Soil Incubation Research Articles

Biochar-derived persistent free radicals and reactive oxygen species reduce the potential of biochar to mitigate soil N2O emissions by inhibiting nosZ

Biochar amendment has been proven to generally reduce soil nitrous oxide (N2O) emissions. However, the effects and underlying mechanisms of biochar-derived reactive oxygen species (ROS) on soil N2O emissions are still unclear. Thus, we firstly weakened the intensities of persistent free radicals (PFRs) within biochar using triethanolamine (TEA) as a quencher, and then used soil incubation methods to compare the potentials of TEA-quenched and un-quenched biochar in mitigating soil N2O emissions. The TEA-quenched biochar generated less hydrogen peroxide (H2O2) and hydroxyl radical (•OH), while having a higher soil N2O emission mitigation potential, than the un-quenched biochar. The N2O emissions and the N2O/(N2O + N2) ratio were significantly, positively, correlated with the generated H2O2 and •OH contents. These results demonstrated that biochar-derived ROS weakened biochar's mitigation of soil N2O emissions. The specific mechanisms of biochar-derived ROS on soil N2O emissions were further explored by a ROS scavenging experiment. It was found that scavenging H2O2 by catalase efficiently hindered the generation of •OH, resulting in decreases in N2O emissions and the N2O/(N2O + N2) ratio. Meanwhile, biochar-derived ROS exhibited a more severe inhibition on N2O reductase gene (nosZ) expression than that on the expression of genes responsible for N2O production (nirK and nirS), indicating that biochar-derived ROS weakened biochar's mitigation of soil N2O emissions by inhibiting microbial N2O reduction. Our results imply that controlling the content of biochar-derived ROS is a promising strategy to maximize biochar's potential for mitigating soil N2O emission.

Bacterial coculture enhanced Cd sorption and As bioreduction in co-contaminated systems.

The bacterial interactions that regulate Cd sorption and As bioreduction in co-contaminated systems are poorly understood. We isolated two bacterial strains, i.e., Pseudomonas aeruginosa and Bacillus licheniformis from a Cd and As co-contaminated soil and compared the effects of monoculture and coculture on microbial Cd sorption and As bioreduction efficiency in the media with different Cd (0, 0.5, 5, 10, 50, 100mg/L) and As(Ⅴ) (0, 90mg/L) concentrations. Compared with monoculture, the bacterial coculture increased the Cd sorption efficiency by up to 32% and the As bioreduction (As(Ⅴ) to As(Ⅲ)) efficiency by up to 28%, associated with the increased abundance of As reduction gene arsB. Based on SEM-TEM and metabolomics, the enhanced efficiency was attributed to bacterial interactions, supported by the differential secretion of extracellular polymeric substances. Notably, the differential lipids and lipid-like molecules, and organoheterocyclic compounds resulted from bacterial interactions compared to monoculture exhibited the highest Cd sorption and As bioreduction. The increased efficiencies by bacterial coculture were verified by soil incubation experiments. These results provide insight on applying specific bacterial coculture and their metabolites to enhance Cd sorption and As bioreduction in effective and sustainable remediation of co-contaminated environments.

Predicting the Stability of Organic Matter Originating from Different Waste Treatment Procedures.

Recycling organic wastes into farmland faces a double challenge: increasing the carbon storage of soil while mitigating CO2 emission from soil. Predicting the stability of organic matter (OM) in wastes and treatment products can be helpful in dealing with this contradiction. This work proposed a modeling approach integrating an OM characterization protocol into partial least squares (PLS) regression. A total of 31 organic wastes, and their products issued from anaerobic digestion, composting, and digestion-composting treatment were characterized using sequential extraction and three-dimension (3D) fluorescence spectroscopy. The apportionment of carbon in different fractions and fluorescence spectra revealed that the OM became less accessible and biodegradable after treatments, especially the composting. This was proven by the decrease in CO2 emission from soil incubation. The PLS model successfully predicted the stability of solid digestate, compost, and compost of solid digestate in the soil by using only the characterized variables of non-treated wastes. The results suggested that it would be possible to predict the stability of OM from organic wastes after different treatment procedures. It is helpful to choose the most suitable and economic treatment procedure to stabilize labile organic carbon in wastes and hence minimize CO2 emission after the application of treatment products to the soil.

