Search

Agroforestry systems (AFS) contribute to carbon (C) sequestration and reduction in greenhouse gas emissions from agricultural lands. However, previously understudied differences among AFS may underestimate their climate change mitigation potential. In this 3‐year field study, we assessed various C stocks and greenhouse gas emissions across two common AFS (hedgerows and shelterbelts) and their component land uses: perennial vegetated areas with and without trees (woodland and grassland, respectively), newly planted saplings in grassland, and adjacent annual cropland in central Alberta, Canada. Between 2018 and 2020 (~April–October), nitrous oxide emissions were 89% lower under perennial vegetation relative to the cropland (0.02 and 0.18 g N m−2 year−1, respectively). In 2020, heterotrophic respiration in the woodland was 53% lower in shelterbelts relative to hedgerows (279 and 600 g C m−2 year−1, respectively). Within the woodland, deadwood C stock was particularly important in hedgerows (35 Mg C ha−1 or 7% of ecosystem C) relative to shelterbelts (2 Mg C ha−1 or <1% of ecosystem C), and likely affected C cycling differences between the woodland types by enhancing soil labile C and microbial biomass in hedgerows. Deadwood C stock was positively correlated with annual heterotrophic respiration and total (to ~100 cm depth) soil organic C, water‐soluble organic C, and microbial biomass C. Total ecosystem C was 1.90–2.55 times greater within the woodland than all other land uses, with 176, 234, 237, and 449 Mg C ha−1 found in the cropland, grassland, planted saplings treatment, and woodland, respectively. Shelterbelt and hedgerow woodlands contained 2.09 and 3.03 times more C, respectively, than adjacent cropland. Our findings emphasize the importance of AFS for fostering C sequestration and reducing greenhouse gas emissions and, in particular, retaining hedgerows (legacy woodland) and their associated deadwood across temperate agroecosystems will help mitigate climate change. [ABSTRACT FROM AUTHOR]

Information about regional‐level carbon (C) stocks in agroforestry systems (AFS), as well as the annual loss of agroforests and associated C stocks, is scarce, limiting our capacity for increasing C sequestration through establishing, retaining, and enhancing these systems. This study quantified regional‐level C stocks and the associated incremental economic value in the forest land‐use component of three common AFS (hedgerows, shelterbelts, and silvopastures), estimated the annual loss of hedgerow and silvopasture forests and the associated C, and assessed the potential to enhance C storage through the expansion of shelterbelts in central Alberta, Canada, using publicly available satellite imagery, previously collected field data and the Google Earth Engine platform. Results showed that forests in the three AFS stored 699.9 million tons (Mt) C across 9.5 million hectares (Mha) of land in central Alberta and were valued at $102.7 billion based on the 2021 Canadian C tax rate of $40 t−1 CO2‐equivalent. Silvopasture forests in the studied region had the highest C stocks, which were 14.2 and 67.2 times that found in hedgerow and shelterbelt forests, respectively. Between 2001 and 2020, forests in hedgerows and silvopastures declined at rates of 468.1 and 1957.1 ha year−1, respectively, leading to an 8.4 Mt decline in total C storage over the 20 years. However, there is potential to establish new shelterbelts at many road/field margins, which could increase C stocks by 2.3 times the current C stocks in shelterbelt forests. These results highlight the importance of retaining existing and establishing new AFS for increasing C sequestration, emphasizing the impact of agroforest loss on reducing C storage within agroecosystems. The development of policies that assist or reward landowners for providing the ecosystem service of C storage by retaining, establishing, and enhancing agroforests as part of existing agroecosystem management should be encouraged for mitigating climate change. [ABSTRACT FROM AUTHOR]

High heterogeneity in the spatial distribution of soil organic carbon (SOC) in grasslands causes uncertainty in estimating its content and storage. In this study, we investigated the spatial distribution of SOC content and storage in the prairies of southern Alberta, Canada, and how it is affected by land use such as irrigated cropping and other environmental conditions such as cattle grazing, slope landscape position and dominant plant species. The mean SOC content was determined to be 11.5 g kg–1 (range: 8.9 to 22.4 g kg–1) in the 0–10 cm layer and 6.8 g kg–1 (range: 4.0 to 13.3 g kg–1) in the 10–30 cm layer; mean SOC storage was 1.59 kg C m–2 (range: 1.23 to 2.78 kg C m–2) in the 0–10 cm layer and 2.07 kg C m–2 (range: 1.21 to 3.62 kg C m–2) in the 10–30 cm layer. The SOC content was significantly affected by slope position in both the 0–10 and 10–30 cm layers, in the following order: bottom >middle > top position. Moreover, SOC storage was higher in sites dominated by shrubs than graminoid/forb communities. Thus, SOC content and storage had distinctly clustered spatial patterns throughout the study area and were significant differences between the 0–10 and 10–30 cm soil layers. Prior land‐use change from arid grassland to irrigated cropland increased SOC content and storage in bulk soils. [ABSTRACT FROM AUTHOR]

Purpose: No-till (NT) and fertilization are common land management practices in agricultural production systems to increase soil quality and crop yield. No-till can be reversed to tillage (termed tillage reversal, TR, in this paper) due to changes in management objectives. Materials and methods: The impact of NT, TR, and TR plus nitrogen (N) fertilization (TRN) treatments on the composition and structure of bacterial communities in a Gray Luvisol was studied in west-central Alberta, Canada. Results and discussion: The structure of bacterial communities was not affected by the TR treatment (compared with NT). The TRN treatment increased the relative abundance of some bacterial taxa groups, e.g., Gemmatimonadetes, Thermoleophilia and Solibacteres, that have chemolithotrophic nitrifying functions as compared with the TR treatment. The decreased relative abundance of some bacterial taxa groups, such as Alphaproteobacteria, Deltaproteobacteria, Spartobacteria, and Planctomycetia that have denitrifying functions, would change the soil's denitrification function in the TRN as compared to the TR treatment. There were more dominant bacterial taxa groups, and the bacterial community had greater inter-annual variations in the TRN than in the NT and TR treatments. Moreover, the function of bacterial communities was affected by the TRN as compared to the NT and TR treatments, based on the predicted metagenomes. Conclusions: We conclude that when TR was applied to the soil with long-term N fertilization, which eliminates N limitation, altered soil bacterial community structure and function over TR applied to the studied Gray Luvisol without long-term N fertilization. Findings from our study have important implications for improving land management practices through tillage and N fertilization to enhance the soil's function and quality in agroecosystems. [ABSTRACT FROM AUTHOR]

