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Abstract The application of biochar to soil is widely recognized as a promising strategy for enhancing the accumulation and stability of soil organic carbon (SOC), which is crucial in mitigating climate change. However, the influence of interactions between plants and biochar on soil microbial communities and their involvement in SOC mineralization and stability remains unclear. This understanding is essential for optimizing carbon (C) sequestration in systems involving plants, soil, and biochar. In this study, employing a 13C natural abundance approach, we investigated the effect of biochar on the maize rhizosphere priming effect (RPE) in paddy soil. We also examined alterations in microbial communities and functional genes related to C degradation and fixation. Over the 99 days of maize growth, biochar application increased RPE and total SOC while decreasing dissolved organic C. It also elevated soil pH, resulting in shifts in fungal and bacterial community structure, favoring oligotrophic species. Fungal and bacterial assemblies were dominated by deterministic and stochastic processes, respectively. While the abundance of fungal guilds varied irregularly, bacterial guilds were uniformly enriched under biochar-plant interactions. Functional traits such as ecoenzymatic activities, bacterial guilds, and functional genes predominantly affected RPE under biochar application. Bacterial functional genes associated with C degradation and fixation were concurrently enhanced with biochar application. Our results indicate that interactions between plants and biochar can enhance native SOC mineralization and accumulation in a short timeframe by modulating functional traits of soil microorganisms, particularly the bacterial community involved in C degradation and fixation. Graphical Abstract

Abstract Forests harbor extensive biodiversity and act as a strong global carbon and nitrogen sink. Although enhancing tree diversity has been shown to mitigate climate change by sequestering more carbon and nitrogen in biomass and soils in manipulative experiments, it is still unknown how varying environmental gradients, such as gradients in resource availability, mediate the effects of tree diversity on carbon and nitrogen accrual in natural forests. Here, we use Canada’s National Forest Inventory data to explore how the relationships between tree diversity and the accumulation of carbon and nitrogen in tree biomass and soils vary with resource availability and environmental stressors in natural forests. We find that the positive relationship between tree functional diversity (rather than species richness) and the accumulation of carbon in tree biomass strengthens with increasing light and soil nutrient availability. Moreover, the positive relationship between tree functional diversity and the accumulation of carbon and nitrogen in both organic and mineral soil horizons is more pronounced at sites with greater water and nutrient availabilities. Our results highlight that conserving and promoting functionally diverse forests in resource-rich environments could play a greater role than in resource-poor environments in enhancing carbon and nitrogen sequestration in Canada’s forests.

Soil metabolomics is an emerging approach for profiling diverse small molecule metabolites, i.e., metabolomes, in the soil. Soil metabolites, including fatty acids, amino acids, lipids, organic acids, sugars, and volatile organic compounds, often contain essential nutrients such as nitrogen, phosphorus, and sulfur and are directly linked to soil biogeochemical cycles driven by soil microorganisms. This paper presents an overview of methods for analyzing soil metabolites and the state-of-the-art of soil metabolomics in relation to soil nutrient cycling. We describe important applications of metabolomics in studying soil carbon cycling and sequestration, and the response of soil organic pools to changing environmental conditions. This includes using metabolomics to provide new insights into the close relationships between soil microbiome and metabolome, as well as responses of soil metabolome to plant and environmental stresses such as soil contamination. We also highlight the advantage of using soil metabolomics to study the biogeochemical cycles of elements and suggest that future research needs to better understand factors driving soil function and health.

Abstract The effects of long-term biochar application on soil phosphorus (P) flux across the root-soil interface and its availability in the rhizosphere of rice (Oryza sativa L) remain unclear. We used diffusive gradients in thin films (DGT), laser ablation-inductively coupled plasma mass spectrometry, and planar optode sensor techniques to characterize, in-situ, the 2D heterogeneity and dynamics of rhizosphere soil P, iron (Fe), sulfur (S) and trace element fluxes, dissolved oxygen and pH in paddy soil, after 10 years of biochar application. Compared to the control (no biochar applied), biochar applied at 4.5, 22.5 and 45.0 Mg ha−1 yr−1 decreased rhizospheric P fluxes by 11.6%, 63.4% and 79.0%, respectively. This decrease under biochar treatments was attributed to changed redox status of Fe and S caused by the lower dissolved oxygen in rhizosphere soil and increased soil pH induced precipitating of soluble inorganic P into insoluble P forms, such as calcium-bound and residual P that are unavailable for crop uptake. Higher application rate of biochar resulted in lower As and Pb fluxes in rice rhizosphere and their availabilities for crop uptake. The in-situ observation results in rice rhizosphere at μm-scale after 10 years of biochar addition directly showed the complex effects of long-term biochar and rhizosphere heterogeneity on P transformation process. Graphical Abstract

