Responses of soil microbial community structure changes and activities to biochar addition: A meta-analysis

Soils and Beyond: Optimizing Sustainability Opportunities for Biochar

Biochar is most commonly considered for its use as a soil amendment, where it has gained attention for its potential to improve agricultural production and soil health. Twenty years of near exponential growth in investigation has demonstrated that biochar does not consistently deliver these benefits, due to variables in biochar, soil, climate, and cropping systems. While biochar can provide agronomic improvements in marginal soils, it is less likely to do so in temperate climates and fertile soils. Here, biochar and its coproducts may be better utilized for contaminant remediation or the substitution of nonrenewable or mining-intensive materials. The carbon sequestration function of biochar, via conversion of biomass to stable forms of carbon, does not depend on its incorporation into soil. To aid in the sustainable production and use of biochar, we offer two conceptual decision trees, and ask: What do we currently know about biochar? What are the critical gaps in knowledge? How should the scientific community move forward? Thoughtful answers to these questions can push biochar research towards more critical, mechanistic investigations, and guide the public in the smart, efficient use of biochar which extracts maximized benefits for variable uses, and optimizes its potential to enhance agricultural and environmental sustainability.

A meta-analysis about the accumulation of heavy metals uptake by Sedum alfredii and Sedum plumbizincicola in contaminated soil

Sedum alfredii and Sedum plumbizincicola typically have high heavy metal (such as Zn and Cd) accumulation capacities with fast growth rates and relatively high Pb tolerance in contaminated soils. We compared the accumulation characteristics of heavy metals in Sedum species through meta-analysis. Furthermore, we analyzed the effects of soil organic matter (SOM) and soil pH on Cd, Pb and Zn accumulation by S. alfredii and S. plumbizincicola and the correlation between various metals. Results showed that the accumulations of Cd and Zn in shoots were higher than that of roots, but Pb accumulated in roots more than shoots. Moreover, there is a significant positive correlation between the accumulation of Zn and Cd in shoots. We found that the heavy metal accumulation rate in shoots was higher with lower soil pH. Sedum species had the highest Cd adsorption capacity in 20-30 g/kg SOM and the highest Zn adsorption capacity in SOM less than 20 g/kg. The accumulation rate of Cd in shoots of S. plumbizincicola was increased with exposure time, while the accumulation rate of Zn was slightly decreased.

Identification of a novel heavy metal resistant Ralstonia strain and its growth response to cadmium exposure

A novel Ralstonia Bcul-1 strain was isolated from soil samples that was closest to Ralstonia pickettii. Broad-spectrum resistance was identified to a group of heavy metal ions and tolerance to concentrations of Cd²⁺ up to 400 mg L^-1. Low concentrations of heavy metal ions did not have distinctive impact on heavy metal resistance genes and appeared to induce greater expression. Under exposure to Cd²⁺, cell wall components were significantly enhanced, and some proteins were also simultaneously expressed allowing the bacteria to adapt to the high Cd²⁺ living environment. The maximum removal rate of Cd²⁺ by the Ralstonia Bcul-1 strain was 78.97% in the culture medium supplemented with 100 mg L^-1 Cd²⁺. Ralstonia Bcul-1 was able to survive and grow in a low nutrient and cadmium contaminated (0.42 mg kg^-1) vegetable soil, and the cadmium removal rate was up to 65.76% in 9th growth. Ralstonia Bcul-1 mixed with biochar could maintain sustainable growth of this strain in the soil up to 75 d and the adsorption efficiency of cadmium increased by 16.23-40.80% as compared to biochar application alone. Results from this work suggests that Ralstonia Bcul-1 is an ideal candidate for bioremediation of nutrient deficient heavy metal contaminated soil.

Lindane degradation in wet-dry cycling soil as affected by aging and microbial toxicity of biochar