In order to better understand factors affecting greenhouse gas (GHG) emissions in Canadian agroforestry systems, we conducted a laboratory incubation study to assess N2O, CO2 and CH4 emissions from soils in response to land use (forestland vs. cropland) and agroforestry system type (hedgerow vs. shelterbelt) in central Alberta, Canada. Emissions of N2O were lower in soils from forestland than cropland, and forest soils acted as a net sink of atmospheric CH4 while cropland soils were weak sources of CH4. However, the forest soil had higher CO2 emission rates than the cropland soil within both agroforestry systems. Soil CH4 oxidation was higher in soil from hedgerow (consisted of natural forest vegetation) than from shelterbelt system (planted forest vegetation), while the former also had lower N2O emissions. Overall, soil CO2 emissions were significantly higher from hedgerow than from shelterbelt systems. Emissions of N2O were positively related with gross nitrification rates and soil pH, and negatively related with gross N immobilization rates. The CO2 emissions were positively related with water‐soluble organic C contents, while CH4 emissions were positively related with clay content, but negatively with gross N immobilization rates and soil organic C content. The global warming potential was higher in forestland soil than in cropland soil within agroforestry systems, and higher in forestland soil of the hedgerow compared to that in shelterbelts. Our results suggest that we need to select land uses or agroforestry systems that have a higher potential of mitigating GHG emissions from soils. [ABSTRACT FROM AUTHOR]

A 2-year field study was conducted to compare the effect of wheat straw, its biochar, and wheat straw plus biochar addition on soil fluxes of CO2, CH4, and N2O during the growing season, and soil properties and crop yield in a Black Chernozemic soil planted to barley (Hordeum vulgare L.) in central Alberta, Canada. The objective was to assess the benefit of applying biochar instead of its feedstock, wheat straw, in improving environmental sustainability. Biochar addition did not affect soil CH4 oxidation, but decreased CO2 and N2O emissions as compared with both wheat straw applied alone and wheat straw and biochar applied together in 2010 and 2011 (p < 0.001), and resulted in a lower global warming potential, indicating that the biochar was effective in mitigating greenhouse gas (GHG) emission from the agricultural soil, as a result of biochar suppressing soil microbial activity and reducing soil N availability. Biochar application reduced N2O emission over 2 years, indicating its longer-term impact. Biochar application alone increased barley yield by 9.9 to 20.4% as compared to the other three treatments, thus reducing yield-scaled greenhouse gas emission intensity by 27.2 to 50.9% (p = 0.013 for the control and p < 0.001 for both wheat straw–amended treatments), with an average reduction of 3.43 t CO2-eq t−1 grain. The application of both wheat straw and its biochar reduced the temperature sensitivity of soil CO2 emission (Q10, p < 0.001), but the application of wheat straw or its biochar alone did not affect Q10, indicating that biochar application reduces the sensitivity to temperature changes of the decomposition of the new organic matter added to the soil. We conclude that (1) the application of wheat straw–derived biochar was preferred to raw wheat straw in mitigating GHG emission and (2) biochar can be an effective management strategy for properly handling crop residues in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Grasslands are important for C storage and supporting livestock production, yet little is understood about how warming interacts with defoliation to alter soil C and N dynamics. We examined how increased growing season temperature and defoliation influenced soil microbial biomass C (MBC) and N (MBN), N mineral dynamics, and greenhouse gas (GHG) flux within the top 15 cm of mineral soil in a northern temperate grassland of Alberta, Canada. We performed a 2-yr experiment with open-top chambers to increase soil temperatures, with warming assessed alone and combined with a single intense midsummer defoliation treatment. Soil MBC and MBN did not respond to warming or defoliation (P > 0.05). Warming increased soil nitrification and net N mineralization in the spring of the second growing season (P < 0.05) but did not persist beyond May. Although warming and defoliation both increased CO2 efflux separately during the first growing season (P < 0.05), the combination of these treatments reduced CO2 efflux to levels similar to the controls, with no lasting effects into the following growing season. Warming also interacted with defoliation to increase N2O flux in the second growing season relative to plots under either warming or defoliation treatment, whereas CH4 uptake was not influenced by our treatments. These results show the complex but transient impacts of warming and defoliation on soil C and N, particularly GHGs. Further research is needed to understand how these northern temperate grasslands respond to long-term factorial experiments involving warming, defoliation, and variation in other factors (e.g., precipitation) [ABSTRACT FROM AUTHOR]

Climate change predictions indicate that extreme drought is likely to become more frequent in the future. In this study, the impact of drought on soil respiration (Rs) and its autotrophic (Ra) and heterotrophic components (Rh) were studied in a cultivated Black Chernozemic soil in central Alberta, Canada. The mean Rs was 24.4% lower in the drought relative to the plots with ambient precipitation (P < 0.001), with a larger decrease in Ra (26.8%) relative to Rh (21.0%), and a higher (P < 0.05) contribution of Rh to Rs under drought (52.8%) than under the ambient condition (47.7%). Both Rs and its Ra and Rh components had an exponential relationship with soil temperature and a quadratic relationship with soil water content. Drought caused a greater decrease in the tipping point of soil water content for Rh (a 39.6% reduction) than for Ra (a 15.1% reduction) relative to the ambient precipitation treatment. In addition, drought resulted in a greater increase in the temperature sensitivity (Q10 values) of Ra (a 45.0% increase) than that of Rh (a 14.1% increase) relative to the ambient precipitation treatment. The results suggest that drought amplified the water limitation effect on CO2 emission, especially that from microbial respiration, and resulted in a tighter relationship between temperature and root or autotrophic respiration, based on this 1-year study. We conclude that it is important to assess the impact of drought on soil respiration components rather than the total soil respiration, and such differential effects of drought on soil respiration components should be incorporated into global carbon circulation models. [ABSTRACT FROM AUTHOR]

Oil sands mining activities in northern Alberta, Canada emit large amounts of nitrogen (N) and sulfur (S) oxides to the atmosphere, increasing N and S deposition. We studied the long-term (2006–2016) effect of elevated concentrations of simulated N and S deposition on soil properties and understory species composition in a mixedwood boreal forest in a two (0 and 30 kg N ha −1 year −1 , as ammonium nitrate) × two (0 and 30 kg S ha −1 year −1 , as sodium sulfate) factorial experiment. Soil (forest floor and 0–15 cm mineral soil) and understory vegetation samples were collected and the cover of understory vegetation was determined in August 2016. Eleven years of N deposition increased (p = .045) total N concentration and decreased (p < .10 unless otherwise indicated) carbon to N ratio by 11 and 7%, respectively, in the forest floor. Sulfur deposition decreased (p = .045) exchangeable calcium concentration by 36% in the mineral soil. Species evenness (by 7%) and the overall diversity (by 7%) were decreased and community composition was changed (p = .008) in the herb stratum by N but not by S deposition, due to species-specific responses to N deposition. However, elevated concentrations of N and S deposition did not change species diversity and composition in the shrub stratum. Decreased foliar phosphorus and potassium concentrations and increased N to phosphorus ratio in some species indicate a potential risk of nutrient imbalance by N deposition. Reducing N emission to minimize its negative effect on boreal forest ecosystems should be a priority in emissions management in the oil sands. [ABSTRACT FROM AUTHOR]