Abstract One strategy to reduce CO2 emissions from cement production is to reduce the amount of Portland cement produced by replacing it with supplementary cementitious materials (SCMs). Biochar is a potential SCM that is an eco-friendly and stable porous pyrolytic material. However, the effects of biochar addition on the performances of Portland cement composites are not fully understood. This meta-analysis investigated the impact of biochar addition on the 7- and 28-day compressive strength of Portland cement composites based on 606 paired observations. Biochar feedstock type, pyrolysis conditions, pre-treatments and modifications, biochar dosage, and curing type all influenced the compressive strength of Portland cement composites. Biochars obtained from plant-based feedstocks (except rice and hardwood) improved the 28-day compressive strength of Portland cement composites by 3–13%. Biochars produced at pyrolysis temperatures higher than 450 °C, with a heating rate of around 10 C min-1, increased the 28-day compressive strength more effectively. Furthermore, the addition of biochar with small particle sizes increased the compressive strength of Portland cement composites by 2–7% compared to those without biochar addition. Biochar dosage of

Abstract The incorporation of organic amendments, such as food waste (FW) and biochar, into soil is an established agronomic practice known for enhancing soil fertility and improving overall soil health. However, the individual and combined effects of FW and biochar on soil properties in microplastic (MP)-contaminated soil–plant systems remain poorly understood. To address this knowledge gap, we conducted a field experiment to investigate the individual and combined effects of polystyrene MPs, FW, and FW-derived biochar on soil properties and lettuce growth. Soil chemical properties were unaffected by the addition of MPs. However, the application of FW and biochar increased the soil pH, with the highest pH (8.2) observed in the combined treatment of biochar and MPs. Despite the presence of MPs, FW application resulted in notable increases in soil electrical conductivity (EC; 2.04 dS m−1), available nitrogen (NO3 −–N: 325.5 mg kg−1, NH4 +–N: 105.2 mg kg−1), available phosphorus (88.4 mg kg−1), and total exchangeable cations (18.6 cmol(+) kg−1). However, these values decreased after lettuce cultivation. In soil cultivated with lettuce, the coexistence of MPs and biochar reduced soil Fluorescein diacetate hydrolase enzyme activity by 46.2% and urease activity by 94.0%. FW addition doubled acid phosphatase activity, whereas FW and its coexistence with MPs decreased alpha diversity. The relative abundance of Actinobacteria decreased with MP application, whereas that of Acidobacteria and Actinobacteria decreased with FW treatment. Gemmatimonadetes and Nitrospirae decreased in soil treated with FW and biochar. The highest relative abundances of Firmicutes and Proteobacteria were observed in the FW-added soils, and Planctomycetes were the highest in the biochar-added soils. FW application negatively affected lettuce growth. Overall, the coexistence of MPs with FW or biochar had limited effects on soil properties and lettuce growth, with FW and biochar serving as the primary factors in modifying soil–plant systems. Future studies should investigate the effects of different MPs and their interactions with organic soil amendments on soil properties and crop growth under different management practices. Graphical Abstract

Abstract Microplastic (MP) pollution in agricultural soils, resulting from the use of plastic mulch, compost, and sewage sludge, jeopardizes the soil microbial populations. However, the effects of MPs on soil chemical properties and microbial communities remain largely unknown. Here, we investigated the effects of different concentration levels (0, 0.1, 1, 3, 5, and 7%; w:w) of low-density polyethylene (LDPE) MPs on the chemical properties and bacterial communities of agricultural soil in an incubation study. The addition of LDPE MPs did not drastically change soil pH (ranging from 8.22 to 8.42). Electrical conductivity increased significantly when the LDPE MP concentrations were between 1 and 7%, whereas the total exchangeable cations (Na+, K+, Mg2+, and Ca2+) decreased significantly at higher LDPE MP concentrations (3–7%). The highest available phosphorus content (2.13 mg kg−1) was observed in 0.1% LDPE MP. Bacterial richness (Chao1 and Ace indices) was the lowest at 0.1% LDPE MP, and diversity indices (Shannon and Invsimpson) were higher at 0 and 1% LDPE MP than at other concentrations. The effect of LDPE MP concentrations on bacterial phyla remained unchanged, but the bacterial abundance varied. The relative abundance of Proteobacteria (25.8–33.0%) was the highest in all treatments. The abundance of Acidobacteria (15.8–17.2%) was also high, particularly in the 0, 0.1, and 1% LDPE MPs. With the increase in LDPE MP concentration, the abundance of Actinobacteria gradually increased from 7.80 to 31.8%. Our findings suggest that different MP concentration levels considerably alter soil chemical properties and microbial composition, which may potentially change the ecological functions of soil ecosystems.