Tracing low-CO2 fluxes in soil incubation and 13C labeling experiments: a simple gas sampling system for respiration and photosynthesis measurements

Tracing low-CO2 fluxes in soil incubation and 13C labeling experiments: a simple gas sampling system for respiration and photosynthesis measurements

Endophytic Bacteria in Ricinus communis L.: Diversity of Bacterial Community, Plant−Growth Promoting Traits of the Isolates and Its Effect on Cu and Cd Speciation in Soil

Ricinus communis L. shows certain tolerance to and good accumulation ability with heavy metals. Endophytic bacteria−enhanced phytoremediation is an effective method to improve heavy metal extraction efficiency. Here, for better application of castor in phytoremediation, the Illumina high−throughput sequencing was carried out to reveal the endophytic bacterial community in the tissues of castor grown in two locations, and traditional microbial cultivation was used to isolate endophytic bacteria from castor. The dominant bacterial phyla were Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes and Acidobacteria, and Proteobacteria was absolutely dominate in all castor tissues. There were significant differences in the composition of endophytic bacterial communities between castor grown in two sites, with obvious variation in the relative abundance of the dominant phylum. The samples from two sites also had their own unique dominant bacterial genera. The analysis of alpha diversity illustrated that the diversity and species richness of endophytic bacteria community in different parts of castor sampled in Tonglushan mining area were lower than those in Gangxia village, Yangxin county. In total, there were 44 endophytic bacteria strains isolated from the tissues of castor, of which 42 strains possessed three or more growth−promoting properties. Most of these isolates were tolerant to Cu or Cd to varying degrees. Eight isolates were selected for further Cu mobilization and soil incubation experiments. Strains TR8, TR18, TR21, YL1, YS3 and YS5 could well solubilize Cu2(OH)2CO3 in medium. Strain YS3 had the best effect on increasing soil DTPA−Cu and DTPA−Cd contents by 8.4% and 6.9%, respectively. Inoculated endophytic isolates were conducive to the conversion of heavy metal forms from insoluble to relatively unstable, and could increase available phosphate content in soil (10.8–29.2%). Therefore, the plant growth−promoting endophytes screened from castor have great application prospects and can provide important support for the microbial−assisted phytoremediation of heavy metal−contaminated soil.

Influence of temperature change on the immobilization of soil Pb and Zn by hydrochar: Roles of soil microbial modulation

Considering the potential effect of the ambient temperature on soil microorganisms during heavy metal immobilization by hydrochar, 60 days of soil incubation was conducted to explore the impact of ambient temperature (5, 25, and 35 °C) on the immobilization of Pb and Zn by chitosan-magnetic sawdust hydrochar (CMSH) and magnetic chitosan hydrochar (MCH). The results showed that soil pH was relatively high and total organic carbon (TOC) was slightly lower in the 35 °C treatment. The diethylenetriaminepentaacetic acid (DTPA) available state content decreased significantly with the temperature increasing. Meanwhile, the ratios of stable Pb and Zn in the sequential extraction method proposed by the European Community Bureau of Reference (BCR) gradually increased with increasing temperature. The heatmap based on microbial community showed that elevated temperature not only favored the enrichment of metal-stable phyla, such as Chloroflexi, but was also involved in inhibiting the growth of Firmicutes, Actinobacteriota, and Proteobacteria. Meanwhile, different genera (Fonticella and Bacillus) in the Firmicutes phylum had distinct responses to temperature as well as to heavy metal immobilization effects. Subsequently, redundancy analysis confirmed that Chloroflexi and Fonticella were positively correlated with temperature and stable state metal content, while Actinobacteriota and Bacillus were negatively correlated with temperature and were positively correlated with DTPA available metal content. Moreover, Pb and Zn indicators displayed significant correlations for the dominant genera (R2 > 0.8, p < 0.02).