Oil sands mining in northern Alberta, Canada, emits large amounts of NOx and SO2 to the atmosphere, which will eventually return to the surrounding forest ecosystems. This study was conducted to determine changes in microbial and enzyme activities, and gross nitrogen transformation rates in a boreal forest soil in response to 10 yr (2006–2015) of elevated levels of nitrogen (N) and sulfur (S) addition. The experiment had a two (0 vs. 30 kg N h–1 yr–1, as NH4NO3) × two (0 vs. 30 kg S ha–1 yr–1, as Na2SO4) factorial design with three blocks. A laboratory incubation experiment was conducted using forest floor and the mineral soil (0–15 cm). Ten years of elevated N and S additions did not affect soil chemical (pH, total C, total N and available N concentrations) and microbiological properties (microbial biomass C and N, soil respiration rate, and enzyme activities related to C and N cycling) and gross N transformation rates. Gross N mineralization (0.54–0.62 and 36–49 mg N kg–1 d–1 for mineral soil and forest floor, respectively) and gross NH4 + immobilization (0.39–0.57 and 10–19 mg N kg–1 d–1, respectively) rates were tightly coupled in both soil layers. Gross NO3- immobilization rates (20–32 mg N kg–1 d–1) were significantly greater than gross nitrification rates (9–20 mg N kg–1) in the forest floor. Our results suggest that the studied boreal forest soil was resilient or resistant to 10 yr of N and S addition and the studied soils were still N limited. Given the current N and S emission and deposition rates in northern Alberta, the risk for N and S deposition to significantly affect gross N transformation rates is low for the studied forest ecosystem. [ABSTRACT FROM AUTHOR]–1) in the forest floor. Our results suggest that the studied boreal forest soil was resilient or resistant to 10 yr of N and S addition and the studied soils were still N limited. Given the current N and S emission and deposition rates in northern Alberta, the risk for N and S deposition to significantly affect gross N transformation rates is low for the studied forest ecosystem. [ABSTRACT FROM AUTHOR]

Forest floor mineral soil mix (FMM) and peat mineral soil mix (PMM) are cover soils commonly used for reclamation of open-pit oil sands mining disturbed land in northern Alberta, Canada; coarse woody debris (CWD) is another source of organic matter for land reclamation. We investigated net nitrogen (N) transformation rates in FMM and PMM cover soils near and away from CWD 4-6 years after oil sands reclamation. Monthly net nitrification and N mineralization rates varied over time; however, mean rates across the incubation periods and microbial biomass were greater (p<0.05) in FMM than in PMM. Net N mineralization rates were positively related to soil temperature (p<0.001) and microbial biomass carbon (p=0.045). Net N transformation rates and inorganic N concentrations were not affected by CWD; however, the greater 15N isotope ratio of ammonium near CWD than away from CWD indicates that CWD application increased both gross N mineralization/nitrification (causing N isotope fractionation) and gross N immobilization (no isotopic fractionation).Microbial biomass was greater near CWD than away from CWD, indicating the greater potential for N immobilization near CWD. We conclude that (1)CWDapplication affected soil microbial properties andwould create spatial variability and diversemicrosites and (2) cover soil type and CWD application had differential effects on net N transformation rates. Applying FMM with CWD for oil sands reclamation is recommended to increase N availability and microsites. [ABSTRACT FROM AUTHOR]

Open-pit mining activities in the oil sands region of Alberta, Canada, create disturbed lands that, by law, must be reclaimed to a land capability equivalent to that existed before the disturbance. Re-establishment of forest cover will be affected by the production and turnover rate of fine roots. However, the relationship between fine root dynamics and tree growth has not been studied in reclaimed oil sands sites. Fine root properties (root length density, mean surface area, total root biomass, and rates of root production, turnover, and decomposition) were assessed from May to October 2011 and 2012 using sequential coring and ingrowth core methods in lodgepole pine ( Pinus contorta Dougl.) and white spruce ( Picea glauca (Moench.) Voss) stands. The pine and spruce stands were planted on peat mineral soil mix placed over tailings sand and overburden substrates, respectively, in reclaimed oil sands sites in Alberta. We selected stands that form a productivity gradient (low, medium, and high productivities) of each tree species based on differences in tree height and diameter at breast height ( DBH) increments. In lodgepole pine stands, fine root length density and fine root production, and turnover rates were in the order of high > medium > low productivity sites and were positively correlated with tree height and DBH and negatively correlated with soil salinity ( P < 0.05). In white spruce stands, fine root surface area was the only parameter that increased along the productivity gradient and was negatively correlated with soil compaction. In conclusion, fine root dynamics along the stand productivity gradients were closely linked to stand productivity and were affected by limiting soil properties related to the specific substrate used for reconstructing the reclaimed soil. Understanding the impact of soil properties on fine root dynamics and overall stand productivity will help improve land reclamation outcomes. [ABSTRACT FROM AUTHOR]

Agroforestry land-use systems have significant potential for increasing soil carbon (C) storage and mitigating increases in atmospheric greenhouse gas (GHG) concentrations. We studied the impact of three agroforestry systems (hedgerow, shelterbelt, and silvopasture) on soil organic C (SOC) and nitrogen (N) in the 0-10 cm mineral layer, by comparing SOC and N distributions in whole soils and three particle-size fractions (<53, 53-250, 250-2000 μm) to assess the potential role of physical protection on soil C and N storage. We assessed thirty-five sites (12 hedgerows, 11 shelterbelts and 12 silvopastures), each comprised of 2 paired plots (forest and adjacent agricultural herbland), that were distributed along a 270 km long north-south soil/climate gradient in central Alberta, Canada. Across all sites, 48.4%, 28.5%, and 23.1% of SOC was found in the fine (<53 μm), medium (53-250 μm) and coarse fractions (250-2000 μm), respectively. Mean SOC in the whole soil was 62.5, 47.7 and 81.3 g kg-1 in hedgerow, shelterbelt and silvopasture systems, respectively. Soil C in the more stable fine fraction was 34.3, 28.8 and 29.3 g kg-1 in the hedgerow, shelterbelt and silvopasture systems, respectively. Within each agroforestry system, the forested land-use consistently had greater total SOC and SOC in all size fractions than the agricultural component. Our results demonstrate the potential for trees to increase soil C sequestration in agroforestry systems within the agricultural landscape. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the critical load (CL) and exceedance (EX) of sulfur (S) deposition, temporal changes in soil chemistry, and H+ budget of soils in plots dominated by Pinus banksiana (jack pine) or Populus tremuloides (trembling aspen, aspen) in two acid-sensitive watersheds to assess the risk of soil acidification by S emissions from oil sands mining in the Athabasca oil sands region (AOSR), Canada. The CLs and EXs were determined by two methods: one was based on bulk deposition and the other based on total deposition (as a sum of bulk deposition and interception deposition). The CLs ranged from 223 to 711 molc ha−1 yr−1 based on bulk deposition. Those values were similar to that obtained based on total deposition. However, EXs based on bulk deposition were significantly lower (p < 0.001) than those based on total deposition due to the relative increase of concentrations in interception deposition, indicating that EXs based on bulk deposition only could underestimate the risk of soil acidification in the AOSR. The S deposition did not exceed CLs in the long-term for both methods. The pH in the forest floor increased and available (as the sum of soluble and adsorbed ) in the forest floor and surface mineral soils increased in both jack pine and aspen stands between 2005 and 2010. The H+ budget ranged from −289 to −130 molc ha−1 yr−1 in jack pine stands and from −510 to −371 molc ha−1 yr−1 in aspen stands. Our results suggest that 1) soils in the studied forest stands have recovered from acidification based on the increasing soil pH over time and the negative H+ budget, and 2) the risk of soil acidification should be assessed by CL and EX calculated based on total deposition. [Copyright &y& Elsevier]

