Boreal Forest Soils Research Articles

Sorption of cesium on boreal forest soil II. The effect of time, incubation conditions, pH and competing cations

Cesium sorption on Olkiluoto mineral soil samples was studied in batch experiments. The effect of incubation time, incubation conditions, pH and competing cations were investigated. The retention of cesium increased with increasing time. In anaerobic conditions the sorption of cesium was lower than in aerobic ones, possibly caused by the formation of NH4 +. Increase in pH promoted the sorption of cesium. Stable cesium reduced the sorption of 134Cs+ the most, and the overall sorption hindering effectivity of cations decreased in the order of stable Cs+ > NH4 + > K+ » Ca2+ > Na+.

Sorption of cesium on boreal forest soil I: the effect of grain size, organic matter and mineralogy

The sorption of cesium was studied using humus and mineral soil samples. The effect of grain size, soil depth, organic matter and mineralogy were evaluated. The smallest grain size showed the highest sorption whilst it was rather equal for larger grains sizes. The sorption of cesium increased with soil depth being the lowest in the humus. Among the mineral soil layers the highest retention was found in the layer enriched with clay fraction. Muscovite retained cesium fairly well in pure water and model soil solution. Quartz showed the poorest sorption in both solutions.

Sorption of niobium on boreal forest soil

Abstract The sorption of niobium (Nb) was investigated on humus and mineral soil samples taken from various depths of a four-metre deep forest soil pit on Olkiluoto Island, southwestern Finland. Mass distribution coefficients, K d, were determined in batch sorption tests. The steady state of Nb sorption was observed in the mineral soil samples already after one week of equilibration, and sorption decreased with depth from a very high value of 185000 mL/g at 0.7 m to 54000 mL/g at 3.4 m. The reason behind this decrease is probably the tenfold reduction in the specific surface area of the soil at the same depth range. Distribution coefficients were clearly lower in the humus layer (1000 mL/g). The K d values determined in pure water at a pH range of 4.7–6.5 were at a high level (above 55000 mL/g), but decreased dramatically above pH 6.5, corresponding to the change in the major Nb species from the neutral Nb(OH)5 to the low-sorbing anionic Nb(OH)6 − and Nb(OH)7 2−. However, the K d values in the model soil solution were in the slightly alkaline range an order of magnitude higher than in pure water, which is probably caused by the formation of calcium niobate surface precipitate or electrostatic interaction between surface-sorbed calcium and solute Nb. Among nine soil constituent minerals kaolinite performed best in retaining Nb in both pure water and model soil solution at pH 8, whereas potassium feldspar showed the poorest sorption. The K d value for kaolinite was above 500000 mL/g in both solutions, while the respective potassium feldspar values were in the range of 120–220 mL/g.

Responses of lodgepole pine (Pinus contorta) and white spruce (Picea glauca) to fertilization in some reconstructed boreal forest soils in the oil sands region

Low nitrogen (N) availability may affect lodgepole pine (Pinus contorta, Pl) and white spruce (Picea glauca, Sw) growth in some reconstructed boreal forest soils in the Athabasca oil sands region in Alberta, Canada. The objective of this study was to investigate the effect of fertilization (N alone or complete fertilizer) on foliar nutrient concentrations in and growth of Pl (planted in soils with tailings sand as a substrate) and Sw (planted in soils with overburden material as a substrate) in a single-tree fertilization study. Two growing seasons after fertilization, both N alone and complete fertilizer treatments increased the height, diameter at breast height and aboveground biomass growth of Sw (p=0.005, 0.009 and 0.015, respectively). In contrast, fertilization did not affect Pl growth. Foliar N concentration and content in current-year needles of Sw were higher following fertilization than in the control treatment in 2012 (p<0.001 for both), but not in 2013. Foliar δ15N in current-year and 1-year-old needles was greater in the fertilization than in the control treatment for Sw (p<0.001 for both), in association with the increase of δ15N in soil NO3−-N. No fertilization effect on foliar micronutrients (Fe, Mn, Cu, Zn, B and Mo) or soil NH4+-N, NO3−-N or dissolved organic N was found in either Pl or Sw sites. We conclude that N was a limiting factor for tree growth in Sw but not in Pl sites and that N fertilization may be used to improve Sw growth in some reclaimed sites with overburden as a substrate in the oil sands region.