Abstract Highly diverse exoenzymes mediate the energy flow from substrates to the multitrophic microbiota within the soil decomposer micro‐food web. Here, we used a “soil enzyme profile analysis” approach to establish a series of enzyme profile indices; those indices were hypothesized to reflect micro‐food web features. We systematically evaluated the shifts in enzyme profile indices in relation to the micro‐food web features in the restoration of an abandoned cropland to a natural area. We found that enzymatic C:N stoichiometry and decomposability index were significantly associated with substrate availability. Furthermore, the higher Shannon diversity index in the exoenzyme profile, especially for the C‐degrading hydrolase, corresponded to a greater microbiota community diversity. The increased complexity and stability of the exoenzyme network reflected similar changes with the micro‐food web networks. In addition, the gross activity of the enzyme profile as a parameter for soil multifunctionality, effectively predicted the substrate content, microbiota community size, diversity, and network complexity. Ultimately, the proposed enzymic channel index was closely associated with the traditional decomposition channel indices derived from microorganisms and nematodes. Our results showed that soil enzyme profile analysis reflected very well the decomposer food web features. Our study has important implications for projecting future climate change or anthropogenic disturbance impacts on soil decomposer micro‐food web features by using soil enzyme profile analysis.

In the background of climate warming, the demand for improving soil quality and carbon (C) sequestration is increasing. The application of biochar to soil has been considered as a method for mitigating climate change and enhancing soil fertility. However, it is uncertain whether the effects of biochar application on C-mineralization and N transformation are influenced by the presence or absence of plant growth-promoting bacteria (PGPB) and soil nitrogen (N) level. An incubation study was conducted to investigate whether the effects of biochar application (0 %, 1 %, 2 % and 4 % of soil mass) on soil respiration, N status, and microbial attributes were altered by the presence or absence of PGPB (i.e., Sphingobium yanoikuyae BJ1) under two soil N levels (N0 and N1 soils as created by the addition of 0 and 0.2 g kg−1 urea- N, respectively). The results showed that biochar, BJ1 strain and their interactive effects on cumulative CO2 emissions were not significant in N0 soils, while the effects of biochar on the cumulative CO2 emissions were dependent on the presence or absence of BJ1 in N1 soils. In N1 soils, applying biochar at 2 % and 4 % increased the cumulative CO2 emissions by 141.0 % and 166.9 %, respectively, when BJ1 was absent. However, applying biochar did not affect CO2 emissions when BJ1 was present. In addition, the presence of BJ1 generally increased ammonium contents in N0 soils, but decreased nitrate contents in N1 soils relative to the absence of BJ1, which indicates that the combination of biochar and BJ1 is beneficial to play the N fixation function of BJ1 in N0 soils. Our results highlight that biochar addition influences not only soil C mineralization but also soil available N, and the direction and magnitude of these effects are highly dependent on the presence of PGPB and the soil N level.

Struvite crystallization is a viable approach for recovering phosphorus from phosphorus-rich solutions such as urine and wastewater. However, designing seed materials to promote crystal growth and enhance the efficiency of struvite crystallization remains an area of active research. In this study, we investigated the seeding characteristics of biochars on struvite crystallization and the impact of biochar feedstock type and production temperature on the process. Microwave-pyrolyzed biochars produced from different feedstocks and under different temperatures were examined as seeding materials for struvite crystallization from urine and the influence of biochar properties on the overall struvite yield, nutrient recovery and struvite crystal size. Sawdust biochar (lignocellulosic biomass) produced at 500 ​°C had the highest struvite yield (7.91 ​g ​L−1), phosphate (97.9%) and ammonium recovery (87.1%), and relative crystal size (85.2%) compared to the non-seeded treatment due to its higher surface area, pore volume, and hydrophobicity of the biochar. Manure pellet biochar (non-lignocellulosic biomass) produced at 500 ​°C also exhibited performance comparable to sawdust biochar produced at 500 ​°C. Increasing pyrolysis temperature increased biochar's hydrophobicity, zeta potential, electrophoretic mobility and bulk density, irrespective of the feedstock type, thereby improving the seeding process. The ash content of biochar was negatively correlated with its surface area, pore volume, and particle size, but positively correlated with biochar's bulk density and suspension stability. In conclusion, feedstock type and pyrolysis temperature significantly affected biochar properties, which interactively influenced struvite crystallization. Therefore, biochars should be carefully selected to improve their efficiency for phosphorus recovery from phosphorus-containing solutions such as urine and wastewater, with the recovered phosphorus being used for soil applications.

Abstract Developing sustainable materials for recovering and recycling nutrients from wastewater is critically needed for nutrients such as phosphorus that have a diminishing supply. Struvite crystallization is emerging as a promising strategy for phosphorus recovery which can be enhanced with seeding through microalgal biochar. The main bottleneck of using microalgae is its high harvesting cost. In this study, an integrated electrocoagulation-flotation (ECF) process is used to recover and at the same time modify the algal surface with magnesium anode and inert carbon cathode. Harvesting efficiency of 98% was achieved with 40.78 mA cm−2, 0.5 cm inter-electrode distance and energy consumption of 4.03 kWh kg−1 in 15 min. The harvested microalgae were pyrolyzed to obtain a yield of 52.90% Mg-laden microalgal biochar. Simultaneously, surface impregnation of 28% magnesium was attained as confirmed by Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Phosphorus recovery and struvite yield of 93.70% and 2.66 g L−1, respectively, were obtained from dosing 1.50 g L−1 Mg-laden microalgal biochar. Comparison of physicochemical characteristics of residual supernatant after microalgal harvesting and struvite recovery showed that the combined use of both the residuals can serve as a sustainable growth medium for microalgae. The overall operating cost of the integrated process was found to be 2.48 USD kg−1 with a total energy consumption of 10.76 kWh kg−1, which was found to be lower than conventional harvesting unit processes such as centrifugation and filtration. This novel approach can help attaining a circular bioeconomy by encompassing nutrient recovery and waste management in an integrated process.

