Genome analysis of Shewanella putrefaciens 4H revealing the potential mechanisms for the chromium remediation.

Microbial remediation of heavy metal polluted environment is ecofriendly and cost effective. Therefore, in the present study, Shewanella putrefaciens stain 4H was previously isolated by our group from the activated sludge of secondary sedimentation tank in a dyeing wastewater treatment plant. The bacterium was able to reduce chromate effectively. The strains showed significant ability to reduce Cr(VI) in the pH range of 8.0 to 10.0 (optimum pH 9.0) and 25-42 ℃ (optimum 30 ℃) and were able to reduce 300 mg/L of Cr(VI) in 72 h under parthenogenetic anaerobic conditions. In this paper, the complete genome sequence was obtained by Nanopore sequencing technology and analyzed chromium metabolism-related genes by comparative genomics The genomic sequence of S. putrefaciens 4H has a length of 4,631,110 bp with a G + C content of 44.66% and contains 4015 protein-coding genes and 3223,  2414, 2343 genes were correspondingly annotated into the COG, KEGG, and GO databases. The qRT-PCR analysis showed that the expression of chrA, mtrC, and undA genes was up-regulated under Cr(VI) stress. This study explores the Chromium Metabolism-Related Genes of S. putrefaciens 4H and will help to deepen our understanding of the mechanisms of Cr(VI) tolerance and reduction in this strain, thus contributing to the better application of S. putrefaciens 4H in the field of remediation of chromium-contaminated environments.

Soil adsorption potential: Harnessing Earth's living skin for mitigating climate change and greenhouse gas dynamics.

Soil adsorption, which could be seen as a crucial ecosystem service, plays a pivotal role in regulating environmental quality and climate dynamics. However, despite its significance, it is often undervalued within the realms of research and policy frameworks. This article delves into the multifaceted aspects of soil adsorption, incorporating insights from chemistry and material science, ecological perspectives, and recent advancements in the field. In exploring soil components and their adsorption capacities, the review highlights how organic and inorganic constituents orchestrate soil's aptitude for pollutant mitigation and nutrient retention/release. Innovative materials and technologies such as biochar are evaluated for their efficacy in enhancing these natural processes, drawing a link with the sustainability of agricultural systems. The symbiosis between soil microbial diversity and adsorption mechanisms is examined, emphasizing the potential for leveraging this interaction to bolster soil health and resilience. The impact of soil adsorption on global nutrient cycles and water quality underscores the environmental implications, portraying it as a sentinel in the face of escalating anthropogenic activities. The complex interplay between soil adsorption mechanisms and climate change is elaborated, identifying research gaps and advocating for future investigations to elucidate the dynamics underpinning this relation. Policy and socioeconomic aspects form a crucial counterpart to the scientific discourse, with the review assessing how effective governance, incentivization, and community engagement are essential for translating soil adsorption's functionality into tangible climate change mitigation and sustainable land-use strategies. Integrating these diverse but interconnected strata, the article presents a comprehensive overview that not only charts the current state of soil adsorption research but also casts a vision for its future trajectory. It calls for an integrated approach combining scientific inquiry, technological innovation, and proactive policy to leverage soil adsorption's full potential to address environmental challenges and catalyze a transition towards a more sustainable and resilient future.

Microbial pathways of nitrous oxide emissions and mitigation approaches in drylands.

Drylands refer to water scarcity and low nutrient levels, and their plant and biocrust distribution is highly diverse, making the microbial processes that shape dryland functionality particularly unique compared to other ecosystems. Drylands are constraint for sustainable agriculture and risk for food security, and expected to increase over time. Nitrous oxide (N2O), a potent greenhouse gas with ozone reduction potential, is significantly influenced by microbial communities in drylands. However, our understanding of the biological mechanisms and processes behind N2O emissions in these areas is limited, despite the fact that they highly account for total gaseous nitrogen (N) emissions on Earth. This review aims to illustrate the important biological pathways and microbial players that regulate N2O emissions in drylands, and explores how these pathways might be influenced by global changes for example N deposition, extreme weather events, and climate warming. Additionally, we propose a theoretical framework for manipulating the dryland microbial community to effectively reduce N2O emissions using evolving techniques that offer inordinate specificity and efficacy. By combining expertise from different disciplines, these exertions will facilitate the advancement of innovative and environmentally friendly microbiome-based solutions for future climate change vindication approaches.

