Microbial Community In Paddy Soil Research Articles

Effects of Biochar and Straw Amendment on Soil Fertility and Microbial Communities in Paddy Soils.

Straw and biochar, two commonly used soil amendments, have been shown to enhance soil fertility and the composition of microbial communities. To compare the effects of straw and biochar on soil fertility, particularly focusing on soil dissolved organic matter (DOM) components, and the physiochemical properties of soil and microbial communities, a combination of high-throughput sequencing and three-dimensional fluorescence mapping technology was employed. In our study, we set up four treatments, i.e., without biochar and straw (B0S0); biochar only (B1S0); straw returning only (B0S1); and biochar and straw (B1S1). Our results demonstrate that soil organic matter (SOM), available nitrogen (AN), and available potassium (AK) were increased by 34.71%, 22.96%, and 61.68%, respectively, under the B1S1 treatment compared to the B0S0 treatment. In addition, microbial carbon (MBC), dissolved organic carbon (DOC), and particulate organic carbon (POC) were significantly increased with the B1S1 treatment, by 55.13%, 15.59%, and 125.46%, respectively. The results also show an enhancement in microbial diversity, the composition of microbial communities, and the degree of soil humification with the application of biochar and straw. Moreover, by comparing the differences in soil fertility, DOM components, and other indicators under different treatments, the combined treatments of biochar and straw had a more significant positive impact on paddy soil fertility compared to biochar. In conclusion, our study revealed the combination of straw incorporation and biochar application has significant impacts and is considered an effective approach to improving soil fertility.

Different microbial communities in paddy soils under organic and nonorganic farming.

Organic agriculture is a farming method that provides healthy food and is friendly to the environment, and it is developing rapidly worldwide. This study compared microbial communities in organic farming (Or) paddy fields to those in nonorganic farming (Nr) paddy fields based on 16S rDNA sequencing and analysis. The predominant microorganisms in both soils were Proteobacteria, Chloroflexi, Acidobacteria, Actinobacteria, and Nitrospirota. The alpha diversity of the paddy soil microbial communities was not different between the nonorganic and organic farming systems. The beta diversity of nonmetric multidimensional scaling (NMDS) revealed that the two groups were significantly separated. Distance-based redundancy analysis (db-RDA) suggested that soil pH and electrical conductivity (EC) had a positive relationship with the microbes in organic paddy soils. There were 23 amplicon sequence variants (ASVs) that showed differential abundance. Among them, g_B1-7BS (Proteobacteria), s_Sulfuricaulis limicola (Proteobacteria), g_GAL15 (p_GAL15), c_Thermodesulfovibrionia (Nitrospirota), two of f_Anaerolineaceae (Chloroflexi), and two of g_S085 (Chloroflexi) showed that they were more abundant in organic soils, whereas g_11-24 (Acidobacteriota), g__Subgroup_7 (Acidobacteriota), and g_Bacillus (Firmicutes) showed differential abundance in nonorganic paddy soils. Functional prediction of microbial communities in paddy soils showed that functions related to carbohydrate metabolism could be the major metabolic activities. Our work indicates that organic farming differs from nonorganic farming in terms of microbial composition in paddy soils and provides specific microbes that might be helpful for understanding soil fertility.

Arsenic methylation and microbial communities in paddy soils under alternating anoxic and oxic conditions

Arsenic (As) methylation in soils affects the environmental behavior of As, excessive accumulation of dimethylarsenate (DMA) in rice plants leads to straighthead disease and a serious drop in crop yield. Understanding the mobility and transformation of methylated arsenic in redox-changing paddy fields is crucial for food security. Here, soils including un-arsenic contaminated (N-As), low-arsenic (L-As), medium-arsenic (M-As), and high-arsenic (H-As) soils were incubated under continuous anoxic, continuous oxic, and consecutive anoxic/oxic treatments respectively, to profile arsenic methylating process and microbial species involved in the As cycle. Under anoxic-oxic (A-O) treatment, methylated arsenic was significantly increased once oxygen was introduced into the incubation system. The methylated arsenic concentrations were up to 2–24 times higher than those in anoxic (A), oxic (O), and oxic-anoxic (O-A) treatments, under which arsenic was methylated slightly and then decreased in all four As concentration soils. In fact, the most plentiful arsenite S-adenosylmethionine methyltransferase genes (arsM) contributed to the increase in As methylation. Proteobacteria (40.8%–62.4%), Firmicutes (3.5%–15.7%), and Desulfobacterota (5.3%–13.3%) were the major microorganisms related to this process. These microbial increased markedly and played more important roles after oxygen was introduced, indicating that they were potential keystone microbial groups for As methylation in the alternating anoxic (flooding) and oxic (drainage) environment. The novel findings provided new insights into the reoxidation-driven arsenic methylation processes and the model could be used for further risk estimation in periodically flooded paddy fields.

