CK Soil Research Articles

The Pb capture mechanism of soil prophylactic agents prepared from phosphorus tailings and the influence of phosphorus speciation on its slow-release mechanism

This research activated phosphorus tailings to prepare a high‑phosphorus core (HPC) for multi-species composite slow-release heavy metal soil prophylactic agents (MCP), aiming to extend the slow-release period of MCP and enhance the efficiency of Pb stabilization. During the preparation of HPC, the proportion of non-apatitic inorganic phosphorus (NAIP) and apatite phosphorus (AP) continuously decreased with increasing polymerization temperature. At 400 °C, polyphosphates (PP) began to form, reaching 74.26 % at 600 °C. Initially, the rapidly soluble NAIP remained the major component of HPC, but the proportion of AP increased with higher polymerization temperatures, reaching 40.8 % at 600 °C. After 120 days of cultivation with four MCPs (MCP 300-21, MCP 400-12, MCP 500-14, MCP 600-14), the total soil phosphorus (TSP), soil organic matter (SOM), and Pb stabilization capacity of the cultivated soil showed significant improvements, reaching maximum values of 2.39 mg/g, 38.16 mg/g, and 45.4 mg/g, respectively, which are 9.9, 4.4, and 5.9 times higher than those of the CK soil. KEGG (Kyoto Encyclopedia of Genes and Genomes) functional prediction analysis indicated that MCPs contribute directly or indirectly to the forms and chemical stability of Pb by stimulating soil physiological and biochemical processes. This research proposes a novel approach for using phosphates in soil heavy metal management strategies and provides new insights into the mechanisms of heavy metal stabilization in soil using environmental functional materials.

Effects of Rosa roxburghii Pomace Biochar on Yield and Quality of Chinese Cabbage and Soil Properties

In order to explore the effect of Rosa roxburghii pomace biochar on the yield and quality of Chinese cabbage and soil properties and realize the resource utilization of R. roxburghii pomace, a pot experiment was conducted to study the effect of R. roxburghii pomace biochar on the yield and quality of Chinese cabbage and soil properties by setting five biochar application rates of 0 % (CK), 1 % (T1), 3 % (T2), 5 % (T3), and 7 % (T4). The results showed that:① The application of R. roxburghii pomace biochar could significantly improve the yield and quality of Chinese cabbage, and the effect was the best at a 5 % biochar application rate. The yield, soluble solids, soluble sugar, vitamin C, total nitrogen, total phosphorus, and total potassium content of Chinese cabbage increased by 71.51 %, 40.14 %, 33.65 %, 38.08 %, 9.03 %, 28.85 %, and 35.38 %, respectively, compared with those in CK. ② The application of biochar from R. roxburghii pomace could significantly improve soil properties and increase soil nutrient content and availability. The effect was better at a 5 % biochar application rate. The soil pH, organic matter, total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus, and available potassium content increased by 41.06 %, 134.84 %, 157.48 %, 140.79 %, 341.75 %, and 627.13 %, respectively, compared with those in CK. The contents of available Fe, Mn, Cu, and Zn and exchangeable Ca and Mg increased by 37.68 %, 61.69 %, 400.00 %, 4 648.84 %, 617.17 %, and 351.42 %, respectively, compared with those in CK. ③ The application of biochar from R. roxburghii pomace could significantly enhance soil enzyme activity. Compared with those in the CK treatment, soil urease, acid phosphatase, catalase, and sucrase increased by 51.43 %-362.86 %, 90.63 %-134.14 %, 21.40 %-85.12 %, and 82.92 %-218.43 %, respectively. ④ Redundancy analysis showed that soil AK; exchangeable Ca, SOM, and AP; and available Zn were the main factors affecting the yield and quality of Chinese cabbage, and there was a significant positive correlation between them. In summary, the application of R. roxburghii pomace biochar can significantly increase the yield and quality of Chinese cabbage and improve soil properties. The preparation of R. roxburghii pomace into biochar can provide a theoretical reference for the rational utilization of R. roxburghii pomace resources.

Soil bacterial community diversity and life strategy during slope restoration on an uninhabited island: changes under the aggregate spray-seeding technique.