This study determined the degradation of lindane in soil amended with biochar to evaluate the effects of biochar aging and microbial toxicity. Two biochars were prepared at 400 and 600 °C (BC₄₀₀ and BC₆₀₀) and subjected to acid washing to remove nutrition (WBC₄₀₀ and WBC₆₀₀). After 89 days of incubation under the alternate "wet-dry" conditions, scanning electron microscopy showed that acid washing rendered biochars especially susceptible to aging with structural collapse and fragmentation, with less surface covering. Aging impeded the release of toxic substances in BC₄₀₀ and BC₆₀₀ with reduced toxicity to degrading microorganisms. Lindane degradation was somewhat stimulated by biochar nutrition but mainly inhibited by adsorption. Acid washing facilitated the release of toxic substances and additionally reduced lindane degradation. The variations in fatty acid saturation degree (SFA/UFA) in soils confirmed the microbial toxicity of 5% WBC₄₀₀ > 5% BC₄₀₀ > 5% BC₆₀₀ > 5% WBC₆₀₀. High-throughput DNA sequencing showed that biochar delayed the formation of dominant degrading microbial communities in soil. Lindane degradation was completed by joint Sphingomonas, Flaviolibacter, Parasegetibacter, Azoarcus, Bacillus and Anaerolinaea. These findings are helpful for better understanding the effect of biochar in soil on long-term degradation of persistent organic pollutants.

Application of biochar in estrogen hormone-contaminated and manure-affected soils: Impact on soil respiration, microbial community and enzyme activity

Biochar as a soil amendment has been proposed for enhancing carbon sequestration and manure-borne hormone contaminant remediation. However, little is known about the ecological risk of biochar application in the soil with hormone contamination. This study investigated the influence of biochar in three manure-impacted soils contaminated with estrogen hormones, natural estrogen 17β-estradiol and synthesized estrogen 17α-ethinylestradiol in a microcosm experiment. Specifically, microbial respiration was periodically determined during microcosm incubation while microbial community phospholipid fatty acids and activities of nutrient (C, N, P, S) cycling related enzymes (β-glucosidase, urease, phosphodiesterase, arylsulfatase) were characterized after the incubation. Results showed that the manure-impacted soils with high SOC generally had greater total microbial biomass, ratios of fungi/bacteria and Gram-positive bacteria/Gram-negative bacteria, and phosphodiesterase activity, but lower urease activity. Additionally, hormones stimulated microbial respiration and biomass, while had little impact on activity of the enzymes. On the other hand, biochar showed negative priming effect by significantly decreasing total microbial biomass by 8.7%-26.4%, CO₂ production by 16.6%-33.5%, and glucosidase activity by 27.1%-41.0% in the three soils. Biochar significantly increased the activity of phosphodiesterase, showed no impact on arylsulfatase, while decreased the activity of urease. Overall, the study suggests that when used in hormone remediation in manure-impact soils, biochar could improve phosphodiesterase activity, but may decrease soil microbial activity and the activity of soil glucosidase and urease.

Does biochar inhibit the bioavailability and bioaccumulation of As and Cd in co-contaminated soils? A meta-analysis

Biochar, an effective and low-cost amendment for immobilizing heavy metals, has been extensively studied. However, the simultaneous inhibition effects of biochar on the plant uptake for arsenic (As) and cadmium (Cd) in co-contaminated soils are still ambiguous due to their distinct environmental behaviors. A meta-analysis was conducted to quantitatively assess the effects using 1030 individual observations from 52 articles. On average, biochar application significantly decreased the bioavailability of Cd in soils by 50.12%, while slightly increased the bioavailability of As in soils by 2.39%. The more instructive result is that biochar application could also simultaneously reduce the concentration of As and Cd in plants by 25.48% and 38.66%, respectively. The orders of the decreased percentage of As and Cd in various tissues were root < stem< leaf < grain, and root < leaf < stem < grain, respectively. According to the analysis of critical factors, manure biochar, low pyrolysis temperature (at <400 °C), low application rate (<2%), and high SOC (>30 g/kg) were more conducive to reduce the bioaccumulation of As and Cd simultaneously in co-contaminated soils. Pristine and modified biochar could inhibit As and Cd accumulation in crops, but their efficiencies need to be further improved to ensure the safety of crop productions. Overall, the meta-analysis suggests that biochar has the potential to remedy the As and Cd co-contaminated soils.

Biochar increases soil microbial biomass but has variable effects on microbial diversity: A meta-analysis

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 (MBC_PLFA)) 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 (MBC_FE) than by MBC_PLFA. 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.