Fungal Community Shifts in Structure and Function across a Boreal Forest Fire Chronosequence.

Forest fires are a common natural disturbance in forested ecosystems and have a large impact on the microbial communities in forest soils. The response of soil fungal communities to forest fire is poorly documented. Here, we investigated fungal community structure and function across a 152-year boreal forest fire chronosequence using high-throughput sequencing of the internal transcribed spacer 2 (ITS2) region and a functional gene array (GeoChip). Our results demonstrate that the boreal forest soil fungal community was most diverse soon after a fire disturbance and declined over time. The differences in the fungal communities were explained by changes in the abundance of basidiomycetes and ascomycetes. Ectomycorrhizal (ECM) fungi contributed to the increase in basidiomycete abundance over time, with the operational taxonomic units (OTUs) representing the genera Cortinarius and Piloderma dominating in abundance. Hierarchical cluster analysis by using gene signal intensity revealed that the sites with different fire histories formed separate clusters, suggesting differences in the potential to maintain essential biogeochemical soil processes. The site with the greatest biological diversity had also the most diverse genes. The genes involved in organic matter degradation in the mature forest, in which ECM fungi were the most abundant, were as common in the youngest site, in which saprotrophic fungi had a relatively higher abundance. This study provides insight into the impact of fire disturbance on soil fungal community dynamics.

Evidences on the Ability of Mycorrhizal Genus Piloderma to Use Organic Nitrogen and Deliver It to Scots Pine.

Ectomycorrhizal (ECM) symbiosis has been proposed to link plant photosynthesis and soil organic matter (SOM) decomposition through the production of fungal enzymes which promote SOM degradation and nitrogen (N) uptake. However, laboratory and field evidence for the existence of these processes are rare. Piloderma sp., a common ECM genus in boreal forest soil, was chosen as model mycorrhiza for this study. The abundance of Piloderma sp. was studied in root tips and soil over one growing season and in winter. Protease production was measured from ectomycorrhiza and soil solution in the field and pure fungal cultures. We also tested the effect of Piloderma olivaceum on host plant organic N nutrition in the laboratory. The results showed that Piloderma sp. was highly abundant in the field and produced extracellular proteases, which correlated positively with the gross primary production, temperature and soil respiration. In the laboratory, Piloderma olivaceum could improve the ability of Pinus sylvestris L. to utilize N from extragenous proteins. We suggest that ECM fungi, although potentially retaining N in their hyphae, are important in forest C and N cycling due to their ability to access proteinaeous N. As Piloderma sp. abundance appeared to be seasonally highly variable, recycling of fungal-bound N after hyphal death may therefore be of primary importance for the N cycling in boreal ecosystems.

Mercury deposition and re-emission pathways in boreal forest soils investigated with Hg isotope signatures.

Soils comprise the largest terrestrial mercury (Hg) pool in exchange with the atmosphere. To predict how anthropogenic emissions affect global Hg cycling and eventually human Hg exposure, it is crucial to understand Hg deposition and re-emission of legacy Hg from soils. However, assessing Hg deposition and re-emission pathways remains difficult because of an insufficient understanding of the governing processes. We measured Hg stable isotope signatures of radiocarbon-dated boreal forest soils and modeled atmospheric Hg deposition and re-emission pathways and fluxes using a combined source and process tracing approach. Our results suggest that Hg in the soils was dominantly derived from deposition of litter (∼90% on average). The remaining fraction was attributed to precipitation-derived Hg, which showed increasing contributions in older, deeper soil horizons (up to 27%) indicative of an accumulation over decades. We provide evidence for significant Hg re-emission from organic soil horizons most likely caused by nonphotochemical abiotic reduction by natural organic matter, a process previously not observed unambiguously in nature. Our data suggest that Histosols (peat soils), which exhibit at least seasonally water-saturated conditions, have re-emitted up to one-third of previously deposited Hg back to the atmosphere. Re-emission of legacy Hg following reduction by natural organic matter may therefore be an important pathway to be considered in global models, further supporting the need for a process-based assessment of land/atmosphere Hg exchange.

Changes in fungal communities along a boreal forest soil fertility gradient.