We investigated the effects of the aggregate spray-seeding (ASS) technique on soil bacterial community diversity, life strategies, and seasonal change. Soil from six plots with original vegetation (CK, n=6) was compared to soil from 15 plots with spray-seeding restoration (SR, n=15) using environmental DNA sequencing. The bacterial Shannon and Chao1 indices of SR soils were significantly greater (P<0.05) than those of CK soils. The Chao1 index for the SR soil bacterial community was significantly greater in summer (P<0.05) than in winter. The ratio of the relative abundance of bacterial K-strategists to r-strategists (K/r) and the DNA guanine-cytosine (GC) content in the SR soil were significantly lower (P<0.05) than those in the CK soil. Principal coordinate analysis revealed significant differences between the SR and CK bacterial communities. The GC content was positively correlated with the K/r ratio. Soil conductivity was negatively associated with the K/r ratio and GC content, indicating that ionic nutrients were closely related to bacterial life strategies. The ASS technique improved soil bacterial diversity, altered community composition, and favored bacterial r-strategists.

Soil microbiome of shiro reveals the symbiotic relationship between Tricholoma bakamatsutake and Quercus mongolica.

Tricholoma bakamatsutake is a delicious and nutritious ectomycorrhizal fungus. However, its cultivation is hindered owing to limited studies on its symbiotic relationships. The symbiotic relationship between T. bakamatsutake and its host is closely related to the shiro, a complex network composed of mycelium, mycorrhizal roots, and surrounding soil. To explore the symbiotic relationship between T. bakamatsutake and its host, soil samples were collected from T. bakamatsutake shiro (Tb) and corresponding Q. mongolica rhizosphere (CK) in four cities in Liaoning Province, China. The physicochemical properties of all the soil samples were then analyzed, along with the composition and function of the fungal and bacterial communities. The results revealed a significant increase in total potassium, available nitrogen, and sand in Tb soil compared to those in CK soil, while there was a significant decrease in pH, total nitrogen, total phosphorus, available phosphorus, and silt. The fungal community diversity in shiro was diminished, and T. bakamatsutake altered the community structure of its shiro by suppressing other fungi, such as Russula (ectomycorrhizal fungus) and Penicillium (phytopathogenic fungus). The bacterial community diversity in shiro increased, with the aggregation of mycorrhizal-helper bacteria, such as Paenibacillus and Bacillus, and plant growth-promoting bacteria, such as Solirubrobacter and Streptomyces, facilitated by T. bakamatsutake. Microbial functional predictions revealed a significant increase in pathways associated with sugar and fat catabolism within the fungal and bacterial communities of shiro. The relative genetic abundance of carboxylesterase and gibberellin 2-beta-dioxygenase in the fungal community was significantly increased, which suggested a potential symbiotic relationship between T. bakamatsutake and Q. mongolica. These findings elucidate the microbial community and relevant symbiotic environment to better understand the relationship between T. bakamatsutake and Q. mongolica.

Effects of Balancing Exchangeable Cations Ca, Mg, and K on the Growth of Tomato Seedlings (Solanum lycopersicum L.) Based on Increased Soil Cation Exchange Capacity

(1) Background: Previous research has demonstrated that the cation exchange capacity (CEC) of soil and the balance of exchangeable cations Ca, Mg, and K are key factors affecting plant growth and development. We hypothesized that balancing exchangeable cations based on increased CEC would improve plant growth and development. (2) Methods: This study conducted a two-phase experiment to evaluate methods for increasing soil CEC and the effects of increasing CEC and balancing Ca, Mg, and K on plant growth. Therefore, we first conducted a soil culture experiment using organic fertilizer, montmorillonite, and humic acid to investigate fertilizers that can effectively increase CEC in the short term. Then, a tomato seedling pot experiment was conducted using the control (CK) and OMHA fertilizer-treated soils collected from soil culture experiments. The CK and OMHA treatment soils were constructed with balanced exchangeable cations and an unbalanced control, respectively. (3) Results: The soil culture experiments revealed that the combination of organic fertilizer, montmorillonite, and humic acid (OMHA treatment) had the most significant effect on increasing CEC. The CEC of the OMHA treatment increased by 41.07%, reaching 27.10 cmol·kg−1. The tomato pot experiments demonstrated that balancing the exchangeable cations in OMHA soil improved the Mg and K nutrition of tomato seedlings and significantly increased SPAD, leaf nitrogen content, and dry weight, while balancing the exchangeable cations in CK soil improved only the K nutrition of tomato seedlings. (4) Conclusions: Overall, balancing exchangeable cations based on increasing CEC can improve soil nutrient availability and alleviate the competition effects of Ca, Mg, and K cations. Low CEC and imbalanced exchangeable cations can be detrimental to tomato seedling growth.

