Paddy Field Soil Research Articles

Distribution and Transformation of Soil Phosphorus Forms under Different Land Use Patterns in an Urban Area of the Lower Yangtze River Basin, South China

Understanding the phosphorus (P) cycle is essential for preventing soil P loss, improving environmental quality, and promoting sustainable agriculture, particularly in urban areas. In this study, a representative city of the lower Yangtze River Basin, Nanchang, was chosen to systematically explore the distribution and transformation of soil P forms, which were extracted by an improved SEDEX method and measured by a standard phosphorus–molybdenum blue method under three land use patterns. The contents of soil P forms were the highest in the dryland and the lowest in the paddy field, with total P accumulation in the upper wasteland and paddy field soils but in the lower dryland soil. The pH value and grain size affected soil P form distributions to a variable extent from one land use pattern to another. The transformation of soil P forms was weak in the wasteland. It was first found that some detrital limestone P (De-P) was transformed into exchangeable P (Ex-P) in the paddy field with authigenic calcium-bound phosphorus (Au-P) and organic phosphorus (OP) transformation, and the transformation between Ex-P and iron-bound phosphorus (Fe-P), Au-P, and between Au-P and OP existed in the dryland. Land use pattern was the dominant driver for the P distribution and transformation of soil P. This study highlights the critical role of land use patterns in affecting the P cycle of soils in urban areas and the importance of sustainable urban land management.

Soil heavy metal pollution and ecological risk assessment in disturbed and undisturbed soil of Morigaon, Assam

Soil heavy metal pollution and ecological risk assessment in disturbed and undisturbed soil of Morigaon, Assam

Evidence that co-existing cadmium and microplastics have an antagonistic effect on greenhouse gas emissions from paddy field soils

Accumulation of microplastics (MPs) and cadmium (Cd) are ubiquitous in paddy soil. However, the combined effects of MPs and Cd on physiochemical and microbial mechanisms in soils and the attendant implications for greenhouse gas (GHG) emissions, remain largely unknown. Here, we evaluated the influence of polylactic acid (PLA) and polyethylene (PE) MPs on GHG emissions from Cd-contaminated paddy soil using a microcosm experiment under waterlogged and drained conditions. The results showed that PLA significantly increased CH4 and N2O emission fluxes and hence the global warming potential (GWP) of waterlogged soil. Soils treated with MPs+Cd showed significantly reduced GWP compared to those treated only with MPs suggesting that, irrespective of attendant consequences, Cd could alleviate N2O emissions in the presence of MPs. Conversely, the presence of MPs in Cd-contaminated soils tended to alleviate the bioavailability of Cd. Based on a structural equation model analysis, both the MPs-derived dissolved organic matter and the soil bioavailable Cd affected indirectly on soil GHG emissions through their direct influencing on microbial abundance (e.g., Firmicutes, Nitrospirota bacteria). These findings provide new insights into the assessment of GHG emissions and soil/cereal security in response to MPs and Cd coexistence that behaved antagonistically with respect to adverse ecological effects in paddy systems.

A NEW FREE-LIVING NEMATODE GENUS TETRATOBRILUS GEN. NOV. (TRIPLONCHIDA: TOBRILIDAE) FROM WEST BENGAL, INDIA

A new free-living nematode Tetratobrilus dentatus gen. nov. sp. nov. under family Tobrilidae Filipjev, 1918 of the order Triplonchida Cobb, 1919 is described from a drowned paddy field soil (mud) in West Bengal, India. It is characterized by heavily sclerotized walls of anterior portion of the buccal cavity, a small dorsal tooth and two sub-ventral stomatal pockets longitudinally, one following another. The first pocket is fused with the posterior portion of the stoma, similar to the genus Epitobrilus, but differs in the presence of two adjacent teeth (vs. one) in the first pocket. The second pocket contains only one tooth. It also possesses smaller anterior setae (less than 40% of head diameter) and a subterminal setae. Males bear six characteristic pitcher-shaped supplements. Comprehensive details regarding the morphological structures, accompanied by figures and morphometric measurements, are presented in this report. An updated key to the genus and other genera of family Tobrilidae is also provided. Key Words: Stomatal pockets, sub-ventral teeth, Tobrilidae, new genus, new species

