Two-year study of biochar: Achieving excellent capability of potassium supply via alter clay mineral composition and potassium-dissolving bacteria activity

Biochar-induced microbial and metabolic reprogramming enhances bioactive compound accumulation in Panax quinquefolius L

Panax quinquefolius L., with a history of over 300 years in traditional Chinese medicine, is notably rich in ginsenosides-its primary bioactive components. Although our previous study found that biochar application could enhance the content of ginsenoside Re, Rg and other contents in P. quinquefolius, its effect on the overall secondary metabolism of P. quinquefolius and its mechanism are still unclear. In this paper, the correlation between plant microbiome and secondary metabolites was studied from the perspective of plant rhizosphere microorganisms and endophytes, and the mechanism of biochar-induced metabolic reprogramming of P. quinquefolius was revealed. The results showed that biochar treatment significantly increased the accumulation of various substances in P. quinquefolius, including nucleosides, glycerophosphocholines, fatty acyls, steroidal glycosides, triterpenoids, and other bioactive compounds. Additionally, biochar treatment significantly enriched beneficial rhizosphere microorganisms such as Bacillus, Flavobacterium, and Devosia, while reducing the relative abundance of harmful fungi like Fusarium. Furthermore, it promoted endophytic Flavobacterium, Acaulospora, and Glomus, and suppressed pathogenic genera such as Plectosphaerella, Cladosporium, and Phaeosphaeria. These shifts in rhizosphere microbial community and endophytes structure and function were closely linked to the accumulation of secondary metabolites (e.g. ginsenosides Rg3, F2) in P. quinquefolius. Overall, our findings suggest that biochar may influence key endophytes and rhizosphere microorganisms to regulate the accumulation of secondary metabolites in P. quinquefolius. Therefore, this study provides valuable insights into the potential application of biochar in Chinese medicine agriculture.

Recruitment of copiotrophic and autotrophic bacteria by hyperaccumulators enhances nutrient cycling to reclaim degraded soils at abandoned rare earth elements mining sites

Hyperaccumulators harbor potentials for remediating rare earth elements (REEs)-contaminated soils. However, how they thrive in low-nutrient abandoned REEs mining sites is poorly understood. Three ferns (REEs-hyperaccumulators Dicranopteris pedata and Blechnum orientale, and non-hyperaccumulator Pteris vittata) along with their rhizosphere soils were collected to answer this question by comparing differences in soil nutrient levels, soil and plant REEs concentrations, and bacterial diversity, composition, and functions. Results observed lower soil pH (4.67-4.95 vs. 7.96), total carbon (TC) (0.35-0.62 vs. 2.84 g kg-1), total nitrogen (TN) (20-23 vs. 133 mg kg-1), and total phosphorus (TP) (81-91 vs. 133 mg kg-1) at sites Dp and Bo than site Pv. Hyperaccumulators efficiently extracted soil REEs and translocated them to fronds (up to 6897-7759 mg kg-1). Bacterial α diversity in three soils did not significantly vary. In contrast, bacterial composition at sites Dp and Bo was dominant by higher abundances of copiotrophic bacteria (18 % vs. 12 %, p_Actinomycetota; 3.3-8.3 % vs. 1.9 %, p_Bacteroidota; 8.3-14 % vs. 6.9 %, c_Gammaproteobacteria) and autotrophic bacteria (18 % vs. 13 %, p_Chloroflexota; 13 % vs. 8.6 %, p_Cyanobacteriota) when compared to site Pv. These bacteria likely acted as nutrient cyclers that promoted the growth of hyperaccumulators, based on functional predictions from DiTing analyses. This study provides new insights into nutrient recovery in abandoned REEs mining sites, offering strategies to reclaim degraded soils using phyto-microbial technology.

The fate and ecological risk of typical diamide insecticides in soil ecosystems under repeated application

Diamide insecticides are the third most widely used class of pesticides worldwide. However, the long-term impacts of repeated diamide applications on soil ecosystems remain unclear. This study investigated chlorantraniliprole (CLP) and cyantraniliprole (CYP) effects on soil ecosystems through simulated repeated exposures. Results showed both exhibited slow degradation in the soil, with repeated applications extending their persistence, particularly for CLP. Both significantly inhibited soil alkaline nitrogen and organic matter accumulation, while reducing urease and sucrase activities, with CLP exerting stronger inhibitory effects. Metagenomic analysis indicated that CLP and CYP notably reduced soil microbial diversity. Additionally, the two insecticides altered the soil microbial community structure and inhibited carbon-nitrogen metabolic pathways. Further analysis revealed that CLP treatment significantly decreased the relative abundances of Mesorhizobium and Marmoricola, whereas CYP treatment primarily reduced Clostridium_sensu_stricto_1. All of these genera exhibited significant positive correlations with key metabolic pathways in soil carbon and nitrogen cycling. Notably, the relative abundance of Sphingomonas increased significantly following CLP and CYP treatments, demonstrating potential degradation capabilities. Overall, both CLP and CYP posed ecological risks to soil ecosystems, with CLP exhibiting more severe impacts. These findings revealed the need for strengthened scientific management in actual production.