Microbial communities in paddy soils: differences in abundance and functionality between rhizosphere and pore water, influence of different soil organic carbon, sulfate fertilization, and cultivation time, and contribution to arsenic mobility and speciation.

Abiotic factors and rhizosphere microbial populations influence arsenic accumulation in rice grains. Despite mineral and organic surfaces are keystones in element cycling, localization of specific microbial reactions in the root/soil/pore water system is still unclear. Here, we tested if original unplanted soil, rhizosphere soil, and pore water represented distinct ecological microniches for arsenic-, sulfur- and iron-cycling microorganisms and compared the influence of relevant factors such as soil type, sulfate fertilization, and cultivation time. In rice open-air-mesocosms with two paddy soils (2.0% and 4.7% organic carbon), Illumina 16S rRNA gene sequencing demonstrated little significant effects of cultivation time and sulfate fertilization that decreased Archaea-driven microbial networks and incremented sulfate reducing and sulfur oxidizing bacteria. Different compartments, characterized by different bacterial and archaeal compositions, had the strongest effect with higher microbial abundances, bacterial biodiversity and interconnections in the rhizosphere versus pore water. Within each compartment, a significant soil type effect was observed. Higher percentage contributions of rhizosphere dissimilatory arsenate- and iron-reducing, arsenite-oxidizing, and, surprisingly, dissimilatory sulfate-reducing bacteria as well as pore water iron-oxidizing bacteria in the lower organic carbon soil supported previous chemistry-based interpretations of a more active S-cycling, a higher percentage of thioarsenates, and lower arsenic mobility by sorption to mixed Fe(II)Fe(III)-minerals in this soil.

A joint role of iron oxide and temperature for methane production and methanogenic community in paddy soils

Microbial methanogenesis in paddy soils contributes approximately one-fifth of global anthropogenic methane (CH4) release, creating severe negative climate feedback. The dynamics of iron oxides in flooded paddy fields, as well as temperature changes, have an impact on CH4 production. However, the relationship between the two, as well as their interactive mechanisms in influencing CH4 production and microbial communities in paddy soils, is not yet clear. Therefore, we investigated the interactive effects of temperature (15, 25 and 35 °C) and iron oxide (ferrihydrite) on CH4 production and methanogenic community structure in two Chinese paddy soils, one subtropical and one temperate. We characterized shifts in microbial communities using high-throughput sequencing of bacteria, archaea and methanogenic mcrA genes following an anaerobic incubation for 90 days. Our results showed that temperature significantly promoted Fe reduction in paddy soils, and both together regulated CH4 production by reducing the number of methanogens. Additionally, the temperature sensitivity of methanogenesis was higher in the temperate than in the subtropical paddy soil. We also demonstrated that ferrihydrite can inhibit methanogenesis by reducing the relative abundance of Methanosarcinales and altering the community patterns of methanogens in these paddy soils. Likewise, increases in temperature changes the relative abundance of Methanosarcinales and Methanobacteriales, promoting methanogenesis. Overall, our results provide new insights into the role of iron oxides and temperature in regulating greenhouse gas emissions from paddy soils.