Smart Agriculture untuk Mewujudkan Ketahanan Pangan Berbasis Lora di Desa Kalipadang-Benjeng Gresik

Increasing agricultural production is a top priority in agricultural development. There are many agricultural problems to be managed. One way to increase rice production is to pay attention to irrigation conditions. In addition to irrigation, rising temperatures also affect the process of flowering and grain filling. At high temperatures, grain because of rice agricultural production will calcify, resulting in a decrease in grain quantity and grain mass. Temperature spikes can also reduce the viability and size of the seeds when they reach the ripe stage. Apart from water and air, farmers also need to pay attention to soil pH and humidity. Many farmers do not yet have accurate indicators to determine soil quality, most farmers only use estimates, the application of the estimation method causes the quality of the soil in paddy fields to be infertile. To overcome this problem, a tool is made to predict the condition of agricultural land by taking data on temperature, humidity, air pressure, soil pH, soil moisture, and water flow rate. The data is then sent to a database to be displayed on a web server, so that farmers can monitor land conditions. It is expected that the parameter results obtained can be used as a preventive measure for farmers when conditions occur that can reduce rice productivity. That way, the condition of the land can be maintained so that crop failure can be minimized. This tool will be implemented in one of the rice fields of the residents of Kalipadang-Benjeng-Gresik Village. Based on data taken using an NPK sensor, wet soil has an average NPK content of 29.3 (Nitrogen); 41 (Phosphorus); 82 (Potassium). Moist soil has an NPK level of 28 (Nitrogen); 40 (Phosphorus); 82 (Potassium), and dry soil has an NPK level of 27.5 (Nitrogen); 39.7 (Phosphorus); 79.1 (Potassium). It can be said that soil moisture is directly proportional to NPK levels.

A Bionic Walking Wheel for Enhanced Trafficability in Paddy Fields with Muddy Soil.

To improve wheel trafficability in soft and muddy soils such as paddy fields, a bionic walking wheel is designed based on the structural morphology and movement mode of the feet of waders living in marshes and mudflats, similar to the muddy soil of paddy fields. The bionic walking wheel adopts the arrangement of double-row wheel legs and staggered arrays to imitate the walking posture of waders. The two legs move alternately, cooperate with each other, and improve the smoothness of movement. The cam inside the bionic walking wheel is used to control the movement mode of the feet. The flippers open before touching the ground to increase the contact area and reduce sinking, and the toes bend and grip the ground while touching the ground to increase traction. Multi-rigid-body dynamics software (Adams View 2020) is used to simulate the movement of the wheel during the wading process, and the movement coordination and interference between the wheel legs are analyzed. The simulation results show that there is no interference between the parts and that the movement smoothness is good. The interaction between the bionic walking wheel and muddy soil was analyzed via coupled EDEM-ADAMS simulation, and the simulation analysis and experiments were conducted and compared with those for a common paddy wheel. The results showed that the bionic walking wheel designed in this paper improved the drawbar pull by 113.56% compared with that of a common paddy wheel and had better anti-sinking performance. By analyzing the effect of toe grip on traction, it was found that the soil under the feet can be disturbed to provide greater traction when the toe is bent downward. This study provides a reference for improving the trafficability of walking mechanisms in soft and muddy soils, such as paddy fields.

A proposed method for determining potentially environmentally available trace metals in paddy soil