Abstract: We conducted a simulated nitrogen (N) and sulfur (S) deposition experiment in the Athabasca oil sands region (AOSR) where NO x and SO2 have been emitted from oil sands mining/extracting and upgrading activities and then deposited to the surrounding ecosystems for decades. To evaluate changes in tree growth rates, N pool sizes, and nutrient losses by S and N deposition, the following four treatments were applied: control (CK), N addition (+N, 30kgNha−1 yr−1), S addition (+S, 30kgSha−1 yr−1), and +NS additions (+NS, 30kgN and 30kgSha−1), from 2006 through 2009. Nitrogen addition increased (p <0.05) tree growth in the +N and +NS treatments, indicating N-limitation in the studied forest, while none of the treatments affected understory growth or soil microbial biomass. The treatments affected inorganic N concentrations in the soil only immediately following N addition. Minimal amounts of were leached below 45cm (considered to be below the main rooting zone) of the soil profile in any of the treatments. Decreases in exchangeable Ca2+ and Mg2+ by N and S additions were likely due to increased tree uptake following increased tree growth in the former and increased leaching with sulfate in the latter. Although the lack of significant N leaching indicates that the risk of N saturation was low after 4yr of elevated N deposition, reduction of exchangeable base cations implies that nutrient imbalance remains a concern in AOSR in the long term. [Copyright &y& Elsevier]

Abstract: The effects of 4years of simulated nitrogen (N) and sulfur (S) depositions on gross N transformations in a boreal forest soil in the Athabasca oil sands region (AOSR) in Alberta, Canada, were investigated using the 15N pool dilution method. Gross NH4 + transformation rates in the organic layer tended to decline (P <0.10, marginal statistical significance, same below) in the order of control (CK, i.e., no N or S addition), +N (30kgNha−1 yr−1), +S (30kgSha−1 yr−1), and +NS treatments, with an opposite trend in the mineral soil. Gross NH4 + immobilization rates were generally higher than gross N mineralization rates across the treatments, suggesting that the studied soil still had potential for microbial immobilization of NH4 +, even after 4years of elevated levels of simulated N and S depositions. For both soil layers, N addition tended to increase (P <0.10) the gross nitrification and NO3 − immobilization rates. In contrast, S addition reduced (P <0.001) and increased (P <0.001) gross nitrification as well as tended (P <0.10) to reduce and increase gross NO3 − immobilization rates in the organic and mineral soils, respectively. Gross nitrification and gross NO3 − immobilization rates were tightly coupled in both soil layers. The combination of rapid NH4 + cycling, negligible net nitrification rates and the small NO3 − pool size after 4years of elevated N and S depositions observed here suggest that the risk of NO3 − leaching would be low in the studied boreal forest soil, consistent with N leaching measurements in other concurrent studies at the site that are reported elsewhere. [Copyright &y& Elsevier]

Soil acidification has been of concern in the oil sands region in Alberta due to increased acid deposition. Using the canopy budget model, and accounting for H+ canopy leaching by organic acids, we determined sources and sinks of H+ in throughfall in jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides) stands in two watersheds from 2006 to 2009. In pine stands, H+ deposition was greater in throughfall than in bulk precipitation while the opposite was true in aspen stands. The annual H+ interception deposition was 148.8–193.8 and 49.7–70.0molc ha−1 in pine and aspen stands, respectively; while the annual H+ canopy leaching was 127.1–128.7 and 0.0–6.0molc ha−1, respectively. The greater H+ supply in pine stands was caused by greater interception deposition of SO4 2− and organic acids released from the pine canopy. Such findings have significant implications for establishing critical loads for various ecosystems in the oil sands region. [Copyright &y& Elsevier]

Abstract: Land-use and land cover strongly influence carbon (C) storage and distribution within ecosystems. We studied the effects of land-use on: (i) above- and belowground biomass C, (ii) soil organic C (SOC) in bulk soil, coarse- (250–2000μm), medium- (53–250μm) and fine-size fractions (<53μm), and (iii) 13C and 15N abundance in plant litter, bulk soil, coarse-, and medium- and fine-size fractions in the 0–50cm soil layer in Linaria AB, Canada between May and October of 2006. Five adjacent land-uses were sampled: (i) agriculture since 1930s, (ii) 2-year-old hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) plantation, (iii) 9-year-old Walker hybrid poplar plantation, (iv) grassland since 1997, and (v) an 80-year-old native aspen (Populus tremuloides Michx.) stand. Total ecosystem C stock in the native aspen stand (223MgCha−1) was similar to that of the 9-year-old hybrid poplar plantation (174MgCha−1) but was significantly greater than in the agriculture (132MgCha−1), 2-year-old hybrid poplar plantation (110MgCha−1), and grassland (121MgCha−1). Differences in ecosystem C stocks between the land-uses were primarily the result of different plant biomass as SOC in the 0–50cm soil layer was unaffected by land-use change. The general trend for C stocks in soil particle-size fractions decreased in the order of: fine>medium>coarse for all land-uses, except in the native aspen stand where C was uniformly distributed among soil particle-size fractions. The C stock in the coarse-size fraction was most affected by land-use change whilst the fine fractions the least. Enrichment of the natural abundances of 13C and 15N across the land-uses since time of disturbance, i.e., from agriculture to 2- and then 9-year-old hybrid poplar plantations or to grassland, suggests shifts from more labile forms of C to more humified forms of C following those land-use changes. [Copyright &y& Elsevier]