Phosphate-solubilizing microorganisms regulate the release and transformation of phosphorus in biochar-based slow-release fertilizer

Coupling phosphate-solubilizing microorganisms (PSM) can improve the availability of phosphorous (P) in biochar-based slow-release P fertilizers (BPF). However, the mechanism in release and transformation of P in BPF regulated by PSM is still unclear. Herein, the biocompatibility and the adhesion behaviors of BPF and PSM (Enterobacter hormaechei Rs-198) in soil were firstly studied, and a 90 days' laboratory-scale soil incubation experiment of BPF and Rs-198 was performed to study the transformation of P of BPF. The results show that BPF has a good biocompatibility for Rs-198 due to its low aromaticity, graphitization and free radicals' content (0.084 mg/g). Rs-198 are adhered to the surface of BPF in soil due to the high negative secondary energy minimum and low total interaction energy between Rs-198 and BPF. Available P in the incubation of BPF and Rs-198 (BR treatment) is significantly higher than that of the incubation of BPF (BF treatment) at initial 60 days. However, the content of available P in BR treatment is much lower compared with that in BF treatment on day 90, which is attributed to the entrapment of released P from BPF by Rs-198 and the formation of polyphosphate (polyP) rather than bound with soil mineral. Overall, this study presents new insights into the transformation of P in BPF regulated by PSM.

Synthesis and performance evaluation of slow-release fertilizers produced from inverse vulcanized copolymers obtained from industrial waste.

To improve crop nutrient uptake efficacy (NUE) and better manage fertilization, slow-release fertilizers (SRFs) are developed by either coating the urea granules or making a composite. Several materials have already been developed, nevertheless, scalability of those materials is still a challenge due to their inherit drawbacks (such as hydrophilicity, crystallinity, non-biodegradability, etc.). Herein, we utilized a biodegradable, green and sustainable copolymer produced from industrial waste (sulfur-petroleum industry waste and myrcene-citrus industry waste) to coat the urea using a facile coating method to develop novel SRFs and achieve better agronomic and environmental advantages. The copolymer was first synthesized using a facile, solvent-free one-pot method called inverse vulcanization followed by Fourier transform infrared spectroscopy (FTIR) analysis to confirm the successful reaction between myrcene and sulfur subsequently coating the copolymer on urea granule. The morphology and coating thickness of coated fertilizers were analysed using scanning electron microscopy (SEM), followed by a nitrogen release test in distilled water and a soil burial test to confirm the biodegradability. The nitrogen release test revealed that the SRF with the maximum coating thickness of 1733 μm releases only 16% of its total nitrogen after 4 days of incubation compared to the pristine urea which releases all its nutrient within 1 day. The soil burial test confirms the biodegradability of the copolymer, as after 50 days of incubation in soil the copolymer loses almost 18.25% of its total weight indicating that the copolymer is degrading.

Long‐term collar deployment leads to bias in soil respiration measurements

Abstract Accurate measurements of soil respiration (Rs) are critical for understanding how soil carbon will respond to environmental changes. However, a commonly used method for Rs measurements, the collar deployment method, may introduce artefacts that cause bias in Rs measurements. Our objective was to quantify the effect of long‐term collar deployment on Rs and to unravel potential causes due to changes in the soil environment. A field experiment (2017–2019) including short‐term (2–3 days before the measurement) and long‐term collar deployment (lasting three consecutive growing seasons) was conducted to assess the methodological effect on Rs in an alpine grassland of the northeastern Tibetan Plateau. Soil incubation was used to further explore the mechanisms underlying the effects of collar deployment. The effect of long‐term collar deployment on Rs varied over time. In the first one and a half growing seasons, no significant difference in Rs was noted under short‐ and long‐term collar deployment. This may be attributed to the negative effects of lower root biomass inside long‐term collars and the positive effects of higher temperature and pulse input of dead roots following collar deployment. Under the long‐term collar, Rs decreased rapidly in the middle of the second growing season and remained low until the end of the experiment, resulting in an 18.2% decrease relative to short‐term collar deployment in the third growing season. Higher soil bulk density and lower root and microbial biomass inside long‐term collars may explain the decrease in Rs and temperature sensitivity (Q10). Soil incubation experiments revealed that the soil organic carbon (SOC) decomposition rate and Q10 were significantly reduced after long‐term collar deployment. Long‐term collars led to substantial underestimates of Rs after more than 2 years. Our findings suggest that such potential artefacts should be considered when interpreting Rs data based on long‐term collar deployment. Long‐term collars should be relocated every 1–2 years to avoid artefacts if feasible. Alternatively, periodic measurements using short‐term collars are recommended to quantify the magnitude of collar artefacts.