ABSTRACT The validity of the Asami-Kumada method (sodium hydrosulfite + EDTA extraction, AK method) for determining the potentially environmentally available trace metals (Cr, Mn, Co, Ni, Cu, Zn, Cd, Pb) in paddy field soil was evaluated. This was accomplished by comparing it with the results of the dilute HNO3 extraction method (ISO method), nitrate acid – perchloric acid degradation method, and dilute hydrochloric acid extraction method on 250 paddy field soil samples. The coefficient of determination for the AK method in metals, excluding Cr, ranged from 0.92 (Ni of non-Andisols) to 0.99 (Mn, Cu, Zn and Cd of non-Andisols) compared to the ISO method. The slope of the linear regression of the AK method’s measured values against those of the ISO method for metals, excluding Cr, ranged from 0.99 (Cd of non-Andisols) to 1.52 (Cu of Andisols). However, the measurements of Fe using the AK method were significantly higher than those obtained using the ISO method. The slope was measured to be 3.6 (for non-Andisols) or 5.7 (for Andisols). The increase in trace metal measurements using the AK method was probably due to the dissolution of Fe oxides and hydroxides, which release trace metals after reduction by sodium hydrosulfite. Thus, although the measured values using the AK method of trace metals, excluding Cr, tended to be slightly higher than those obtained using the ISO method as Fe oxides and hydroxides dissolved, the measured values of those metals by both methods were closely correlated. The AK method is a viable alternative to the ISO method for measuring the potentially environmentally available trace metal contents, excluding Cr, in paddy field soils. Additionally, the AK method conveniently measures free Fe oxides simultaneously.

Nitrogen-based fertilizers differentially affect protist community composition in paddy field soils

Nitrogen-based fertilizers differentially affect protist community composition in paddy field soils

Calibration and Testing of Parameters for the Discrete Element Simulation of Soil Particles in Paddy Fields

The parameters of the discrete element simulation model for rice field soils serve as valuable data references for investigating the dynamic characteristics of the walking wheel of high-speed precision seeding machinery in paddy fields. The research specifically targets clay loam soil from a paddy field in South China. Calibration of essential soil parameters was achieved using EDEM_2022 software (and subsequent versions) discrete element simulation software, employing the Edinburgh Elasto-Plastic Adhesion (EEPA) nonlinear elastic-plastic contact model. The tillage layer and plough sub-base layer underwent calibration through slump and uniaxial compression tests, respectively. Influential contact parameters affecting slump and axial pressure were identified through a Plackett–Burman test. The optimal contact parameter combinations for the discrete element model of the tillage layer and plough sub-base layer were determined via a quadratic rotational orthogonal test. The accuracy of the discrete element simulation model’s parameters for paddy field soils was further validated through a comparative analysis of the simulation test’s cone penetration and the field soil trench test. Results indicate that the Coefficient of Restitution, surface energy, Contact Plasticity Ratio, and Tensile Exp significantly influence slump (p < 0.05). Additionally, the Coefficient of Restitution, Contact Plasticity Ratio, coefficient of rolling friction, and Tangential Stiff Multiplier significantly impact axial pressure (p < 0.05). Optimal contact parameters for the plough layer were achieved with a particle recovery coefficient of 0.49, a surface energy of 18.52 J/m2, a plastic deformation ratio of 0.45, and a tensile strength of 3.74. For the plough subsoil layer, optimal contact parameters were a particle recovery coefficient of 0.47, a coefficient of interparticle kinetic friction of 0.32, a plastic deformation ratio of 0.49, and a tangential stiffness factor of 0.31. Results from the cone penetration test reveal no significant disparity in compactness between the actual experiment and the simulation test. The calibrated discrete element model’s contact parameters have been verified as accurate and reliable. The findings of this study offer valuable data references for understanding the dynamic characteristics of the walking wheel of the entire machinery in high-speed precision seeding in paddy fields.

Phosphorus forms and adsorption properties of paddy field soils and potential risk to Indawgyi Lake, Myanmar

