Paddy Soil Research Articles

Various microbial taxa couple arsenic transformation to nitrogen and carbon cycling in paddy soils.

Arsenic (As) metabolism pathways and their coupling to nitrogen (N) and carbon (C) cycling contribute to elemental biogeochemical cycling. However, how whole-microbial communities respond to As stress and which taxa are the predominant As-transforming bacteria or archaea in situ remains unclear. Hence, by constructing and applying ROCker profiles to precisely detect and quantify As oxidation (aioA, arxA) and reduction (arrA, arsC1, arsC2) genes in short-read metagenomic and metatranscriptomic datasets, we investigated the dominant microbial communities involved in arsenite (As(III)) oxidation and arsenate (As(V)) reduction and revealed their potential pathways for coupling As with N and C in situ in rice paddies. Five ROCker models were constructed to quantify the abundance and transcriptional activity of short-read sequences encoding As oxidation (aioA and arxA) and reduction (arrA, arsC1, arsC2) genes in paddy soils. Our results revealed that the sub-communities carrying the aioA and arsC2 genes were predominantly responsible for As(III) oxidation and As(V) reduction, respectively. Moreover, a newly identified As(III) oxidation gene, arxA, was detected in genomes assigned to various phyla and showed significantly increased transcriptional activity with increasing soil pH, indicating its important role in As(III) oxidation in alkaline soils. The significant correlation of the transcriptional activities of aioA with the narG and nirK denitrification genes, of arxA with the napA and nirS denitrification genes and of arrA/arsC2 with the pmoA and mcrA genes implied the coupling of As(III) oxidation with denitrification and As(V) reduction with methane oxidation. Various microbial taxa including Burkholderiales, Desulfatiglandales, and Hyphomicrobiales (formerly Rhizobiales) are involved in the coupling of As with N and C metabolism processes. Moreover, these correlated As and N/C genes often co-occur in the same genome and exhibit greater transcriptional activity in paddy soils with As contamination than in those without contamination. Our results revealed the comprehensive detection and typing of short-read sequences associated with As oxidation and reduction genes via custom-built ROCker models, and shed light on the various microbial taxa involved in the coupling of As and N and C metabolism in situ in paddy soils. The contribution of the arxA sub-communities to the coupling of As(III) oxidation with nitrate reduction and the arsC sub-communities to the coupling of As(V) reduction with methane oxidation expands our knowledge of the interrelationships among As, N, and C cycling in paddy soils. Video Abstract.

Sustainable Nitrogen Management in Rice Farming: Spatial Patterns of Nitrogen Availability and Implications for Community-Level Practices

Sustainable nitrogen management is crucial for long-term food security and environmental protection in rice farming systems. However, the spatial patterns of nitrogen availability at the community level remain poorly understood, hindering the development of effective sustainable management strategies. This study introduces a novel application of spatial autoregressive analysis to investigate available nitrogen distribution in paddy soils across a rice farming community in Kyoto, Japan. Soil samples from 61 plots, including organically farmed ones, were analyzed for available nitrogen and various physicochemical properties. Contrary to the hypothesis of high variability between adjacent plots, significant positive spatial autocorrelation in available nitrogen was observed, revealing previously unrecognized community-level patterns. The spatial Durbin model outperformed traditional regression approaches and revealed complex spatial interactions in soil properties. Water-soluble organic carbon and humus content showed strong but opposing effects, with a positive direct impact but negative spatial interaction, suggesting topography-driven accumulation processes. Water-soluble nitrogen exhibited reverse patterns with negative direct effects but positive spatial interaction, indicating potential nutrient transport through water movement. These findings highlight the importance of considering both direct and indirect spatial effects in understanding soil fertility patterns, challenging the conventional plot-by-plot management approach. This methodological advancement provides new perspectives for more effective, community-scale soil management strategies in rice farming systems. Moreover, it demonstrates an innovative approach to maximizing the value of outsourced soil analysis data, providing a model for more comprehensive utilization of such data in agricultural research. By enabling more targeted and efficient nitrogen management practices that consider both plot-level processes and landscape-scale interactions, this study potentially contributes to the development of more sustainable and resilient rice production systems.