Inoculation of cadmium-tolerant bacteria to regulate microbial activity and key bacterial population in cadmium-contaminated soils during bioremediation

The perennial ryegrass Lolium perenne can be used in conjunction with cadmium (Cd)-tolerant bacteria such as Cdq4–2 (Enterococcus spp.) for bioremediation of Cd-contaminated soil. In this study, a theoretical basis was provided to increase the efficiency of L. perenne remediation of Cd-contaminated soil using microorganisms to maintain the stability of the soil microbiome. The experimental design involved three treatment groups: CK (soil without Cd addition) as the control, 20 mg·kg–1 Cd-contaminated soil, and 20 mg·kg–1 Cd-contaminated soil + Cdq4–2, all planted with L. perenne. The soil was collected on day 60 to determine the soil microbial activity and bacterial community structure and to analyze the correlation between soil variables, the bacterial community, available Cd content in the soil, Cd accumulation, and L. perenne growth. The soil microbial activity and bacterial community diversity decreased under Cd stress, and the soil microbial community composition was changed; while inoculation with Cdq4–2 significantly increased soil basal respiration and the activities of urease, invertase, and fluorescein diacetate (FDA) hydrolase by 83.65%, 79.72%, 19.88%, and 96.15% respectively; and the stability of the community structure was also enhanced. The Actinobacteriota biomass, the amount of available Cd, and the above- and belowground Cd content of L. perenne were significantly negatively correlated with the total phosphorus, total potassium, and pH. The activity of urease, invertase, and FDA hydrolase were significantly positively correlated with the biomasses of Acidobacteriota and L. perenne and significantly negatively correlated with the Chloroflexi biomass. Further, the available soil Cd content and the above- and belowground Cd levels of L. perenne were significantly positively correlated with the Actinobacteriota biomass and significantly negatively correlated with the Gemmatimonadetes biomass. Overall, inoculating Cd-tolerant bacteria improved the microbial activity, diversity, and abundance, and changed the microbial community composition, facilitating the remediation of Cd-contaminated soil by L. perenne.

Bacterial response to the combined pollution of benzo[a]pyrene and decabromodiphenyl ether in soil under flooding anaerobic condition

This study investigated the interaction between the co-pollutants of Benzo[a]pyrene (BaP) and decabromodiphenyl ether (BDE-209) and the bacterial community in soil under flooding anaerobic condition. Three levels of combined pollution (at nominal concentrations of 1, 5, and 25 mg/kg, respectively, for each pollutant), their corresponding sterilized controls, and a blank control (CK) were set up. During the incubation time of 270 days, BaP attenuated more easily than BDE-209. The second-order rate constant of BaP attenuation was negatively correlated with the Ln value of initial BaP concentration. Maximal difference in bacterial community occurred between the CK soil and the highly polluted soil. Desulfomonilaceae, Parcubacteria and Rhodanobacter were probably involved in BaP and BDE-209 degradation, while Nitrosomonadaceae, Phenylobacterium and Mitochondria were significantly suppressed by BaP and BDE-209 or their degrading products. Genes narI, bcrC, fadJ, had, dmpC, narG and CfrA were involved in the degradation of BaP and BDE-209. Impacts of BaP and BDE-209 on metabolisms of carbon, nitrogen and sulfur were not significant. The results provide guidance for the management and remediation of the contaminated soil.