The largest freshwater and oligotrophic lake in northern Myanmar, called Indawgyi Lake, is at potential risk of eutrophication due to the phosphorus (P) export from nearby paddy fields. In this study, the P status of the soil of paddy fields and its potential mobility to the lake water to cause eutrophication have been evaluated. The Indawgyi Lake is the third largest lake in Asia and became a UNESCO biosphere reserve in June 2017 for its outstanding contribution to providing habitat for threatened birds and aquatic species. Although many other sources, e.g. high tourist interest, loss of natural forest areas, the gathering of pilgrims and lack of proper wastewater treatment plants are contributing to the P nutrients input to the lake, the increase of paddy fields around the lake area and use of synthetic fertiliser which exports to the lake is considered to the primary source of P export to the lake. In this study, the soil P was examined with different P extracted methods and P export to the lake was calculated. The extracted P differed in order and magnitude with different methods, and the order was increased in accordance with CaCl2 < DL-P < Olsen-P < BD-P < HCL-P < TP and for iron, it was HCl-Fe < TFe. All extracted Olsen-P was below 10 mg kg−1, which is below the critical level (30–172 mg kg−1) for P loss. On the other hand, the soil has a high P sorption capacity, and the maximum sorption capacity among the soil samples that were done with the Langmuir equation is 0.790 mg g−1. Our findings suggested that paddy fields are not contributing to the eutrophication of the lake at present. However, comparing the historical map around the lake area from 1944 to 2017, it has been found that the area of paddy fields around the lake has increased almost three-fold from 1944 to 2017. As a result of increasing paddy fields and synthetic fertiliser use, we can say that P export from paddy fields can cause severe eutrophication to the lake in the near future.

CH4 and N2O emissions and their potential control by rice biomass biochar: The case of continuously flooded paddy fields in Indonesia - A review

Methane (CH4) and nitrous oxide (N2O) are the two most important greenhouse gases (GHG) from flooded paddy fields in Indonesia. This review aims to characterise CH4 and N2O emissions from flooded paddy fields by published data analysis and to examine the potential of biochar from rice straw (RSB) and rice husk (RHB) to mitigate the emissions in Indonesia. A comparison of various box-plot datasets of CH4 emissions showed that the different types of flooded paddy field soil cause varying amounts of CH4 emissions from various regions in Indonesia. Sequentially, CH4 emissions of flooded paddy fields from highest to lowest are Alluvial of Kalimantan and Sulawesi, Andisols of Java, Ultisols of Sumatra, Alfisols of Java and Bali and Inceptisols of Java and Bali, with a mean of 1062, 505, 446, 135 and 64 kg ha-1 season-1, respectively. The organic amendments application combined with chemical fertilisers is the principal driver of anthropogenic CH4 emissions from paddy fields. However, N chemical fertiliser application contributes only about 0.37% of the N2O flux, 0.69 kg ha-1 season-1. The produced biochar number was insufficient effectively to reduce CH4 and N2O emissions, at least 20 tonnes ha-1 year-1, in addition to the pyrolysis process to produce biochar, releasing CH4 emissions. Yet, with its recalcitrant properties and continuous application, RSB and RHB potentially reduce CH4 and N2O emissions from paddy fields.

Soil Fertility Evaluation in Long-term Paddy Field on Small Island: A Preliminary Research in Savana Jaya Village, Buru Island, Maluku Province, Indonesia

Efforts to increase rice production continue to face severe challenges, primarily attributed to the declining quality of paddy field soil resources. This study aims to investigate the management of fertilizer utilization and chemical properties of six rice paddy soils in Savana Jaya Village, Waeapo District, Buru Regency. Additionally, it seeks to assess the soil fertility status after 10 to 40 years of continuous rice planting and recommend an approach for fertilizer application. These fields were selected using a purposive sampling method. The soil samples were analyzed total nitrogen (N), potential phosphorus (P), and potential potassium (K) content, as well as cation exchange capacity (CEC). Rice production data was collected by interviewing farmers. The results showed that the soil organic C content and the total N were very low to low, the potential P status was moderate to very high, the potential K status was low to moderate, and the CEC-s of all fields were very low. The soil fertility status of all fields was very low. Organic matter is essential for maintaining the health and fertility of paddy soil, particularly in small islands where the soil is often subjected to intensive use of inorganic fertilizers, posing potential environmental contamination concerns.

Ferrihydrite Addition Activated Geobacteraceae, the Most Abundant Iron-reducing Diazotrophs, and Suppressed Methanogenesis by Heterogeneous Methanogens in Xylan-amended Paddy Soil Microcosms.