Impact of dairy wastewater on paddy rice cultivation, leachate microbes, and soil health under alternate wetting and drying irrigation

Impact of dairy wastewater on paddy rice cultivation, leachate microbes, and soil health under alternate wetting and drying irrigation

Effects of a Novel Tripyrasulfone Herbicide on Key Soil Enzyme Activities in Paddy Rice Soil

Weeds significantly impact paddy yields, and herbicides offer a cost-effective, rapid, and efficient solution compared to manual weeding, ensuring agricultural productivity. Tripyrasulfone, a novel 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor developed by Qingdao Kingagroot Chemicals Co., Ltd., has demonstrated high efficacy when applied post-emergence, causing characteristic foliar bleaching in susceptible weed species, distinct from conventional acetolactate synthase, acetyl-CoA carboxylase, and synthetic auxin herbicides. This study investigates the impact of tripyrasulfone on the activity of key soil enzymes (urease (UE), acid phosphatase (ACP), sucrase (SC), catalase (CAT), and dehydrogenase (DHA)) in paddy soils from Jilin Province and Shandong Province. Different doses of tripyrasulfone (0.1, 1.0, and 2.5 mg kg−1) were applied, and the enzymatic activities were measured. Results indicated that tripyrasulfone initially inhibited UE and ACP activities before activating them. On the 20th day after treatment, UE activity had returned to control levels, whereas ACP activity remained significantly higher, showing long-lasting activation. SC and CAT activities were inhibited but gradually recovered to control levels. Furthermore, DHA activity was activated with a sustained effect, remaining significantly higher than the control group even 20 days after treatment. Overall, the impact of tripyrasulfone on soil enzyme activities diminished over time, suggesting that tripyrasulfone posed minimal long-term ecological risk to soil health.

Kinetic study, byproducts characterization and photodegradation pathway of profoxydim in a biochar water soil system

The study focused on the photodegradation of profoxydim, a low-toxicity cyclohexanedione herbicide commonly used in rice crops, under simulated sunlight conditions. Profoxydim’s behavior in paddy field conditions is not well understood, and this research aimed to fill that gap, particularly examining the effect of commonly utilized organic amendments such as biochar (BC) on its degradation. Results indicated that profoxydim degrades rapidly, with a half-life of 2.4 ± 0.3 h in paddy water and 1.03 ± 0.1 h in paddy soil. However, when BC was introduced, the degradation slowed significantly, extending the half-lives to 3.1 ± 0.2 h in water and 3.07 ± 0.5 h in soil. The study identified five degradation products (DPs) using TOF mass accuracy measurements and MS/MS spectra fragmentation. Two of these DPs were found to be more stable than profoxydim itself. Additionally, the research proposed a novel photodegradation pathway, highlighting processes such as homolytic C-N bond cleavage, photoisomerization, and photoinduced oxidation. The study’s findings contribute new insights into the environmental fate of profoxydim, offering a deeper understanding of its transformation in rice paddy fields and aiding in the assessment of potential risks associated with its residues in agricultural environments.

Role of methanotrophic communities in atmospheric methane oxidation in paddy soils