Biochar and compost effects on soil microbial communities and nitrogen induced respiration in turfgrass soils

We examined the effect of a labile soil amendment, compost, and recalcitrant biochar on soil microbial community structure, diversity, and activity during turfgrass establishment. Two application rates of biochar (B1 at 12.5 t ha-1and B2 at 25 t ha-1), a 5 centimeter (cm) green waste compost treatment (CM) in top soil, a treatment with 12.5 t ha-1 biochar and 5 cm compost (B1+CM), and an unamended control (CK) treatment were prepared and seeded with tall fescue. Overall, results of phospholipid fatty acid analysis (PLFA) profiling and Illumina high-throughput sequencing of 16S rRNA genes amplified from soil DNA revealed significant shifts in microbial community structures in the compost amended soils whereas in biochar amended soils communities were more similar to the control, unamended soil. Similarly, increases in enzymatic rates (6-56%) and nitrogen-induced respiration (94%) were all largest in compost amended soils, with biochar amended soils exhibiting similar patterns to the control soils. Both biochar and compost amendments impacted microbial community structures and functions, but compost amendment, whether applied alone or co-applied with biochar, exhibited the strongest shifts in the microbial community metrics examined. Our results suggest application of compost to soils in need of microbiome change (reclamation projects) or biochar when the microbiome is functioning and long-term goals such as carbon sequestration are more desirable.

Responses of Low-Quality Soil Microbial Community Structure and Activities to Application of a Mixed Material of Humic Acid, Biochar, and Super Absorbent Polymer

Low-quality soil for land reuse is a crucial problem in vegetation quality and especially to waste disposal sites in mining areas. It is necessary to find suitable materials to improve the soil quality and especially to increase soil microbial diversity and activity. In this study, pot experiments were conducted to investigate the effect of a mixed material of humic acid, super absorbent polymer and biochar on low-quality soil indexes and the microbial community response. The indexes included soil physicochemical properties and the corresponding plant growth. The results showed that the mixed material could improve chemical properties and physical structure of soil by increasing the bulk density, porosity, macro aggregate, and promote the mineralization of nutrient elements in soil. The best performance was achieved by adding 3 g·kg^-1 super absorbent polymer, 3 g·kg^-1 humic acid, and 10 g·kg^-1 biochar to soil with plant total nitrogen, dry weight and height increased by 85.18%, 266.41% and 74.06%, respectively. Physicochemical properties caused changes in soil microbial diversity. Acidobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, Nitrospirae, Planctomycetes, and Proteobacteria were significantly positively correlated with most of the physical, chemical and plant indicators. Actinobacteria and Armatimonadetes were significantly negatively correlated with most measurement factors. Therefore, this study can contribute to improving the understanding of low-quality soil and how it affects soil microbial functions and sustainability.

Soil nematode community and crop productivity in response to 5-year biochar and manure addition to yellow cinnamon soil

Background

Manure and biochar soil amendments have shown many benefits to soil quality and crop productivity. This study aimed to reveal the effects of biochar and manure applications on soil fertility improvement and crop productivity in yellow cinnamon soil.

Results

This study based on a 5-year field experiment. Four treatments were designed, included the control (CK), biochar amendment, manure amendment, and both biochar and manure amendment (BM). The results showed that: after five years, both biochar and manure treatment improved soil structure by increasing soil mean weight diameter (MWD), and soil water and nutrient supply was also increased by increasing the contents of water content, available potassium and available phosphorus. The productivity was also enhanced as wheat yield under the biochar, manure, and BM treatments increased by 3.59–11.32% compared with CK. In addition, biochar and manure treatment increased soil microbial biomass carbon (MBC) by > 15%, and soil total nematode abundance was significantly increased. Furthermore, the nematode community structure was significantly affected by biochar and manure treatment, dominant trophic group in CK was herbivores, but bacterivores were dominant in the biochar and manure treatments. The distribution of nematode genera was closely related to soil chemical properties and microbial biomass. Increases in the Shannon's diversity index, and decreases in the dominance index and summed maturity index after the 5-year treatment indicated a sustainable soil ecosystem after the biochar and manure applications.

Conclusions

These findings indicate that biochar and manure result in better soil quality and increased productivity in yellow cinnamon soil.