Long-term effects of biochar on soil chemistry, biochemistry, and microbiota: Results from a 10-year field vineyard experiment

Application of biochar to soil has been recommended as a carbon sequestration approach that can also improve soil physical and chemical properties. The addition of biochar to soil can change the physicochemical properties of the soil, leading to a subsequent modification of the microbial community. However, the long-term implications of these changes remain insufficiently elucidated. Here, we examined soil chemical and biochemical properties of the bulk soil and employed next-generation sequencing techniques to analyze the microbiological properties of both bulk and rhizosphere soils after 10 years of biochar application. Specifically, we compared these properties between soil treated with two doses of biochar, i.e., SB and DB, and untreated soil, i.e., CK. After 10 years, biochar application increased the soil organic carbon from 12.7 g.kg−1 in CK to 17.3 and 23.1 g.kg−1, in SB and DB, respectively. Moreover, biochar application led to a slight decrease in soil bulk density, and increased the soil pH value 6.33 in CK to 7.07 in DB. Moreover, our findings revealed a distinct taxonomic signature within bacteria; however, this signature was not observed in terms of diversity. Specifically, we observed an increase in the abundance of oligotrophic bacteria compared to copiotrophic bacteria. The double dose of biochar increased the fungal species richness in the rhizosphere, particularly of Basidiomycota yeasts, from a relative abundance of 9.4 % in the CK soil to 17.0 % in the SB soil and 24.8 % in the DB soil and reduced putative plant pathogens like Phaeoacremonium and Aspergillus. Biochar amendment can significantly improve soil physical, chemical, and biological fertility on the long-term even under intensive viticulture management, with no detectable detrimental effects on microbial diversity and soil functions, and potential of soil organic carbon storage.

Flooding drives the temporal turnover of antibiotic resistance gene in manure-amended soil–water continuum

Rice paddy soil is a hotspot of antibiotic resistance genes (ARGs) due to the application of organic fertilizers. However, the temporal dynamics of ARGs in rice paddy soil and its flooded water during the growing season remain underexplored. In this study, a microcosm experiment was conducted to explore the ARG profiles in a long term (130 days) flooded two-phase manure-amended soil–water system. By using high-throughput quantitative PCR array, a total of 23–98 and 34–85 ARGs were detected in the soil and overlying water, respectively. Regression analysis exhibited significant negative correlations between ARG profile similarities and flooding duration, indicating that flooding significantly altered the resistome (P < 0.001). This finding was validated by the increased ARG abundance in the soil and the overlying water, for example, after 130 days flooding, the abundance of ARGs in CK soil was increased from 0.03 to 1.20 copies per 16S rRNA. The PCoA analysis further suggested pig manure application resulted in distinct ARG profiles in the soil–water continuum compared with those of the non-amended control (Adonis, P < 0.05). The Venn diagram showed that all ARGs detected in the pig manure were present in the treated soil. Twelve ARGs (e.g., sul1) were shared among the pig manure, manure-amended soil, and overlying water, indicating that certain manure- or soil-borne ARGs were readily dispersed from the soil to the overlying water. Moreover, the enhanced relationships between the ARGs and mobile genetic elements in pig manure applied soil–water continuum indicate that the application of organic matter could accelerate the emergence and dissemination of ARGs. These findings suggested that flooding represents a crucial pathway for dispersal of ARGs from the soil to the overlying water. Identification of highly mobile ARGs in the soil–water continuum is essential for assessing their potential risk to human health and promoting the development of sustainable agricultural practices to mitigate their spread.

Simultaneous and long-term effective immobilization of lead, cadmium and arsenic in multi-contaminated soil by ferrihydrite-supported animal-derived biochar

The multi-contaminants of cationic Pb/Cd and anionic As in soils is difficult to simultaneously immobilize by common chemical amendments. Here, a novel ferrihydrite-supported animal-derived biochar (FAB) was prepared and added to pristine Pb/Cd/As-contaminated soil for incubation of 150 days. The amendment using FAB elevated soil pH and reduced soil electric conductivity and the release of soil dissolved organic carbon. After the addition of 3 %w/w FAB (FAB3 %), the bioavailability of Pb, Cd, and As decreased to 9.2, 57.5, and 7.6 mg/kg, respectively, which were 96 %, 47 %, and 36 % lower than that of the control soil (CK). The exchangeable Pb and Cd and specifically sorbed As were transformed into residual Pb, carbonate- and Fe-Mn oxide-bound Cd, and well-crystallized Fe-Al oxide-bound As, respectively. The diversity of soil bacterial community increased after FAB treatment. Dynamic leaching and first-order attenuation simulation experiments showed that FAB3 % can decrease the leachable heavy metal(loid)s to negligible concentration in real soil within 3–7 years, whereas that in CK soil was around 12 years. X-Ray adsorption near edge structure analysis showed that FAB immobilized heavy metal(loid)s in soil by forming pyromorphite coprecipitate with Pb(II), ion exchange between Cd(II) and Ca(II) in the hydroxyapatite component, and complexation between the ferrihydrite component and As(V).