Soil pH management for mitigating N2O emissions through nosZ (Clade I and II) gene abundance in rice paddy system.

Soil nitrous oxide (N2O) is produced by abiotic and biotic processes, but it is solely consumed by denitrifying microbes-encoded by nosZ genes. The nosZ gene includes two groups i.e. Clade I and Clade II, which are highly sensitive to pH. Managing pH of acidic soils can substantially influence soil N2O production or consumption through nosZ gene abundance. Nevertheless, the response of nosZ (Clade I and Clade II) to pH management needs elucidation in acidic soils. To clarify this research question, a pot experiment growing rice crop was conducted with three treatments: control (only soil), low dose of dolomite (LDD), and high dose of dolomite (HDD). The soil pH increased from 5.41 to 6.23 in the control, 6.5 in LDD and 6.8 in HDD treatment under flooded condition. The NH4+ and NO3- contents increased and reached the maximum at 30.4 and 21.5 mg kg-1, respectively, in HDD treatment under flooding condition. The contents of dissolved organic carbon and microbial biomass carbon showed a swift rise at midseason aeration and reached maximum at 30.7 and 101 mg kg-1 in the HDD treatment. Clade I, Clade II and 16S rRNA genes abundance increased with the onset of flooding, and occurred maximum in the HDD treatment. A peak in N2O emissions (5.96 µg kg-1 h-1) occurred at midseason events in the control when no dolomite was added. Dolomite application significantly (p ≤ 0.001) suppressed N2O emissions, and HDD treatment was more effective in reducing emissions. Pearson correlation, linear regressions and principal component analysis displayed that increased soil pH and Clade I and Clade II were the main controlling factors for N2O emission mitigation in acidic soil. This research demonstrates that ameliorating soil acidity with dolomite application is a potential option for the mitigation of N2O emissions.

Efficient removal of Cr(VI) and As(V) from an aquatic system using iron oxide supported typha biochar.

The removal of Cr(VI) and As(V) from aqueous solutions has been a worldwide concern. In this study, Typha biochar (FBC) with magnetic iron oxide was prepared by impregnating Typha with FeCl3 and performing pyrolysis, and the possible mechanism of Cr(VI) and As(V) removal was investigated by combining characterization means and adsorption experiments. The results showed that the modified Typha biochar is rich in pores and has the potential to eliminate Cr and As through processes such as exchange and reduction. The single molecule uptake capacities of FBC for Cr(VI) and As(V) were 32.82 and 21.56 mg g-1, respectively. The adsorption process is spontaneous heat absorption, and the adsorption results are also consistent with the proposed secondary kinetic model. FBC still had >60% removal efficiency in the second and third reuse of Cr(VI), indicating its good recyclability. Therefore, this study confirms that FBC can effectively remove both Cr(VI) and As(V).

Ascription of nosZ gene, pH and copper for mitigating N2O emissions in acidic soils.

Soil nitrous oxide (N2O) emissions are alarming for global warming and climate change. N2O reduction is carried out only by nosZ gene encoded N2O-reductase, which is highly sensitive to acidic pH and copper (Cu) contents. Therefore, a microcosm study was conducted to examine the attribution of soil pH management, Cu supply and nosZ gene abundance for N2O emission mitigation. Cu was applied at the dose of 0, 10, 25 and 50 mg kg-1 to three acidic soils (Soil 1, 2 and 3) without and with dolomite (0 and 5 g kg-1). Cu application and soil pH increment substantially enlarged the abundance of nosZ gene, and consequently mitigated soil N2O emissions; highest reduction with 25 Cu mg kg-1. Decline in NH4+ and subsequently accumulation of NO3-, and large contents of MBC and DOC in dolomite treated soils led to a substantial N2O reduction. The cumulative N2O emissions were lowest in the treatment of 25 Cu mg kg-1 with dolomite application for each soil. Results suggest that soil pH increment, an adequate Cu supply, and nosZ gene abundance can potentially lower soil N2O emissions in acidic soils.

The effects of continuous straw returning strategies on SOC balance upon fresh straw incorporation.