Soil microbiome-induced changes in the priming effects of 13C-labelled substrates from rice residues

Knowledge gap exists to understand the soil CO₂ emission and microbial group response to substrates of whole plant residues and derived biochar. We used ¹³C-labelled substrates (rice straw, roots and biochar) to track influences of their decomposition on soil priming effect (PE) and phospholipid fatty acid (PLFA) composition during one-year incubation. Organic substrates at 1% (w/w) level increased soil pH, available nitrogen (AN) and available phosphorus (AP), especially during the first 45 days of incubation. After incubation, 44% of the added straw was mineralized to ¹³CO₂, followed by roots (~35%) and biochar (~5%). Straw and roots amendment caused positive PE during 4-360 day of the incubation, where a lowest value of 41.9 mg C kg^-1 was observed. Biochar amendment caused negative PE during 56-150 day of the incubation, where a largest value of -99.0 mg C kg^-1 was observed. Analysis of ¹³C-labelled PLFA enabled the differentiation of microbial groups during substrates utilization. Gram positive bacteria (G⁺) and general bacteria groups were dominated in co-metabolizing both the native soil organic carbon (SOC) and substrates after straw and roots amendment. Gram negative bacteria (G^-), especially identified by PLFA biomarkers cy17:0 and cy19:0, preferentially utilizes the ¹³C-labelled biochar but not promoting soil priming effect. Soil pH, SOC, AN and AP all explained changes of total and ¹³C-labelled PLFA contents (>75%, p < .05). Evidences showed that biochar is best in sequestering soil C pool, followed by straw and roots, and soil microbial groups in utilization of organic substances mediated SOC mineralization.

Biochar—A Panacea for Agriculture or Just Carbon?

The sustainable production of food faces formidable challenges. Foremost is the availability of arable soils, which have been ravaged by the overuse of fertilizers and detrimental soil management techniques. The maintenance of soil quality and reclamation of marginal soils are urgent priorities. The use of biochar, a carbon-rich, porous material thought to improve various soil properties, is gaining interest. Biochar (BC) is produced through the thermochemical decomposition of organic matter in a process known as pyrolysis. Importantly, the source of organic material, or ‘feedstock’, used in this process and different parameters of pyrolysis determine the chemical and physical properties of biochar. The incorporation of BC impacts soil–water relations and soil health, and it has been shown to have an overall positive impact on crop yield; however, pre-existing physical, chemical, and biological soil properties influence the outcome. The effects of long-term field application of BC and how it influences the soil microcosm also need to be understood. This literature review, including a focused meta-analysis, summarizes the key outcomes of BC studies and identifies critical research areas for future investigations. This knowledge will facilitate the predictable enhancement of crop productivity and meaningful carbon sequestration.

Influence of Aged Biochar Modified by Cd2+ on Soil Properties and Microbial Community

Biochar is a promising addition for cadmium-contaminated soil in-situ remediation, but its surface properties change after aging, cadmium adsorption is not well-documented, and subsequent environmental effects are still unknown. In this study, wood-derived (Eucalyptus saligna Sm.) biochar was pre-treated to simulate aging and the cadmium sorption process. We then analyzed the resulting physicochemical characteristics. We conducted comparative incubation studies on three age stages of biochar under cadmium adsorption or no cadmium adsorption and then measured soil properties and microbial communities after incubation. Biochar addition raised soil organic carbon (SOC), and aging significantly increased C/N ratios. Aged biochar promoted higher microbial abundance. Aged biochar treatments possessed different microflora with more gram-positive bacteria, significantly altering gram-positive/gram-negative bacteria ratios. Aging significantly increased the oxygen-containing functional groups (OCFGs) and surface area (SA) of biochar. Thus, aged biochar adsorbed more cadmium. Cadmium-binding biochar increased the proportion of gram-negative bacteria and decreased the proportions of gram-positive bacteria and fungi. Similar patterns in phospholipid fatty acids (PLFAs) across adsorption treatments indicated that changes in microbial communities due to the effects of cadmium were confined. The results reveal that biochar aging altered microbial community structure and function more than cadmium binding.

Critical study of crop-derived biochars for soil amendment and pharmaceutical ecotoxicity reduction

In this study, biochars (BCs) produced from crops (straw and seeds) were tested for the applicability as additive to soils. The effect on pH, water capacity and cation exchange capacity of soil were tested. The ability for the sorption of pharmaceuticals (beta-blockers, anti-inflammatory drugs, sulfonamides, 17α-ethinylestradiol, carbamazepine, caffeine) using the batch sorption test was performed, and the effect of water pH was investigated. In addition, the metals removed from the biochar was analyzed as a potential toxicity factor. The mechanism of adsorption (Langmuir, Freundlich) was tested for sulfadimetoxine. The effect of the rye-derived biochar on water cress germination and the reduction of the sulfonamides toxicity to this plant was tested. The advantages of crop-derived biochar application to different soils (sand soil, clay soil and reference soil) was presented. It was found that tested BCs effectively increase the water capacity of soils, especially sand type soil, but in the same time it had increase the pH of pure-buffering soils. The driving force of pharmaceutical sorption was its ionization form - the highest sorption occurs for cations, medium for neutral forms, while the lowest sorption for anions. The opposite situation have been noted for desorption from biochar. The washing of biochars increases sorption for the neutral and anionic species, but not for the cations. The application of biochars into the soils can from one site protect the plants from toxic impact of sulfonamides, but from the other hamper the root prolongation by the pH increase.