Paddy fields are a major emission source of the greenhouse gas methane. In the present study, the addition of ferrihydrite to xylan-amended paddy soil microcosms suppressed methane emissions. PCR-based and metatranscriptomic ana-lyses revealed that the addition of ferrihydrite suppressed methanogenesis by heterogeneous methanogens and simultaneously activated Geobacteraceae, the most abundant iron-reducing diazotrophs. Geobacteraceae may preferentially metabolize xylan and/or xylan-derived carbon compounds that are utilized by methanogens. Geomonas terrae R111 utilized xylan as a growth substrate under liquid culture conditions. This may constitute a novel mechanism for the mitigation of methane emissions previously observed in ferric iron oxide-applied paddy field soils.

Effect of cultivation practice on the heavy metal content of rice paddy field soil in Western Ghats of India

Effect of cultivation practice on the heavy metal content of rice paddy field soil in Western Ghats of India

Development of a Novel Internally Controlled HrpB1 Gene-Based Real-Time qPCR Assay for Detection of Burkholderia pseudomallei.

Melioidosis, caused by category B bioterrorism agent Burkholderia pseudomallei, is a seasonal disease of tropical and subtropical regions with a high mortality rate. An early and culture-independent detection ofB. pseudomalleiis required for the appropriate disease management and prevention. The present study is designed to identify novel and unique sequences ofB. pseudomalleiand development of quantitative polymerase chain reaction (qPCR) assay. A novel B. pseudomallei-specific target sequence was identified by in silico analysis for the qPCR assay development. The specificity of the developed assay was assessed using purified DNA of 65 different bacterial cultures, and the sensitivity was estimated using a cloned target gene. Further, a type III secretion protein HrpB1 (HrpB1) gene-based duplex qPCR assay incorporating suitable extraction and amplification control was developed, and its viability was assessed in different clinical and environmental matrices for the detection of B. pseudomallei. In this study, an 80-nucleotide-longB. pseudomallei-specific region within the geneHrpB1was identified by computational analysis. The developedHrpB1-based qPCR assay was highly specific forB. pseudomalleidetection when evaluated with 65 different bacterial cultures. The sensitivity of the qPCR assay with theHrpB1-recombinant plasmid was found to be five copies per qPCR reaction. The assay's detection limit was found to be 5 × 102 CFU/mL for human blood and urine, 5 × 101 CFU/mL in river water, and 2 × 103 CFU/gm in paddy field soil. The results of the study showed the applicability of a novelHrpB1-based qPCR assay for sensitive and specific detection ofB. pseudomalleiin diverse clinical and environmental samples.

Morchella esculenta cultivation in fallow paddy fields and drylands affects the diversity of soil bacteria and soil chemical properties.

The properties of paddy field (DT) and dry land (HD) soil and food production can be enhanced by the cultivation of Morchella esculenta (ME) during the fallow period. However, whether ME cultivation affects the soil health and microbial diversity of paddy fields and drylands during the cultivation period remains unclear, and this has greatly limited the wider use of this cultivation model. Here, we analyzed the soil chemical properties and bacterial diversity (via metabarcoding sequencing) of DT and HD soils following ME cultivation. Our findings indicated that ME cultivation could enhance soil health. The content of soil phosphorus and potassium (K) was increased in DT soil under ME cultivation, and the K content was significantly higher in HD soil than in DT soil under ME cultivation. ME cultivation had a weak effect on alpha diversity, and ME cultivation affected the abundance of some genera of soil bacteria. The cultivation of ME might reduce the methane production capacity of DT soil and enhance the nitrogen cycling process of HD soil based on the results of functional annotation analysis. Network analysis and correlation analysis showed that Gemmatimonas, Bryobacter, and Anaeromyxobacter were the key bacterial genera regulating soil chemical properties in DT soil under ME cultivation, and Bryobacter, Bacillus, Streptomyces, and Paenarthrobacter were the key taxa associated with the accumulation of K in HD soil. The results of our study will aid future efforts to further improve this cultivation model.