Short-Term Alteration of Soil Physicochemical Characteristics Induced by Biochar Application on a Ferric Acrisol

Biochar (incinerated organic waste by-product) has shown promise in enhancing soil fertility and agricultural productivity. Soil quality plays an essential role in the success of agricultural activities, with soil enhancement being crucial for optimizing crop yields and fostering soil fertility. An experiment with different biochar types was arranged in a randomized complete block design. The biochar [coconut husk (CH) biochar and sugarcane bagasse (SB) biochar] was evenly hand mixed with the soil after plowing to 30 cm depth. A one-time application of biochar was done. There was a total of six treatments: SB biochar, SB biochar plus nitrogen (N), phosphorus (P), potassium (K) (SB + NPK), CH biochar, CH biochar plus NPK (CB + NPK), NPK, and control (CT), with three replicates for each treatment. The area of each plot was 3 m2 (3 m × 1 m) to assess the effects of biochar application on the soil physical and chemical characteristics of Ferric Acrisol with cabbage (Fortune F1 variety) as a test crop in Ghana. Soil bulk density, porosity, pH, organic carbon (OC), available N, total P, available K, available calcium (Ca), electrical conductivity (EC), and cation exchange capacity (CEC) were determined. CH and SB addition improved soil bulk density (1.21 g·cm-3 and 1.29 g·cm-3), leading to a significant (p < 0.05) improvement in the total porosity (54.29% and 51.10%), respectively, at 0-30 cm soil depth compared to the presoil condition (1.5 g·cm-3). Additionally, CH and SB significantly (p < 0.05) impacted the soil chemical characteristics and fertility of the tested soil. The results showed that biochar application is crucial for C sequestration, reduction in pH (SB-7.36 and CH-7.44 compared to the presoil condition (4.93) at 0-30 cm soil depth), and soil fertility enhancement. Applying biochar to soils can therefore be considered a potential solution to improve soil fertility for sustainable crop production.

Biochar affects soil properties over 1 m depth in an alkaline soil of north China Plain

Biochar has been shown to enhance soil quality and agricultural yields. Previous studies about biochar's effect on soil properties mainly concentrated on the top 30 cm layer but less on the subsoils. Given the subsoil's active role in climate change mitigation and its significance for nutrient cycling and crop productivity, understanding biochar's effects at depth is crucial. This study explored the responses of soil organic carbon (SOC), total nitrogen, available potassium, available phosphorus, pH, and electrical conductivity to different doses of biochar addition (0, 10, 20, and 30 Mg/ha) over the 1 m depth of alkaline soil. Additionally, the impact of biochar on soil microbial community was assessed in the top 20 cm. Results demonstrated that biochar addition can increase SOC and improve soil properties in deep soil horizons. Specifically, a 30 Mg/ha biochar addition increased SOC by 1.2-10.1 Mg C/ha in the 10-40 cm layer and by 3 Mg C/ha in the 60-80 cm depth over two years. Additionally, biochar addition at this rate increased total nitrogen by 0.2-0.3 g N/kg in the 10-40 cm depth and elevated available potassium across the 1 m profile, with a maximum increment of 313 mg/kg in the surface 10 cm and a minimum of 97 mg/kg in the 40-60 cm depth. While biochar application did not increase available phosphorus, it resulted in a minor decrease in soil pH (<0.7 units) and a slight increase in electrical conductivity. Moreover, biochar addition did not significantly alter the soil microbial community. Our findings underscore the importance of considering subsoils when evaluating biochar's impact on soil properties. We suggest that subsoils should be considered when estimating the potential of cropland management for increasing soil carbon sequestration and improving soil conditions.