Continuous straw returning is widely encouraged for augmenting soil organic carbon (SOC) in arable lands. However, the magnitude of changes in net SOC related to native SOC mineralization and new SOC development upon fresh straw incorporation remains elusive, particularly in soils after continuous straw returning with different strategies. To address this, soil that had undergone nine years of straw returning with different strategies (NS, non-straw returning; DS, direct straw returning; IS, indirect straw returning) was incubated with fresh 13C-labeled straw for 45 days. Fresh straw incorporation stimulated native SOC-derived CO2 emission in DS soil, which in turn promoted straw-derived CO2 emission in IS soil. Overall, the amounts of newly developed SOC from straw (2.41-2.59 g C/kg soil) overcompensated for the native SOC losses (0.91-1.37 g C/kg soil) by mineralization, and led to net C sequestration in all treatments. No obvious difference was found in the amounts of SOC sequestrated from straw between the DS and NS soils, while the amount of native SOC mineralization increased by 40-50% in the DS soil relative to other treatments, thus resulting in lower net C sequestration in the DS soil (1.21 g C/kg soil) than IS and NS soil (1.43 and 1.65 g C/kg for IS and NS soil, respectively). Spearman's correlation analyses indicated a significant (p < 0.01) and positive correlation between SOC contents and native soil C mineralization, while the soil microbial index played a greater role in influencing fresh straw sequestration (p < 0.01). In conclusion, the DS soil showed a weaker effect on SOC sequestration than IS after 9 years of practices, upon fresh straw incorporation. This difference may be attributed to the magnitude of native SOC mineralization in the soil. Besides the straw-C input rate, results emphasize that native soil C protection should be also considered in long-term SOC sequestration practices.

Enzyme activities and organic matter mineralization in response to application of gypsum, manure and rice straw in saline and sodic soils.

Saline and alkaline soils are a challenge for sustainable crop production. The use of organic and inorganic amendments is a common practice to increase the fertility of salt-affected soils that can trigger faster carbon (C) and nitrogen (N) cycling. We examined the effects of gypsum (Gyps), farm manure (Manure) and rice straw (Straw) on enzyme activities, organic matter mineralization and CO2 emissions in two salt-affected soils [Solonchak (saline); pH: 8, electrical conductivity (EC): 6.5, sodium adsorption ratio (SAR): 2.5, and Solonetz (alkaline sodic); pH: 8.9, EC: 1.6, SAR: 17]. Gypsum addition decreased soil pH up to 0.62 and 0.30 units, SAR 1.2 and 5.2 units, and EC 2.9 and 1.4 units in Solonchak and Solonetz, respectively. Dissolved organic C, microbial biomass C, dissolved organic N, mineral N (NO3- and NH4+), enzyme activities (urease, invertase, catalase, phosphatase, phenol-oxidase), alkali extractable phenols, and available phosphorous increased with the application of all amendments in both soils. Solonetz released more CO2 than Solonchak, whereas maximum CO2 emissions were common after manure application (3140 mg kg-1 in Solonchak, and 3890 mg kg-1 in Solonetz). We conclude that high SAR and low EC increase CO2 emissions through accelerated C and N cycling and manure decomposition in Solonetz soils.

Fe(III) stabilizing soil organic matter and reducing methane emissions in paddy fields under varying flooding conditions.

The role of iron (Fe) in soil organic matter (SOM) stabilization and decomposition in paddy soils has recently gained attention, but the underlying mechanisms during flooding and drying periods remain elusive. As the depth water layer is maintained in the fallow season, there will be more soluble Fe than during the wet and drainage seasons and the availability of oxygen (O2) will be different. To assess the influence of soluble Fe on SOM mineralization during flooding, an incubation experiment was designed under oxic and anoxic flooding conditions, with and without Fe(III) addition. The results showed that Fe(III) addition significantly (p < 0.05) decreased SOM mineralization by 14.4 % under oxic flooding conditions over 16 days. Under anoxic flooding incubation, Fe(III) addition significantly (p < 0.05) decreased 10.8 % SOM decomposition, mainly by 43.6 % methane (CH4) emission, while no difference in carbon dioxide (CO2) emission was noticed. These findings suggest that implementing appropriate water management strategies in paddy soils, considering the roles of Fe under both oxic and anoxic flooding conditions, can contribute to SOM preservation and mitigation of CH4 emissions.

