Biochar has been extensively studied as a soil amendment for carbon sequestration and for improving soil quality; however, a systematic understanding of the responses of soil microbial biomass and ...diversity to biochar addition is lacking. Here, a meta-analysis of 999 paired data points from 194 studies shows that biochar increases microbial biomass but has variable effects on microbial diversity. Generally, the effects of biochar on microbial biomass are dependent on biochar properties, while that on microbial diversity is dependent on soil properties. The application of biochar, particularly that produced under low temperature and from nutrient-rich feedstocks, could better increase soil microbial biomass (based on phospholipid fatty acid analysis (MBCPLFA)) and diversity. The increases of total microbial biomass with biochar addition are greater in the field than in laboratory studies, in sandy than in clay soils, and when measured by fumigation-extraction (MBCFE) than by MBCPLFA. The bacterial biomass only significantly increases in laboratory studies and fungal biomass only in soils with pH ≤ 7.5 and soil organic carbon ≤30 g kg−1. The increases in total microbial diversity with biochar addition were greater in acidic and sandy soils with low soil organic carbon content and in laboratory incubation studies. In addition, long-term and low-rate addition of biochar always increases microbial diversity. To better guide the use of biochar as a soil amendment, we suggest that establishing long-term and field studies, using a standard method for measuring microbial communities, on different soil types should be our emphasis in future research.
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•Biochar effects on microbial biomass varied by analytic methods•Biochar effects on microbial biomass more depended on biochar property•Biochar effects on microbial diversity more depended on soil property•Biochar increased microbial diversity in sandy soils with low SOC•A low rate of and long-term biochar addition resulted in higher microbial diversity
•Nitrate in 28% of tested groundwater exceeded WHO's maximum contaminant level.•Cropland and landfill were the two largest sources of nitrate in groundwater.•A high resolution map of reactive ...nitrogen leakage to groundwater was constructed.•Anthropogenic factors explained majority of groundwater nitrate source variation.•Source appointment results matched well with the sampling data of groundwater nitrate.
Identifying the sources of reactive nitrogen (N) and quantifying their contributions to groundwater nitrate concentrations are critical to understanding the dynamics of groundwater nitrate contamination. Here we assessed groundwater nitrate contamination in China using literature analysis and N balance calculation in coupled human and natural systems. The source appointment via N balance was well validated by field data via literature analysis. Nitrate was detected in 96% of groundwater samples based on a common detection threshold of 0.2mgNL−1, and 28% of groundwater samples exceeded WHO's maximum contaminant level (10mgNL−1). Groundwater nitrate concentrations were the highest beneath industrial land (median: 34.6mgNL−1), followed by urban land (10.2mgNL−1), cropland (4.8mgNL−1), and rural human settlement (4.0mgNL−1), with the lowest found beneath natural land (0.8mgNL−1). During the period 1980–2008, total reactive N leakage to groundwater increased about 1.5 times, from 2.0 to 5.0TgNyear−1, in China. Despite that the contribution of cropland to the total amount of reactive N leakage to groundwater was reduced from 50 to 40% during the past three decades, cropland still was the single largest source, while the contribution from landfill rapidly increased from 10 to 34%. High reactive N leakage mainly occurred in relatively developed agricultural or urbanized regions with a large population. The amount of reactive N leakage to groundwater was mainly driven by anthropogenic factors (population, gross domestic product, urbanization rate and land use type). We constructed a high resolution map of reactive N source appointment and this could be the basis for future modeling of groundwater nitrate dynamics and for policy development on mitigation of groundwater contamination.
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.
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•Pollution status and probabilistic health risk of heavy metal in agriculture soils across China was determined.•Chinese population face severe cancer risks of heavy metal exposure as their risk value exceeded the benchmark.•The spatial distribution of high-risk areas and that of cancer villages were correlated.•Priority metals and critical exposure factors for further risk control were identified.