Boreal forests harbour diverse fungal communities with decisive roles in decomposition and plant nutrition. Although changes in boreal plant communities along gradients in soil acidity and nitrogen (N) availability are well described, less is known about how fungal taxonomic and functional groups respond to soil fertility factors. We analysed fungal communities in humus and litter from 25 Swedish old-growth forests, ranging from N-rich Picea abies stands to acidic and N-poor Pinus sylvestris stands. 454-pyrosequencing of ITS2 amplicons was used to analyse community composition, and biomass was estimated by ergosterol analysis. Fungal community composition was significantly related to soil fertility at the levels of species, genera/orders and functional groups. Ascomycetes dominated in less fertile forests, whereas basidiomycetes increased in abundance in more fertile forests, both in litter and humus. The relative abundance of mycorrhizal fungi in the humus layer remained high even in the most fertile soils. Tolerance to acidity and nitrogen deficiency seems to be of greater importance than plant carbon (C) allocation patterns in determining responses of fungal communities to soil fertility, in old-growth boreal forests.

Monoterpenes and higher terpenes may inhibit enzyme activities in boreal forest soil

Plant secondary compounds, including terpenes, potentially play an important role in controlling the decomposition process in boreal forest soil. However, the role of terpenes is not well understood, and their direct influence on enzyme activity is not well-known. The aim of this study was to examine the possible effects of common monoterpenes and higher terpenes on the activity of enzymes crucial in C, N, P, S cycling, i.e. β-glucosidase, chitinase, protease, acid phosphatase and arylsulfatase. Monoterpenes (α-pinene, carene, myrcene), diterpenes (abietic acid and colophony), and triterpene (β-sitosterol) were used. Studies were done in two environments, in vitro (studies without soil) and in vivo (studies with soil). Soil experiments were conducted using humus layers of two different birch stands, the first N-poor with high organic matter content and the second N-rich with a lower organic matter content. In general, all the terpenes studied showed inhibitory potential against enzymes in in vitro studies. In the soil incubation studies, both of the measured enzymes, chitinase and β-glucosidase, showed some decrease in activity when exposed to different terpenes. Our study suggests that terpenes modify the enzyme machinery in boreal forest soil.

Erratum to: Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.

A warmer climate reduces the bioreactivity of isolated boreal forest soil horizons without increasing the temperature sensitivity of respiratory CO2 loss

Changes in the carbon (C) balance of boreal forest ecosystems may impact the global C cycle and climate. The degree to which antecedent temperature regime and mineral protection of soil organic matter (OM) influence the temperature response of boreal soil C pools remains unknown, however. To investigate these phenomena on time scales relevant to anthropogenic climate change, we quantified the temperature response of four soil C pools (L, F and H organic horizons and B mineral horizon) within soil profiles collected from replicated sites representing two regions along a climate transect (“regional warming”) during a 480-day incubation at 5 and 15 °C (“experimental warming”). We hypothesized that 1) warmer region soils would exhibit reduced bioreactivity, a measure of C lability assessed via cumulative soil C mineralization, relative to colder region soils, paralleling a decrease in bioreactivity with depth in both regions, and 2) temperature sensitivity of C mineralization (denoted as Q10) would increase with decreasing bioreactivity congruent with the “C quality-temperature” (CQT) hypothesis, with a smaller effect in mineral soil where physico-chemical protection likely occurs. Cumulative C mineralization decreased from surface L to deeper horizons and from the cold to warm region for organic F and H horizons only. This decrease in soil bioreactivity with depth was paralleled by an increase in Q10 with depth as expected, except in mineral soil where Q10 was similar to or lower relative to the overlying organic layer. The lower bioreactivity in F and H horizons of the warm relative to the cold region was not, however, associated with a greater Q10. A warmer regional climate in these otherwise similar forests thus resulted in reduced bioreactivity of isolated soil C pools without increasing the temperature sensitivity of soil C mineralization. This suggests that assumptions about temperature sensitivity of C mineralization based on the propensity for isolated organic C pools to undergo mineralization may not be valid in some organic-rich, boreal forest soils.

Production and retention of methylmercury in inundated boreal forest soils.