Leaf Litter Breakdown and Soil Microbes in Catalpa bungei Plantations in Response to Various Fertilization Regimes

Litter decomposition propels the geochemical cycle by returning nutrients to soil. Soil microbial communities play an important role during litter breakdown wherein various fertilization regimes are conducted. In this study, we carried out a five-year fertilization experiment in a young Catalpa bungei plantation in northern China. The fertilization strategies employed mainly included the integration of water and fertilizer (WF), hole fertilization (HF), and no fertilization (CK) as a control. We tracked the decomposition dynamics of leaf litter and identified the major microbial communities involved in litter breakdown for each fertilization regime. The results showed that fertilization increased the biomass and C content of leaf litter, and the C storage in the HF forest was higher than that in the WF forest. Fertilization significantly decreased leaf litter decomposition and nutrient release and prolonged the duration of breakdown. The breakdown of litter in the WF stand was slower than that in the HF stand, but the diversities of bacteria and fungi were higher in the WF soil. The community structures of bacteria and fungi in the WF soil showed obvious differences compared to those in the CK and HF soils. Fertilization strengthened competitive relationships but decreased cooperative interaction among microbes. The abundances of saprophytic fungi and decomposing bacteria in the WF soil were lower than those in the HF soil. The key flora, including Arthrobacter and Neocosmospora, regulated litter breakdown in the HF and WF forests. In addition, Arthrobacter, Filobasidium, and Coprinopsis were mainly involved in the decomposition process in the nonfertilized forests. Thus, studying the biomass and initial quality of litter treated with different fertilization measures and exploring the characteristics of nutrient release during litter decomposition are both of significant value with regard to deepening understanding of the effects of different fertilization methods on litter breakdown and their associated response mechanisms.

The Presence of the Biochar Interlayer Effectively Inhibits Soil Water Evaporation and Salt Migration to the Soil Surface

To reveal the mechanisms of water conservation and soil salinity control in the biochar interlayer, the effects of biochar addition as an interlayer on soil water infiltration, evaporation, and salt transport were studied. Through the indoor soil-column simulation test, soil columns were set up by packing homogeneous soil (CK) and biochar spacers into columns at different burial depths of 10, 20, and 30 cm. The biochar interlayer decreased the infiltration capacity of the soil, with the average infiltration rate decreasing from 0.72 cm·h−1 to the ranges of 0.39–0.48 cm·h−1 in the CK soil column, and salt leaching efficiency was improved. The salt content in the bottom layer of soil in the CK column was reduced to within the range of 19.96–47.46% compared with that in the barrier soil column. The presence of the biochar interlayer improved the distribution of soil water and salt. The soil water content in the upper layer above the interlayer was around 7.79–13.68% higher than that in CK, whereas the average salt content was 6.44–60.40% lower than that in CK. The biochar interlayer inhibited soil water evaporation, and cumulative evaporation in this layer decreased by 32.34–42.10% compared with that in CK. The salt accumulation in the interlayer in the soil column decreased within the range of 16.36–51.36% compared with that in the CK soil column. The biochar interlayer could not only retain water for a long time, but also adsorb the salt leached from the upper layer, and thus, inhibit the reverse salt flux from the lower layer. The creation of the biochar interlayer of 30 cm could play a role in soil salinity control and water conservation, and can also provide a basis and reference for the improvement of saline-alkali farmland in arid and semi-arid areas.

Two recyclable and complementary adsorbents of coal-based and bio-based humic acids: High efficient adsorption and immobilization remediation for Pb(II) contaminated water and soil