Unearthing the soil-bacteria nexus to enhance potassium bioavailability for global sustainable agriculture: A mechanistic preview

Established as a plant macronutrient, potassium (K) substantially bestows plant growth and thus, global food production. It is absorbed by plants as potassium cation (K+) from soil solution, which is enriched through slow-release from soil minerals or addition of soluble fertilizers. Contribution of bioavailable K+ from soil is usually insignificant (< 2 %), although the earth's crust is rich in K-bearing minerals. However, K is fixed largely in interlayer spaces of K-bearing minerals, which can be released by K-solubilizing bacteria (KSB) such as Bacillus, Pseudomonas, Enterobacter, and Acidithiobacillus. The underlying mechanisms of K dissolution by KSB include acidolysis, ion exchange reactions, chelation, complexolysis, and release of various organic and inorganic acids such as citric, oxalic, acetic, gluconic, and tartaric acids. These acids cause disintegration of K-bearing minerals and bring K+ into soil solution that becomes available to the plants. Current literature review updates the scientific information about microbial species, factors, and mechanisms governing the bio-intrusion of K-bearing minerals. Moreover, it explores the potential of KSB not only for K-solubilization but also to enhance bioavailability of phosphorus, nitrogen, and micronutrients, as well as its other beneficial impact on plant growth. Thus, in the context of sustainable agricultural production and global food security, utilization of KSB may facilitate plant nutrient availability, conserve natural resources, and reduce environmental impacts caused by chemical fertilizers.

Effect of Combined Application of Wood Vinegar Solution and Biochar on Saline Soil Properties and Cotton Stress Tolerance

Biomass pyrolysis by-products, such as biochar (BC) and wood vinegar (WV), are widely used as soil conditioners and efficiency enhancers in agriculture. A pot experiment was conducted to examine the effects of WV, both alone and in combination with BC, on soil properties in mildly saline soil and on cotton stress tolerance. The results demonstrated that BC and WV application, either individually or together, increased soil nutrient content. The combined application was more effective than the individual applications, resulting in a 5.18-20.12% increase in organic matter, a 2.65-15.04% increase in hydrolysable nitrogen, a 2.23-58.05% increase in effective phosphorus, and a 2.71-29.38% increase in quick-acting potassium. Additionally, the combined application of WV and BC led to greater improvements in cotton plant height, net photosynthetic rate (Pn), leaf nitrate reductase (NR), superoxide dismutase (SOD), and catalase (CAT) activities compared to the application of BC or WV alone. The enhancements in this study varied across different parameters. Plant height showed an increase of 14.32-21.90%. Net photosynthetic rate improved by 13.56-17.60%. Leaf nitrate reductase increased by 5.47-37.79%. Superoxide dismutase and catalase showed improvements of 5.82-64.95% and 10.36-71.40%, respectively (p < 0.05). Moreover, the combined treatment outperformed the individual applications of WV and BC, resulting in a significant decrease in MDA levels by 2.47-51.72% over the experimental period. This combined treatment ultimately enhanced cotton stress tolerance. Using the entropy weight method to analyze the results, it was concluded that the combined application of WV and BC could enhance soil properties in mildly saline soils, increase cotton resistance, and hold significant potential for widespread application.

Characteristics of Rhizosphere Microbiome, Soil Chemical Properties, and Plant Biomass and Nutrients in Citrus reticulata cv. Shatangju Exposed to Increasing Soil Cu Levels

The prolonged utilization of copper (Cu)-containing fungicides results in Cu accumulation and affects soil ecological health. Thus, a pot experiment was conducted using Citrus reticulata cv. Shatangju with five Cu levels (38, 108, 178, 318, and 388 mg kg-1) to evaluate the impacts of the soil microbial processes, chemistry properties, and citrus growth. These results revealed that, with the soil Cu levels increased, the soil total Cu (TCu), available Cu (ACu), organic matter (SOM), available potassium (AK), and pH increased while the soil available phosphorus (AP) and alkali-hydrolyzable nitrogen (AN) decreased. Moreover, the soil extracellular enzyme activities related to C and P metabolism decreased while the enzymes related to N metabolism increased, and the expression of soil genes involved in C, N, and P cycling was regulated. Moreover, it was observed that tolerant microorganisms (e.g., p_Proteobacteria, p_Actinobacteria, g_Lysobacter, g_Sphingobium, f_Aspergillaceae, and g_Penicillium) were enriched but sensitive taxa (p_Myxococcota) were suppressed in the citrus rhizosphere. The citrus biomass was mainly positively correlated with soil AN and AP; plant N and P were mainly positively correlated with soil AP, AN, and acid phosphatase (ACP); and plant K was mainly negatively related with soil β-glucosidase (βG) and positively related with the soil fungal Shannon index. The dominant bacterial taxa p_Actinobacteriota presented positively correlated with the plant biomass and plant N, P, and K and was negatively correlated with plant Cu. The dominant fungal taxa p_Ascomycota was positively related to plant Cu but negatively with the plant biomass and plant N, P, and K. Notably, arbuscular mycorrhizal fungi (p_Glomeromycota) were positively related with plant P below soil Cu 108 mg kg-1, and pathogenic fungi (p_Mortierellomycota) was negatively correlated with plant K above soil Cu 178 mg kg-1. These findings provided a new perspective on soil microbes and chemistry properties and the healthy development of the citrus industry at increasing soil Cu levels.