The Flooded Uplands Dynamics Experiment (FLUDEX) was an ecosystem-scale study examining the production of methylmercury (MeHg) and greenhouse gases from reservoirs constructed on an upland boreal forest landscape in order to quantify their dependence upon carbon stores. We detail the within-reservoir production and storage of MeHg before, during, and nine years after the experiment. The reservoirs were net MeHg producers during the first two years of flooding, and net demethylating systems afterward. During years 1-3, a rapid pulse of MeHg and total Hg was observed in floodwater, followed by substantial increases in MeHg in seston and sediment. Resampling of the dry reservoirs nine years after the experiment ended indicated that organic soil MeHg was still 8 to 52-fold higher than preflood conditions, and averaged 86% of the levels recorded at the end of the third flooding year. Both total Hg and MeHg retention in soil were a strong function of organic carbon content. The time scale of soil MeHg retention may help explain the decadal time lag frequently observed for the decrease of piscivorous fish Hg concentrations in new reservoirs. Predicted extreme precipitation events associated with climate change may serve to make landscapes more susceptible to this process.

Drying and substrate concentrations interact to inhibit decomposition of carbon substrates added to combusted Inceptisols from a boreal forest

Climate change is expected to alter the mechanisms controlling soil organic matter (SOM) stabilization. Under climate change, soil warming and drying could affect the enzymatic mechanisms that control SOM turnover and dependence on substrate concentration. Here, we used a greenhouse climate manipulation in a mature boreal forest soil to test two specific hypotheses: (1) Rates of decomposition decline at lower substrate concentrations, and (2) reductions in soil moisture disproportionately constrain the degradation of low-concentration substrates. Using constructed soil cores, we measured decomposition rates of two polymeric substrates, starch and cellulose, as well as enzyme activities associated with degradation of these substrates. The greenhouse manipulation increased temperature by 0.8 °C and reduced moisture in the constructed cores by up to 90 %. We rejected our first hypothesis, as the rate of starch decomposition did not decrease with declining starch concentration under control conditions, but we did find support for hypothesis two: Drying led to lower decomposition rates for low-concentration starch. We observed a threefold reduction in soil respiration rates in bulk soils in the greenhouses over a 4-month period, but the C losses from the constructed cores did not vary among our treatments. Activities of enzymes that degrade cellulose and starch were elevated in the greenhouse treatments, which may have compensated for moisture constraints on the degradation of the common substrate (i.e., cellulose) in our constructed cores. This study confirms that substrate decomposition can be concentration-dependent and suggests that climate change effects on soil moisture could reduce rates of decomposition in well-drained boreal forest soils lacking permafrost.

Logging residue harvest may decrease enzymatic activity of boreal forest soils

Nowadays conventional stem-only harvest where logging residues are left on the site is often displaced by whole-tree harvest, in which logging residues are harvested for use as bioenergy. Logging residues consist of tree branches and tops of stems with needles. The aim of this study was to evaluate the effect of logging residue harvest on soil enzyme activities involved in C, N and P cycling, namely β-glucosidase, β-glucosaminidase, protease and acid phosphatase in relation to other soil characteristics (i.e. soil respiration, net N mineralization, microbial biomass C and N). Soil samples were taken from the humus layer of five study sites, differing in fertility, dominating tree species and time elapsed after treatment. The study sites were Norway spruce (Picea abies, (L.) Karst) and Scots pine (Pinus sylvestris L.) stands in different parts of Finland. Four of the study sites were single-tree experiments, where thinning was performed 4–5 years before this study and 3–4 different doses of logging residues (from 0 up to 37.5 Mg ha−1) were distributed on a circle around a single tree in 3 replicates. The last field experiment had been thinned twice, 23 and 13 years ago; the treatments in 3 replicates were whole-tree harvest and stem-only harvest. In the whole-tree harvest vs. stem-only harvest experiment, activities of β-glucosidase, β-glucosaminidase, acid phosphatase were similar in both treatments. In general, in the single-tree experiment with pine, enzymes raised the activity in response to increasing amount of logging residue. The pattern was less clear for the spruce single-tree experiment, but acid phosphatase and protease activities increased with the increase in amount of logging residue. In general, other soil characteristics were less affected than enzyme activities by logging residue removal; however, in some sites logging residues seemed to increase net C and N mineralization with increasing logging residue amount. Our results suggest that retaining logging residues on the site can increase soil enzyme activities and C and N mineralization.