Long‐term elevated nitrogen (N) input from anthropogenic sources may cause soil acidification and decrease crop yield, yet the response of the belowground microbial community to long‐term N input ...alone or in combination with phosphorus (P) and potassium (K) is poorly understood. We explored the effect of long‐term N and NPK fertilization on soil bacterial diversity and community composition using meta‐analysis of a global dataset. Nitrogen fertilization decreased soil pH, and increased soil organic carbon (C) and available N contents. Bacterial taxonomic diversity was decreased by N fertilization alone, but was increased by NPK fertilization. The effect of N fertilization on bacterial diversity varied with soil texture and water management, but was independent of crop type or N application rate. Changes in bacterial diversity were positively related to both soil pH and organic C content under N fertilization alone, but only to soil organic C under NPK fertilization. Microbial biomass C decreased with decreasing bacterial diversity under long‐term N fertilization. Nitrogen fertilization increased the relative abundance of Proteobacteria and Actinobacteria, but reduced the abundance of Acidobacteria, consistent with the general life history strategy theory for bacteria. The positive correlation between N application rate and the relative abundance of Actinobacteria indicates that increased N availability favored the growth of Actinobacteria. This first global analysis of long‐term N and NPK fertilization that differentially affects bacterial diversity and community composition provides a reference for nutrient management strategies for maintaining belowground microbial diversity in agro‐ecosystems worldwide.
This study explored the effects of long‐term N and NPK fertilization on soil bacterial community in agro‐ecosystems using a meta‐analysis of datasets across the globe. The long‐term N fertilization significantly decreased soil bacterial diversity, changed bacterial community composition, and favored the growth of Actinobacteria and Proteobacteria over Acidobacteria. The negative effect of N fertilization on bacterial diversity disappeared when N is coapplied with P and K. This study represents an important step forward for understanding the connection between elevated nutrient inputs, shifts in soil microbial communities, and altered ecosystem functioning.
Ammonia (NH3) emission from agricultural sources has contributed significantly to air pollution, soil acidification, water eutrophication, biodiversity loss, and declining human health. Although ...there are numerous strategies for reducing NH3 emission from agricultural systems, the effectiveness of these measures is highly variable. Furthermore, the integrated assessment of measures to reduce NH3 emission both from livestock production and cropping systems based on animal and crop type is lacking. Therefore, we conducted a global meta-analysis and integrated assessment of measures to reduce NH3 emission from agricultural systems. Most of the studied mitigation strategies were effective in reducing NH3 emission. In the livestock production system, dietary additive, urease inhibitor (UI), manure acidification and deep manure placement have the highest mitigation potential relative to other mitigation strategies, with reduction ranges of 35.1–54.2%, 24.3–68.7%, 88.8–95.0%, and 93.8–99.7%, respectively, relative to the control, while manure storage management could significantly reduce NH3 emission by 70.0–82.1%. In the cropping system, fertilizer source, use of enhanced efficiency fertilizers, and method of field application are most effective for reducingNH3 emission. The use of ammonium nitrate, controlled release fertilizer (CRF), and deep placement of fertilizers could reduce NH3 emission by 88.3, 56.8, and 48.0%, respectively. Choosing a proper fertilizer is critical for decreasing NH3 emission from cropping systems. We conclude that carefully planned and adopted strategies suited for local conditions are promising for minimizing NH3 emission from agricultural systems on a global scale, while possible effects of those mitigation measures on the emission of greenhouse gases should be studied in the future.
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•We assessed strategies for mitigating agricultural NH3 emission by animal and crop type.•Most mitigation strategies significantly reduced NH3 emission.•Changing fertilizer type from urea to ammonium nitrate was the most effective measure to reduce NH3 emission from cropland.•Manure acidification is most effective to reduce emission from livestock systems.
Ammonia emission from agricultural sources could be markedly reduced by mitigation measures based on this meta-analysis.
Advanced basal cell carcinomas (BCCs) frequently acquire resistance to Smoothened (SMO) inhibitors through unknown mechanisms. Here we identify SMO mutations in 50% (22 of 44) of resistant BCCs and ...show that these mutations maintain Hedgehog signaling in the presence of SMO inhibitors. Alterations include four ligand binding pocket mutations defining sites of inhibitor binding and four variants conferring constitutive activity and inhibitor resistance, illuminating pivotal residues that ensure receptor autoinhibition. In the presence of a SMO inhibitor, tumor cells containing either class of SMO mutants effectively outcompete cells containing the wild-type SMO. Finally, we show that both classes of SMO variants respond to aPKC-ι/λ or GLI2 inhibitors that operate downstream of SMO, setting the stage for the clinical use of GLI antagonists.