Humic acid can effectively bind heavy metals and is a promising remediation agent for heavy metals-contaminated water and soil. Many successful applications of humic acid have been reported, but rarely studied the specific process and mechanism of heavy metal removal by humic acids from water and soil, especially the simultaneous application of coal-based and bio-based humic acids. In this work, two kinds of coal-based and bio-based humic acid materials (CHA and BHA) from weathered coal and rice husk were industrially produced and studied their Pb(II) adsorption and immobilization characteristics and mechanisms in water and soil. The batch adsorption experiments obtained the Pb(II) adsorption by CHA and BHA both were spontaneous and endothermic monolayer chemisorption and controlled by three rate-limiting steps (bulk, film, and pore) in the adsorption process. CHA and BHA had highly efficient Pb(II) adsorption capacities, obtained their maximum adsorption capacity was 201 and 188 mg g−1, respectively. In addition to the two main adsorption mechanisms of ion exchange and surface complexation, electrostatic interaction, precipitation reaction, and π-π interaction were also involved. Soil culture experiments showed that CHA and BHA both exhibited a highly efficient immobilization effect on Pb(II)-contaminated soil, and CHA and BHA had a better synergistic promotion effect. Compared with the CK soil, the content of DTPA-Pb(II) decreased by 10.2–13.2% and the content of RES-Pb(II) increased by 14–22% in soils treated with different humic acids. Ion exchange, complexation, precipitation, and electrostatic attraction promote the transformation of unstable Pb(II) to stable Pb(II), which was of great significance for the immobilization of Pb(II) in soil. Overall, CHA and BHA have the potential to be used as green, efficient, and promising adsorbents to remove and immobilize Pb(II) from wastewater and soil.

Soil nutrient cycling and bacterial community structure in response to various green manures in a successive Eucalyptus (Eucalyptus urophylla × Eucalyptus grandis) plantation

AbstractSuccessive cultivation of short‐rotation eucalyptus plantations often cause serious decline in soil quality in China, which limits sustainable production. Green manure application is a potential strategy for improving soil fertility while ensuring ecological sustainability. Nevertheless, the impacts of various green manure species on soil quality in eucalyptus plantations remain unclear. In the present study, we investigated how soil nutrient cycling and bacterial communities respond to various green manure species (Legume and Gramineae), namely Tephrosia candida, Sesbania cannabina, Lolium perenne, and Pennisetum purpureum (PP). A batch experiment was conducted using eucalyptus plantation (E. urophylla × E. grandis) soil mixed with green manures for 60 days. According to the results, the PP treatment had the highest soil respiration rate among the five treatments, suggesting that PP application had the optimal effects on soil organic matter and residue decomposition. Furthermore, applying green manure increased bacterial diversity significantly when compared to CK (soil without green manure). Among the treatments, the PP treatment increased bacterial functional groups associated with the nitrogen cycle significantly, which result in rapid nutrient turnover. The rapid decomposition under PP may be responsible for the structural and functional changes in bacterial communities. Overall, the PP green manure is the optimal amendment for rapid nutrient supply in degraded eucalyptus plantations over the short term. Our results could facilitate sustainable management of successive eucalyptus plantations; nevertheless, extra investigations are needed to verify the long‐term impacts of PP green manure in the field.

The relationship between soil aggregate-associated potassium and soil organic carbon with glucose addition in an Acrisol following long-term fertilization

Subtropical Acrisols have low soil organic carbon (SOC) and potassium (K) availability. However, the relationship between K distribution of aggregates and SOC levels is unclear. Five soil samples were collected from a long-term fertilization experiment in an Acrisol. Different K fertilization treatments included CK (without any fertilizer), ZK (zero rate of chemical K fertilizer), KF (conventional rate of chemical K fertilizer added to ZK treatment), KM (KF treatment including the application of fresh pig manure, and KS (KF treatment with half of crop straw returned to the field). Then, an incubation experiment was conducted in which different rates of glucose were added to attain 5 increased levels in SOC with 0, 10%, 20%, 50%, and 100% in the CK, ZK, KF, KM, and KS treatments. Compared with no glucose addition, glucose addition improved these > 2 mm aggregates by 9.16%− 104.19% among all soils. With increased SOC percentage, the > 2 mm aggregate increased. A non-linear equation indicated that there were significant correlations between > 2 mm aggregates and SOC content in KF, KM, and KS soils. The exchangeable K (EK) and non-exchangeable K (NEK) contents of > 2 mm aggregates were highest in KM soil, followed by KS and KF soils, while CK and ZK soils were the lowest. The linear equations indicated that the EK and NEK stock of > 2 mm aggregates could be increased by 8.41–9.10 kg ha−1 and 15.73–20.65 kg ha-, respectively, in all K fertilized soils, when SOC was increased by 1 g kg−1. The slopes of linear equations also showed that the growth rate for NEK stock of > 2 mm aggregates in KM soil (20.65 kg ha−1) was higher than those of KS and KF soils (15.73 and 17.59 kg ha−1). Additionally, the slopes of linear equations indicated that the growth rate for proportions of EK and NEK stock of > 2 mm aggregates in KM soil (1.14% and 1.64%) were lower than those in KS soil (2.22% and 2.28%). Combined with CK, ZK, KF, KM, and KS soils, the proportion of EK and NEK stock of > 2 mm aggregates increased by 1.62% and 2.32% along with increased SOC by 1 g kg−1. Therefore, the EK and NEK stock of > 2 mm aggregates increased through glucose addition in the Acrisol. However, these increases varied by fertilization treatments, which caused different SOC and K levels.