Abstract 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.

The accumulation of phytolith-occluded carbon (PhytOC) in Moso bamboo could be a novel long-term carbon sequestration strategy. The objective of this study was to investigate the effects of temperature change and different fertilization on PhytOC accumulation. The pot experiment was established with different fertilization (including control (CK), nitrogen fertilizers (N), silicon fertilizers (Si), and a combination of nitrogen and silicon (NSi)) under high- and low-temperature. Despite the different fertilization, the PhytOC accumulation of the high-temperature group increases by 45.3% on average compared with the low-temperature group, suggesting higher temperature is greatly beneficial to the PhytOC accumulation. Fertilization significantly increases the accumulation of PhytOC (increased by 80.7% and 48.4% on average for the low- and high-temperature group, respectively) compared with CK. However, the N treatment increased both Moso bamboo biomass and PhytOC accumulation. The difference in the accumulation of PhytOC in Si and NSi was insignificant, indicating the combination of N and Si didn’t bring extra benefit to PhytOC accumulation compared to Si fertilizer alone. These results indicated the application of nitrogen fertilizer is a practical and effective method for enhancing long-term carbon sequestration for Moso bamboo. Based on our study, we conclude that global warming poses a positive effect on promoting the long-term carbon sequestration of Moso bamboo.

Abstract In macroecology, the concept of r‐ and K‐strategy has been widely applied, yet, there have been limited studies on microbial life‐history strategies in temperate grasslands using multiple sequencing approaches. Total phospholipid fatty acid (PLFA) analysis, high‐throughput meta‐genomic sequencing, and GeoChip technologies were used to examine the changes in microbial life‐history traits in a chronosequence of restored grasslands (1, 5, 10, 15, 25, and 30 years since restoration). Grassland restoration increased the relative abundances of Actinobacteria, Proteobacteria, and Bacteroidetes but reduced the relative abundances of Acidobacteria, Planctomycetes, and Chloroflexi. PLFA analysis revealed that grassland restoration reduced the fungi:bacteria and Gram‐positive:Gram‐negative bacteria ratios. Combined with the meta‐genomic data, we found that grassland restoration shifted microorganisms from oligotrophic (K‐) to copiotrophic (r‐) groups, consistent with the increased rRNA operon copy number of the microbial community. Structural equation modeling showed that soil properties positively (p

Converting rice husk to biochar is one of the solutions to manage crop residues by transforming waste into a value-added material that has broad benefits to the environment when biochar is applied to the soil. This study investigated the impact of the application of rice husk and its biochar at different doses (i.e., 0, 10, and 30 t ha−1) on soil carbon stability, the property of water-soluble soil organic matter, and the abundance and diversity of microbial communities in a Lei bamboo (Phyllostachys praecox) forest soil 262 days after their application. The application of rice husk, especially at 30 t ha−1, increased dissolved organic carbon due to the high labile carbon (C) (e.g., cellulose, hemicellulose, polysaccharides) content in the rice husk. The biochar treatments stimulated the release of humic-like substances (e.g., (poly) phenols) into the soil solution, increased the aromatic C content by 412–557%, and increased the relative abundance of Chloroflexi, Planctomycetota, and Proteobacteria compared to the control. This study shows that biochar application, particularly at 30 t ha−1, enhanced the C stability by turning organic C into recalcitrant forms in the soil, demonstrating the merit of converting rice husk into biochar before its application to the soil.

The effect and mechanistic evidence of biochar on the (im)mobilization of potentially toxic elements (PTEs) in multi-contaminated soils, with respect to the role of surface-functional groups and organic/inorganic compounds of biochar, are poorly understood. Herein, biochars produced from grass residues, rice straw, and wood were applied to a mining-soil contaminated with As, Cd, Pb, and Zn for 473-d. Biochars did not reduce the mobilization of Cd and Zn, whereas they simultaneously exhibited disparate effects on As and Pb mobilization. The phenolic hydroxyl and carboxylic groups on the wood biochar’s surfaces promoted the conversion of Pb2+ into PbCO3/Pb(OH)2 and/or PbO, minimally by the rice and grass biochars. Rice and grass biochars led to the dissolution of scorodite and the formation of less stable forms of Fe-oxide-bound As (i.e., goethite and ferrihydrite); furthermore, it resulted in the reduction of As(V) to As(III). The PTEs mobilization and phytoavailability was mainly governed by the release of dissolved aliphatic- and aromatic-carbon, chloride, sulfur chemistry, phosphate competition, and the electrostatic repulsion in biochar-treated soils. In conclusion, pristine-biochar has a limited impact on the remediation of multi-contaminated soils, and the use of modified-biochar, possessing higher surface areas and functionality and active exchange sites, are preferred under such conditions.