Impact of site-preparation on soil-surface CO&lt;sub&gt;2&lt;/sub&gt; fluxes and litter decomposition in a clear-cut in Sweden

Boreal forest soil contains significant amounts of organic carbon. Soil disturbance, caused for example by site preparation or stump extraction, may increase decomposition and thus lead to higher CO emissions, contributing to global warming. The aim of this study was to quantify responses of soil-surface CO fluxes (R) and litter (needle and root) decomposition rates following various kinds of soil disturbance commonly caused by mechanical site preparation and stump harvest. For this purpose four treatments were applied in a clear-cut site in central Sweden: i) removal of the humus layer and top 2 cm of mineral soil, ii) placement of a humus layer and 2 cm of mineral soil upside down on top of undisturbed soil, forming a double humus layer buried under mineral soil, iii) heavy mixing of the humus layer and mineral soil, and iv) no disturbance (control). R measurements were acquired with a portable respiration system during two growing seasons. To assess the treatments’ effects on litter decomposition rates, needles or coarse roots (Ø = 6 mm) were incubated in litterbags at positions they would be located after the treatments (buried, or on top of the soil). The results indicate that site preparation-simulating treatments have no effect or may significantly reduce, rather than increase, CO emissions during the following two years. They also show that buried litter decomposes more rapidly than litter on the surface, but in other respects the treatments have little effect on litter decomposition rates.22ss2

Combined effects of abiotic factors on Collembola communities reveal precipitation may act as a disturbance

Global increases in temperature and atmospheric CO2, coupled with increasingly sporadic and intense precipitation regimes, may affect the biodiversity of boreal forest communities, potentially leading to shifts in functional process rates such as decomposition. However, the effects of these factors on microarthropod community composition have not been thoroughly studied in combination in controlled settings. We conducted a full factorial experiment exposing moss/soil mesocosms to three temperatures (11.5, 15.5, and 19.5 °C), two CO2 levels (430 ppm and 750 ppm), and three moisture levels (drought, intermediate, and saturated conditions) for 18 weeks. Following treatment, we quantified effects on species diversity of a representative group of mesofaunal microarthropods, the Collembola. We also quantified the effects of these factors on the distribution of collembolan body sizes as an indicator of functional changes in the community. We found that moisture regime was a dominant factor, with increased precipitation leading to decreased collembolan abundance and richness. The mechanisms of these detrimental effects are unclear but may be due to the saturation of air-filled soil pore space or competition with moisture-tolerant species. Severe precipitation regimes caused a general loss of abundance in species of all sizes, which may have long term effects on boreal forest soil food webs.

Low-Level Nitrogen Addition Promotes Net Methane Uptake in a Boreal Forest across the Great Xing'an Mountain Region, China

Chronic nitrogen (N) deposition may alter the amount and direction of methane (CH4) uptake in boreal forest soils, but the critical level of N deposition eliciting the alteration of soil CH4 uptake remains unknown. In a cold-temperate coniferous forest in the Great Xing' an Mountain of northeastern China, NH4NO3 fertilizer was added at four rates: control (0 kg N ha(-1) year(-1)), low N (10 kg N ha(-1) year(-1)), medium N (20 kg N ha' year(-1)), and high N (40 kg N ha(-1) year(-1)). Soil atmospheric CH4 fluxes as well as soil temperature, soil moisture, mineral N, dissolved organic carbon (DOC), and pH values were determined to explore the main factors controlling soil CH4 uptake fluxes under different N addition levels. Our results showed that N addition did not alter soil temperature, soil moisture, and soil NH4+-N concentrations. Low N rather than medium and high N significantly increased soil DOC and NO3--N concentrations in mineral horizon as well as soil CH4 uptake fluxes. In addition, soil acidification occurred in the fertilized forest soils, because soil pH declined by 0.4 unit. CH4 uptake in the cold-temperate forest soil was dominated by soil moisture followed by soil DOC and soil mineral N. Low N seemed to stimulate soil CH4 uptake through increasing the contents of soil DOC and NO3--N. These results suggest that low-level N addition (< 20 kg N ha-1 year(-1)) can promote CH4 uptake in the cold-temperate coniferous forest soil, which is also conducive to carbon sequestration of the boreal forests.