Nitrogen dynamics affected by biochar and irrigation level in an onion field

Soil amended with biochar has many potential environmental benefits, but its influence on the fate of nitrogen (N) under irrigated conditions is unclear. The objective of this research was to determine the effects of biochar and interactions with irrigation on N movement in soil, gas emissions, and leaching. A three-year study was conducted in an onion field with three main irrigation treatments (50, 75, and 100% of a reference that provided sufficient water for plant growth) and three biochar amendment rates (0 or control, low char - applied first year at 29 Mg ha^-1, and high char - added both first and second year for a total 58 Mg ha^-1) as sub-treatments in a split-plot design. Nitrogen fertilizer was applied three times during first year growing season, but weekly the second year. Ammonia (NH₃) volatilization, nitrous oxide (N₂O) emission, and nitrate (NO₃^-) in soil pore water were monitored during growing season, and annual N (total and NO₃^-) changes in soil profile were determined for first two years. Nitrate leaching was measured in the third year. Ammonia volatilization was affected by fertilization frequency with higher loss (5-8% of total applied) when fertilizer was applied in large doses during the first year compared to the second year (4-5%). Nitrous oxide emissions were ≤0.1% of applied N for both years and not affected by any treatments or fertilization frequency. Nitrate concentration in soil profile increased significantly as irrigation level dropped, but most of the NO₃^- was leached by winter rain. There was no significant biochar effect on total N gas emissions or soil NO₃^- accumulation, but significant irrigation effect and interaction with biochar were determined on soil NO₃^- accumulation. High leaching was associated with biochar amendment and higher irrigation level. Irrigation strategies are the key to improving N management and developing the best practices associated with biochar.

A novel calcium-based magnetic biochar is effective in stabilization of arsenic and cadmium co-contamination in aerobic soils

This study developed a novel calcium-based magnetic biochar by pyrolysing rice straw mixed with calcium carbonate and iron oxide for stabilization of contamination of multiple metals. A 160-day incubation study was conducted to investigate its performance in stabilization of cadmium and arsenic co-contamination in soil. Both biochar and Ca-MBC treatments increased soil pH, decreased the bioavailability of cadmium. Ca-MBC decreased but biochar enhanced the bioavailability of arsenic. The BCR (European Community Bureau of Reference) sequential extraction confirmed Ca-MBC facilitated the transformation of the unstable fraction of arsenic to stable fractions. The stabilization mechanisms were explored through synchrotron-based micro X-ray fluorescence and X-ray absorption near edge structure. The results show that Ca-MBC remediated the dual contamination of arsenic and cadmium through (1) elevated pH and cation exchange capacity (for Cd); (2) the formation of bi-dentate chelate and ternary surface complexes on the surface of iron oxide; (3) enhanced adsorption ability of porous biochar. In addition, Ca-MBC increased the abundance and diversity of bacterial community, and modified the relative abundances of bacterial taxa, leading to a shift of the composition. These new insights provide valuable information for stabilization of co-contamination of arsenic and cadmium in soil using the potential material Ca-MBC.

Organic soil additives for the remediation of cadmium contaminated soils and their impact on the soil-plant system: A review

Immobilization is among the most-suitable strategies to remediate cadmium (Cd) contaminated sites. Organic additives (OAs) have emerged as highly efficient and environment-friendly immobilizers to eradicate Cd contamination in a wide range of environments. This review article is intended to critically illustrate the role of different OAs in Cd immobilization and to highlight the key findings in this context. Owing to the unique structural features (high surface area, cation exchange capacity (CEC), presence of many functional groups), OAs have shown strong capability to remediate Cd polluted soils by adsorption, electrostatic interaction, complexation and precipitation. Research data is compiled about the efficiency of different OAs (bio-waste, biochar, activated carbon, composts, manure, and plant residues) applied alone or in combination with other amendments in stabilization and renovation of contaminated sites. In addition to their role in remediation, OAs are widely advocated for being classical sources of essential plant nutrients and as agents to improve the soil health and quality which has also been focused in this review. OAs may contain considerable amounts of metals and therefore it becomes essential to assess their final contribution. Elimination of Cd contamination is essential to attenuate the contaminant effect and to produce the safe food. Therefore, deployment of environment-friendly remediation strategies (alone or in combination with other suitable technologies) should be adopted especially at early stages of contamination.

