% in the N-amended plots. Comparisons of aliphatic and aromatic carbon compounds, two broad categories of Soil carbon compounds, revealed no between treatment differences. However, G-lignins were found in higher relative abundance in the fertilized Soils, while proteins were detected in lower relative abundance. Finally, the activities of two Soil enzymes involved in N cycling changed in response to chronic N amendments. These results suggest that chronic N fertilization induces significant shifts in Soil carbon dynamics that correspond to shifts in microbial community structure and function.
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seasonal dynamics of previously unknown fungal lineages in Tundra Soils
Science, 2003Co-Authors: Christopher W Schadt, David A Lipson, Andrew P Martin, Steven K SchmidtAbstract:The finding that microbial communities are active under snow has changed the estimated global rates of biogeochemical processes beneath seasonal snow packs. We used microbiological and molecular techniques to elucidate the phylogenetic composition of undersnow microbial communities in Colorado, the United States. Here, we show that Tundra Soil microbial biomass reaches its annual peak under snow, and that fungi account for most of the biomass. Phylogenetic analysis of Tundra Soil fungi revealed a high diversity of fungi and three novel clades that constitute major new groups of fungi (divergent at the subphylum or class level). An abundance of previously unknown fungi that are active beneath the snow substantially broadens our understanding of both the diversity and biogeochemical functioning of fungi in cold environments.
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endogenous methanogenesis stimulates oxidation of atmospheric ch4 in alpine Tundra Soil
Microbial Ecology, 2002Co-Authors: Amy E West, Steven K SchmidtAbstract:Experiments were done to test the hypothesis that atmospheric CH 4 oxidizers in a well-drained alpine Tundra Soil are supported by CH 4 production from anaerobic microsites in the Soil. Soil was subjected to 22 days of anaerobic conditions with elevated H 2 and CO 2 in order to stimulate methanogenesis. This treatment stimulated subsequent atmospheric CH 4 consumption, probably by increasing Soil methanogenesis. After removal from anaerobic conditions, Soils emitted CH 4 for up to 6 h, then oxidized atmospheric CH 4 at 111 (±5.7) pmol (g dry weight) -1 h -1 , which was more than 3 times the rate of control Soils. Further supporting our hypothesis, additions of lumazine, a highly specific inhibitor of methanogenesis, prevented the stimulation of atmospheric CH 4 oxidation by the anaerobic treatment. The method used to create anaerobic conditions with elevated H 2 and CO 2 also elevated headspace CH 4 concentrations. However, elevated CH 4 concentrations under aerobic conditions did not stimulate CH 4 oxidation as much as preexposure to H 2 and CO 2 under anaerobic conditions. Anaerobic conditions created by N 2 flushing did not stimulate atmospheric CH 4 oxidation, probably because N 2 flushing inhibited methanogenesis by removing necessary precursors for methane production. We conclude that anaerobic conditions with elevated H 2 and CO 2 stimulate atmospheric CH 4 oxidation in this dry alpine Tundra Soil by increasing endogenous CH 4 production. This effect was prevented by inhibiting methanogenesis, indicating the importance of endogenous CH 4 production in a CH 4 -consuming Soil.
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acetate stimulates atmospheric ch4 oxidation by an alpine Tundra Soil
Soil Biology & Biochemistry, 1999Co-Authors: Amy E West, Steven K SchmidtAbstract:Abstract Experiments were conducted to determine the effects of various carbon substrates on the oxidation of atmospheric CH 4 by an alpine Tundra Soil. Acetate, formate, methanol, trimethylamine and yeast extract were tested. Acetate and formate (500 μg C (g d.w.) −1 ) stimulated CH 4 oxidation rates from 300 to 1192.8 (±97.2) and 1036.8 (±33.6) pg C (g d.w.) −1 h −1 , respectively. In contrast, methanol did not cause an increase in maximal CH 4 oxidation rates, but methanol-treated Soil maintained peak rates of CH 4 oxidation longer than control Soil. In parallel with the CH 4 data, acetate additions stimulated acetate utilization, whereas methanol did not stimulate methanol utilization in the Soil. This indicates that the mechanism by which acetate stimulates Soil CH 4 oxidation may not be the same as that by which methanol sustains Soil CH 4 oxidation. Growth of methanotrophs on acetate has not been reported previously. Therefore, these data indicate that either there is a novel strain of methanotroph in this Soil, or that acetate stimulates atmospheric CH 4 oxidation by increasing methanogenesis, which in turn increases the supply of methane to the methane oxidizers in this Soil.
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microbial responses to nitrogen additions in alpine Tundra Soil
Soil Biology & Biochemistry, 1996Co-Authors: Melany C Fisk, Steven K SchmidtAbstract:Abstract Soil nitrogen transformations were measured the year following nitrogen fertilization of alpine Kobresia myosuroides meadows to determine the influence of greater plant production and N content on net N mineralization and the microbial N pool. Previously fertilized Soils contained substantially greater amounts of organic N than control Soils. The average increase in Soil organic N accounted for 75% of total added N and, although variable, this quantity suggests a large capacity for retention of added N in these Soils. Nitrogen transformations and more active pools also responded to fertilization. Net N mineralization, nitrification and Soil inorganic N concentrations clearly were higher in fertilized than in control plots throughout the snow-free season. The most pronounced increase in mineralization in fertilized relative to control Soils occurred during the second half of the snow-free period (mid-July-October), primarily after the short alpine growing season (June-mid-August). Although the Soil microbial N pool was not affected by fertilization during the growing season, microbial N did increase in the fall in fertilized compared to control Soils, coinciding with the time of greatest N mineralization. The late season net uptake of N into the microbial pool exceeded by several times present rates of anthropogenic N inputs to these Soils, and the microbial biomass may act as an increasingly important short-term sink for available N if N deposition to these areas continues to increase.
Maria Tuomi - One of the best experts on this subject based on the ideXlab platform.
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stomping in silence conceptualizing trampling effects on Soils in polar Tundra
Functional Ecology, 2021Co-Authors: Maria Tuomi, Maria Vaisanen, Henni Ylanne, Francis Q Brearley, Isabel C Barrio, Kari Anne BrathenAbstract:Ungulate trampling modifies Soils and interlinked ecosystem functions across biomes. Until today, most research has focused on temperate ecosystems and mineral Soils while trampling effects on cold and organic matter-rich Tundra Soils remain largely unknown. We aimed to develop a general model of trampling effects on Soil structure, biota, microclimate and biogeochemical processes, with a particular focus on polar Tundra Soils. To reach this goal, we reviewed literature about the effects of trampling and physical disturbances on Soils across biomes and used this to discuss the knowns and unknowns of trampling effects on Tundra Soils. We identified the following four pathways through which trampling affects Soils: (a) Soil compaction; (b) reductions in Soil fauna and fungi; (c) rapid losses in vegetation biomass and cover; and (d) longer term shifts in vegetation community composition. We found that, in polar Tundra, Soil responses to trampling pathways 1 and 3 could be characterized by nonlinear dynamics and Tundra-specific context dependencies that we formulated into testable hypotheses. In conclusion, trampling may affect Tundra Soil significantly but many direct, interacting and cascading responses remain unknown. We call for research to advance the understanding of trampling effects on Soils to support informed efforts to manage and predict the functioning of Tundra systems under global changes. A free Plain Language Summary can be found within the Supporting Information of this article. (Less)