Wetland systems are known methane (CH4) sources. However, flooded rice fields are periodically drained. The paddy soils can absorb atmospheric CH4 during the dry seasons due to high-affinity methane-oxidizing bacteria (methanotroph). Atmospheric CH4 uptake can be induced during the low-affinity oxidation of high-concentration CH4 in paddy soils. Multiple interacting factors control atmospheric CH4 uptake in soil ecosystems. Broader biogeographical data are required to refine our understanding of the biotic and abiotic factors related to atmospheric CH4 uptake in paddy soils. Thus, here, we aimed to assess the high-affinity CH4 oxidation activity and explored the community composition of active atmospheric methanotrophs in nine geographically distinct Chinese paddy soils. Our findings demonstrated that high-affinity oxidation of 1.86 parts per million by volume (ppmv) CH4 was quickly induced after 10,000 ppmv high-concentration CH4 consumption by conventional methanotrophs. The ratios of 16S rRNA to rRNA genes (rDNA) for type II methanotrophs were higher than those for type I methanotrophs in all acid-neutral soils (excluding the alkaline soil) with high-affinity CH4 oxidation activity. Both the 16S rRNA:rDNA ratios of type II methanotrophs and the abundance of 13C-labeled type II methanotrophs positively correlated with high-affinity CH4 oxidation activity. Soil abiotic factors can regulate methanotrophic community composition and atmospheric CH4 uptake in paddy soils. High-affinity methane oxidation activity, as well as the abundance of type II methanotroph, negatively correlated with soil pH, while they positively correlated with soil nutrient availability (soil organic carbon, total nitrogen, and ammonium-nitrogen). Our results indicate the importance of type II methanotrophs and abiotic factors in atmospheric CH4 uptake in paddy soils. Our findings offer a broader biogeographical perspective on atmospheric CH4 uptake in paddy soils. This provides evidence that periodically drained paddy fields can serve as the dry-season CH4 sink. This study is anticipated to help in determining and devising greenhouse gas mitigation strategies through effective farm management in paddy fields.

Investigating the effects of various irrigation methods on bacterial communities in paddy soil

Different irrigation methods can impact the micro-ecological environment of paddy soil, affecting crop growth. This study focuses on County A, a key grain production area on China’s East Coast, where 20 plots each of intermittent and flood irrigation were selected and labeled as Group I and Group F, respectively. Soil's basic physicochemical properties and heavy metal content were measured in the laboratory, and high-throughput sequencing was used to analyze soil bacterial communities. The study evaluated the impact mechanisms of different irrigation methods on these bacterial communities. Results indicate: (1) Intermittent irrigation significantly increased bacterial richness, evenness, and diversity, enhancing microbial community diversity and stability. (2) Intermittent irrigation notably raised the abundance of 9 bacterial genera (e.g., Nitrospira, H16) while reducing the abundance of 7 genera (e.g., Geobacter, Sphingomonas). (3) The soil environment in Group I was stable, with bacterial communities influenced by SMC, pH, and Cu; Group F was affected by multiple environmental factors. Intermittent irrigation provides a stable environment that supports bacterial diversity and abundance, contributing to a richer community structure. (4) Intermittent irrigation optimizes moisture, significantly enhancing bacterial functions such as energy production, cell wall biosynthesis, repair, and signal transduction. These findings suggest that intermittent irrigation improves bacterial community stability and diversity, which is crucial for enhancing the overall quality of paddy fields.

The effects of long-term rice straw and biochar return on soil humus composition and structure in paddy soil

The effects of long-term rice straw and biochar return on soil humus composition and structure in paddy soil

Inhibition of autotrophic nitrifiers in a nitrogen-rich paddy soil by elevated CO2

Inhibition of autotrophic nitrifiers in a nitrogen-rich paddy soil by elevated CO2

Enterobacter-infecting phages in nitrogen-deficient paddy soil impact nitrogen-fixation capacity and rice growth by shaping the soil microbiome

Bacteriophages (“phage”) play important roles in nutrient cycling and ecology in environments by regulating soil microbial community structure. Here, metagenomic sequencing showed that a low relative abundance of nitrogen-fixing bacteria but high abundance of Enterobacter-infecting phages in paddy soil where rice plants showed nitrogen deficiency. From soil in the same field, we also isolated and identified a novel virulent phage (named here as Apdecimavirus NJ2) that infects several species of Enterobacter and characterized its impact on nitrogen fixation in the soil and in plants. It has the morphology of the Autographiviridae family, with a dsDNA genome of 39,605 bp, 47 predicted open reading frames and 52.64 % GC content. Based on genomic characteristics, comparative genomics and phylogenetic analysis, Apdecimavirus NJ2 should be a novel species in the genus Apdecimavirus, subfamily Studiervirinae. After natural or sterilized field soil was potted and inoculated with the phage, soil nitrogen-fixation capacity and rice growth were impaired, the abundance of Enterobacter decreased, along with the bacterial community composition and biodiversity changed compared with that of the unadded control paddy soil. Our work provides strong evidence that phages can affect the soil nitrogen cycle by changing the bacterial community. Controlling phages in the soil could be a useful strategy for improving soil nitrogen fixation.

