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Peat accumulation in high latitude wetlands represents a natural long-term carbon sink, resulting from the cumulative excess of growing season net ecosystem production over non-growing season (NGS) net mineralization in soils. With high latitudes experiencing warming at a faster pace than the global average, especially during the NGS, a major concern is that enhanced mineralization of soil organic carbon will steadily increase CO 2 emissions from northern peatlands. In this study, we conducted laboratory incubations with soils from boreal and temperate peatlands across Canada. Peat soils were pretreated for different soil moisture levels, and CO 2 production rates were measured at 12 sequential temperatures, covering a range from − 10 to + 35 °C including one freeze–thaw event. On average, the CO 2 production rates in the boreal peat samples increased more sharply with temperature than in the temperate peat samples. For same temperature, optimum soil moisture levels for CO 2 production were higher in the peat samples from more flooded sites. However, standard reaction kinetics (e.g., Q 10 temperature coefficient and Arrhenius equation) failed to account for the apparent lack of temperature dependence of CO 2 production rates measured below 0 °C, and a sudden increase after a freezing event. Thus, we caution against using the simple kinetic expressions to represent the CO 2 emissions from northern peatlands, especially regarding the long NGS period with multiple soil freeze and thaw events.

Coarse woody debris (CWD) is a dynamic source of nutrients in managed forests of eastern North America. The temporal patterns of nutrient export from CWD are challenging to study, and efficient methods are lacking. We made empirical measurements of CWD density, volume, and nutrient concentrations in 5 stages of decay, and paired them with a decay class transition model to project the long-term nutrient dynamics of CWD in a managed northern hardwood forest. The model was used to describe stand-level changes in CWD nutrient pools over 40 years following a selection harvest, and to compare CWD nutrient pools in managed and unmanaged stands. The C content of CWD decreased throughout decay, and mirrored density losses. N, P, and Ca content increased throughout decay, Mg content remained relatively constant, and K was rapidly lost. At the stand level, despite a rapid loss of mass and density, the model projected an initial gain in total N, P and Ca stored in CWD during the first 4–8 years after harvest, whereas net C, Mg, and K began to decrease immediately. The average volume, mass, C and K stocks of CWD in managed stands were approximately 10% lower than unmanaged stands, and N, P, Ca, and Mg were up to 16% lower. This is the first study to use a decay class transition model to study the dynamics of nutrients other than C, and the model serves as a template upon which other models of CWD decay can be built.

ABSTRACT Methane emission feedbacks in wetlands are predicted to influence global climate under climate change and other anthropogenic stressors. Herein, we review the taxonomy and physiological ecology of the microorganisms responsible for methane production in peatlands. Common in peat soils are five of the eight described orders of methanogens spanning three phyla (Euryarchaeota, Halobacterota and Thermoplasmatota). The phylogenetic affiliation of sequences found in peat suggest that members of the thus-far-uncultivated group Candidatus Bathyarchaeota (representing a fourth phylum) may be involved in methane cycling, either anaerobic oxidation of methane and/or methanogenesis, as at least a few organisms within this group contain the essential gene, mcrA, according to metagenomic data. Methanogens in peatlands are notoriously challenging to enrich and isolate; thus, much remains unknown about their physiology and how methanogen communities will respond to environmental changes. Consistent patterns of changes in methanogen communities have been reported across studies in permafrost peatland thaw where the resulting degraded feature is thermokarst. However much remains to be understood regarding methanogen community feedbacks to altered hydrology and warming in other contexts, enhanced atmospheric pollution (N, S and metals) loading and direct anthropogenic disturbances to peatlands like drainage, horticultural peat extraction, forestry and agriculture, as well as post-disturbance reclamation. Peat-forming wetlands and peatland microorganisms that produce the greenhouse gas methane.