Selected bacterial strains enhance phosphorus availability from biochar-based rock phosphate fertilizer

Purpose

The co-pyrolysis of biomass and soluble phosphates generates biochar-based phosphate fertilizers (BBF), which may enhance phosphorus (P) input in soil and P uptake by plants. Conversely, pyrolysis of biomass impregnated with rock phosphate results in low P solubility and may not supplement plant requirement in short term. However, bacterial strains promoting rock phosphate solubilization increases P use efficiency and can be applied to BBFs.

Methods

An in vitro assay was conducted to investigate the solubilization profile of five bacterial strains (Pseudomonas sp.—UFPI-B5-8A, Burkholderia fungorum—UFLA 04-155, Acinetobacter sp.—UFLA 03-09, Paenebacillus kribbensis—UFLA 03-10, and Paenibacillus sp.—UFLA 03-116) isolated from common bean and cowpea nodules in a rock phosphate BBF. Additionally, a pot trial was carried out aiming to investigate the influence on maize growth by inoculation of three selected strains under a rock phosphate BBF fertilization.

Results

Inoculations with UFPI B5-8A, UFLA 04-155, and UFLA 03-09 were efficient in solubilizing P in vitro, being closely associated with pH decrease, likely due to the release of organic acids. As for the pot trial, the dose of 400 mg kg−1 of P in the BBF using UFPI B5-8A significantly increased maize shoot dry matter. All strains significantly enhanced P availability in the soil.

Conclusions

Bacterial inoculation in biochar-based rock phosphate aiming to improve its fertilizer value is an inexpensive and sustainable strategy to improve maize growth and enhance available P in soil and should be further explored.

The Role of Biochar in Reducing the Bioavailability and Migration of Persistent Organic Pollutants in Soil-Plant Systems: A Review

The amendment of biochar in soils contaminated with persistent organic pollutants (POPs) is an environmentally friendly in situ remediation measure. Numerous studies focused on the application of biochars to reduce the uptake of POPs by plants in soils. In this review, we summarized the role of biochar in reducing the migration of POPs in soil-plant systems. The mechanisms of biochar reducing the bioavailability of POPs in the soil, i.e. immobilization and promoted biodegradation, and the influencing factors are fully discussed. Especially in rhizosphere amended with biochar, the synergistic effect of POPs-root exudates-microorganisms on the reduced bioavailability of POPs is analyzed. This paper suggests that future researches should focus on the long-term environmental fate of POPs sorbed on high-temperature biochars and the long-term impacts of low-temperature biochars on the interaction of POPs-root exudates-rhizosphere microorganisms. All the above are necessary for efficient and safe use of biochar for remediating POP-contaminated farmland soils.

Biochar accelerates the removal of tetracyclines and their intermediates by altering soil properties

Tetracyclines accumulation in soil environment potentially threatens agroecosystem safety. Interestingly, biochar could clean up organic pollutants, but to what extent biochar affects the removal of tetracyclines is unknown. To investigate it, five types of biochars derived from cow manure (CMB) and other four plant materials were respectively added into soils contaminated with a mixture of tetracycline, oxytetracycline, and chlortetracycline for 60-day incubation in the dark. Three parent tetracyclines and their corresponding intermediates (epitetracycline, anhydrotetracycline, epianhydrotetracycline, epioxytetracycline, epichlortetracycline, and demethylchlortetracycline) were respectively determined and named as TTCs, OTCs and CTCs. Obtained results showed biochar especially CMB could effectively remove the antibiotics (P < 0.05). Compared to control, the removal rate of TTCs, OTCs and CTCs respectively increased by up to 10.86%, 10.29% and 10.12% in CMB-added soil. The increased removal rate of the antibiotics after biochar addition was due to the increasing accessibilities for degrading microorganisms via the elevating electrical conductivity. Moreover, biochar addition might stimulate these microbial activities through the increase of C and N supplement. Our results indicate biochar accelerates the removal of tetracyclines and their intermediates by altering soil properties and thus increasing the antibiotics accessibilities, which provide insights into how biochar accelerates the removal for these antibiotics.