Effects of water regimes on soil N2O, CH4 and CO2 emissions following addition of dicyandiamide and N fertilizer.

Water regimes strongly impact soil C and N cycling and the associated greenhouse gases (GHGs, i.e., CO2, CH4 and N2O). Therefore, a study was conducted to examine the impacts of flooding-drying of soil along with application of nitrogen (N) fertilizer and nitrification inhibitor dicyandiamide (DCD) on GHGs emissions. This study comprised four experimental treatments, including (i) control (CK), (ii) dicyandiamide, 20 mg kg-1 (DCD), (iii) nitrogen fertilizer, 300 mg kg-1 (N) and (iv) DCD + N. All experimental treatments were kept under flooded condition at the onset of the experiment, and then converted to 60% water filled pore space (WFPS). At flooding stage, N2O emissions were lower as compared to 60% WFPS. The highest cumulative N2O emission was 0.98 mg N2O-N kg-1 in N treated soil due to high substrates of mineral N contents, but lowest (0.009 mg N2O-N kg-1) in the DCD treatment. The highest cumulative CH4 emissions (80.54 mg CH4-C kg-1) were observed in the N treatment, while uptake of CH4 was observed in the DCD treatment. As flooded condition converted to 60% WFPS, CO2 emissions gradually increased in all experimental treatments, but the maximum cumulative CO2 emission was 477.44 mg kg-1 in the DCD + N treatment. The maximum dissolved organic carbon (DOC) contents were observed in N and DCD + N treatments with the values of 57.12 and 58.92 mg kg-1, respectively. Microbial biomass carbon (MBC) contents were higher at flooding while lower at transition phase, and increased at the initiation of 60% WFPS stage. However, MBC contents declined at the later stage of 60% WFPS. The maximum MBC contents were 202.12 and 192.41 mg kg-1 in N and DCD + N treatments, respectively. Results demonstrated that water regimes exerted a dramatic impact on C and N dynamics, subsequently GHGs, which were highly controlled by DCD at both flooding and 60% WFPS conditions.

Earthworms promote the transfer of 15N-urea to lettuce while limit appreciably increase 15N losing to environment.

Earthworm activities not only increase nitrogen (N) uptake by crops, but also lead to N losing to environment. Thus, the present study examined the transformation of 15N-labeled urea with and without earthworms (Metaphire guillelmi) in a soil-lettuce system. We evaluated lettuce 15N uptake, 15N losses including N2O emission, NH3 volatilization and leaching, as well as 15N remaining in soil. Results showed that 15N-urea uptakes by lettuce significantly increased from 33.07% to 42.72% with earthworm presence. However, little difference was found on the total amounts of leaching and gaseous losses (N2O emission and NH3 volatilization) from 15N-urea between the treatment with and without earthworms (4.04 and 5.38%, respectively). Most of the 15N-urea remained in the soil, accounting for 48.44% and 60.65% of the 15N-urea in soil with and without earthworm presence. We conclude that earthworms enhanced the transfer of 15N-urea to lettuce without appreciably increasing the 15N-urea loss from soil to the environment.

Appraisal of different land use systems for heterotrophic respiration in a Karst landscape.

Soil respiration, particularly heterotrophic respiration (RH), is a potent source of carbon dioxide (CO2) in the atmosphere. The current research focuses on the evaluation of RH for six land use systems including sloping cropland (SC), shrub land (SD), grassland (GD), shrub & grassland (SGD), newly abandoned cropland (NC) and afforested forest (AF). Heterotrophic respiration showed a diverse seasonal pattern over a year long period that was affected by various soil properties and climatic variables across the six land use systems in a subtropical Karst landscape. The lowest RH scores were found in the SD site (annual cumulative soil CO2 flux: 2447 kg C ha-1), whereas the maximum heterotrophic respiration occurred in the SF site (annual cumulative soil CO2 13597 kg C ha-1). The values of RH were: SC site: 3.8-191.5 mg C m-2 h-1, NC site: 1.04-129 mg C m-2 h-1, GD site: 3.6-100.7 mg C m-2 h-1, SGD site: 0.3-393.5 mg C m-2 h-1, SD site: 3-116 mg C m-2 h-1, and SF site: 10.6-398.2 mg C m-2 h-1. Highly significant (p ≤ 0.01) and positive correlations between RH rate and soil temperature were found for the studied land use types (correlation coefficients as follows; SC: 0.77, NC: 0.61, GD: 0.283, SGD: 0.535, SD: 0.230, SF: 0.85). However, water filled pore space (WFPS), NH4+, NO3-, dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations showed varied (positive and negative) correlations with RH. The overall results show that soil temperature can be considered as the most limiting factor for RH among all the sites studied in the present research. In these environments, soil heterotrophic respiration significantly correlated with soil temperature, highlighting the significance of climate on heterotrophic respiration.