Modulation of irrigation-induced microbial nitrogen‑iron redox to per- and polyfluoroalkyl substances' water-soil interface release in paddy fields: Activation or immobilization?

Understanding the modulation of paddy field irrigation to the migration of per- and polyfluoroalkyl substances (PFAS) at the water-soil interface is pivotal for the management of PFAS pollution in paddy soil and surrounding surface water environments. In flooded soils, soil organic matter was transformed into aromatic protein-like dissolved organic matter (DOM). Meanwhile, Na+, K+, and Mg2+ were translocated into extracellular polymeric substances (EPS) under the catalysis of cation channel enzymes (p < 0.05), provided ion bridging for the binding of DOM and PFAS, and accelerated the accumulation of C4–C9 PFAS in overlying water (41.79–99.14 %). Short-chain PFAS's accumulation in soil solution of drought soils was stimulated by microorganisms secreting soluble microbial by-product-like DOM (53.15–97.96 %). Furthermore, PFAS's distribution in flood soils was dominated by bacterial denitrification and iron-reduction, whereas iron-oxidation and ammoxidation controlled that in drought soils. The transformation of organic carbon including CO and COC caused by irrigation-induced redox modulated PFAS cross-media translocation. Iron‑nitrogen redox in flooded paddy soils immobilized the PFAS's migration into overlying water (p < 0.05). Our findings have profound implications for PFAS's pollution control, surface water environmental protection, and rice production security in paddy fields.

Pollution assessment, ecological risk and source identification of heavy metals in paddy soils and rice grains from Salem, South India

The present study investigated concentrations of metals (Cu, Zn, Fe, Mn, Ni, Pb, and Cd) in paddy soils and rice tissues of nine different widely used indica rice varieties in Salem district, India. The order of DTPA soil available metal contents (mg kg-1) were Fe (33.50) > Mn (8.86) > Cu (2.58) > Pb (1.99) > Zn (1.67) > Ni (1.48) > Cd (0.13). Pollution load index (PLI) levels for Cd (1.28) were ‘moderately polluted’, contamination factor (CF) and enrichment factor (EF) values for all metals showed ‘medium contamination’ and ‘less enrichment’ except for Cu and Pb. Ecological risk factor (ERF) and potential ecological risk index (PRI) values of Cd (31.94 and 287.50) showed ‘moderate risk’ and ‘strong ecological risk’. Bio-accumulation factor (BAF) levels of Cd (48.12) and Pb (27.89) are classified as ‘high concentrators’. Translocation factor (TF) values of Pb (2.9), Cd (2.5) and Ni (1.7) were greater than one for roots to plants. Children had higher target hazard quotient (THQ) and hazard index (HI) values for Cd, Pb and Ni than adults. Principal component analysis (PCA) revealed with all parameters that they fell within the two primary factors 1 and 2, with an eigenvalue of 4.69 (33.52% variation) and 3.73 (26.66% variation), respectively. However, cluster analysis (CA) revealed three distinct groups between the metals studied. Although the soil metal contents were within the permissible levels, the grain Cd (6.07 mg kg-1), Pb (56.20 mg kg-1), and Fe (116.11 mg kg-1) contents in all the rice varieties exceeded the prescribed limits of 0.4, 0.2, and 15 mg kg-1, respectively. Our findings will provide important data for metal enrichment in soils to implement more effective measures to reduce the contamination of metals in paddy fields.