Nitrogen Dynamics in an Established Alfalfa Field under Low Biochar Application Rates

Sustainable nitrogen (N) management in agroecosystems is crucial for supporting crop production and reducing deleterious N losses. Biochar application with N-fixing legumes offers promise for increasing soil N retention and input. Strategic, low application rates (112 kg ha−1) of pine and coconut feedstock biochars were tested in an established alfalfa (Medicago sativa) field. Soil inorganic N and plant growth, N concentrations, and δ15N were monitored over a growing season to follow mineral N availability, and plant N uptake and sourcing. Microbial and gene abundance and enzyme activity were measured to assess the potential for N cycling processes to occur. Biochar application had minimal effects on measured parameters. However, significant temporal dynamics in N cycling and correlations between alfalfa δ15N and soil N availability indicate differing plant N sourcing over time. Our findings indicate that low application rates of biochar in established alfalfa fields do not significantly affect N cycling, and that managing alfalfa to maximize N fixation, for example by intercropping, may be a better solution to increase N stocks and retention in this system. To determine when biochar can be beneficial for alfalfa N cycling, we need additional research to assess various economically-feasible biochar application rates at different alfalfa growth stages.

Microbial community structure and the relationship with soil carbon and nitrogen in an original Korean pine forest of Changbai Mountain, China

BACKGROUND

The broad-leaved Korean pine mixed forest is an important and typical component of a global temperate forest. Soil microbes are the main driver of biogeochemical cycling in this forest ecosystem and have complex interactions with carbon (C) and nitrogen (N) components in the soil.

RESULTS

We investigated the vertical soil microbial community structure in a primary Korean pine-broadleaved mixed forest in Changbai Mountain (from 699 to 1177 m) and analyzed the relationship between the microbial community and both C and N components in the soil. The results showed that the total phospholipid fatty acid (PLFA) of soil microbes and Gram-negative bacteria (G-), Gram-positive bacteria (G+), fungi (F), arbuscular mycorrhizal fungi (AMF), and Actinomycetes varied significantly (p < 0.05) at different sites (elevations). The ratio of fungal PLFAs to bacterial PLFAs (F/B) was higher at site H1, and H2. The relationship between microbial community composition and geographic distance did not show a distance-decay pattern. The coefficients of variation for bacteria were maximum among different sites (elevations). Total soil organic carbon (TOC), total nitrogen (TN), soil water content (W), and the ratio of breast-height basal area of coniferous trees to that of broad-leaved tree species (RBA) were the main contributors to the variation observed in each subgroup of microbial PLFAs. The structure equation model showed that TOC had a significant direct effect on bacterial biomass and an indirect effect upon bacterial and fungal biomass via soil readily oxidized organic carbon (ROC). No significant relationship was observed between soil N fraction and the biomass of fungi and bacteria.

CONCLUSION

The total PLFAs (tPLFA) and PLFAs of soil microbes, including G-, G+, F, AMF, and Actinomycetes, were significantly affected by elevation. Bacteria were more sensitive to changes in elevation than other microbes. Environmental heterogeneity was the main factor affecting the geographical distribution pattern of microbial community structure. TOC, TN, W and RBA were the main driving factors for the change in soil microbial biomass. C fraction was the main factor affecting the biomass of fungi and bacteria and ROC was one of the main sources of the microbial-derived C pool.

Reduction in Hg phytoavailability in soil using Hg-volatilizing bacteria and biochar and the response of the native bacterial community

Biological approaches are considered promising and eco-friendly strategies to remediate Hg contamination in soil. This study investigated the potential of two 'green' additives, Hg-volatilizing bacteria (Pseudomonas sp. DC-B1 and Bacillus sp. DC-B2) and sawdust biochar, and their combination to reduce Hg(II) phytoavailability in soil and the effect of the additives on the soil bacterial community. The results showed that the Hg(II) contents in soils and lettuce shoots and roots were all reduced with these additives, achieving more declines of 12.3-27.4%, 24.8-57.8% and 2.0-48.6%, respectively, within 56 days of incubation compared to the control with no additive. The combination of DC-B2 and 4% biochar performed best in reducing Hg(II) contents in lettuce shoots, achieving a decrease of 57.8% compared with the control. Pyrosequencing analysis showed that the overall bacterial community compositions in the soil samples were similar under different treatments, despite the fact that the relative abundance of dominant genera altered with the additives, suggesting a relatively weak impact of the additives on the soil microbial ecosystem. The low relative abundances of Pseudomonas and Bacillus, close to the background levels, at the end of the experiment indicated a small biological disturbance of the local microbial niche by the exogenous bacteria.