For mass culture of photosynthetic green microalgae, industrial flue gases can represent a low-cost resource of CO2. However, flue gases are often avoided, because they often also contain high levels of SO2 and/or NO2, which cause significant acidification of media to below pH 3 due to production of sulfuric and nitric acid. This creates an unsuitable environment for the neutrophilic microalgae commonly used in large-scale commercial production. To address this issue, we have looked at selecting acid-tolerant microalgae via growth at pH 2.5 carried out with samples bioprospected from an active smelter site. Of the eight wild samples collected, one consisting mainly of Coccomyxa sp. grew at pH 2.5 and achieved a density of 640 mg L−1. Furthermore, three previously bioprospected green microalgae from acidic waters (pH 3–4.5) near abandoned mine sites were also re-acclimated down to their in-situ pH environment after approximately 4 years spent at neutral pH. Of those three, an axenic culture of Coccomyxa sp. was the most successful at re-acclimating and achieved the highest density of 293.1 mg L−1 and maximum daily productivity of 38.8 mg L−1 day−1 at pH 3. Re-acclimation of acid-tolerant species is, therefore, achievable when directly placed at their original pH, but gradual reduction in pH is recommended to give the cells time to acclimate.

There is interest in utilizing wood ash as an amendment in forestry operations as a mechanism to return nutrients to soils that are removed during harvesting, with the added benefit of diverting this bioenergy waste material from landfill sites. Existing studies have not arrived at a consensus on what the effects of wood ash amendments are on soil biota. We collected forest soil samples from studies in managed forests across Canada that were amended with wood ash to evaluate the effects on arthropod, bacterial and fungal communities using metabarcoding of F230, 16S, 18S and ITS2 sequences as well as enzyme analyses to assess its effects on soil biotic function. Ash amendment did not result in consistent effects across sites, and those effects that were detected were small. Overall, this study suggests that ash amendment applied to managed forest systems in amounts (up to 20 Mg ha −1 ) applied across the 8 study sties had little to no detectable effects on soil biotic community structure or function. When effects were detected, they were small, and site-specific. These non-results support the application of wood ash to harvested forest sites to replace macronutrients (e.g., calcium) removed by logging operations, thereby diverting it from landfill sites, and potentially increasing stand productivity.

How ecosystem functioning changes with microbial communities remains an open question in natural ecosystems. Both present-day environmental conditions and historical events, such as past differences in dispersal, can have a greater influence over ecosystem function than the diversity or abundance of both taxa and genes. Here, we estimated how individual and interactive effects of microbial community structure defined by diversity and abundance, present-day environmental conditions, and an indicator of historical legacies influenced ecosystem functioning in lake sediments. We studied sediments because they have strong gradients in all three of these ecosystem properties and deliver important functions worldwide. By characterizing bacterial community composition and functional traits at eight sites fed by discrete and contrasting catchments, we found that taxonomic diversity and the normalized abundance of oxidase-encoding genes explained as much variation in CO 2 production as present-day gradients of pH and organic matter quantity and quality. Functional gene diversity was not linked to CO 2 production rates. Surprisingly, the effects of taxonomic diversity and normalized oxidase abundance in the model predicting CO 2 production were attributable to site-level differences in bacterial communities unrelated to the present-day environment, suggesting that colonization history rather than habitat-based filtering indirectly influenced ecosystem functioning. Our findings add to limited evidence that biodiversity and gene abundance explain patterns of microbiome functioning in nature. Yet we highlight among the first time how these relationships depend directly on present-day environmental conditions and indirectly on historical legacies, and so need to be contextualized with these other ecosystem properties.

Biochar particles have been hypothesized to provide unique microhabitats for a portion of the soil microbial community, but few studies have systematically compared biochar communities to bulk soil communities. Here, we used a combination of sequencing techniques to assess the taxonomic and functional characteristics of microbial communities in four-year-old biochar particles and in adjacent soils across three forest environments. Though effects varied between sites, the microbial community living in and around the biochar particles had significantly lower prokaryotic diversity and higher eukaryotic diversity than the surrounding soil. In particular, the biochar bacterial community had proportionally lower abundance of Acidobacteria, Planctomycetes , and β-Proteobacteria taxa, compared to the soil, while the eukaryotic biochar community had an 11% higher contribution of protists belonging to the Aveolata superphylum. Additionally, we were unable to detect a consistent biochar effect on the genetic functional potential of these microbial communities for the subset of the genetic data for which we were able to assign functions through MG-RAST. Overall, these results show that while biochar particles did select for a unique subset of the biota found in adjacent soils, effects on the microbial genetic functional potential appeared to be specific to contrasting forest soil environments.