New insights into aqueous Hg(II) photoreduction from paddy field system to natural water: Gear effect of straw returning and soil tillage

Soil dissolved organic matter (SDOM) has a strong complex with divalent mercury (Hg(II)) and can affect the fate of aqueous Hg(II) photoreduction. However, little is known about the influence of straw returning and soil tillage on the composition of SDOM in paddy soil and Hg(II) photoreduction in paddy water. Here, we demonstrate that the combined drivers of long-term straw returning and tillage can result in higher degrees of aromatization, and the enrichment of oxygen-containing functional groups in surface SDOM. Hg(II) photoreduction under low Hg/DOC conditions is mainly constrained by the composition of SDOM, whereas solar radiation emerged as a dominant controlling factor associated with high ratio of Hg/DOC. By increasing the release of SDOM and mobility of Hg(II), reducing the stability of Hg(II)-SDOM complexes, and potentially enhancing generation of reactive intermediates, gear effect of straw returning and soil tillage significantly enhanced Hg(II) photoreduction in the presence of surface SDOM from 0-40cm (maximum photoreduction percentage can reach 44.76 ± 2.24%). Previous inventories of Hg(0) emissions from paddy field system may have overlooked or underestimated this critical process. Future modeling work should be carried out to evaluate the role of straw returning and soil tillage on global Hg cycle.

Evaluation of climate conditions and ecological traits that limit the distribution expansion of alien Lolium rigidum in Japan

Invasive alien plants cause severe global problems; therefore, determining the factors that lead to the success or failure of invasion is a critical question in the field of invasion ecology. In this study, we aimed to determine the factors underlying differences in the distribution range of alien plants in Japan by investigating why Lolium multiflorum thrives in a wide range of habitats while L. rigidum is mainly distributed on sandy beaches. We initially evaluated environmental niche suitability through species distribution modelling and subsequently examined whether species traits influence the differences in range expansion between the two species. We used MaxEnt modelling to identify potential environmental niches for both species. The analysis revealed that L. rigidum was considerably less suited to the Japanese climate compared to L. multiflorum, with high summer precipitation in Japan identified as one of the climatic factors limiting the distribution of L. rigidum. Given that these winter annual plants remain dormant as seeds during summer, in subsequent experiments, we buried seeds in paddy field soil and sandy beach sand during summer and evaluated their survival rate in autumn. The survival rate of L. rigidum seeds was significantly lower than that of L. multiflorum, particularly in paddy soil. Factors contributing to seed mortality may include the decay or early germination of L. rigidum seeds under Japan’s high rainfall conditions. This study emphasises the importance of considering local environmental factors alongside climate niche modelling in the risk assessment of invasive species. Moreover, the integration of species distribution modelling for large-scale evaluations and manipulation experiments for fine-scale assessments proved effective in identifying climatic conditions and species traits influencing the success or failure of alien species invasion.

Influence of Trenchless Subsurface Drainage with a Rice Husk Filling System on Soybean Productivity Under a Poorly Drained Paddy Field for Future Applications in Smart Agriculture

In South Korea, paddy fields are increasingly being planted with soybeans to address rice supply and demand issues and increase soybean self-sufficiency. The field crops cannot grow healthily without adequate drainage due to the paddy fields storing water easily. In this study, we identified that Rice Husk Filling Drainage Method (RHDM) technology improved soil permeability and soil aeration. We also found that the soil moisture content was reduced and the water table remained at a lower level in the RHDM plot as compared to the control plot. The soybean moisture stress index showed that in the RHDM plot, the safety standard for stress due to excessive moisture at the 2 m interval was met. The soybean yield was increased by up to 35% in the 2 m RHDM construction interval compared to the control plot. In addition, the high hydraulic conductivity of the rice husk used as the hydrophobic material confirmed sufficient drainage performance and was considered economically advantageous. Therefore, our results show that RHDM is a highly efficient and economical drainage method in poorly drained paddy soils. Drainage management is essential for stable crop production in poorly drained paddy fields. Our research findings suggest that an efficient open field water management method is viable, which we believe will lead to future advances in open field smart agriculture.

Unprecedented N2O production by nitrate-ammonifying Geobacteraceae with distinctive N2O isotopocule signatures.