Global development has been heavily reliant on the overexploitation of natural resources since the Industrial Revolution. With the extensive use of fossil fuels, deforestation, and other forms of land-use change, anthropogenic activities have contributed to the ever-increasing concentrations of greenhouse gases (GHGs) in the atmosphere, causing global climate change. In response to the worsening global climate change, achieving carbon neutrality by 2050 is the most pressing task on the planet. To this end, it is of utmost importance and a significant challenge to reform the current production systems to reduce GHG emissions and promote the capture of CO2 from the atmosphere. Herein, we review innovative technologies that offer solutions achieving carbon (C) neutrality and sustainable development, including those for renewable energy production, food system transformation, waste valorization, C sink conservation, and C-negative manufacturing. The wealth of knowledge disseminated in this review could inspire the global community and drive the further development of innovative technologies to mitigate climate change and sustainably support human activities.

Heavy metal accumulation in agriculture soils is of particular concern in China, while the status and probabilistic health risks of metal contamination in Chinese agriculture soils have been rarely studied at the national scale. In this study, we compiled a database of heavy metal concentrations in Chinese agriculture soils and selected six heavy metals for pollution assessment and risk screening: arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb) and Zinc (Zn). Monte Carlo simulation was employed to assess the probabilistic health risks, the associated uncertainties, as well as variations in toxicity parameters, ingestion rate and body weight. Results indicated that the concentrations of Cd were elevated above their reference standard and Cd had the highest mean geo-accumulation index (Igeo) of 1.79. Moreover, the mean hazard index (HI) through exposure to six heavy metals was 1.85E−01 and 2.87E−02 for children and adults, respectively, with 2.2% of non-cancer risks for children that exceeded the guideline value of 1. In contrast, 95.0% and 90.0% of the total cancer risks (TCR) through exposure to six heavy metals for children and adults, respectively, exceeded the guideline value of 1E−06. Six metals were ranked based on their percent of risk outputs exceeding the guideline values. Arsenic had the high exceedance of both cancer and non-cancer risks, while both Cr and Cd were metals with high concern that had high exceedance of cancer risk. Sensitivity analyses indicated that metal concentrations and ingestion rate of soil were the predominant contributors to total risk variance. Overall, the adverse health risks induced by exposure to heavy metals contaminated farmland were elevated. Results from this study may provide valuable implications for public health professionals and policy-makers to design effective strategy to manage nation-wide farmland and reduce heavy metal exposure. Keywords: Agriculture soil, Heavy metal, Probabilistic risk, Monte Carlo simulation, Risk level ranking

Root foraging enables plants to obtain more soil nutrients in a constantly changing nutrient environment. Little is known about the adaptation mechanism of adventitious roots of plants dominated by asexual reproduction (such as tea plants) to soil potassium heterogeneity. We investigated root foraging strategies for K by two tea plants (low-K tolerant genotype “1511” and low-K intolerant genotype “1601”) using a multi-layer split-root system. Root exudates, root architecture and transcriptional responses to K heterogeneity were analyzed by HPLC, WinRHIZO and RNA-seq. With the higher leaf K concentrations and K biological utilization indexes, “1511” acclimated to K heterogeneity better than “1601”. For “1511”, maximum total root length and fine root length proportion appeared on the K-enriched side; the solubilization of soil K reached the maximum on the low-K side, which was consistent with the amount of organic acids released through root exudation. The cellulose decomposition genes that were abundant on the K-enriched side may have promoted root proliferation for “1511”. This did not happen in “1601”. The low-K tolerant tea genotype “1511” was better at acclimating to K heterogeneity, which was due to a smart root foraging strategy: more roots (especially fine roots) were developed in the K-enriched side; more organic acids were secreted in the low-K side to activate soil K and the root proliferation in the K-enriched side might be due to cellulose decomposition. The present research provides a practical basis for a better understanding of the adaptation strategies of clonal woody plants to soil nutrient availability.

Efforts to reduce greenhouse gas (GHG) emissions from cattle production have led to modifications of livestock diet composition aimed at reducing CH4 emissions from enteric fermentation. These diet modifications can result in varied manure types that may differentially affect GHG emissions when applied to soil. The purpose of this experiment was to examine the effect of different manure types on GHG emissions. We conducted an incubation experiment, comparing the manure from livestock fed a corn-based diet (CM) to that from livestock fed a traditional barley-based diet (BM). The manures were applied to three soil types (with varied soil fertility and pH) and compared to a control (without manure application). Carbon dioxide (CO2) emissions were greater from CM than from BM across all soil types (29.1 and 14.7 mg CO2-C kg−1, respectively). However, CM resulted in lower N2O emissions relative to BM in the low fertility soil (4.21 and 72.67 μg N2O-N kg−1, respectively) and in lower CH4 emissions relative to BM in the two acidic soils (0.5 and 2.5 μg CH4-C kg−1, respectively). Total GHG emissions (sum of CO2, N2O, and CH4) were similar between CM and BM across all soil types, but CM (unlike BM) had 52–66% lower emissions in the low fertility soil relative to both CM and BM in the high fertility soil. Our study shows that manure and soil type interact to affect GHG emissions and that CM may mitigate N2O emissions relative to BM when applied to low fertility soils.