Abstract: Sequestering C in biomass and soils in hybrid poplar plantations can help mitigate global climate change caused by the rising atmospheric CO2 concentration. However, the impact of the establishment of hybrid poplar plantations on C and N storage and dynamics is poorly understood. We studied the distribution and temporal changes of C and N in soil organic matter (SOM) density fractions in 2-, 5-, 11-, and 13-year-old (age as in 2006) hybrid poplar stands that form a chronosequence by sampling the plantations in both 2004 and 2006. Sodium polytungstate (SPT, density=1.6 g mL-1) was used to fractionate the soil into light (LF, density<1.6 g mL-1), occluded light (LFo, density<1.6 g mL-1) and heavy fractions (HF density>1.6 g mL-1). The results showed that C and N concentrations (g kg-1 of fraction) in the SOM density fractions decreased in the order of LFo>LF>HF, while the C/N ratio was in the order of LF>LFo>HF. The amount of C and N stored in the LF, LFo and HF fractions and bulk soil in the top 10 cm of soil was: 149-504, 70-336, 1380-2876 and 1617-3776 g m-2, respectively, for C, and 6-26, 3-20, 149-271 and 152-299 g m-2, respectively, for N. From 2004 to 2006, C and N storage decreased in the LF and LFo fractions but increased in the HF fraction in the youngest stand. However, stand-age effects were likely muted by high inherent soil variability among the stands. Carbon storage in the light fraction was responsive in the short term to hybrid poplar plantation establishment. [Copyright &y& Elsevier]

Cattle production is a large source of greenhouse gas (GHG) emissions from the Canadian livestock sector. Efforts to reduce CH4 emissions from enteric fermentation have led to modifications of diet composition for livestock, resulting in a corresponding change in manure properties. We studied the effect of applying manure from cattle fed a barley-based diet with and without the methane inhibitor supplement, 3-nitrooxypropanol (3-NOP), on soil GHG emissions. Three soils common to Alberta, Canada, were used: a Black Chernozem, a Dark Brown Chernozem, and a Gray Luvisol. We compared the supplemented (3-NOPM) and non-supplemented manure (BM) amendments to a composted 3-NOPM (3-NOPC) amendment and a control with no manure amendment (CK). In an 84-day laboratory incubation experiment, 3-NOPM had significantly lower cumulative CO2 emissions compared to BM in both the Black Chernozem and Gray Luvisol. The cumulative N2O emissions were lowest for 3-NOPC and CK and highest for 3-NOPM across all soil types. Cumulative CH4 emissions were only affected by soil type, with a net positive flux from the fine-textured Gray Luvisol and Dark Brown Chernozem and a net negative flux from the coarse-textured Black Chernozem. Cumulative anthropogenic GHG emissions (CO2-equivalent) from soil amended with 3-NOPM were significantly higher than those for both BM and CK amendments in the Black Chernozem, while the cumulative anthropogenic GHG emissions from the 3-NOPC treatment were similar to or significantly lower than those for the BM and CK treatments across all soil types. We conclude that soil GHG emissions resulting from the 3-NOPM amendment are dependent on soil type and 3-NOPM could potentially increase soil GHG emissions compared to BM or CK. Although we show that the composting of 3-NOPM prior to soil application can reduce soil GHG emissions, the composting process also releases GHGs, which should also be considered in assessing the life-cycle of manure application. Our results provide a first look at the potential effect of the next stage in the life cycle of 3-NOP on GHG emissions. Further research related to the effect of soil properties, particularly in field studies, is needed to assess the best management practices related to the use of manure from cattle-fed diets supplemented with 3-NOP as a soil amendment. [ABSTRACT FROM AUTHOR]

Adaptive multi-paddock (AMP) grazing is a form of rotational grazing in which small paddocks are grazed with high densities of livestock for short periods, with long recovery periods prior to regrazing. We compared the fluxes of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), from soils of AMP-grazed grasslands to paired neighboring non-AMP-grazed grasslands across a climatic gradient in Alberta, Canada. We further tested GHG responses to changes in temperature (5 °C vs. 25 °C) and moisture levels (permanent wilting point (PWP), 40% of field capacity (0.4FC), or field capacity (FC)) in a 102-day laboratory incubation experiment. Extracellular enzyme activities (EEA), microbial biomass C (MBC) and N (MBN), and available-N were also measured on days 1, 13, and 102 of the incubation to evaluate biological associations with GHGs. The 102-day cumulative fluxes of CO2, N2O, and CH4 were affected by both temperature and moisture content (p < 0.001). While cumulative fluxes of N2O were independent of the grazing system, CH4 uptake was 1.5 times greater in soils from AMP-grazed than non-AMP-grazed grasslands (p < 0.001). There was an interaction of the grazing system by temperature (p < 0.05) on CO2 flux, with AMP soils emitting 17% more CO2 than non-AMP soils at 5 °C, but 18% less at 25 °C. The temperature sensitivity (Q10) of CO2 fluxes increased with soil moisture level (i.e., PWP < 0.4FC ≤ FC). Structural equation modelling indicated that the grazing system had no direct effect on CO2 or N2O fluxes, but had an effect on CH4 fluxes on days 1 and 13, indicating that CH4 uptake increased in association with AMP grazing. Increasing soil moisture level increased fluxes of GHGs—directly and indirectly—by influencing EEAs. Irrespective of the grazing system, the MBC was an indirect driver of CO2 emissions and CH4 uptake through its effects on soil EEAs. The relationships of N-acetyl-β glucosaminidase and β-glucosidase to N2O fluxes were subtle on day 1, and independent thereafter. AMP grazing indirectly affected N2O fluxes by influencing N-acetyl-β glucosaminidase on day 13. We conclude that AMP grazing has the potential to mitigate the impact of a warmer soil on GHG emissions by consuming more CH4 compared to non-AMP grazing in northern temperate grasslands, presumably by altering biogeochemical properties and processes. [ABSTRACT FROM AUTHOR]

Abstract: The impact of chronic air pollution such as increased CO2 and NO x emissions on forest ecosystems in the Athabasca oil sands region in Alberta, Canada, was investigated in Pinus banksiana (jack pine) and Populus tremuloides (trembling aspen, aspen) stands in two watersheds (NE7 and SM8) located at different distances from the main emission sources of oil sands mining and upgrading facilities, using δ13C, δ15N, and Ca/Al of soil and tree ring samples as indicators. Watershed NE7 was exposed to greater amounts of acid deposition due to its closeness to the mining and upgrading area. The δ15N in the forest floor was lower (p <0.05) in NE7 (ranged from −1.42 to −0.87‰) than in SM8 (−0.54 to 1.43‰), implying a greater amount of recent deposition of 15N-depleted N in NE7. Tree ring δ13C gradually decreased over time for both tree species/watersheds, indicating the influence of 13C-depleted CO2 emitted from industrial sources. Tree ring N concentration and δ15N were not different between watersheds and did not significantly change with time. Interestingly, however, the difference between watersheds (NE7–SM8) that is expressed as Diff_N (for N) increased with concomitant decreases in Diff_δ15N over time, implying greater increases in 15N-depleted N input in NE7 than in SM8. Such trends were stronger in aspen stands (R 2 =0.64 and p <0.001 for Diff_N and R 2 =0.44 and p <0.01 for Diff_δ15N between 1964 and 2009) than in jack pine stands. We conclude that δ15N in the forest floor and differences in N and δ15N of tree rings between watersheds are useful indicators reflecting the impact of spatial variations of air pollution on forest stands in the Athabasca oil sands region in western Canada. [Copyright &y& Elsevier]