Temperature sensitivity of heterotrophic soil CO2 production increases with increasing carbon substrate uptake rate

Temperature profoundly affects saprotrophic respiration rates, and carbon quality theory predicts that the rates' temperature sensitivity should increase as the quality of the carbon source declines. However, reported relationships between saprotrophic respiration responses to temperature and carbon quality vary widely. Some of this variability may arise from confounding effects related to both substrate quality and substrate availability. The importance of these variables, as well as substrate diffusion and uptake rates, for the temperature sensitivity of saprotrophic respiration has been validated theoretically, but not empirically demonstrated. Thus, we tested effects of varying substrate uptake rates on the temperature sensitivity of organic carbon degradation.For this purpose we created a model system using the organic layer (O-horizon), of a boreal forest soil, specifically to test effects of varying monomer uptake and release rates. The addition of both monomers and polymers generally increased the temperature sensitivity of saprotrophic respiration. In response to added monomers, there was a linear increase in the temperature sensitivity of both substrate-induced respiration and the specific growth rate with increasing rate of substrate uptake as indicated by the CO2 production at 14 °C. Both of these responses diverge from those predicted by the carbon quality theory, but they provide the first empirical evidence consistent with model predictions demonstrating increased temperature sensitivity with increased uptake rate of carbon monomers over the cell membrane. These results may explain why organic material of higher carbon quality induces higher temperature responses than lower carbon quality compounds, without contradicting carbon quality theory.

Can we measure condensed tannins from tannin–protein complexes? – A case study with acid–butanol assay in boreal forest soil organic layer

Tannins may influence nitrogen cycle in forest soil. To understand the role of tannins in the decomposition process, we need to know their amount in the soil. Measurements of soil tannins meet great difficulties as tannins may undergo substantial retention. The main aim of this study was to assess the influence of complexation with proteins on condensed tannins (CT) retention. We measured the amount of extractable CT in the humus layer after additions of i) CT, ii) CT followed by addition of bovine serum albumin, BSA (uncomplexed before addition) or iii) CT–BSA complexes. Samples were taken from the humus layer of two sites; Norway spruce soil, which had high levels of organic matter and CT, and silver birch soil, which had lower levels of organic matter and CT. For tannin additions, we used CT extracted and purified from Norway spruce needles. To estimate extractable CT, we employed acid–butanol assay which is commonly used in condensed tannin chemistry. The complexation of CT with BSA remarkably decreased CT recovery from the humus layer in comparison to CT added alone or without prior complexation. The recovery of added CT also depended on the forest soil, and was higher in spruce soil. As complexation with proteins strongly decreases the recovery of CT it should be taken into account in studies concerning tannins in humus layer. According to our studies, only some of the CT from the CT–BSA complex in humus layer can be detected in the assay.

Combined influence of fire and salvage logging on carbon and nitrogen storage in boreal forest soil profiles

Boreal forest soils are a significant component of the global C cycle. Although wildfire and subsequent salvage logging are major disturbances in this ecosystem, their combined influence on soil organic carbon (SOC) and total soil nitrogen (N) storage is poorly understood. Our objective was to investigate the recent influence of fire and post-fire salvage logging on SOC and total soil N stocks and distribution in the profile of boreal forest soils. We measured SOC and total N concentrations, bulk density and pH of organic, surface mineral (0–15cm depth) and subsurface mineral (15–40cm depth) soil horizons on 14 different fires (burned 2005–2007) in Quebec, Canada. Each site comprised three treatments: a control stand (CTR), a recently burned (<7years) stand that was not salvaged logged (B-NL) and a recently burned (<7years) stand that was salvage logged (B-L) within 2years after the fire. Our results showed that fire-affected stands had less SOC and total N stored in organic horizons, and that post-fire salvage logging reduced SOC concentration in the organic horizon, but promoted SOC and total N enrichment in the subsurface mineral soil. We conclude that mechanical disturbance of recently burned stands can contribute to the mixing of the forest floor and organic matter with the mineral soil, and influence the depth distribution of SOC and total N in the soil profile. When the entire soil profile was considered, SOC and total N stocks were equivalent in burned versus burned and salvage-logged sites. Further research should focus on how disturbance type and intensity influence the molecular nature of soil organic matter and the mechanisms by which SOC and total soil N are retained in the different soil horizons.