Rising demand for ruminant meat and dairy products in developing nations drives increasing GHG and ammonia emissions from livestock. Authors show here that only long-term adoption of global best-practice in sustainable intensification buffered by a short-term coping strategy of green-source trading can offer a way forward.

Conducting integrated analysis of the source, exposure and health risk of heavy metals is critical for developing mitigation strategies of soil contamination. Taking the former electronic waste (e-waste) dismantling center in China as an example this study quantitatively apportioned source contribution of soil heavy metals in this area by statistical analysis and positive matrix factorization (PMF) model. Furthermore, the human health risk of identified sources were quantified by combining source profiles and exposure risk assessment. The seven heavy metals investigated were arsenic (As), cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb) and Zinc (Zn). Results indicated that agricultural soils were mainly contaminated with Cd and Cu. Parent material and pesticide, fertilizer application, industrial discharge, and vehicle emission accounted for 46.6, 22.2, and 31.2%, respectively, of the accumulation of metals in the soil. Moreover, these sources contributed 52.9, 19.0, and 28.1%, respectively of the total non-cancer risk. For the total cancer risk, the contribution of these three sources was 39.2, 45.3, and 15.5%, respectively. Despite that industrial discharge contributed the least to the accumulation of metals (22.2%), it contributed the most to the total cancer risk (45.3%). Reducing industrial emission was crucial for minimizing the heavy metal input to agricultural soils and preventing potential health hazard. These findings could provide support for environmental protection authority to improve the management and risk prevention of contaminated farmland. Keywords: Exposure, E-waste, Health risk, Heavy metal, Source apportionment, Source contribution

Abstract A flexible and self-healing supercapacitor with high energy density in low temperature operation was fabricated using a combination of biochar-based composite electrodes and a polyampholyte hydrogel electrolyte. Polyampholytes, a novel class of tough hydrogel, provide self-healing ability and mechanical flexibility, as well as low temperature operation for the aqueous electrolyte. Biochar is a carbon material produced from the low-temperature pyrolysis of biological wastes; the incorporation of reduced graphene oxide conferred mechanical integrity and electrical conductivity and hence the electrodes are called biochar-reduced-graphene-oxide (BC-RGO) electrodes. The fabricated supercapacitor showed high energy density of 30 Wh/kg with ~90% capacitance retention after 5000 charge–discharge cycles at room temperature at a power density of 50 W/kg. At −30 °C, the supercapacitor exhibited an energy density of 10.5 Wh/kg at a power density of 500 W/kg. The mechanism of the low-temperature performance excellence is likely to be associated with the concept of non-freezable water near the hydrophilic polymer chains, which can motivate future researches on the phase behaviour of water near polyampholyte chains. We conclude that the combination of the BC-RGO electrode and the polyampholyte hydrogel electrolyte is promising for supercapacitors for flexible electronics and for low temperature environments.

Forestlands are widely distributed in the dominantly agricultural landscape in western Canada, and they play important ecological functions; such forestlands (e.g., shelterbelts) accumulate soil organic matter and may receive a substantial amount of nitrogen in the form of surface and subsurface runoff from adjacent croplands and become a significant source of emissions of greenhouse gases (GHGs) such as CO2, N2O, and CH4. Biochar and nitrapyrin applications could potentially mitigate GHG emissions, but their co-application in forest soils has not been studied. We investigated the effect of the application of biochars produced at low (300 °C; BC300) and high temperatures (700 °C; BC700) using canola (Brassica napus L.) straw and the effect of their co-application with nitrapyrin on GHG emissions and soil properties in a 35-day laboratory incubation experiment using forest soils collected from five shelterbelt sites. Results showed no significant interaction effect of biochar and nitrapyrin on the global warming potential (GWP) of the GHG emissions, and the GWP was 15.8% lower in the soil with nitrapyrin than without nitrapyrin application treatments. The GWP was significantly enhanced by BC300 addition due to a 26.9% and 627.1% increase in cumulative CO2 and N2O emissions, respectively, over the 35-day incubation. The GWP significantly decreased by BC700 addition due to a 27.1% decrease in cumulative CO2 emissions. However, biochar addition did not affect CH4 emissions, while nitrapyrin decreased CH4 uptake by 50.5%. With BC300 addition, soil-dissolved organic carbon and microbial biomass carbon increased by 26.5% and 33.9%, respectively, as compared to no biochar addition (CK). Soil pH increased by 0.16 and 0.37 units after the addition of BC300 and BC700, respectively. Overall, the effect of biochar and nitrapyrin was independent in mitigating GHG emissions and was related to the type of biochar applied and changes in soil properties.

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.