Dissimilatory nitrate reduction to ammonium (DNRA), driven by nitrate-ammonifying bacteria, is an increasingly appreciated nitrogen-cycling pathway in terrestrial ecosystems. This process reportedly generates nitrous oxide (N2O), a strong greenhouse gas with ozone-depleting effects. However, it remains poorly understood how N2O is produced by environmental nitrate-ammonifiers and how to identify DNRA-derived N2O. In this study, we characterize two novel enzymatic pathways responsible for N2O production in Geobacteraceae strains, which are predominant nitrate-ammonifying bacteria in paddy soils. The first pathway involves a membrane-bound nitrate reductase (Nar) and a hybrid cluster protein complex (Hcp-Hcr) that catalyzes the conversion of NO2- to NO and subsequently to N2O. The second pathway is observed in Nar-deficient bacteria, where the nitrite reductase (NrfA) generates NO, which is then reduced to N2O by Hcp-Hcr. These enzyme combinations are prevalent across the domain Bacteria. Moreover, we observe distinctive isotopocule signatures of DNRA-derived N2O from other established N2O production pathways, especially through the highest 15N-site preference (SP) values (43.0‰-49.9‰) reported so far, indicating a robust means for N2O source partitioning. Our findings demonstrate two novel N2O production pathways in DNRA that can be isotopically distinguished from other pathways.IMPORTANCEStimulation of DNRA is a promising strategy to improve fertilizer efficiency and reduce N2O emission in agriculture soils. This process converts water-leachable NO3- and NO2- into soil-adsorbable NH4+, thereby alleviating nitrogen loss and N2O emission resulting from denitrification. However, several studies have noted that DNRA can also be a source of N2O, contributing to global warming. This contribution is often masked by other N2O generation processes, leading to a limited understanding of DNRA as an N2O source. Our study reveals two widespread yet overlooked N2O production pathways in Geobacteraceae, the predominant DNRA bacteria in paddy soils, along with their distinctive isotopocule signatures. These findings offer novel insights into the role of the DNRA bacteria in N2O production and underscore the significance of N2O isotopocule signatures in microbial N2O source tracking.

Optimal Relationship Between As and Cd in Porewater of Paddy Soils with Variations in pe + pH: Insight from Trade-Off Value Analysis

The remediation of paddy soils co-contaminated with As and Cd is tricky. It is difficult to decrease Cd and As availability simultaneously due to their opposite geochemical characteristics. Finding the optimal trade-off relationship between As and Cd availability in paddy soils is a significant task that is necessary to guide the construction of water management measures. This study investigated the dissolution characteristics of As, Cd, Fe, Mn, DOC, DOM, and various As and Cd fractions in soils via the microcosm system and calculated the optimal trade-off value for available As and Cd in porewater. The results showed that the total As in porewater increased rapidly when the soil Eh was reduced to −104 mV. Meanwhile, the total Cd in porewater decreased dramatically when the soil Eh was below 62 mV. Under flooding and drainage conditions, Fe/Mn (oxyhydro)oxides play a vital role in regulating Cd dissolution in paddy soils, while Fe/Mn (oxyhydro)oxides organically bind sulfide together to determine the dissolution of As. Additionally, the optimal pe + pH response to the minimum trade-off value of available As and Cd in porewater was found to be 6.6, which indicates a moderate reduction status. Therefore, further research should apply the optimal pe + pH to construct water management measures to safely utilize co-contaminated paddy fields.

Four birds with one stone: applying nitrification inhibitor on the basis of percarbamide restores yield, decreases fungicide residue, enhances soil multifunctionality and stimulates bacterial community.

Fungicide residues were frequently detected in vegetables and soils, which severely affected crop yields and qualities. Reasonable nitrogen management might promote yields and decrease fungicide carbendazim residues in plant-soil systems. Current study explores comprehensive relationships among carbendazim residues, crop yields, soil multifunctionalities and endophytic and soil bacterial communities after applying nitrification inhibitors (3,4-dimethylpyrazole phosphate and dicyandiamide) and percarbamide to different soils. Combined nitrification inhibitor and percarbamide additions produced multi-effects on restoring yields, declining fungicide residues, promoting soil multifunctionalities and stimulating bacterial communities. Relative to the control, percarbamide application promoted carbendazim dissipations in upland soils but decreased bacterial community diversities and stabilities in different soils. Compared to exclusive percarbamide, extra dicyandiamide applications decreased carbendazim residues by 25.8% in upland soils and 70.2% in paddy soils, declined carbendazim residues in carrots via improving soil pH, ammonium nitrogen (NH4 +-N) and Proteobacteria ratios. Relative to percarbamide application alone, extra dicyandiamide addition promoted the dry carrot yields by 133.2% in upland soils and 33.5% in paddy soils via promoting soil NH4 +-N, Acidobacteriota and Actinobacteriota ratios and bacterial community diversities and stabilities. Upland soil multifunctionality improvements diminished soil carbendazim residues via promoting soil pH and NH4 +-N, and paddy soil multifunctionalities and endophytic bacterial community structures generated negative influences on carrot carbendazim residues. Our study suggested that nitrification inhibitor on the basis of percarbamide generated multi-effects on the different crop-soil systems: restoring carrot yields, reducing carbendazim contents, promoting soil multifunctionalities and stimulating bacterial community diversities and stabilities. © 2024 Society of Chemical Industry.