Straw Addition Enhances Crop Yield, Soil Aggregation, and Soil Microorganisms in a 14-Year Wheat-Rice Rotation System in Central China

Straw return utilizes waste resources to reduce the use of chemical fertilizers worldwide. However, information is still lacking on the relative impact of straw return on soil fertility, the nutrient composition of different soil aggregates, and soil microbial communities. Therefore, this study aimed to understand the effects of different management practices on the crop yield, soil fertility, and soil community composition in a 14-year wheat-rice rotation system. The treatments included a control (without fertilizer and straw addition), chemical fertilization (NPK), straw return without fertilizer (S), and straw addition with chemical fertilizer (NPKS). The results showed that NPKS improved the wheat and rice yield by 185.12% and 88.02%, respectively, compared to the CK treatment. Additionally, compared to the CK treatment, the N, P, and K contents of the wheat stem were increased by 39.02%, 125%, and 20.23% under the NPKS treatment. Compared to the CK treatment, SOM, TN, TP, AN, AP, AK, CEC, AFe, AMn, ACu, and AZn were increased by 49.12%, 32.62%, 35.06%, 22.89%, 129.36%, 48.34%, 13.40%, 133.95%, 58.98%, 18.26% and 33.33% under the NPKS treatment, respectively. Moreover, straw addition promoted the creation and stabilization of macro-aggregates in crop soils. The relative abundance of macro-aggregates (0.25-2 mm) increased from 37.49% to 52.97%. Straw addition was associated with a higher proportion of aromatic and carbonyl carbon groups in the soil, which, in turn, promoted the formation of macro-aggregates. Redundancy analysis showed that straw return significantly increased the microbial community diversity. These findings demonstrate that straw addition together with chemical fertilizer could increase the crop yield by improving soil fertility, soil aggregate stability, and the diversity of fungi.

Active microbial population dynamics and life strategies drive the enhanced carbon use efficiency in high-organic matter soils

Microbial carbon use efficiency (CUE) is a critical parameter that controls carbon storage in soil, but many uncertainties remain concerning adaptations of microbial communities to long-term fertilization that impact CUE. Based on H218O quantitative stable isotope probing coupled with metagenomic sequencing, we disentangled the roles of active microbial population dynamics and life strategies for CUE in soils after a long-term (35 years) mineral or organic fertilization. We found that the soils rich in organic matter supported high microbial CUE, indicating a more efficient microbial biomass formation and a greater carbon sequestration potential. Organic fertilizers supported active microbial communities characterized by high diversity and a relative increase in net growth rate, as well as an anabolic-biased carbon cycling, which likely explains the observed enhanced CUE. Overall, these results highlight the role of population dynamics and life strategies in understanding and predicting microbial CUE and sequestration in soil.IMPORTANCEMicrobial CUE is a major determinant of global soil organic carbon storage. Understanding the microbial processes underlying CUE can help to maintain soil sustainable productivity and mitigate climate change. Our findings indicated that active microbial communities, adapted to long-term organic fertilization, exhibited a relative increase in net growth rate and a preference for anabolic carbon cycling when compared to those subjected to chemical fertilization. These shifts in population dynamics and life strategies led the active microbes to allocate more carbon to biomass production rather than cellular respiration. Consequently, the more fertile soils may harbor a greater microbially mediated carbon sequestration potential. This finding is of great importance for manipulating microorganisms to increase soil C sequestration.

Alterations in the composition and metabolite profiles of the saline-alkali soil microbial community through biochar application

Saline-alkali soil poses significant chanllenges to sustainable development of agriculture. Although biochar is commonly used as a soil organic amendment, its microbial remediation mechanism on saline-alkali soil requires further confirmation. To address this, we conducted a pot experiment using cotton seedlings to explore the potential remediation mechanism of rice straw biochar (BC) at three different levels on saline-alkaline soil. The results showed that adding of 2% biochar greatly improved the quality of saline-alkaline soil by reducing pH levels, electrical conductivity (EC), and water-soluble ions. Moreover, biochar increased the soil organic matter (SOM), nutrient availability and extracellular enzyme activity. Interestingly, it also reduced soil salinity and salt content in various cotton plant tissues. Additionally, biochar had a notable impact on the composition of the microbial community, causing changes in soil metabolic pathways. Notably, the addition of biochar promoted the growth and metabolism of dominant salt-tolerant bacteria, such as Proteobacteria, Bacteroidota, Acidobacteriota, and Actinobacteriota. By enhancing the positive correlation between microorganisms and metabolites, biochar alleviated the inhibitory effect of salt ions on microorganisms. In conclusion, the incorporation of biochar significantly improves the soil microenvironment, reduces soil salinity, and shows promise in ameliorating saline-alkaline soil conditions.