The purpose of our study was to determine whether earthworms facilitate the burial of surface-applied wood ash. We mixed a fluorescent tracer powder with fly ash from a commercial biomass boiler to track and quantify ash burial in microcosms containing different densities of the deep-burrowing anecic earthworm Lumbricus terrestris L. While passive incorporation of the wood ash-tracer mix from the surface in the absence of earthworms was limited (rarely penetrating more than 2 cm below the surface), earthworms increased the amount of ash-tracer found belowground and the maximum depths at which ash-tracer was observed (up to 16 cm deep). We suspect that earthworms facilitated wood ash burial primarily by creating burrows down which wood ash could be carried by water and by burying wood ash-covered leaf litter. Earthworms may help increase the efficacy of wood ash amendment in ecosystems where it is impractical to manually mix amendments into the soil (e.g. forests).

Peatlands are important players in climate change–biosphere feedbacks via long-term net carbon (C) accumulation in soil organic matter and as potential net C sources including the potent greenhouse gas methane (CH₄). Interactions of climate, site-hydrology, plant community, and groundwater chemical factors influence peatland development and functioning, including C dioxide (CO₂) and CH₄ fluxes, but the role of microbial community composition is not well understood. To assess microbial functional and taxonomic dissimilarities, we used high throughput sequencing of the small subunit ribosomal DNA (SSU rDNA) to determine bacterial and archaeal community composition in soils from twenty North American peatlands. Targeted DNA metabarcoding showed that although Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla on average, intermediate and rich fens hosted greater diversity and taxonomic richness, as well as an array of candidate phyla when compared with acidic and nutrient-poor poor fens and bogs. Moreover, pH was revealed to be the strongest predictor of microbial community structure across sites. Predictive metagenome content (PICRUSt) showed increases in specific genes, such as purine/pyrimidine and amino-acid metabolism in mid-latitude peatlands from 38 to 45° N, suggesting a shift toward utilization of microbial biomass over utilization of initial plant biomass in these microbial communities. Overall, there appears to be noticeable differences in community structure between peatland classes, as well as differences in microbial metabolic activity between latitudes. These findings are in line with a predicted increase in the decomposition and accelerated C turnover, and suggest that peatlands north of 37° latitude may be particularly vulnerable to climate change.

Biochar additions can improve soil fertility and sequester carbon, but biochar effects have been investigated primarily in agricultural systems. Biochar from spruce and maple sawdust feedstocks (with and without inorganic phosphorus in a factorial design) were added to plots in a commercially managed temperate hardwood forest stand in central Ontario, Canada; treatments were applied as a top‐dressing immediately prior to fall leaf abscission in September 2011. Forests in this region have acidic, sandy soils, and due to nitrogen deposition may exhibit phosphorus, calcium, and magnesium limitation. To investigate short‐term impacts of biochar application on soil nutrient supply and greenhouse gas fluxes as compared to phosphorus fertilization, data were collected over the first year after treatment application; linear mixed models were used to analyze data. Two to six weeks after treatment application, there were higher concentrations of potassium in spruce and maple biochar plots, and phosphorus in spruce biochar plots, as compared to the control treatment. There were higher concentrations of calcium, magnesium, and phosphorus in the phosphorus plots. In the following spring and summer (9–12 months after treatment application), there were higher soil calcium concentrations in maple biochar plots, and phosphorus plots still had higher soil phosphorus concentrations than control plots. No treatment effects on fluxes of carbon dioxide, methane, or nitrous oxide were detected in the field; however, laboratory incubations after 12 months showed higher microbial respiration in soils from maple biochar plots as compared to spruce biochar, despite no effect on microbial biomass. The results suggest that the most important short‐term impact of biochar additions in this system is the increased supply of the limiting plant nutrients phosphorus and calcium. We expect that larger changes in mineral soil physical and chemical properties will occur when the surface‐applied biochar becomes incorporated into the soil after a few years.