Effects of organic composite fertilizer on soil nitrogen status and mineralization

A short-term soil incubation experiment was set up to obtain information to clarify the effect of our developed organic composite fertilizer on soil nitrogen mineralization. The composite was designed to have beneficial effects on the properties of chicken manure and to improve soil water management properties in addition to organic matter replenishment. In the incubation experiment, two different additives, bentonite, and super absorbent polymer, were used to enhance the properties of fermented chicken manure. Developed prototype products were tested in a four-week-long soil incubation experiment in two typical Hungarian soils: brown forest soil with a sandy texture and chernozem soil at two different water capacities (40 w/w % and 60 w/w %). Soil pH, and inorganic nitrogen forms, like nitrate and ammonium, were measured weekly. Furthermore, the potentially mineralized nitrogen and net mineralization rate were calculated. The applied composite was not affected the soil pH significantly in the examined period. The soil nitrate and ammonium ratio was changed during the incubation as the ammonium content in the soil decreased while nitrate content increased continuously throughout the experiment. This suggests that the incubation experiment successfully monitored the delicate balance of soil nitrogen forms. It was found that the chernozem soil type had a higher mineralization potential compared to brown forest soil due to its higher nutrient and organic matter contents. Moreover, our results pointed out that soil moisture content did not significantly affect the mineralization process. The amount of mineral nitrogen, generated per week can be described by a linear relationship for both soil types and water regimes. The composite product showed efficacy in promoting mineralization processes, particularly in soils with low nutrient status and mineralization potential.

PENGARUH KOMPOS DAUN KEMIRI SUNAN (Reutealis trisperma (Blanco) Airy Shaw) TERHADAP KESUBURAN ENTISOL

Leaves of Reutealis trisperma (locally known as kemiri Sunan) are potential sources of organic matter and improve soil fertility, especially by increasing soil nutrient availability. This study aimed to analyze the impact of the application of compost using kemiri Sunan leaves as raw material on soil fertility, such as pH, total N and soil organic C. This study used a completely randomized design with six treatments and four replications. The treatments were without compost (control), compost 4 t ha-1, compost 8 t ha-1, compost 12 t ha-1, compost 16 t ha-1 and compost 20 t ha-1. This study used a PVC pipe with a diameter of 14 cm and a height of 60 cm for the composting process and using polybags for the soil incubation process. The leaves were mixed with EM4, molasses, and water in a ratio of 1:1:50; after mixing, all the ingredients were put into a tube, and observations were made. The soil was then mixed with compost according to the treatment dose of compost 0; 4; 8; 12; 16; 20 t ha-1, then added water until it reached field capacity and then put into a polybag and incubated for 30 days. Observations were made at 0, 15, and 30 days after incubation. The results of this study showed that the application of waste compost of kemiri Sunan leaves had a significantly increased soil pH, total N, and organic C. The best application of kemiri Sunan leaf compost was found at a dose of 20 t ha-1 .

Cropping system drives microbial community response to simulated climate change and plant inputs

The soil microbiome’s role in regulating biogeochemical processing is critical to the cycling and storage of soil organic carbon (C). The function of the microbiome under different land management uses has become a focal area of research due to the interest in managing soil C to mitigate climate change. This study investigates the structural and functional response of soil microbiomes from annual monoculture (corn [<i>Zea mays</i> L.]) and perennial diversified (prairie) cropping systems, both under no-till management for bioenergy production. We used a full factorial soil incubation study to understand the influence of temperature and moisture on microbial C decomposition in these soils, with and without addition of cellulose as a model plant residue. Overall, perennial prairie soil supported distinct microbiomes with more diverse prokaryotic and fungal communities compared to annual corn soil. The less diverse corn microbiome was sensitive to the addition of C, resulting in significantly higher respiration compared to prairie, and this increased respiration was amplified under warmer temperatures. In contrast to C loss from the corn soil as carbon dioxide (CO₂), prairie soil had significantly higher extracellular enzyme activities and small increases in microbial biomass, illustrating cropping system-specific tradeoffs between microbial C allocation. Specific community structure shifts occurred with added cellulose, where fast-growing, motile decomposers became more abundant under wet conditions, while a small subset of fungi dominated under dry conditions. These differential responses of fungi and bacteria reflect microbial traits important for accessing substrates like plant residues. These changes in community structure due to moisture and cellulose amendment were not necessarily reflected in community function, as potential enzyme activities of most hydrolases were insensitive to temperature and C amendment on this short time scale. Lower respiration occurred in prairie compared to corn soil in response to increased available C and temperature, indicating a more resistant prairie microbiome that may be beneficial when confronted with climate change. These findings support deploying perennial and diversified systems in place of annual monocultures as bioenergy feedstocks, cover crops, buffer strips, or urban greenspaces as part of a land management strategy and highlight the importance of microbial activity in developing sustainable agroecosystems.