Long-term integrated rice-crayfish culture disrupts the microbial communities in paddy soil

The integrated rice-crayfish culture (IRCC) mode has been developed for more than twenty years in China, but little information could be obtained on the microbial communities in paddy soil under this mode. This study used 16SrRNA and ITS Illumina high-throughput sequencing to investigate microbial communities, diversity, and function in paddy soil under different IRCC times (0, 2, 4, 6, and 10 years). With increasing culture time, IRCC mode altered the relative abundance of dominant taxa, showing a significant decrease in the relative abundance of Actinobacteria and Chytridiomycota, with an increase in Proteobacteria and Firmicutes. The species richness and diversity of bacteria/fungi in 10-year IRCC paddy soil were significantly lower than in other groups (P < 0.05). Bacterial functional potential prediction by PICRUSt2 and phenotype prediction by BugBase showed that long-term IRCC significantly reduced the relative abundance of carbohydrate metabolism and increased the relative abundance of pathogenic potential and anaerobic phenotype (P < 0.05). Saprotrophs and pathotrophs dominated the fungal communities, and higher relative abundances of the plant pathogens, fungal parasites and lichen pathogens were found in IRCC soil (2- and 4-year) (P < 0.05). Microbial communities were mainly influenced by ammonium nitrogen, nitrate nitrogen, soil moisture content, and total carbon. Long-term IRCC could significantly change microbial communities and functions, while reducing microbial diversity in paddy soil. A “resting period” is recommended to ensure the sustainable development of ecological agriculture in paddy fields.

Differential Microbial Communities in Paddy Soils Between Guiyang Plateaus and Chengdu Basins Drive the Incidence of Rice Bacterial Diseases.

Southwest China has the most complex rice-growing regions in China. With great differences in topography, consisting mainly of basins and plateaus, ecological factors differ greatly between regions. In this study, bulk paddy soils collected from long-term rice fields in Chengdu (basins) and Guiyang (plateaus) were used to study the correlation between microbial diversity and the incidence of rice bacterial diseases. Results showed that the microbial community composition in paddy soils and the microbial functional categories differed significantly between basins and plateaus. They shared >70% of the dominant genera (abundance >1%), but the abundance of the dominant genera differed significantly. Functional analysis found that bulk paddy soils from Chengdu were significantly enriched in virulence factor-related genes; soils from Guiyang were enriched in biosynthesis of secondary metabolites, especially antibiotics. Correspondingly, Chengdu was significantly enriched in leaf bacterial pathogens Acidovorax, Xanthomonas, and Pseudomonas. Greenhouse experiments and correlation analysis showed that soil chemical properties had a greater effect on microbial community composition and positively correlated with the higher incidence of rice bacterial foot rot in Guiyang, whereas temperature had a greater effect on soil microbial functions and positively correlated with the higher severity index of leaf bacterial diseases in Chengdu. Our results provide a new perspective on how differences in microbial communities in paddy soils can influence the incidence of rice bacterial diseases in areas with different topographies.

Influences of arsenate and/or phosphate adsorption to ferrihydrite on iron-reducing and arsenic-reducing microbial communities in paddy soil revealed by rRNA-13C-acetate probing

Iron (oxyhydr)oxides [Fe(III)] are important adsorbents of arsenate [As(V)] and phosphate in paddy soils, and microbial Fe(III) reduction is hence central to biogeochemical cycles of arsenic and phosphorus. Nevertheless, how Fe(III) reducers and As(V) reducers at the community level respond to As(V) and phosphate adsorption in paddy soils remain unclear. Here, we explored the influences of arsenate and/or phosphate adsorption to ferrihydrite on active acetate-dependent Fe(III)-reducing and As(V)-reducing microbial communities in a paddy soil, using 13C-acetate-based rRNA-stable isotope probing (SIP). During anaerobic SIP incubations, the arsenate and/or phosphate adsorption to ferrihydrite retarded Fe(III) reduction to various extents, with arsenate alone or combined with phosphate having greater inhibitory effects than phosphate alone. 16S rRNA-based sequencing results revealed that the adsorption of arsenate alone or combined with phosphate markedly enriched several Fe(III) reducers that have also been found to enable arsenate reduction, especially Geobacter genus. This was coincided with the pronounced increment in transcript abundance of arsenate-respiring gene (arrA) induced by the presence of arsenate and further confirmed by cloning and sequencing result which indicated that Geobacter spp. harboring arrA gene were the major As(V) reducers herein. In contrast, the presence of arsenate led to a remarkable decline in other Fe(III) reducers, including Dechloromonas and Thermincola genera, which have rarely been reported to be related to arsenate transformation. Furthermore, all these identified Fe(III) reducers declined significantly by phosphate adsorption alone. Additionally, the adsorption of phosphate to ferrihydrite not only boosted the reduction of adsorbed As(V), but also enriched the respiratory As(V)-reducing microbes containing arrA gene. These findings demonstrate that the adsorption of arsenate and/or phosphate inhibits Fe(III) reduction while promotes As(V) reduction, and shifts the Fe(III)-reducing and As(V)-reducing microbial communities in paddy soils. Overall this study provides novel insights into intricate biogeochemical coupling between iron, arsenic and phosphorus in paddy soils.