Influence of silicon and chitosan on growth and physiological attributes of maize in a saline field.

Soil salinity is the main constraint for crop productivity in many parts of the world. Application of silicon (Si) and chitosan (Chi) can improve crop growth under saline soil conditions. The current study was aimed to examine the effects of Si and Chi on mitigation of salinity, morphological and physiological attributes as well as the antioxidant system of maize (Zea mays L.) under saline soil conditions. A field experiment was conducted that comprised of nine treatments as follows: (i) Control (no amendment), (ii) Silicon 40 kg ha-1 (Si1), (iii) Chitosan 15 kg ha-1 (Chi1), (iv) Si1 + Chi1, (v) Silicon 80 kg ha-1 (Si2), (vi) Chitosan 30 kg ha-1 (Chi2), (vii) Si2 + Chi2, (viii) Si1 + Chi2 and (ix) Si2 + Chi1. Application of Si and Chi substantially improved the morphological and physiological attributes as well as antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of maize plants, and combined application of Si and Chi was more effective when compared with Si and Chi treatments separately. Membrane stability index was improved by 25%, relative water content by 26%, chlorophyll a by 69% and b by 56% with combined application of Si and chitosan (Si2 + Chi2) compared with control. The SOD, POD and CAT increased by 36%, 38% and 65% with Si2 + Chi2 compared with control. The results suggest that Si and Chi application is the possible option for alleviating salinity stress in maize plant. Further research is suggested to examine Si and Chi effects on various crop's growth.

Editorial: New Research on Soil Degradation and Restoration.

The Virtual Special Issue (VSI) "New Research on Soil Degradation and Restoration" was proposed by the Guest-Editors (the authors of this editorial piece) to Journal of Environmental Management taking into account the following aspects: (a) Firstly, soil degradation is a main issue all over the world; (b) Secondly, physical, chemical and biological degradation of soil environments need detailed research, also going deeper in some new aspects poorly covered up to now; and (c) Similarly, new quality research on restoration of degraded soils, dumping sites, different areas affected by mining activities, and so on, would be clearly useful in order to prevent and/or solve critical environmental hazards. As a result, 110 manuscripts were submitted to the VSI by authors from around the world, and near 50 high quality works were finally published. The Guest-Editors of the VSI consider that the papers published will be of great interest for researchers working in this field, as well as for the overall community, as they include aspects clearly relevant at a global level.

Pathways of nitrogen loss and optimized nitrogen management for a rice cropping system in arid irrigation region, northwest China.

The reactive nitrogen (N) loss of the rice cropping system in the arid region shows a different pattern from that of subtropical humid region due to different climate types and crop management. However, little attention has been paid to this region. To fill this knowledge gap, a two-year (2009-2010) field observation was conducted in the Ningxia irrigation region, northwest China, to explore the major pathway of N loss following local farmers' optimal practice. Further, we determined the site-specific emission factors of ammonia and nitrous oxide, rate of surface runoff and subsurface (leaching and seepage) to improve the inventory resolution of arid irrigation region. Results showed that ammonia volatilization (45%-49% of total N loss), leaching and seepage (30%-33% of total N loss) were proved to be the primary factors of N loss in rice paddy fields. The emission factor of ammonia (21%) and N leaching rate (7.5%) following farmers' practice were 2.1 and 5.4 times higher than the country-specific default value in China. The country-specific N runoff rate and emission factor of N2O could be directly adopted in this region. A 20% reduction of N fertilizer to farmers' practice (300 kg N ha-1) alongside the application of organic fertilizer (30% N in synthetic fertilizer was substituted by pig manure) were considered to be the optimal N rate in this region. Our study can narrow the gap between researches on N loss in arid regions and subtropical humid regions. Meanwhile, the results can provide specific advice on N loss mitigation for policy makers in arid irrigation regions.