Biochar amendment effects on the activities of soil carbon, nitrogen, and phosphorus hydrolytic enzymes: a meta-analysis

The aim of this meta-analysis was to synthesize the effects of biochar amendment on soil enzyme activities (SEAs) related to carbon (C), nitrogen (N), and phosphorus (P) cycling. Based on 401 paired comparisons from 43 published studies, the SEAs and main influential factors were analyzed in response to biochar characteristics, soil properties, and experiment conditions. Results showed that biochar additions to soils overall increased the N- and P-cycling SEAs by 14 and 11%, respectively. The enhancement of the N- and P-cycling SEAs was mainly attributable to the microbial stimulation by biochar properties (i.e., nutrient content and porosity) and soil nutrients (e.g., soil organic C and total N). The enhancement was the most significant under the conditions with biochars produced at low temperatures and using feedstock materials with high nutrient content, and biochar applications in acidic or neutral soils, coarse or fine soils, and farmland soils. Biochar additions to soils overall reduced the C-cycling SEAs by 6.3%. The C-cycling SEAs were greatly suppressed under the conditions with low and very high biochar loads, biochars produced at high temperatures and with feedstock materials of herb and lignocellulose, and biochar applications in alkaline, fine, and forest soils. The results were mainly related to the adsorption and inhibition effects of biochars and soil properties (e.g., liming effect, high biochar porosity and aromatic C content) on fungi and the enzymes. Biochar feedstock, C/N and load, and soil total N were the main influential factors on the SEAs. The results from this study demonstrate that biochar amendment is beneficial to improving soil N and P cycling and C sequestration.

Impacts of different biochar types on the anaerobic digestion of sewage sludge

Pyrolysis temperature and feedstock types had a pronounced effect on biochar properties, and biochar could facilitate the anaerobic digestion process.

Soil Matrix Determines the Outcome of Interaction Between Mycorrhizal Symbiosis and Biochar for Andropogon gerardii Growth and Nutrition

Biochar has been heralded as a multipurpose soil amendment to sustainably increase soil fertility and crop yields, affect soil hydraulic properties, reduce nutrient losses, and sequester carbon. Some of the most spectacular results of biochar (and organic nutrient) inputs are the terra preta soils in the Amazon, dark anthropogenic soils with extremely high fertility sustained over centuries. Such soil improvements have been particularly difficult to achieve on a short run, leading to speculations that biochar may need to age (weather) in soil to show its best. Further, interaction of biochar with arbuscular mycorrhizal fungi (AMF), important root symbionts of a great majority of terrestrial plants including most agricultural crops, remains little explored. To study the effect of aged biochar on highly mycotrophic Andropogon gerardii plants and their associated AMF, we made use of softwood biochar, collected from a historic charcoal burning site. This biochar (either untreated or chemically activated, the latter serving as a proxy for freshly prepared biochar) was added into two agricultural soils (acid or alkaline), and compared to soils without biochar. These treatments were further crossed with inoculation with a synthetic AMF community to address possible interactions between biochar and the AMF. Biochar application was generally detrimental for growth and mineral nutrition of our experimental plants, but had no effect on the extent of their root colonized by the AMF, nor did it affect composition of their root-borne AMF communities. In contrast, biochar affected development of two out of five AMF (Claroideoglomus and Funneliformis) in the soil. Establishment of symbiosis with AMF largely mitigated biochar-induced suppression of plant growth and mineral nutrition, mainly by improving plant acquisition of phosphorus. Both mycorrhizal and non-mycorrhizal plants grew well in the acid soil without biochar application, whereas non-mycorrhizal plants remained stunted in the alkaline soils under all situations (with or without biochar). These different and strong effects indicate that response of plants to biochar application are largely dependent on soil matrix and also on microbes such as AMF, and call for further research to enable qualified predictions of the effects of different biochar applications on field-grown crops and soil processes.