Animal manures promoted soil phosphorus transformation via affecting soil microbial community in paddy soil

Animal manures are reported as good substitutes for chemical fertilizers to mobilize soil phosphorus (P). However, the mechanisms on how different types of manures regulate microbial biomass involved in P mobilization remain unclear. In this study, we conducted a two-year field experiment to investigate variations in soil microbial biomass carbon (MBC) and P (MBP) and P fractions after 30% animal manures substitution (pig manure (PM), chicken manure (CM), and dairy manure (DM)) in paddy soil. Furthermore, a 30-day incubation experiment was used to explore the mechanisms of soil P transformation induced by 100% manures addition. Two-year field experiment results showed that, compared to the chemical NPK fertilizer, 30% manure substitution didn't influence rice and wheat yields significantly but decreased soil total P loss from runoff by 3.2%. However, 30% manure substitution significantly enhanced MBC and MBP by 11.3–18.4% and 57.1–81.2%, respectively, which also promoted the transformation of moderately labile P (M-P) to labile P (L-P). Moreover, the incubation experiment also convinced that all manures caused higher MBC than chemical P fertilizer. Meanwhile, compared to the no P fertilizer, manures increased L-P and organic P by 2.7%–14.7% and 6.4%–20.0%, respectively. Redundancy analysis indicated that soil MBC/MBP ratio was the main factor to soil L-P and M-P, indicating that animal manures can improve soil microbial abundance and thus promote M-P to L-P in soil. Among three animal manures, PM could improve the mobilization potential of P mostly, due to the highest C source activity by 13C NMR analysis. Our study indicated that animal manures especially PM can be considered as a good candidate for agricultural P management in paddy soils because of their capacity to promote soil P transformation.

Characteristics of Microbial Utilization for Crop Residue-Derived C in Paddy and Upland Soils

Two typical subtropical agricultural soils, a flooded paddy soil and its adjacent upland, were collected and then incubated with or without 13C-labeled crop residue (maize straw) for 40 days. During the incubation, the mineralization rate of the crop residue was monitored, and the 13C incorporated into fungal and bacterial phospholipid fatty acid (PLFA) was quantified. At the early stage (0.25-1 days), the mineralization rate of crop residue was faster in paddy soil than that in upland soil, whereas the opposite trend was observed from 2 to 20 days. At the late stage (21-40 days), the mineralization rate was similar in both soils. At the end of incubation, 11% of the total crop residue was mineralized in paddy soil, which was about half of that in upland soil (20%). Although paddy soil had a higher amount of microbial biomass (indicated by total PLFA), the total amounts of 13C-PLFA were comparable in both soils, and the enrichment ratio (proportion of 13C to total C in PLFA) was lower in paddy soil than that in upland soil. This indicated that the microbial community in paddy soil was less active in the uptake of crop residue C than that in upland soil. During the incubation, the residue-derived 13C was mainly distributed in bacterial PLFA (up to 86% of total 13C-PLFA, including 59% in gram-positive and 27% in gram-negative bacteria) in paddy soil, and up to 75% of total 13C-PLFA distributed in fungal PLFAs was in upland soil. Thus, bacteria dominated the utilization of crop residue in paddy soil versus fungi in upland soil. Compared with that in upland soil, the microbial activity was suppressed in the anaerobic condition caused by flooding in paddy soil, with a stronger inhibition of fungi than bacteria. Considering the discrepancies of life strategies and necromass turnover between bacteria and fungi, the different dominant microbial groups in the utilization of crop residue in water-logged and well-drained conditions could lead to the distinct accumulation and stabilization of microbial-derived organic matter in paddy and upland soils.