Effect of rice straw, biochar and calcite on maize plant and Ni bio-availability in acidic Ni contaminated soil.

Metals that contaminate soil is one of the major problems seriously affecting sustainable agriculture worldwide. Nickel (Ni) toxicity to agricultural crops is a global problem. Mobility of heavy metals present in contaminated soil can be reduced by the amendment of soil passivators, which will ultimately reduce the risk of them entering the food chain. A greenhouse pot experiment was conducted to investigate the effects of rice straw (RS), biochar derived from rice straw (BI) and calcium carbonate (calcite) on Ni mobility and its up take by maize (Zea maize L.) plant. Maize crop was grown in Ni spiked (100 mg kg-1) soil with three application rates of passivators (equivalent to 0, 1and 2% of each RS, BI and calcite) applied separately to the soil. Results revealed that the post-harvest soil properties (pH, DOC and MBC), plant phenology (plant height, root length, total dry weight) and physiological characteristics were significantly enhanced with passivator application. Additionally, incorporating passivator into the soil reduced Ni mobility (DTPA) by 68%, 88.9% and 79.3%, and leachability (TCLP) by 72.4%, 76.7% and 66.7% for RS, BI and calcite, respectively at 2% application rate. The Ni concentration in the maize shoots reduced by 30%, 95.2% and 95% and in the roots by 56%, 66% and 63.8% with RS, BI and calcite at 2% application rate, respectively. These findings suggest that the application of 2% biochar (BI) is very promising in reducing Ni uptake, and can reduce toxicity to plants, decrease mobility and leachability in the soil.

The influence of soil temperature, methanogens and methanotrophs on methane emissions from cold waterlogged paddy fields.

Paddy fields are major sources of atmospheric methane (CH4). However, CH4 emissions from cold-waterlogged paddy fields, a major type of paddy soil in China, remain unclear. Here we investigated the CH4 emissions and associated influential factors in cold-waterlogged paddy fields at two sites (Yangxin County and Daye City) in Hubei Province, South China. Normal paddy fields matched with parental material and cropping system were used as the controls. The CH4 emissions from cold-waterlogged fields were significantly higher than those from normal fields with (3.0-4.4-fold) or without (3.5-8.6-fold) rice. Rice planting increased CH4 emissions by 59-78% in cold-waterlogged fields and by 85-247% in normal fields. CH4 instantaneous fluxes were positively correlated with soil temperature and methanogen mcrA (methyl coenzyme M reductase alpha subunit) and methanotroph pmoA (methane monooxygenase) copy numbers at the annual scale. Under rice planting, mcrA copy number was higher in cold-waterlogged fields than in normal fields at both sites, whereas pmoA copy number had the same trend at the Daye site only. Soil temperature and water content influenced mcrA and pmoA copy numbers in the normal paddy fields, whereas soil organic matter content was more influential in the cold-waterlogged paddy fields. These findings suggest that perennial waterlogging is a prerequisite for substantial CH4 emissions from cold-waterlogged paddy fields, and it promotes the proliferation of methanogens and methanotrophs under rice planting. Therefore, CH4 production-oxidation processes are more active in cold-waterlogged paddy fields than in normal paddy fields.

Role of sepiolite for cadmium (Cd) polluted soil restoration and spinach growth in wastewater irrigated agricultural soil.