Abstract: The risk of soil acidification is high in the Athabasca oil sands region (AOSR) in Alberta, Canada, due to elevated SO2 emission and the resultant acid deposition to sensitive, coarse-textured soils. Understanding the sulfate adsorption characteristics of soils sensitive to acidification will help establish critical loads of acid deposition in AOSR. Sulfate adsorption properties were evaluated and relationships between sulfate adsorption and soil properties were examined for soils in two contrasting watersheds (NE7 and SM8) in AOSR. The experimental data fitted well to both the Langmuir and the Freundlich models. The sulfate adsorption capacity was greater for soils in SM8 than in NE7 (p <0.01), even though it was relatively low in both watersheds as compared to other acid-sensitive soils in eastern North America. Based on the additional sulfate adsorbed when a soil was treated with 40mL of 200mg L−1 solution, the weakly developed Podzolic B horizon (Bfj)in NE7 could adsorb more sulfate than the Ae horizon while no difference was found among other horizons. In SM8, the Bfj and illuviated B (Bt) horizons had greater ability to adsorb sulfate than the other horizons, likely caused by the presence of muscovite in the Bfj and Bt horizons. The additional sulfate adsorbed accounted for about 80% of the total sulfate adsorption capacity and was correlated with pHNaF (soil pH extracted with 1 MNaF) and ΔpHNaF(the difference between pHNaF and pH measured with deionized water), with the following relationships: sulfate adsorption (mg kg−1)=exp(2.03 pHNaF – 18.0)+50.2 (R 2 =0.63, p <0.001) and sulfate adsorption (mg kg−1)=exp(1.83 ΔpHNaF – 6.57) + 48.9 (R 2 =0.70, p <0.001). The ΔpHNaF was likely a better indicator of the soil’s sulfate adsorption capacity than pHNaF as the former excludes the effect of soil acidity. Our study indicates that the soil’s capacity to adsorb sulfate should be considered in determining the critical load for acid deposition in AOSR in Alberta. [Copyright &y& Elsevier]

Pulp mill biosolids (hereafter 'biosolids') could be used as an organic amendment to improve soil fertility and promote crop growth; however, it is unclear how the application of biosolids affects soil greenhouse gas emissions and the mechanisms underlying these effects. Here, we conducted a 2-year field experiment on a 6-year-old hybrid poplar plantation in northern Alberta, Canada, to compare the effects of biosolids, conventional mineral fertilizer (urea), and urea + biosolids on soil CO 2 , CH 4 N 2 O emissions, as well as soil chemical and microbial properties. We found that the addition of biosolids increased soil CO 2 and N 2 O emissions by 21 and 17%, respectively, while urea addition increased their emissions by 30 and 83%, respectively. However, the addition of urea did not affect soil CO 2 emissions when biosolids were also applied. The addition of biosolids and biosolids + urea increased soil dissolved organic carbon (DOC) and microbial biomass C (MBC), while urea addition and biosolids + urea addition increased soil inorganic N, available P and denitrifying enzyme activity (DEA). Furthermore, the CO 2 and N 2 O emissions were positively, while the CH 4 emissions were negatively associated with soil DOC, inorganic N, available phosphorus, MBC, microbial biomass N, and DEA. In addition, soil CO 2 , CH 4 and N 2 O emissions were also strongly associated with soil microbial community composition. We conclude that the application of the combination of biosolids and chemical N fertilizer (urea) could be a beneficial approach for both the disposal and use of pulp mill wastes, by reducing greenhouse gas emissions and improving soil fertility. • The addition of pulp mill biosolids ("biosolids") increased soil CO 2 and N 2 O. • Urea addition had stronger positive effects on soil CO 2 and N 2 O than biosolids did. • Urea addition did not affect soil CO 2 when biosolids were also applied. • Soil microorganisms play a critical role in the regulation of GHG emissions. [ABSTRACT FROM AUTHOR]

• We studied in-situ responses of GHGs to warming, altered precipitation and defoliation. • The temperate grassland was a source for CO 2 , N 2 O but a sink for CH 4 during the study. • GHG fluxes were decoupled from microbial biomass in the study. • Precipitation was the primary driver directly regulating CO 2 and N 2 O fluxes. Grasslands store large quantities of organic carbon (C) and thus can markedly impact global climate change if they are disturbed. How practices such as grazing intensity and climate change interact to affect soil greenhouse gas (GHG) fluxes within native northern temperate grasslands is unclear. We investigated the responses of three major GHGs (CO 2 , N 2 O and CH 4) to temperature (ambient vs. warmed), precipitation (ambient vs. reduced or increased) and defoliation (no defoliation vs. low- or high-intensity defoliation) treatments in a factorial experiment over a two-year period in a native northern temperate grassland in Alberta, Canada. Growing season mean soil gas fluxes across all treatments were 93.8 mg CO 2 m−2 h−1, −0.025 mg CH 4 m−2 h−1, and 0.003 mg N 2 O m−2 h−1, suggesting that this grassland was a source for CO 2 and N 2 O, but a sink for CH 4 over the study period. Structural equation modeling showed that increased precipitation, rather than warming or defoliation, was the primary driver directly regulating fluxes of CO 2 and N 2 O. While increased precipitation also increased microbial biomass C (MBC), the latter had little impact on GHG fluxes, suggesting that MBC was not a critical factor regulating the precipitation-GHG flux relationship. Warming and precipitation effects on CH 4 fluxes depended on the month of sampling during the growing season. Warming decreased CH 4 uptake but only in mid-July, while increased precipitation reduced CH 4 uptake across all sampling dates except early August, at which time increased precipitation increased CH 4 uptake. Our study shows that short-term soil GHG fluxes in this native grassland are relatively resilient to moderate warming and defoliation, but sensitive to altered precipitation. Increased precipitation was the main contributor to short-term GHG fluxes in this temperate grassland via changes in CO 2 efflux. [ABSTRACT FROM AUTHOR]

Abstract: Soil pH can be affected by land use change and acid deposition and is one of the primary regulators of nutrient cycling in the soil. In this study, two soils from adjacent forest and grassland sites in central Alberta were subjected to different pH treatments to evaluate the short-term effects of pH on soil gross N transformations using the 15N tracing technique and calculated by the numerical model FLUAZ. For the forest soil, gross immobilization increased faster than gross N mineralization rates with increasing soil pH, leading to a declining pattern in net N mineralization rates; however, none of those rates changed with pH in the grassland soil. In contrast, the increase in pH significantly stimulated gross and net nitrification rates while soil acidification decreased gross and net nitrification rates for both the forest and grassland soils. The ratio of gross nitrification to gross immobilization rates (N/IA) was significantly increased by KOH addition but declined to nearly zero by HCl addition for each soil. The low and high KCl addition treatments partially or completely inhibited gross nitrification rates, respectively, but gross mineralization was less sensitive to salt additions than the nitrification process. We conclude that based on the short-term laboratory incubation experiments both pH and salt (osmotic effect) affected gross N transformations and pH had contrasting effects on gross and net nitrogen mineralization but not on nitrification in the adjacent forest and grassland soils. [Copyright &y& Elsevier]