Microbial communities in paddy soil as influenced by nitrogen fertilization and water regimes

AbstractPlastic film mulching (PM) cultivation is an important measure to alleviate the seasonal shortage of water resources. Long‐term nitrogen (N) fertilization under PM cultivation may be more conducive to enhance the ecological relationship between microbial communities involved in nutrient cycling. In this study, the effects of long‐term application of chemical N fertilizer (common prilled urea [PU]) or no N fertilization on the microbial community composition under the traditional flooding (TF) cultivation and PM cultivation were comparatively analyzed. The results demonstrated that water regimes had significant effects on all soil properties except alkali‐hydrolyzable N. Compared with TF cultivation, PM cultivation increased pH and available phosphorus (AP) by 1.14 and 13.67%, respectively, and decreased organic matter and available potassium (AK) by 6.07 and 8.39%, respectively. Nitrogen fertilization levels had significant effects on soil AP and AK, with increases of 1.39 and 1.82 mg kg−1 in PU treatment compared with CK, respectively. Neither water regime nor N fertilization level had a significant influence on soil microbial richness (Chao index) and diversity (Shannon index). However, water regimes played critical roles in driving microbial community changes. Network analysis showed that the microbial community had nonrandom co‐occurrence pattern. Myrmecridium, Defluviicoccus, Emericellopsis, Pseudarthrobacter, and Syntrophorhabdus were the keystone taxa. A higher relative abundance of Defluviicoccus, Emericellopsis, and Syntrophorhabdus was observed in the CKPM treatment, and a higher relative abundance of Myrmecridium and Pseudarthrobacter was observed in the PUPM treatment. Therefore, PM cultivation is an effective measure to improve potential beneficial taxa of soil microbial communities.

Assembly of functional microbial communities in paddy soil with long-term application of pig manure under rice-rape cropping system

Organic farming is considered an efficient approach to improve soil fertility for sustainable agriculture. However, its soil micro-ecological effects and functions in intensive rice cropping systems are still obscure. Twelve soil samples were collected from a field experiment with four treatments such as M0 (no pig manure), M1 (1.6 t ha−1 pig manure), M2 (3.2 t ha−1 pig manure) and M3 (4.8 t ha−1 pig manure) after eight rice-oilseed rape rotation. Soil chemical property, enzyme activity and abundant/rare bacterial or fungal communities were analyzed to investigate the effect of conversion to organic farming with continuous pig manure application on soil microbiota. Stochastic processes controlled the assembly of abundant taxa, and deterministic processes dominated rare taxa. The composition and network construction of bacterial and fungal communities were significantly affected by pig manure, with changes in soil property and enzyme activity. Based on partial least squares path modeling (PLS-PM), pig manure application affected bacteria construction and enzyme activities by increasing soil carbon (C) and nitrogen (N). In summary, long-term pig manure application promotes specific microbial associations known to be involved in degrading complex organic compounds, and improving soil fertility such as soil enzyme activities. This research provides insight into understanding the processes behind changes in bacterial and fungal communities in paddy soil after conversion to organic farming.

Dissolved organic carbon drives nutrient cycling via microbial community in paddy soil

Microbial mediated iron cycling drives the biogeochemical cycling of carbon, nitrogen, sulfur, and phosphorus. However, the fate of the microbial community and the relative metabolic pathways in paddy soil after the addition of biogas slurry are poorly understood. In this study, the response of functional genes was investigated by growing one-season rice in paddy soils in a pot experiment. Seven treatments were prepared: 1) control (CK); 2) organic carbon (OC); 3) fertilizer (F); 4) 5% of biogas slurry (B05); 5) 10% of biogas slurry (B10); 6) 15% of biogas slurry (B15); 7) 20% of biogas slurry (B20). In the biogas slurry treatments, Geobacter increased more than in the other treatments during rice growth, which were structured by TOC. Particularly, in the B10 treatment, the relative abundance of Geobacter was 1.6 and 14.8 times higher than that of CK at the heading and mature stages, respectively. At the heading stage, the addition of biogas slurry and OC shifted the microbial phosphorus-transformation communities differently. There were no significant differences in the carbon, nitrogen, and sulfur metabolic pathways between the two treatments. At the mature stage, the carbon: nitrogen: phosphorus balance was significantly influenced by the regulation of functional gene expression and metabolic activities. These findings provide insight into the key factors affecting carbon, nitrogen, sulfur, phosphorus, and iron during rice growth after carbon inputs.