Health Risk Assessment and Environmental Benchmark of Cadmium in Farmland Soils around the Gangue Heap of Coal Mine, Chongqing

To analyze the health risk assessment and environmental benchmark of cadmium in farmland soils surrounding the gangue heap of a coal mine in Chongqing, Hakanson, the ecological risk index and health risk assessment were used. Meanwhile, the soil environmental reference value of the regional cultivated land was inverted based on the species sensitive distribution model (SSD). The results showed that the dryland soil was polluted by Cd, with an over-standard rate of 55.8%, and the paddy field soil was polluted by Cd, with an over-standard rate of 31.6%. The corn was polluted by Cd, with an over-standard rate of 4.4%, and the rice was not polluted by Cd. The Hakanson ecological risk index showed that Cd was mainly characterized in soils by high ecological risk and considerable ecological risk. The health risk assessment indicated that Cd presented low non-carcinogenic risk by corn and rice; however, it showed acceptable carcinogenic risk by corn and unacceptable carcinogenic risk by rice in this study. The sensitivity analysis of health risks showed that the content of Cd was the most sensitive. The SSD inversion showed that the reference values for Cd in dryland soil of pH ≤ 5.5, 5.5<pH ≤ 6.5, 6.5<pH ≤ 7.5, and pH>7.5 had HC5 values of 0.491, 0.382, 0.376, and 0.588 mg·kg-1, respectively, and that for Cd in paddy soil had an HC5 value of 0.807 mg·kg-1. The reverse analysis showed that the HC5 of Cd in dryland soil (pH ≤ 7.5) and paddy soil was relatively relaxed and was higher than the soil risk screening values, which showed that the current standard was relatively loose. However, the HC5 of Cd in dryland soil (pH>7.5) was lower than the soil risk screening values, which showed that the current standard was relatively strict. It is suggested that the current soil standard could be adjusted in this area.

Planobacterium oryzisoli sp. nov., a novel bacterium isolated from roots of rice plant.

A Gram-negative, aerobic, short rod-shaped, non-motile, non-spore forming bacterium, designated strain GCR5T, was isolated from soil of paddy field. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain GCR5Tbelongs to the genus Planobacterium and is related to Planobacterium taklimakanense NCTC 13490T (96.1%, 16S rRNA gene sequence similarity). Colonies on R2A were white but they turn into bright yellow after exponential growth. They produce carotenoid pigment after 5-6days of incubation, before that carotenoid pigment was not found. The major isoprenoid quinone was MK-6, and major cellular fatty acids were iso-C15:0, anteiso-C15:0 and iso-C17:0 3OH. Polar lipids include phosphatidylethanolamine, three unidentified phosphoglycolipids, three unidentified glycolipids, one unidentified aminophosphoglycolipid and five unidentified polar lipids. The strain GCR5T was found to have a 2,106,200bp linear genome with G + C content of 43.7%. The ANI, dDDH and AAI values between the strain GCR5T and the type strains of phylogenetically related species were 60.2-71.1%, 19-24.3%, and 60.2-69.6%, respectively. The strain designated GCR5T produced indole acetic acid (IAA) in the presence of tryptophan only, and auxin responsive genes and tryptophan biosynthesis genes were found in its genome. Based on its polyphasic characteristics, strain GCR5T represents a novel species within the genus Planobacterium, for which the name Planobacterium oryzisolisp. nov. was proposed. The type strain is GCR5T (= KCTC 82713T = TISTR 2996T = TBRC 15746T).Repositories: The draft genome and 16S rRNA gene sequences of strain GCR5T have been deposited at GenBank/EMBL/DDBJ under accession numbers JADKYY000000000 and MN955408, respectively.