Biochar can be used as an adsorbent for phosphate removal in aquatic environments to treat eutrophication problems. Designing biochars that have large phosphate adsorption capacity through altering pyrolysis conditions and applying activation techniques will improve phosphate removal efficiency. In this study, four pine sawdust biochars were produced at 300 and 550 °C with and without steam activation. Batch sorption experiments including isotherm and kinetic studies were conducted to understand how phosphate removal capabilities and adsorption mechanisms of biochars were affected by pyrolysis temperature and steam activation. Our results showed that the steam activation and pyrolysis temperature did not affect phosphate adsorption by the biochars. The four biochars removed

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.

The success of oil sands reclamation can be impacted by soil salinity depending on the materials used for soil reconstruction and the capping strategies applied. Using both a greenhouse-based column experiment and numerical modeling, we examined the potential pathways of salt migration from saline groundwater into the rooting zone under different capping strategies (the type and the thickness of the barrier layer) and water balance scenarios. The experimental results showed that there would be salinity issues in the cover soil within several growing seasons if there was a shallow saline groundwater table and if the soil was not properly reconstructed. The thickness of the barrier layer was the most significant factor affecting the upward movement of saline groundwater and salt accumulation in the cover soil. The suitable thickness of the barrier layer for preventing the upward movement of saline groundwater and salt accumulation in the cover soil for each material varied. A numerical simulation for a 15-year period further indicates that, when the cover soil was 50 cm of peat-mineral soil mix and when wet, dry, or normal climatic conditions were considered, the minimum barrier thickness to restrain salt intrusion into the cover soil in the long term was about 75 or 200 cm for coarse tailings sand or overburden barrier material, respectively. In view of the above, to minimize salt migration into the rooting zone and ensure normal plant growth, oil sands reclamation should consider salt migration when designing soil capping strategies.

Data on the effect of vegetation and land use type on soil organic carbon (SOC) distribution in particle-size and density fractions in the subtropical forest region in China will improve our understanding of the C sequestration potential of those different vegetation-land use types. We quantified SOC in particle size (coarse, medium and fine) and density fractions (light and heavy) under four types of common forest vegetation-land uses: an evergreen broad-leaf forest, a pine forest, a managed chestnut forest and an intensively managed bamboo forest in subtropical China. The SOC in the 0–20 and 20–40 cm soil layers was the highest in the bamboo forest (31.6–34.8 g·C·kg−1), followed by the evergreen broad-leaf forest (10.2–19.9 g·C·kg−1), the pine forest (8.5–13.6 g·C·kg−1) and the chestnut forest (6.3–12.2 g·C·kg−1). The SOC was largely in the coarse fraction under the evergreen broad-leaf, pine and bamboo forests, while it was largely in the fine fraction in the chestnut forest, suggesting that SOC in the chestnut forest was likely more stable than that in the other forest vegetation-land use types. The SOC in the light fraction under the four forest vegetation-land use types ranged from 1.4 to 13.1 g·C·kg−1 soil, representing 21%–37% of the total organic C; this suggests that the majority of the SOC was in the better protected, heavy fraction. We conclude that forest vegetation-land use type (and the associated management practices) influenced SOC distribution in particle size and density fractions in the studied subtropical forests in southeastern China.

Shelterbelt systems play pivotal roles in providing goods and services to the rural community and the society at large, but phosphorus (P) cycling in shelterbelt systems is poorly studied, while P cycling and availability would be linked to the ecological function and services of shelterbelt systems. This study was conducted to understand how long-term (>30 years) land-use between cropland and forestland in shelterbelt systems affect soil P status. We investigated modified Kelowna (PKelowna) and Mehlich-3 (PMehlich) extractable P, P fractions (by sequential chemical fractionation), P sorption properties in the 0−10 and 10−30 cm soils and their relationship in six pairs of the cropland areas and adjacent forestland (each pair constitutes a shelterbelt system) in central Alberta. Both PKelowna and PMehlich in the 0−10 cm soil were greater in the cropland than in the forestland. The PKelowna ranged from 10 to 170 and 2 to 57 mg kg−1 within the cropland areas and forestland, respectively. The inorganic P fraction in the 0−30 cm depth was significantly related to PKelowna (R2 = 0.55) and PMehlich (R2 = 0.80) in cropland, but organic P fraction was not significantly related with neither PKelowna nor PMehlich. The iron (Fe) and aluminum (Al) associated P (Fe/Al-P) explained ~50% and ~45% of the variation of PKelowna in the 0−30 cm soil in the cropland and forestland, respectively. The Fe/Al-P and organic P fractions in the 0−10 cm soil were greater in the cropland than in the forestland. The differences in availability and P forms depending on the land use type in shelterbelts suggest that P management needs to be land-use type-specific for shelterbelt systems.