• Tree areas of agroforestry systems (AFS) stored more C than adjacent herblands. • Surface organic horizon contained 10% of the C stored in the tree area of AFS. • C storage in surface organic horizon was positively related to tree age. • Establishing AFS can be an effective strategy for climate change mitigation. Agroforestry systems (AFS) are increasingly being recognized as sustainable land-use systems that can increase carbon (C) sequestration and improve food security. However, the relative contributions of various C pools to the overall C stock of AFS and their dependence on factors such as tree age, species diversity and density is still unclear in many regions. Using an equivalent soil mass approach, we investigated the effect of three different AFS (hedgerow, shelterbelt, and silvopasture) and their component land-use types (treed areas and adjacent cropland/grassland) on various C pools across 36 sites in central Alberta, Canada. On average, the treed area within AFS stored 178.5 t ha−1 more C relative to adjacent cropland or grassland, although the total C stock did not differ among the three AFS types. Most of the C in the treed area of AFS was stored in the mineral soil (61%), overstory trees (28%), and the LFH (litter, partially decomposed litter and humus, 10%) layer, while midstory trees, shrubs, and understory vegetation together accounted for the remaining 1% of the C storage. The C stock size in the treed area was closely associated with tree stand characteristics of the three AFS, with the C pool size in the LFH positively related to tree age. Our results highlight that the amount of C stored in the LFH layer is substantial and should be considered when assessing C storage within AFS and suggest that investing in AFS can be an effective strategy for meeting part of Canada's C reduction goals to mitigate climate change. [ABSTRACT FROM AUTHOR]

How land-use and soil depth affect soil organic carbon (SOC) quality and stability, properties that are key to the long-term storage of C, is poorly understood in agroforestry systems. We examined the effects of land-use (forest vs. annual cropland) and soil depth (0–10 vs. 10–30 cm) on the quality (availability of C for decomposition), structural stability (composition of C functional groups), and thermal stability (energy yield and temperature characteristics during thermal oxidation) of SOC in a hedgerow system in central Alberta, using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and thermal analysis methods. The SOC quality (proportion of O-alkyl C) was higher, while the proportion of H- and C-substituted aromatic C and structural stability (hydrophobicity index (HB/HI), aromaticity index (ARM), and alkyl index (A/OA)) were all lower in the forest than in the cropland. The SOC also had lower thermal stability (higher energy density and lower temperature at which 50% of the mass was lost (TG-T 50)) in the forest than in the cropland. Between the two soil depths, SOC quality (proportion of N-alkyl C, O-alkyl C and di-O-alkyl C) was higher, but the proportion of H- and C-substituted aromatic C and structural and thermal stabilities were lower, within the surficial 0–10 cm layer than in the 10–30 cm soil. We conclude that while the forest land-use within the hedgerow system had a higher SOC quality, it had lower SOC structural and thermal stabilities, suggesting that SOC under the forest land-use may be more susceptible to decline under climate change or other forms of anthropogenic disturbance. • Soil organic C (SOC) quality and structural and thermal stabilities in hedgerow were studied. • NMR and thermal analyses were used to study energy density and quality of SOC. • SOC quality was greater but structural and thermal stability was lower in forest than in cropland. • SOC thermal stability was lower in the surface than in the subsurface soil layer. • Land-use type and soil depth significantly affected SOC quality and stability. [ABSTRACT FROM AUTHOR]