Linking the potential activities of methanogens and methanotrophs to their communities under different fertilization regimes in coastal saline paddy soils

Methane (CH4) emissions are primarily dependent on the net balance between the activities of methanogens and methanotrophs. Straw returning (straw residue incorporation) and nitrogen (N) fertilizer applications are two of the most frequent agronomic practices applied to ensure rice yield, and they also profoundly affect the behavior of methanogens and methanotrophs. However, the effect of rice straw or its biochar combined with N fertilizer on the activities and compositions of methanogens and methanotrophs is still not well understood, especially in rice root zone soil in coastal saline paddy fields. Moreover, only few studies linking communities and functions of methanogens and methanotrophs are available, resulting in a lack of adequate indicators to predict methane production potential (MPP) or methane oxidation potential (MOP), for improving fertilizer strategies. Here, through quantitative PCR (qPCR), high-throughput sequencing, network analysis and linear regression model, we investigated the response of the abundances, compositions and activities of methanogens and methanotrophs to rice straw or its biochar combined with N fertilizer in rice root zone soil in coastal regions, and explored the relationships between MPP and methanogenic compositions as well as MOP between methanotrophic compositions, respectively. Therefore, a combination of pot and mesocosm experiment was conducted including seven fertilizer treatments: CK, without N fertilizer and rice straw return; SN100, 100 % N plus straw return; SN80, 80 % N plus straw return; SN60, 60 % N plus straw return; BN100, 100 % N plus rice biochar return; BN80, 80 % N plus biochar return; and BN60, 60 % N plus biochar return. Results showed that irrespective of MPP, MOP, or methanogenic and methanotrophic abundance, they all decreased significantly (P < 0.05), with the reduction of N application under the condition of combined straw or biochar with N fertilizer in coastal saline paddy soils. Moreover, compared with straw, biochar could significantly (P < 0.05) reduce MPP and methanogenic abundances, whereas improve MOP and methanotrophic abundances under the same N application rate. The models incorporating mcrA gene copy and soil dissolved organic carbon (DOC) could accurately predict MPP, while MOP was best predicted by a model incorporating pmoA gene copy and NO3−-N. The family Methanobacteriaceae and Methanosarcinaceae were dominant in the methanogenic co-occurrence and keystone patterns. Correspondingly, the genera Methylocystis and Metilomonas were dominant in the methanotrophic co-occurrence pattern, and genus Methylocystis was also the keystone members in coastal saline root zone soil of rice. Soil DOC and salinity were the key factors in shaping the methanogenic co-occurrence and keystone patterns, whereas the methanotrophic co-occurrence and keystone patterns were mainly regulated by NO3−-N. Furthermore, methanogenic keystone taxa were more suitable for predicting MPP than their co-occurrence pattern. Our findings provide insights into the possibility of key microbial taxa for predicting MPP or MOP for low-carbon production fertilizer application strategies in coastal saline paddy soils.

Electric field-enabled aptasensing interfacial engineering to simultaneously enhance specific preconcentration and electrochemical detection of mercury and lead ions

Aptamers with strong affinity to heavy metal ions (HMIs) allow fabrication of electrochemical sensors with high selectivity and sensitivity, while controllable regulation of aptamer-HMI recognition at the sensing interface, which is vital for better analytical performance, remains challenging. Here, an electric field-based strategy for engineering an aptasensing interface was proposed to realize the specific preconcentration and accurate detection of mercury (Hg2+) and lead (Pb2+) ions with a ratiometric electrochemical sensor. The working principle is to apply an electric field to drive HMIs to approach the aptamer and retain the orientation of the DNA structure. Anthraquinone-2-carboxylic acid (AQ)-labeled complementary DNA was designed to simultaneously bind a ferrocene (Fc)-labeled aptamer for Hg2+ and a methylene blue (MB)-labeled aptamer for Pb2+, and the sensing interface was fabricated with this presynthesized DNA structure. For preconcentration, an electric field of 3.0 V pushed HMIs to approach the aptamer and retained the orientation of DNA to favor the following recognition; for detection, the oriented DNA in 2.5 V electric field offered a stable current of AQ as a reference. In this way, currents of AQ, Fc and MB were used to produce ratiometric signals of IAQ/IFc and IAQ/IMB for Hg2+ and Pb2+, respectively. Such a strategy allowed the simultaneous detection of Hg2+ and Pb2+ within 30 min with detection limits of 0.69 pM and 0.093 pM, respectively. The aptasensor was applied for soil, water, and crayfish analysis in paddy fields. The electric field-enabled strategy offers a new way to fabricate high-performance electrochemical aptasensor for HMIs detection.