Plantation management practices could markedly change the sequestration of phytolith-occluded carbon (PhytOC) in plants and soils. However, for Moso bamboo (Phyllostachys pubescens) plantations, the effect of intensive plantation management (including fertilization, tillage, and removal of understory vegetation) on the accretion rate of PhytOC in the soil-plant system is much less understood than extensive management (without fertilization, tillage, and removal of understory vegetation). The objectives of this study were to investigate the effect of intensive and extensive management practices on the production, accumulation, and runoff of PhytOC and their distribution in physical fractions in Moso bamboo plantations. Our results showed that intensive management (1) increased PhytOC production mainly due to increased forest productivity; (2) increased PhytOC storage in the heavy fraction but decreased its storage in the light fraction of organic matter, resulting in the lack of effect on soil PhytOC storage; (3) increased the rate of dissolution of phytolith and the loss of PhytOC in runoff; and (4) promoted PhytOC sequestration in the soil-plant system, mostly in the plants, due to the greater rate of PhytOC production than the rate of loss. We conclude that intensive bamboo plantation management practices are beneficial to increasing long-term PhytOC sequestration in the soil-plant system.

Agroforestry practices that intentionally integrate trees with crops and/or livestock in an agricultural production system could enhance carbon (C) sequestration and reduce greenhouse gas (GHG) emissions from terrestrial ecosystems, thereby mitigating global climate change. Beneficial management practices such as enrichment planting and the application of soil amendments can affect C sequestration and GHG emissions in agroforestry systems; however, such effects are not well understood. A literature review was conducted to synthesize information on the prospects for enhancing C sequestration and reducing GHG emissions through enrichment (i.e., in-fill) tree planting, a common practice in improving stand density within existing forests, and the application of organic amendments to soils. Our review indicates that in agroforests only a few studies have examined the effect of enrichment planting, which has been reported to increase C storage in plant biomass. The effect of adding organic amendments such as biochar, compost and manure to soil on enhancing C sequestration and reducing GHG emissions is well documented, but primarily in conventional crop production systems. Within croplands, application of biochar derived from various feedstocks, has been shown to increase soil organic C content, reduce CO2 and N2O emissions, and increase CH4 uptake, as compared to no application of biochar. Depending on the feedstock used to produce biochar, biochar application can reduce N2O emission by 3% to 84% as compared to no addition of biochars. On the other hand, application of compost emits less CO2 and N2O as compared to the application of manure, while the application of pelleted manure leads to more N2O emission compared to the application of raw manure. In summary, enrichment planting and application of organic soil amendments such as compost and biochar will be better options than the application of raw manure for enhancing C sequestration and reducing GHG emissions. However, there is a shortage of data to support these practices in the field, and thus further research on the effect of these two areas of management intervention on C cycling will be imperative to developing best management practices to enhance C sequestration and minimize GHG emissions from agroforestry systems.

We currently have a poor understanding of how different soil sampling methods (pedogenetic horizon versus fixed-depth) influence the evaluation of soil properties. Here, 159 soil profiles were sampled from larch (Larix gmelinii) plantations in northeast China using both the pedogenetic horizon and fixed-depth sampling methods. Analysis of variance was used to determine how sampling method influences the assessment of the spatial variation in the concentration and storage of soil organic C (SOC) and N (SON), as well as how these properties are affected by tree age-group (40 years). In both the 20 cm (surface) and 80 cm (whole profile) sampling depths, pedogenetic sampling resulted in 1.2- to 1.4-fold higher SOC and SON concentrations than fixed-depth sampling. Surface soil nutrient storage between the two sampling methods was not significantly different, but was it was 1.2-fold higher (p < 0.05) with pedogenetic sampling than with fixed-depth sampling in the whole soil profile. For a given error limit in SOC and SON assessments, fixed-depth sampling had a 60%~90% minimum sampling intensity requirement compared with pedogenetic horizon sampling. Additionally, SOC was 1.1- to 1.3-fold greater in the >40 years age-group than in the

Screening and selecting tree genotypes that are responsive to N additions and that have high nutrient use efficiencies can provide better genetic material for short-rotation plantation establishment. A pot experiment was conducted to test the hypotheses that (1) sweetgum (Liquidambar styraciflua L.) families have different patterns in biomass production and allocation, N uptake, and N use efficiency (NUE), because of their differences in growth strategies, and (2) sweetgum families that are more responsive to N additions will also have greater nutrient use efficiencies. Seedlings from two half-sib families (F10022 and F10023) that were known to have contrasting responses to fertility and other stress treatments were used for an experiment with two levels of N (0 vs. 100 kg N/ha equivalent) and two levels of P (0 vs. 50 kg P/ha equivalent) in a split-plot design. Sweetgum seedlings responded to N and P treatments rapidly, with increases in both size and biomass production, and those responses were greater with F10023 than with F10022. Growth response to N application was particularly strong. N and P application increased the proportional allocation of biomass to leaves. Under increased N supply, P application increased foliar N concentration and content, as well as total N uptake by the seedlings. However, NUE was decreased by N addition and was higher in F10023 than in F10022 when P was not limiting. A better understanding of genotype by fertility interactions is important in selecting genotypes for specific site conditions and for optimizing nutrient use in forestry production.