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•Functional SMO mutations are detected in the majority of SMO inhibitor-resistant BCCs•Resistance occurs by suppressing drug responsiveness and SMO autoinhibition•SMO mutants explain both intrinsic and acquired tumor resistance•Inhibition of aPKC-ι/λ or GLI2 bypasses SMO variants to suppress Hedgehog signaling
Atwood et al. identify key SMO mutations that confer resistance to SMO inhibitors in basal cell carcinomas (BCC) and show that these mutants respond to aPKC-ι/λ or GLI2 inhibitors, providing potential approaches for treating BCCs resistant to SMO inhibitors.
Soil gross nitrogen (N) mineralization (GNM), a key microbial process in the global N cycle, is mainly controlled by climate and soil properties. This study provides for the first time a ...comprehensive analysis of the role of soil physicochemical properties and climate and their interactions with soil microbial biomass (MB) in controlling GNM globally. Through a meta‐analysis of 970 observations from 337 published papers from various ecosystems, we found that GNM was positively correlated with MB, total carbon, total N and precipitation, and negatively correlated with bulk density (BD) and soil pH. Our multivariate analysis and structural equation modeling revealed that GNM is driven by MB and dominantly influenced by BD and precipitation. The higher total N accelerates GNM via increasing MB. The decrease in BD stimulates GNM via increasing total N and MB, whereas higher precipitation stimulates GNM via increasing total N. Moreover, the GNM varies with ecosystem type, being greater in forests and grasslands with high total carbon and MB contents and low BD and pH compared to croplands. The highest GNM was observed in tropical wet soils that receive high precipitation, which increases the supply of soil substrate (total N) to microbes. Our findings suggest that anthropogenic activities that affect soil microbial population size, BD, soil substrate availability, or soil pH may interact with changes in precipitation regime and land use to influence GNM, which may ultimately affect ecosystem productivity and N loss to the environment.
By a meta‐analysis of 970 observations from 337 published papers, we found that gross N mineralization (GNM) is driven by soil microbial biomass and dominantly influenced by soil bulk density and precipitation, whereby GNM increases with increasing soil microbial biomass and precipitation and decreasing soil bulk density. The higher total soil N and soil pH accelerate GNM via increasing soil microbial biomass. We suggest that management activities that affect soil microbial population size, soil bulk density, soil substrate availability, or soil pH may interact with future changes in precipitation regime to influence GNM, and ultimately, ecosystem productivity.
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•An intergraded source-exposure risk approach was developed.•Interrelationships among source, sink and human health were assessed.•Parent material and agrochemical application caused ...the highest non-cancer risk.•Industrial activities caused the highest total cancer risk.•Reducing industrial discharge and agrochemical use is key for alleviating human health risk.
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.
Adsorption of lead(II) using carbon-rich chars is an environmentally sustainable approach to remediate lead(II) pollution in industrial wastewater. We studied mechanisms for lead(II) adsorption from ...synthetic wastewater by biochars produced by microwave-assisted pyrolysis and hydrochars by hydrothermal carbonization at three temperatures using four feedstocks. Lead(II) adsorption was highest (165 mg g−1) for canola straw biochar produced at 500 °C. Except for chars derived from sawdust, biochars outperformed hydrochars for lead(II) adsorption due to changes in solution pH driven by char pH. As char production temperature increased, lead(II) adsorption decreased in hydrochar mainly due to interaction with aromatic carbon but increased in biochar due to precipitation as hydrocerussite and lead oxide phosphate. Lead(II) adsorption also occurred via surface complexation and cation-ᴨ interaction, as the data fitted well to Freundlich, Langmuir and Temkin models, and the pseudo-first and pseudo-second order kinetic models, depending on feedstock type and production temperature. More than 80% of lead(II) adsorption occurred in the first 3 h for both types of chars; with a few exceptions, adsorption continued for almost 24 h. We conclude that production method, production temperature and feedstock type are crucial factors to consider in designing chars as adsorbents for removing lead(II) from wastewater.
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•Biomass wastes were converted into chars using microwave & hydrothermal methods.•Physicochemical properties of the chars were driven by the conversion method.•Biochars adsorb lead(II) from an aqueous solution better than hydrochars.•Lead(II) precipitated as hydrocerussite and lead oxide phosphate on biochars.•Precipitation is not a significant mechanism for lead(II) removal by hydrochars.
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