Effect of goethite-loaded montmorillonite on immobilization of metal(loid)s and the micro-ecological soil response in non-ferrous metal smelting areas

In this work, the immobilization stabilization and mechanism of heavy metal(loid)s by goethite loaded montmorillonite (GMt) were investigated, and the soil microbial response was explored. The simulated acid rain leaching experiment showed that GMt had a higher acid tolerance and the more stable heavy metal(loid)s fixation ability. The soil incubation demonstrated that GMt significantly decreased the available Cd, Zn, Pb and As concentration. Interestingly, higher immobilization of heavy metals was observed by GMt in highly acid leached and acidic soils. The richness and diversity of bacterial communities improved after the addition of GMt. GMt induced the enrichment of the excellent functional bacteria of the phylum Proteobacteria as well as the genus Massilia and Sphingomonas. The main immobilization mechanisms of heavy metal(loid)s by GMt include electrostatic interaction, complexation, precipitation and oxidation. The addition of the GMt also optimizes the soil bacterial community structure, which further facilitates the immobilization of heavy metal(loid)s. Our results confirm that the novel GMt has a promising application in the immobilization and stabilization of heavy metal(loid)s contaminated soils in non-ferrous metal smelting areas.

Variations in organic carbon mineralization of the biological soil crusts following revegetation in the Tengger Desert, North China

Revegetation is an effective measure to combat desertification worldwide, which parallelly facilitates the colonization and development of biological soil crusts (BSCs), and thereby affecting C cycles of BSCs in desert regions. However, knowledge about soil organic carbon (SOC) mineralization of BSCs and the involved mechanisms during long-term revegetation process in desert is rather limited. In this study, SOC mineralization rates of the mobile sand dune (MSD) and the BSCs in revegetated sites along chronosequence in the Tengger Desert were investigated, and the relationships between the SOC mineralization and the characteristics of vegetation and BSCs, soil properties and incubation temperature (T) and soil water content (SWC) were analyzed. The results showed that SOC mineralization rate of the BSCs and the corresponding subsoils was significantly greater than those of the MSD, and it increased considerably with increasing site age, regardless of the T, SWC, soil layer and sampling time (p < 0.001). The maximum instantaneous mineralization rates (MIR), cumulative CO2-C release (CCR) and the potentially mineralizable SOC (C0) of BSCs and subsoils were 1.29–12.63, 3.67–23.16 and 3.78–23.41 times, and 0.16–2.26, 0.12–1.84 and 0.17–1.26 times greater than those of the MSD, respectively; while the proportion of C0 to total SOC (C0/SOC) decreased by 31–88 % and 24–72 % in comparison with MSD, respectively. The mineralization rate increased with T and SWC, and the temperature sensitivity of BSCs increased with site age, indicating that the loss of SOC would be accelerated with the succession of BSCs upon the future global change. The variation magnitude of SOC mineralization was largely dependent on revegetation-induced changes in the properties of BSCs and the incubation T and SWC, and their interactions. The C:N, pH, and the activities of POD and PPO and DOC, and the coverage of moss-dominated crusts, SOC, C:N, the content of clay and silt and AYL activity were the main factors affecting SOC mineralization of BSCs and the subsoils, respectively. These results indicated that multiple factors that co-varied with the succession of BSCs led to variable SOC mineralization. Our findings suggested that planting xerophytic shrubs in desert drives the development and the SOC mineralization of BSCs, but decreased SOC loss due to mineralization, leading to SOC sequestration.