Isolation of Heavy Metal-Tolerant and Anti-Phytopathogenic Plant Growth-Promoting Bacteria from Soils.

In this study, by isolating multifunctional soil bacteria that can promote plant development, resist heavy metals, exhibit anti-phytopathogenic action against plant diseases, and produce extracellular enzymes, we hope to improve the effectiveness of phytoremediation techniques. To isolate multifunctional soil bacteria, we used soils with diverse characteristics as isolation sources. To look into the diversity and structural traits of the bacterial communities, We conducted amplicon sequencing of the 16S rRNA gene on five types of soils and predicted functional genes using Tax4Fun2. The isolated bacteria were evaluated for their multifunctional capabilities, including heavy metal tolerance, plant growth promotion, anti-phytopathogenic activity, and extracellular enzyme activity. The genes related to plant growth promotion and anti-phytopathogenic activity were most abundant in forest and paddy soils. Burkholderia sp. FZ3 and FZ5 demonstrated excellent heavy metal resistance (≤ 1 mM Cd and ≤ 10 mM Zn), Pantoea sp. FC24 exhibited the highest protease activity (24.90 μmol tyrosine·g-DCW-1·h-1), and Enterobacter sp. PC20 showed superior plant growth promotion, especially in siderophore production. The multifunctional bacteria isolated using traditional methods included three strains (FC24, FZ3, and FZ5) from the forest and one strain (PC20) from paddy field soil. These results indicate that, for the isolation of beneficial soil microorganisms, utilizing target gene information obtained from isolation sources and subsequently exploring target microorganisms is a valuable strategy.

Differential effects of pH on cadmium accumulation in Artemisia argyi growing in low and moderately cadmium-contaminated paddy soils

BackgroundPhytoremediation is affected by physical and chemical properties of the soil such as soil pH, moisture, and nutrient content. Soil pH is a key element influencing Cd bioavailability and can be easily adjusted in agricultural practices. The soil pH level may relate to the effectiveness of phytoremediation; however, this has not been extensively investigated. In the current study, we evaluated the effect of Cd contamination level (0.56 and 0.92 mg/kg) and soil pH (5, 6, and 7) on Cd accumulation and allocation in Artemisia argyi, a fast-growing perennial crop.ResultsOur results indicated that higher soil Cd concentrations reduce A. argyi biomass, and the loss of the root mass was particularly significant. Higher soil pH decreased Cd content in stems and roots of A. argyi cultivated in moderately Cd-polluted soil, and increased Cd content in stems and roots of the plant grown in low Cd-polluted soil. Higher soil pH decreased the percentage of Cd distributed in the soluble fraction and cell walls and increased the percentage of Cd in the organelles of leaf cells for moderate soil Cd levels. The bioconcentration and translocation factor exceeded 4.0 and 1.0, respectively, across all tested treatments, indicating that A. argyi is a promising candidate for phytoremediation. Notably, the effects of soil pH on Cd accumulation and subcellular distribution in A. argyi differed between low and moderately Cd-contaminated soils.ConclusionAdjustments to soil pH based on the degree of Cd contamination can enhance Cd extraction by A. argyi, thereby reducing the overall remediation cycle of cadmium-polluted paddy fields of South China.Graphical