" Assessing the impact of biochar on microbes in acidic soils: Alleviating the toxicity of aluminum and acidity"

In arable soils, anthropogenic activities such as fertilizer applications have intensified soil acidification in recent years. This has resulted in frequent environmental problems such as aluminum (Al) and H+ stress, which negatively impact crop yields and quality in acidic soils. Biochar, as a promising soil conditioner, has attracted much attention globally. The present study was conducted in a greenhouse by setting up 2% biochar rate to investigate how biochar relieves Al3+ hazards in acidic soil by affecting soil quality, soil environment, and soil microbiomes. The addition of biochar significantly improved soil fertility and enzyme activities, which were attributed to its ability to enhance the utilization of soil carbon sources by influencing the activity of soil microorganisms. Moreover, the Al3+ contents were significantly decreased by 66.61-88.83% compared to the C0 level (without biochar treatment). In particular, the results of the 27Al NMR suggested that forms of AlVI (Al(OH)2+, Al(OH)+ 2, and Al3+) were increased by 88.69-100.44% on the surface of biochar, reducing the Al3+ stress on soil health. The combination of biochar and nitrogen (N) fertilizer contributed to the augmentation of bacterial diversity. The application of biochar and N fertilizer increased the relative abundance of the majority of bacterial species. Additionally, the application of biochar and N fertilizer had a significant impact on soil microbial metabolism, specifically in the biosynthesis of secondary metabolites (lipids and organic acids) and carbon metabolic ability. In conclusion, biochar can enhance soil microbial activity and improve the overall health of acidic soil by driving microbial metabolism. This study offers both theoretical and technical guidance for enhancing biochar in acidified soil and promoting sustainable development in farmland production.

Iron-modified biochar reduces nitrogen loss and improves nitrogen retention in Luvisols by adsorption and microbial regulation

Nitrogen (N) loss poses a great threat to global environmental sustainability. The application of modified biochar is a novel strategy to improve soil nitrogen retention and alleviate the negative effects caused by N fertilizers. Therefore, in this study iron modified biochar was used as a soil amendment to investigate the potential mechanisms of N retention in Luvisols. The experiment comprised five treatments i.e., CK (control), 0.5 % BC, 1 % BC, 0.5 % FBC and 1 % FBC. Our results showed that the intensity of functional groups and surface structure of FBC was improved. The 1 % FBC treatment showed a significant increment in soil NO₃^--N, dissolved organic nitrogen (DON), and total nitrogen (TN) content by 374.7 %, 51.9 %, and 14.4 %, respectively, compared with CK. The accumulation of N in cotton shoots and roots was increased by 28.6 % and 6.6 % with 1 % FBC addition. The application of FBC also stimulated the activities of soil enzymes related to C and N cycling i.e., β-glucosidase (βG), β-Cellobiohydrolase (CBH), and Leucine aminopeptidase (LAP). In the soil treated with FBC, a significant improvement in the structure and functions of the soil bacterial community was found. FBC addition altered the taxa involved in the N cycle by affecting soil chemical properties, especially for Achromobacte, Gemmatimonas, and Cyanobacteriales. In addition to direct adsorption, the regulation of FBC on organisms related to N-cycling also played an important role in soil nitrogen retention.

Iva xanthiifolia leaf extract reduced the diversity of indigenous plant rhizosphere bacteria

BACKGROUND

Iva xanthiifolia, native to North America, is now widely distributed in northeastern China and has become a vicious invasive plant. This article aims to probe the role of leaf extract in the invasion of I. xanthiifolia.

METHODS

We collected the rhizosphere soil of Amaranthus tricolor and Setaria viridis in the invasive zone, the noninvasive zone and the noninvasive zone treated with extract from I. xanthiifolia leaf, and obtained I. xanthiifolia rhizosphere soil in the invasive zone. All wild plants were identified by Xu Yongqing. I. xanthiifolia (collection number: RQSB04100), A. tricolor (collection number: 831,030) and S. viridis (collection number: CF-0002-034) are all included in Chinese Virtual Herbarium ( https://www.cvh.ac.cn/index.php ). The soil bacterial diversity was analyzed based on the Illumina HiSeq sequencing platform. Subsequently, taxonomic analysis and Faprotax functional prediction were performed.