Methane and carbon dioxide emissions from the forest floor of a black spruce forest on permafrost in interior Alaska

High-latitude warming has stimulated CO2 and CH4 emissions from permafrost peatland. This study evaluated growing season CH4 and CO2 emissions from a forest floor of a lowland black spruce forest on permafrost in interior Alaska using automated-closed chambers, anaerobic incubation of peat soils and next-generation sequencing. The CH4 emissions from May to October were 723 ± 432 mg C m−2 and 829 ± 628 mg C m−2 from the two Carex wet plots, 124 ± 76 mg C m−2 from the Sphagnum moss plot, and 11 mg C m−2 from the lichen plot (± denotes standard deviation of different years). The CH4 emissions in the peak season showed diurnal variations with a single peak around noon or double peaks depending on the plots. The CH4 emissions were an order of magnitude lower than those for other northern wetlands, possibly because deep, cold peats regulated CH4 production and oxidation at the dry aerobic surface layer. Low water table positions strongly inhibited CH4 emissions in 2018, suggesting the importance of dissolved CH4 pool at the bottom of the active layer. The future trajectory of CH4 emissions could substantially change with water conditions, deep soil temperatures, and sedge compositions.

Evaluation of Alkaline Hydrolyzable Organic Nitrogen as an Index of Nitrogen Mineralization Potential of Some Coastal Savannah Soils of Ghana

Numerous biological and chemical methods have been proposed over the years for estimating the nitrogen (N) mineralization capacity of soils; however, none of them has found general use in soil fertility testing. The efficacy of a recently proposed alkaline hydrolysis method for assessing N availability in soils compared with the standard long-term incubation technique for determining potentially available N was evaluated. The nitrogen mineralization of 12 surface soils incubated under aerobic conditions at 25 °C for 26 weeks was determined. Field-moist soils were direct-steam distilled with 1 M KOH or 1 M NaOH; the NH3 released was trapped in boric acid, and its concentration was determined successively every 5 min for 40 min. The cumulative N mineralized or hydrolyzed was fitted to the first-order exponential equation to determine the potentially mineralizable N (No) and an analogous “potentially hydrolyzable N (Nmax)” for the soils. The flush of CO2 (fCO2) following the rewetting and incubation of air-dried soils under aerobic conditions for 3 days was also determined. The results showed that the Nmax values differed considerably among the soils, indicating differences in the chemical nature and reactivity of the organic N content of the soils, and were significantly correlated with No and fCO2 values. The estimated Nmax and No values ranged from 105 to 371 mg N kg−1 and 121 to 292 mg kg−1, respectively. Based on the simple and inexpensive nature of the alkaline hydrolysis procedure, the reduction in the incubation time required to obtain No (months to minutes), and the strong association between Nmax and No, we concluded that Nmax is a good predictor of the biologically discrete and quantifiable labile pool of mineralizable soil organic N (ON), and the use of the alkaline hydrolyzable ON as a predictor of No merits consideration for routine use in soil testing laboratories for estimating the N-supplying capacity of soils.

Enhancement of soil high-molecular-weight polycyclic aromatic hydrocarbon degradation by Fusarium sp. ZH-H2 using different carbon sources

High-molecular-weight PAHs (HMW-PAHs) in soil cannot be easily degraded. However, nutrient supplementation could stimulate the growth of exogenously added strains to enhance the degradation of HMW-PAHs in polluted soil. This study evaluated the applicability of Fusarium sp. ZH-H2, a polycyclic aromatic hydrocarbon (PAH)-degrading strain isolated by our research group, for the bioremediation of contaminated soil from the Hebei coal mining area in China. A soil incubation experiment was conducted to investigate the effect of two carbon sources and different carbon, nitrogen, and phosphorus (C:N:P) ratios on the remediation of high-molecular-weight PAHs (HMW-PAHs) in soil by Fusarium sp. ZH-H2, as well as the induction of lignin peroxidase activity. Our findings indicated that the HDF2 treatment (equal parts of humic acid and starch as carbon sources at a 50:1:0.5 C:N:P ratio) enhanced the removal rate of total HMW-PAHs from soil, reaching a maximum removal rate of 37.15 %. The removal rates of Pyr (a 4-ring PAH), BaP (a 5-ring PAH), and BghiP (a 6-ring PAH) were the highest in HDF2 treatment, and the removal rates were 39.51 %, 54.63 %, and 38.60 %, respectively. Compared with the ZH-H2 treatment, different carbon sources and C:N:P ratios significantly induced soil lignin peroxidase activity and the HDF2 treatment also resulted in the highest enzyme activity (up to 34.68 U/L). Furthermore, there was a significant or highly significant linear positive correlation between the removal rate of HMW-PAHs and enzyme activity in all cases. Our findings suggest that the optimal HMW-PAH degradation performance and enhancement of lignin peroxidase activity by ZH-H2 were achieved when both starch and humic acid were used as carbon sources at a C:N:P ratio of 50:1:0.5.