Grasslands are globally abundant and provide many ecosystem services, including carbon (C) storage. While grasslands are widely subject to livestock grazing, the influence of grazing on grassland ecosystem C remains unclear. We studied the effect of long-term livestock grazing on C densities of different ecosystem components in 110 northern temperate grasslands across a broad agroclimatic gradient in Alberta, Canada. These grasslands stored 50 to 180 t ha -1 C in live and dead vegetation, as well as soil C to 30 cm depth, with the majority as soil organic C (SOC). The mulch layer comprised a large amount of C (~18 t ha -1 C) especially within humid grasslands. Although grazing reduced C densities in litter mass, total ecosystem C was 8.5 % greater under grazing (127.8 t ha -1 ) compared to those non-grazed (117.8 t ha -1 ), primarily due to increases in SOC and roots. Increases in SOC were consistently observed in the 0-15 cm layer across all climatic conditions, with changes in SOC of the 15-30 cm layer inversely related to aridity. A structural equation model revealed that increased SOC under grazing was indirectly attributed to increases in eudicot rather than graminoid biomass. In addition, SOC increased with graminoid quality (i.e., a reduced carbon to nitrogen ratio), which together with elevated eudicots, increased litter and mulch C, and ultimately enhanced SOC densities. When applied to spatial maps of habitat type and land use (livestock grazing) activity across the region, an area of ~3.8 M ha of grassland was projected to contain an additional 17.1 M t of C under grazing, primarily in mesic grasslands, worth an estimated $3.1 B (Cdn.) under current C valuation guidelines in Canada. Overall, these results highlight the importance of grasslands for C storage and establishing policies that maintain and promote their sustainable use, including light to moderate grazing., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Applying organic amendments to soil can increase soil organic carbon (SOC) storage and reduce greenhouse gas (GHG) emissions generated by agriculture, helping to mitigate climate change. However, it is necessary to determine which type of amendment produces the most desirable results. We conducted a 3-y field study comparing one-time addition of manure compost and its biochar derivative to a control to assess their effects on SOC and GHG emissions at ten annually cropped sites in central Alberta, Canada. Manure compost and biochar were applied at equivalent carbon rates (7 Mg ha -1 ) and tilled into the surface 10 cm of soil. Two years post-treatment, biochar addition increased surface (0-10 cm) SOC by 12 and 10 Mg ha -1 relative to the control and manure addition, respectively. Therefore, biochar addition led to the sequestration of SOC at a rate of 2.5 Mg ha -1 y -1 relative to the control. No treatment effect on deeper (10-100 cm) or cumulative SOC was found. In 2018 and 2019, manure addition increased cumulative GHG (sum of CO 2 , CH 4 , and N 2 O) emissions by 33%, on average, due to greater CO 2 emissions relative to both the control and biochar addition. In contrast, in 2020, biochar addition reduced cumulative GHG emissions by an average of 21% due to lower CO 2 emissions relative to both the control and manure addition. Our study shows that the application of biochar, rather than its manure compost feedstock, increased surface SOC sequestration and had either no effect on (first two years) or reduced GHG emissions (year three) relative to the control. We recommend that policy and carbon sequestration initiatives focus on optimizing biochar production-application systems to fully realize the potential of biochar application as a viable climate change mitigation practice in agriculture., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Adaptive multi-paddock (AMP) grazing, a grazing system in which individual paddocks are grazed for a short duration at a high stock density and followed by a long rest period, is claimed to be an effective tool to sustainably manage and improve grasslands and enhance their ecosystem services. However, whether AMP grazing is superior to conventional grazing (n-AMP) in reducing soil greenhouse gas (GHG) emissions is unclear. Here, we measured CO 2 , CH 4 , and N 2 O fluxes between August 2017 and August 2019 in 12 pairs of AMP vs. n-AMP ranches distributed across an agro-climatic gradient in Alberta, Canada. We found that field GHG fluxes did not differ between AMP and n-AMP grazing systems, but instead were regulated by specific management attributes, environmental conditions, and soil properties, including cattle stocking rate, cultivation history, soil moisture content, and soil bulk density. Specifically, we found that seasonal mean CO 2 emissions increased with increasing cattle stocking rates, while CH 4 uptake was lower in grasslands with a history of cultivation. Seasonal mean CO 2 emissions increased while CH 4 uptake decreased with increasing soil moisture content. In addition, CH 4 uptake decreased with increasing soil bulk density. Observed N 2 O emissions were poorly predicted by the management, environmental conditions, and soil properties investigated in our study. We conclude that AMP grazing does not have an advantage over n-AMP grazing in reducing GHG fluxes from grasslands. Future efforts to develop optimal management strategies (e.g., the use of sustainable stocking rates and avoided cultivation) that reduce GHG emissions should also consider the environmental conditions and soil properties unique to every grassland ecosystem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Long-term livestock grazing (here after 'grazing') affects carbon (C) and nutrient cycling in grassland ecosystems, in part by altering the quantity and quality of litter inputs. Despite their spatial extent and size of carbon and nutrient stocks, the effect of grazing on grassland biogeochemical cycling through the mediation of microbial activity remains poorly understood. To better understand the relationship between grazing and C and nutrient cycling in litter, we conducted an 18-month long study in paired grasslands previously grazed and nongrazed by cattle for 25 years, measuring extracellular enzyme activity (EEA) in various plant litter samples. Litter sources, including seven grass species dominant in one or more subregions and possessing divergent responses to grazing, as well as a community mix of litter sourced from each site, were tested at 15 sites spanning three grassland subregions in Alberta, Canada. We quantified EEAs associated with C cycling (β-glucosidase, β-Cellobiosidase and β-xylosidase), nitrogen (N) cycling (N-acetyl-glucosaminidase) and phosphorus (P) cycling (phosphatase). In general, litter in grasslands exposed to grazing had greater activity of C-liberating and P-liberating enzyme (β-xylosidase and phosphatase) in the mesic grasslands of the Foothills Fescue subregion (P ≤ 0.10). Observed EEAs were strongly mediated by litter type, with greater EEAs in litter of grass species known to increase in abundance under long-term grazing, including Poa pratensis in the Foothills Fescue subregion, and Bouteloua gracilis in arid grasslands of the Mixedgrass Prairie. In contrast, Pascopyrum smithii litter had the lowest enzyme activities in all subregions. We also found that EEAs changed through time (0-18 months) with consistently high levels detected at 1 (June 2014), 6 (October 2014) and 18 months (October 2015) after placement. Overall, these findings indicate grazing enhances EEA, and thus C and N-cycling, in northern temperate grasslands., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The role of agroforestry systems in mitigating greenhouse gas (GHG) emission from agricultural soils during spring thaw (early April to mid-May) has been poorly studied. Soil CO 2 , CH 4 and N 2 O fluxes were measured from treed areas and adjacent herblands (areas without trees) during spring thaw in 2014 and 2015 at 36 agroforestry sites (12 hedgerow, 12 shelterbelt and 12 silvopasture) in central Alberta, Canada. Fluxes of those GHGs varied with agroforestry systems and land-cover types. We found greater CO 2 emission (P < 0.001) and CH 4 uptake (P < 0.05), but lower N 2 O emission (P < 0.01) in the silvopasture than in the hedgerow and shelterbelt systems, with no difference between the last two systems. Treed areas in general had greater CO 2 emissions (P < 0.001) and CH 4 uptake (P < 0.01), and lower N 2 O emissions (P < 0.001) than the herblands. Soil temperature, moisture content, organic C content and soil available N concentration affected GHG fluxes. The global warming potential (GWP) was greater (P < 0.05) in the silvopasture than in the hedgerow or shelterbelt systems over the two spring thaw seasons examined, and greater (P < 0.05) in the treed areas than in the herblands during the cool spring in 2015. However, the GWP per unit soil organic C was lower in the treed areas (0.004-0.101%) than in the herblands (0.005-0.225%). As compared to previously reported mean growing season GHG emission (15.4 g CO 2 -eq m -2  day -1 ), the GWP of these land uses during spring thaw was small (<5% of the annual GWP) due to the short spring period (6 weeks) and the small GHG emission (2.5 g CO 2 -eq m -2  day -1 ). Although GHG emissions during spring thaw were small compared to those in the growing season, they should not be ignored., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Forest floor mineral soil mix (FMM) and peat mineral soil mix (PMM) are cover soils commonly used for upland reclamation post open-pit oil sands mining in northern Alberta, Canada. Coarse woody debris (CWD) can be used to regulate soil temperature and water content, to increase organic matter content, and to create microsites for the establishment of microorganisms and vegetation in upland reclamation. We studied the effects of CWD on soil microbial community level physiological profile (CLPP) and soil enzyme activities in FMM and PMM in a reclaimed landscape in the oil sands. This experiment was conducted with a 2 (FMM vs PMM) × 2 (near CWD vs away from CWD) factorial design with 6 replications. The study plots were established with Populus tremuloides (trembling aspen) CWD placed on each plot between November 2007 and February 2008. Soil samples were collected within 5 cm from CWD and more than 100 cm away from CWD in July, August and September 2013 and 2014. Microbial biomass was greater (p<0.05) in FMM than in PMM, in July, and August 2013 and July 2014, and greater (p<0.05) near CWD than away from CWD in FMM in July and August samplings. Soil microbial CLPP differed between FMM and PMM (p<0.01) according to a principal component analysis and CWD changed microbial CLPP in FMM (p<0.05) but not in PMM. Coarse woody debris increased microbial community functional diversity (average well color development in Biolog Ecoplates) in both cover soils (p<0.05) in August and September 2014. Carbon degrading soil enzyme activities were greater in FMM than in PMM (p<0.05) regardless of distance from CWD but were not affected by CWD. Greater microbial biomass and enzyme activities in FMM than in PMM will increase organic matter decomposition and nutrient cycling, improving plant growth. Enhanced microbial community functional diversity by CWD application in upland reclamation has implications for accelerating upland reclamation after oil sands mining.