RESULTS

The results showed that the leaf extract significantly reduced the diversity of indigenous plant rhizosphere bacteria. A. tricolor and S. viridis rhizobacterial phylum and genus abundances were significantly reduced under the influence of I. xanthiifolia or its leaf extract. The results of functional prediction showed that bacterial abundance changes induced by leaf extracts could potentially hinder nutrient cycling in native plants and increased bacterial abundance in the A. tricolor rhizosphere related to aromatic compound degradation. In addition, the greatest number of sensitive Operational Taxonomic Units (OTUs) appeared in the rhizosphere when S. viridis was in response to the invasion of I. xanthiifolia. It can be seen that A. tricolor and S. viridis have different mechanisms in response to the invasion of I. xanthiifolia.

CONCLUSION

I. xanthiifolia leaves material has potential role in invasion by altering indigenous plant rhizosphere bacteria.

Potassium assisted pyrolysis of Chinese Baijiu distillers' grains to prepare biochar as controlled-release K fertilizer

A novel K-loaded biochar as controlled-release K fertilizer was prepared through K assisted pyrolysis of distillers' grains (DGs, typical solid-byproducts of Chinese Baijiu) under different atmospheres (N₂ and CO₂) and temperatures (400 and 800 °C). The fabricated DGs-based biochar exhibited high K loading (200.20-232.33 mg/g), and the release kinetics and column leaching experiments suggested that K-loaded biochar exhibited excellent controlled release performance in a long term. Compared with other biochar, the K-loaded biochar prepared at CO₂ and 400 °C has lower cumulative release ratio of 82.35 %, and could retain the durative K release at ~0.5 % for 25 d. The release kinetics suggested that the K release behavior was dominated by dissolution, electrostatic attraction, adsorption, confinement effect, and chemical interaction. Furthermore, pot experiments revealed that K-loaded biochar could promote the growth of Komatsuna, in which the fresh weight and chlorophyll relative content of Komatsuna cultivated with biochar prepared at CO₂ and 400 °C reached 0.146 g and 41.95 after 25 d growth, respectively. The above results suggested that the K-loaded biochar exhibited excellent utilization potential as a controlled-release K fertilizer, facilitating the sustainable development and resource valorization of Baijiu industry.

Biochar application as a soil potassium management strategy: A review

The established practices of intensive agriculture, combined with inadequate soil Κ replenishment by conventional inorganic fertilization, results in a negative environmental impact through the gradual exhaustion of different forms of K reserves in soils. Although biochar application as soil amendment has been established as an approach of integrated nutrient management, few works have focused on the impact of biochar application to soil K availability and crop uptake. This review provides an up-to-date analysis of the published literature, focusing on the impact of biochar in the availability of potassium in soil and crop growth. First, the effect of biomass type and pyrolysis temperature on potassium content of biochar was assessed. Second, the influence of biochar addition to the availability of potassium in soil and on potassium soil dynamics was examined. Finally, alternative methods for estimating available K in soils were proposed. The most promising biomasses in terms of potassium content were grape pomace, coffee husk and hazelnut husk however, these have not been widely utilized for biochar production. Higher pyrolysis temperatures (>500 °C) increase the total potassium content whereas lower temperatures increase the water-soluble and exchangeable potassium fractions. It was also determined that biochar has considerable potential for enhancing K availability through several distinct mechanisms which eventually lead directly or indirectly to increased K uptake by plants. Indirect mechanisms mainly include increased K retention capacity based on biochar properties such as high cation exchange capacity, porosity, and specific surface area, while the direct supply of K can be provided by K-rich biochar sources through purpose-made biochar production techniques. Research based on biochar applications for soil K fertility purposes is still at an early stage, therefore future work should focus on elucidating the mechanisms that define K retention and release processes through the complicated soil-biochar-plant system.

30-Month Pot Experiment: Biochar Alters Soil Potassium Forms, Soil Properties and Soil Fungal Diversity and Composition in Acidic Soil of Southern China

Biochar has a significant impact on improving soil, nutrient supply, and soil microbial amounts. However, the impacts of biochar on soil fungi and the soil environment after 30 months of cultivation experiments are rarely reported. We studied the potential role of peanut shell biochar (0% and 2%) in the soil properties and the soil fungal communities after 30 months of biochar application under different soil potassium (K) levels (100%, 80%, 60%, 0% K fertilizer). We found that biochar had a promoting effect on soil K after 30 months of its application, such as the available K, water-soluble K, exchangeable K, and non-exchangeable K; and increments were 125.78%, 124.39%, 126.01%, and 26.63% under biochar and K fertilizer treatment, respectively, compared to control treatment. Our data revealed that p_Ascomycota and p_Basidiomycota were the dominant populations in the soil, and their sub-levels showed different relationships with the soil properties. The relationships between c_sordariomycetes and its sub-level taxa with soil properties showed a significant positive correlation. However, c_Dothideomycetes and its sub-group demonstrated a negative correlation with soil properties. Moreover, soil enzyme activity, especially related to the soil C cycle, was the most significant indicator that affected the community and structure of fungi through structural equation modeling (SEM) and redundancy analysis (RDA). This work emphasized that biochar plays an important role in improving soil quality, controlling soil nutrients, and regulating fungal diversity and community composition after 30 months of biochar application.