Varying microbial utilization of straw-derived carbon with different long-term fertilization regimes explored by DNA stable-isotope probing

The decomposition processes of crop residues, which represent the largest organic carbon input in agricultural ecosystems, are determined by soil microbes. However, the impact of different long-term fertilization practices on residue decomposition has not been clearly established. In this study, a microcosm experiment using 13C-labeled maize residues and high-throughput sequencing was performed to investigate bacterial and fungal microbes utilizing straw-derived carbon in soils under separate regimes of long-term fertilization (CK: no fertilizer; NPK: mineral fertilizers; NPKS: mineral fertilizers plus straw). During the 60-day incubation period, a total of 524 bacterial OTUs and 72 fungal OTUs, which utilized straw-derived carbon, were identified and were found to be primarily distributed in the bacterial phyla of Proteobacteria, Actinobacteria and Bacteroidetes, and the fungal class of Sordariomycetes within Ascomycota. The three fertilized soils exhibited distinct straw-utilizing microbial communities along the decomposition process, in which key bacterial taxa (Flavobacterium, Nocardioides, Pseudomonas, Pseudoxanthomonas, Agromyces and Herpetosiphon) and key fungal taxa (Pleosporaceae, Lasiosphaeriaceae and Chaetomiaceae) exhibited significantly positive relationships with extracellular enzymes activities, thereby accelerating the straw decomposition process. Furthermore, due to higher nutrient availability, microbes can rapidly respond to straw addition, therefore, more bacteria and fungi, which are referred to as rapid responders, were identified in NPK and NPKS soils, relative to CK soils. Hierarchical and variation Partitioning (HP) analysis revealed a strong potential impact of multiple edaphic factors in shaping the microbial community to utilize the straw-derived carbon. N resources (NO3−-N and TN) and β-glucosidase were found to be significantly positively correlated with microbial utilizers’ community. In conclusion, our findings elucidate the processes of establishment of microbial community and straw decomposition, as well as the association between microbial communities and edaphic factors under different long-term fertilization regimes.

Maize (Zea mays L.) Seedlings Rhizosphere Microbial Community as Responded to Acidic Biochar Amendment Under Saline Conditions

Biochar has extensively been used for multiple purposes in agriculture, including improving soil microbial biomass. The current study aimed to investigate the effect of acidic biochar on maize seedlings’ rhizosphere bacterial abundance under salinity. There were seven treatments and three replicates in a controlled greenhouse coded as B0S1, B1S1, and B2S1 and B0S2, B1S2, and B2S2. CK is control (free of biochar and salt); B0, B1, and B2 are 0, 15, and 30 g biochar (kg soil)–1; and S1 and S2 are 2.5 and 5 g salt pot–1 that were amended, respectively. After harvesting the maize seedlings, the soil samples were collected and analyzed for soil microbial biomass, bacterial abundance, and diversity. The results revealed that relative abundance of Proteobacteria, Actinobacteria, and Chloroflexi increased on phylum level, whereas Actinomarinales, Alphaproteobacteria, and Streptomyces enhanced on genus level, respectively, in B2S1 and B2S2, when compared with CK and non-biochar amended soil under saline conditions. The relative abundance of Actinomarinales was positively correlated with total potassium (TK) and Gematimonadetes negatively correlated with total phosphorus (TP). Biochar addition slightly altered the Ace1, Chao1, and alpha diversity. Principal component analysis corresponded to the changes in soil bacterial community that were closely associated with biochar when compared with CK and salt-treated soils. In conclusion, acidic biochar showed an improved soil microbial community under salinity.