Metals that contaminate soil are one of the major problems seriously affecting sustainable agriculture worldwide. Cadmium (Cd) toxicity to agricultural crops is a global problem. Mobility of Cd in contaminated soil can be minimized by the amendment of soil passivators which will ultimately reduce its movement from soil to plants. A pot study was performed to evaluate the impact of sepiolite from 1% to 5% on Cd solubility and its accumulation in spinach tissues. Soil pH, Cd fractionation, Cd accumulation in spinach tissue and Cd adsorption mechanism were determined. Results were recorded that soil pH was increased from 0.3 to 1.0 units with the increasing rate of sepiolite from 1% to 5%. Similarly, Cd contents in acid soluble phase was decreased by 42.8% and increased in residual phase by 35.8% at 5% rate, relative to control. Moreover, the significant reduction in Cd uptake by spinach shoots and roots was occurred by 26.2% and 30.6% at 5% rate, respectively. Furthermore, the maximum Cd adsorption capacity 37.35 mg g-1 was recorded at 5% rate relative to control. The analysis of FTIR, XRD and SEM also confirm the ability of sepiolite for Cd polluted soil restoration and thereby, reduces its phytoavailability in polluted soil to alleviate food security challenges.

Biochar mitigates the N2O emissions from acidic soil by increasing the nosZ and nirK gene abundance and soil pH.

Nitrous oxide (N2O) is a pervasive greenhouse gas, and soil management practices greatly affect its release into the atmosphere. Soil pH management (particularly increasing the pH) using biochar can seriously affect soil N2O emissions. The current incubation experiment was conducted to explore the response of N2O emissions from acidic soils using various doses of biochar. Soil with a pH of 5.48 was treated with rice straw biochar at different doses (0%, 1% and 2%) and incubated with 60% water-filled pore spaces (WFPS). The experiment was conducted in a completely randomized design (CRD) with three replications. The soil N2O emissions, pH, NH4+-N, NO3--N, microbial biomass carbon (MBC), and nosZ and nirK gene abundance were determined at various intervals throughout the study. The biochar application (2%) increased the soil pH (from 5.48 to 6.11), triggered the transformation of nitrogen, and augmented the abundance of nosZ and nirK genes. Higher magnitudes of cumulative soil N2O emissions (48.60 µg kg-1) were noted in the control (no biochar) compared to 1% (28.10 µg kg-1) and 2% (14.50 µg kg-1) biochar application. The 2% biochar application more effectively decreased the soil N2O emissions, mainly because of the increased nosZ and nirK gene abundance at higher soil pH levels. The findings suggest that the amelioration of acidic soil with rice straw biochar can considerably control soil N2O emissions by elevating the soil pH and the abundance of nosZ and nirK genes.

Soil phosphorus transformation characteristics in response to molybdenum supply in leguminous crops.

Phosphorus (P) is one of the most restrictive essential elements to crop growth and development due to less availability in the soil system. Previous studies have reported the synergistic effects between molybdenum (Mo) and P fertilizer on P uptake in various crops. However, an induced long term effect of Mo on soil P dynamics in the rhizosphere and non-rhizosphere has not been reported yet in leguminous crops. In this study, a long term field experiment was conducted to explore the P transformation characteristics and bioavailability in Mo-deficient (-Mo) and Mo-enriched (+Mo) soil under leguminous (broad bean-soybean) cropping system. The results indicated that long-term Mo application increased the plant dry matter accumulation (14.23%-35.27%, for broad bean; 24.40%-37.46%, for soybean) from March-September. In rhizosphere soil, the percent decrease in pH (8.10%) under +Mo treatment of the soybean crop was recorded more during September as compared to broad bean crop. Under Mo supply, H2O-Pi fraction increased up to 28.53% and 43.67% while for NaHCO3-Pi this increase was up to 5.61% and 11.98%, respectively in the rhizosphere soil of broad bean and soybean, whereas, residual-P exhibited the highest proportion of P fractions. Moreover, compared with -Mo, +Mo treatments significantly increased the soil acid phosphatase (broad bean = 17.43 µmol/d/g; soybean = 28.60 µmol/d/g), alkaline phosphatase (broad bean = 3.34 µmol/d/g; soybean 6.35 µmol/d/g) and phytase enzymes activities (broad bean = 2.45 µmol/min/g; soybean = 5.91 µmol/min/g), transcript abundance of phoN/phoC genes and microbial biomass P (MBP) in rhizosphere soil. In crux, the findings of this study suggest that long term Mo application enhanced P bioavailability through increased available P, MBP, P related enzymes activities and their genes expressions which may represent a strategy of Mo to encounter P deficiencies in the soil system.