Biochar as a soil amendment in the tree establishment phase: What are the consequences for tree physiology, soil quality and carbon sequestration?

Trees play a pivotal role in the urban environment alleviating the negative impacts of urbanization, and for this reason, local governments have promoted strongly tree planting policies. However, poor soil quality and neglect tree maintenance (e.g., irrigation and fertilization) can seriously mine the plant health status during the tree establishment phase. The use of biochar to provide long-lasting C to the soil and, at the same time, improving soil properties (e.g., improved water holding capacity), soil enzymes activities and NPK concentrations, is a promising research field. Therefore, with a two-step experiment, the study aimed to assay the physiological responses of a commonly used urban tree species (Tilia × europaea L.) to 1.5 % (w/w) biochar amendment (B), and secondly, to assess the ability of trees, grown in biochar amended soil, to tolerate a period of drought. Biochar amendment increased P and K availability in the soil, resulting in higher P and K concentrations in B than control leaves, according to the leaf stage. This induced B trees, higher values in both total biomass than controls (+22 %) in well-watered plants. Moreover, the higher water availability in soil amended with biochar helped B trees to tolerate water stress, with better leaf photosynthetic performances and a faster recovery than stressed controls after the re-watering. This study highlights the dual function of the biochar, improving CO₂ sequestration and soil properties, and at the same time, enhancing plant physiological responses to environmental constraints. The use of biochar at the tree planting, especially in an urban environment, is a feasible and environmentally sustainable strategy to improve the success during the tree establishment phase.

The Use of Raw Poultry Waste as Soil Amendment Under Field Conditions Caused a Loss of Bacterial Genetic Diversity Together with an Increment of Eutrophic Risk and Phytotoxic Effects

Poultry waste has been used as fertilizer to avoid soil degradation caused by the long-term application of chemical fertilizer. However, few studies have evaluated field conditions where livestock wastes have been used for extended periods of time. In this study, physicochemical parameters, metabarcoding of the 16S rRNA gene, and ecotoxicity indexes were used for the characterization of chicken manure and poultry litter to examine the effect of their application to agricultural soils for 10 years. Poultry wastes showed high concentrations of nutrients and increased electrical conductivity leading to phytotoxic effects on seeds. The bacterial communities were dominated by typical members of the gastrointestinal tract, noting the presence of pathogenic bacteria. Soils subjected to poultry manure applications showed statistically higher values of total and extractable phosphorous, increasing the risk of eutrophication. Moreover, while the soil bacterial community remained dominated by the ones related to the biogeochemical cycles of nutrients and plant growth promotion, losses of alpha diversity were observed on treated soils. Altogether, our work would contribute to understand the effects of common local agricultural practices and support the adoption of the waste treatment process in compliance with environmental sustainability guidelines.

14 year applications of chemical fertilizers and crop straw effects on soil labile organic carbon fractions, enzyme activities and microbial community in rice-wheat rotation of middle China

Traditional fertilization management can damage soil structure and lead to severe soil erosion. The practice of crop straw returning to the field reduces the negative impact of straw burning and improves soil quality. We investigated the effects of these agricultural practices on soil organic carbon components, enzyme activities, and soil microorganisms over 14 years of field experiments. Specifically, we studied four management strategies: no fertilizer or crop straw returning (CK), traditional chemical fertilization (NPK), crop straw returning (S), and crop straw returning with chemical fertilizer (NPKS). We found NPKS treatments significantly (P < 0.05) increased the dissolved organic carbon (DOC), microbial biomass carbon (MBC), particulate organic carbon (POC) and readily oxidized organic carbon (ROC) concentrations by 79.32 %, 82.16 %, 92.46 %, and 104.32 % relative to CK. Furthermore, under NPKS, the activities of soil enzymes related C, N, and P (α-glucosidase (αG), β-glucosidase (βG), cellulase (CBH), xylanase (βX), acetyl β-glucosaminidase (NAG), leucine aminopeptidase (LAP), and acid phosphate (AP)) were increased by 54.66 %, 113.26 %, 76.73 %, 52.41 %, 45.74 %, 56.69 %, and 68.92 % relative to CK, respectively. Redundancy analysis and structural equation modelling showed that straw returning had positive effects on soil microbial community diversity and richness, and also improved microbial activity which is favorable in the degradation of soil carbon. Furthermore, we found that soil fungi were more sensitive than bacteria to changes in soil carbon composition and enzyme activities following straw returning. These results suggest that straw returning combined with chemical fertilizer can be an effective strategy to improve soil labile organic carbon components, enzyme activities, and ecological function of microorganisms.