Potential of basalt dust to improve soil fertility and crop nutrition

The search for higher yields, lower production costs, and increased sustainability in agriculture implies optimizing crop nutritional management. In this sense, basalt dust has shown potential to improve soil fertility and crop nutrition. Thus, the goal was to evaluate the potential use of basalt dust in a controlled environment. First, an experiment was carried out on soils with contrasting textures (sandy and medium) under a random design, with four replications. These soils were incubated with basalt dust doses for 90 days, and later analyzed for chemical properties. Then, after soil incubation, four experiments were carried out in a pot system, where maize and bean plants were grown, with four replications. Plant shoots were evaluated for dry weight and macro- and micronutrient accumulations. The results of the incubation test showed that basalt dust increased available phosphorus, potassium, calcium, and magnesium levels in the soil about twenty, ten, fifteen, and thirteen times higher than those without the basalt dust, respectively. Maize and bean plants grown in soils enriched with basalt dust showed macro and micronutrient accumulations, up to five times higher than plants without the use of basalt dust. These results showed the usefulness of basalt dust in aiding nutritional management in agriculture. • The potential of basalt dust as sustainable fertilizer is showed. • Basalt dust can increase crop yields and improve soil health. • Ours results may favor the use of basalt dust in agriculture. • Significant potential for highly weathered soils in the tropics.

Evaluation of rice straw and its transformation products on norfloxacin degradation and antibiotic resistome attenuation during soil incorporation

Straw incorporation into reclaimed soils has been demonstrated to increase soil nutrients and has the potential to efficiently increase crop production. However, which incorporation mode is more helpful in the control of antibiotic resistance genes (ARGs) remains unknown. In this study, we systematically compared the occurrence of antibiotic resistome in norfloxacin contaminated soils amended with rice straw (RS) and the transformation products, biochar (RSB) and ash (RSA). RS significantly promoted the degradation of norfloxacin (0.0648 d−1, 3 times faster than control), whereas RSB had little effect and RSA hindered the degradation. Based on metagenomic analysis, RS and RSB significantly reduced the ARGs relative abundance (0.1421 and 0.1991 compared to 0.2540 in control) at the end of soil incubation. Adonis test indicated that all of amendment treatments significantly affect the microbial communities in soils, whereas only RS and RSB significantly affect the variation of antibiotic resistome. Procrustes analysis confirmed the association of microbial communities and ARGs. Network analysis further revealed that the reduction in Actinobacteria was the main reason for the general decrease of ARGs relative abundance during soil incorporation, whereas Proteobacteria and Bacteroidetes were responsible for temporary promotion of ARGs in RS and RSB at the early stage. Finally, scientifically setting up the usage of rice straw and optimizing the preparation process of biochar are suggested for the synchronous control of the risk of antibiotics and ARGs during soil incorporation.

Soil Storage Conditions Alter the Effects of Tire Wear Particles on Microbial Activities in Laboratory Tests.

In this study, we focused on the fact that soil storage conditions in the laboratory have never been considered as a key factor potentially leading to high variation when measuring effects of microplastics on soil microbial activity. We stored field-collected soils under four different conditions [room-temperature storage, low-temperature storage (LS), air drying (AD), and heat drying] prior to the experiment. Each soil was treated with tire wear particles (TWPs), and soil microbial activities and water aggregate stability were investigated after soil incubation. As a result, microbial activities, including soil respiration and three enzyme activities (β-glucosidase, N-acetyl-β-glucosaminidase, and phosphatase), were shown to depend on soil storage conditions. Soil respiration rates increased with the addition of TWPs, and the differences from the control group (no TWPs added) were more pronounced in the AD TWP treatment than in soils stored under other conditions. In contrast, phosphatase activity followed an opposing trend after the addition of TWPs. The AD soil had higher phosphatase activity after the addition of TWPs, while the LS soil had a lower level than the control group. We suggest that microplastic effects in laboratory experiments can strongly depend on soil storage conditions.