Variation of Microbial Community in Healthy and Disease-Susceptible Tobacco Soils

Soil microbes are vital for the development of plant growth. Little is known about how the discrepancy of microbes mediate the microbial community structure of healthy (CK) and disease-susceptible soils with black root rot (BR, Thielaviopsisbasicola) and root-knot nematode (RK, Meloidogyne incognita; M. javanica) of flue-cured tobacco (Nicotianatabacum L.). In this study, we analyzed the soil and microbial properties, and showed the differences of soil microbial composition and diversity between soils. Specially, soil was more acid with lower diversity, higher nutrient content with higher abundance of Proteobacteria, Ascomycota, Basidiomycota in the disease-susceptible soils. While, compared with disease-susceptible soils, the protease and urease activities, as well as soil pH, available potassium content, and the relative abundance of beneficial bacterial and fungal genera (including Bacillus, Micromonospora, Lysobacter, Microvirga, Chaetomium and Arthrobotrys) were higher in CK soils. The variations of soil physiochemical factors and enzyme activities resulted in differences in microbial community structure and composition between healthy and disease-infected flue-cured tobacco soils. Our results bring novel insights to control the disease-susceptible of flue-cured tobacco fields through management of rhizosphere community struture.

Quantifying influence of tillage practices on soil aggregate microstructure using synchrotron‐based micro‐computed tomography

AbstractStudying the internal structure of soil aggregates is an insightful way to improve the understanding of soil aggregation process. However, it is still not clear how the macroaggregate pore structure is influenced by the application of long‐term tillage practices. In this study, we aimed to determine the differences in macroaggregate pore structure among long‐term tillage practices using micro‐computed tomography (SR‐μCT). Soil samples were collected from no tillage (NT) and ridge tillage (RT) plots and surrounding fields under conventional tillage (CT) and uncultivated soils (CK). The results showed that the diameters of most pores were greater than 30 μm, but &gt;100 μm pores had the greatest percentage of total macroaggregate porosities in all four soils, that is NT, RT, CT and CK. The CK soil had a higher aggregate porosity of &lt;30 μm and 30–60 μm, as well as a lower porosity of &gt;100 μm than the NT, RT and CT soils. Total porosities within soil macroaggregates in both CK and CT were significantly lower than those in RT and NT, but the porosities of 30–60 μm and 60–100 μm within soil macroaggregates in both CK and RT were no significance. There were no significant differences in pore parameters between CK and RT. The CK and RT had higher mean weight diameter (MWD) and aggregate‐associated SOC contents than CT. Therefore, the pore structure of RT was similar to CK with good soil structure. Overall, RT was more appropriate tillage system to protect soil aggregate structure in black soils of Northeast China.

Long-Term Fertilization Shapes the Putative Electrotrophic Microbial Community in Paddy Soils Revealed by Microbial Electrosynthesis Systems.

Electrotrophs play an important role in biogeochemical cycles, but the effects of long-term fertilization on electrotrophic communities in paddy soils remain unclear. Here, we explored the responses of electrotrophic communities in paddy soil-based microcosms to different long-term fertilization practices using microbial electrosynthesis systems (MESs), high-throughput quantitative PCR, and 16s rRNA gene-based Illumina sequencing techniques. Compared to the case in the unfertilized soil (CK), applications of only manure (M); only chemical nitrogen, phosphorous, and potassium fertilizers (NPK); and M plus NPK (MNPK) clearly changed the electrotrophic bacterial community structure. The Streptomyces genus of the Actinobacteria phylum was the dominant electrotroph in the CK, M, and MNPK soils. The latter two soils also favored Truepera of Deinococcus-Thermus or Arenimonas and Thioalkalispira of Proteobacteria. Furthermore, Pseudomonas of Proteobacteria and Bacillus of Firmicutes were major electrotrophs in the NPK soil. These electrotrophs consumed biocathodic currents coupled with nitrate reduction and recovered 18-38% of electrons via dissimilatory nitrate reduction to ammonium (DNRA). The increased abundances of the nrfA gene for DNRA induced by electrical potential further supported that the electrotrophs enhanced DNRA for all soils. These expand our knowledge about the diversity of electrotrophs and their roles in N cycle in paddy soils and highlight the importance of fertilization in shaping electrotrophic communities.