Augmentation characteristics and microbial community dynamics of low temperature resistant composite strains LTF-27

Biogas production in the cold regions of China is hindered by low temperatures, which led to slow lignocellulose biotransformation. Cold-adapted lignocellulose degrading microbial complex community LTF-27 was used to investigate the influence of hydrolysis on biogas production. After 5 days of hydrolysis at 15 ± 1 °C, the hydrolysis conversion rate of the corn straw went up to 22.64%, and the concentration of acetic acid increased to 2596.56 mg/L. The methane production rates of total solids (TS) inoculated by LTF-27 reached 204.72 mL/g, which was higher than the biogas (161.34 mL/g), and the control group (CK) inoculated with cultural solution (121.19 mL/g), the methane production rate of volatile solids (VS) increased by 26.88% and 68.92%, respectively. Parabacteroides, Lysinibacillus, and Citrobacter were the main organisms that were responsible for hydrolysis. While numerous other bacteria genera in the gas-producing phase, Macellibacteroides were the most commonly occurring one. Methanosarcina and Methanobacteriaceae contributed 86.25% and 11.80% of the total Archaea abundance during this phase. This study proves the psychrotrophic LTF-27's applicability in hydrolysis and biomass gas production in low temperatures.

Four-year biochar study: Positive response of acidic soil microenvironment and citrus growth to biochar under potassium deficiency conditions

Biochar has direct or indirect effects on soil microorganisms, but the changes in soil metabolism are rarely monitored and analyzed. In addition, the potassium (K) effect of biochar has not attracted much attention. This study set up a four-year experiment with acid soil and citrus as the test soil and plants, respectively. The long-term effects of biochar on the acid soil microenvironment and citrus growth were explored from soil properties (nutrient contents, microbial communities, and metabolites) and citrus growth (nutrient contents, reactive oxygen species (ROS), and root endophytes). The results showed that the four-year amendment of biochar in acid soil was very significant, in which the soil pH was increased by 1 unit, organic matter and cation exchange capacity (CEC) increased by 120.77% and 16.21%, respectively. Biochar improved the K availability of soil by increasing the number and metabolic activity of Azotobacter and Pseudomonas, and finally effectively alleviated the K deficiency of citrus. From the perspective of available K content, 2% biochar reduced the 20% conventional K application rate. The pH, organic matter, and cation exchange capacity (CEC) were the most important factors affecting the bacterial community structure, while the fungal community was more sensitive to the change in the nutrient environment. Biochar mainly stimulated the progress of soil metabolism by affecting the metabolic activity of bacterial communities. Biochar application increased some of the beneficial bacteria in the soil, i.e., the relative abundance of Pseudarthrobacter increased by 700 times. However, biochar and exogenous K did not significantly affect arbuscular mycorrhizal fungi (AMF) and endophytic bacteria in citrus roots. In general, biochar has a long-term and positive response to the acidic soil microenvironment and citrus growth, as well as promotion value in the agricultural field.

Effects of Fe-Mn impregnated biochar on enzymatic activity and bacterial community in phthalate-polluted brown soil planted with wheat

A pot experiment was carried out on brown soil polluted by dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) to investigate the effects of biochar (BC) derived from corn straw and Fe-Mn oxide modified biochar composites (FMBC) on the bioavailability of DBP and DEHP, as well as ecosystem responses in rhizosphere soil after wheat ripening. The results indicate that the application of BC and FMBC significantly increases soil organic matter, pH, available nitrogen (AN), Olsen phosphorus, and available potassium (AK); reduces the bioavailability of DBP and DEHP; enhances the activities of dehydrogenase, urease, protease, β-glucosidase, and polyphenol oxidase; and decreases acid phosphatase activity. No changes in richness and diversity, which were measured by Illumina MiSeq sequencing, were observed following BC and FMBC application. The bacterial community structure and composition varied with DBP/DEHP concentrations and BC/FMBC additions in a nonsystematic way and no significant trends were observed. In addition, FMBC exhibited better performance in increasing soil properties and decreasing the bioavailability of DBP and DEHP compared with BC. Hence, the FMBC amendment may be a promising way of developing sustainable agricultural environmental management.