Influence of elemental sulfur on cadmium bioavailability, microbial community in paddy soil and Cd accumulation in rice plants

Cadmium (Cd) is highly toxic to living organisms and the contamination of Cd in paddy soil in China has received much attention. In the present study, by conducting pot experiment, the influence of S fertilizer (S0) on rice growth, iron plaque formation, Cd accumulation in rice plants and bacterial community in rice rhizosphere soil was investigated. The biomass of rice plants was significantly increased by S0 addition (19.5–73.6%). The addition of S0 increased the formation of iron plaque by 24.3–45.8%, meanwhile the amount of Cd sequestered on iron plaque increased. In soil treated with 5 mg/kg Cd, addition of 0.2 g/kg S0 decreased the diffusive gradients in thin films (DGT) extractable Cd by 60.0%. The application of S0 significantly decreased the concentration of Cd in rice grain by 12.1% (0.1 g/kg) and 36.6% (0.2 g/kg) respectively. The addition of S0 significantly increased the ratio of Acidobacteria, Bacteroidetes in rice rhizosphere soil. Meanwhile, the ratio of Planctomycetes and Chloroflexi decreased. The results indicated that promoting Fe- and S-reducing and residue decomposition bacterial in the rhizosphere by S0 may be one biological reason for reducing Cd risk in the soil-rice system.

Dynamics of methane emission and archaeal microbial community in paddy soil amended with different types of biochar

Biochar, as a valuable and eco-friendly material generated from greenwaste, has a potential to mitigate CH4 emission in rice paddy soil. However, the response of methanogenesis and associated archaeal community in paddy soil to biochar amendment remains controversial. In this study, we explored the effect of three different biochars (derived from rice straw, orange peel or bamboo powder, respectively) on CH4 emission and associated archaeal microbial community in paddy soil of southern China within 90 days of anaerobic incubation. Results showed that biochar amendment overall inhibited CH4 emission in paddy soil. Significant decrease of α-diversity of archaeal community was observed in all samples in the end of incubation as revealed by 16S rRNA gene sequencing, and the addition of biochars mitigated the loss of archaeal biodiversity in paddy soil. Incubation time was found to be the major driver for the succession of archaeal community. Besides, Methanosaeta, Methanocella, Methanobacterium and Methanosarcina were mainly responsible for CH4 production. In addition, biochars had no significant effect on altering relative abundance of methanogens. Overall, our study demonstrated that the addition of three different types of biochar reduced methane emission and total archaeal diversity, while caused no significant change in methanogenic communities in paddy soil.

Effect of Pesticides and Chemical Fertilizers on the Nitrogen Cycle and Functional Microbial Communities in Paddy Soils: Bangladesh Perspective.

The concept of the Nitrogen (N) cycle has been modified over the years based on certain new pathways, including comammox, anammox, and DNRA (dissimilatory nitrate reduction to ammonium). Comammox, nitrification, anammox, denitrification, DNRA, and nitrogen fixation pathways play key roles in the N cycle in paddy soils. Pesticides and chemical fertilizers' effects on the N cycle in paddy soils together with the possible manifestation of these newly discovery pathways are the focus of this review. Both chemical fertilizers and pesticides' overuse affect nitrifying archaea/bacteria and denitrifying and anammox bacteria, while heavy metals affect the nitrification rates in paddy soils. To add extra value to this study, we quantified the comammox amoA single copy gene from the Nitrospira strain 'Nitrospira inopinata'. This review will help researchers access the latest information on the N cycle, particularly in the light of the most recent discoveries.

Winter Drainage and Plastic Film Mulching Mitigate CH &lt;sub&gt;4&lt;/sub&gt; Emission by Regulating Function and Structure of Methanogenic Microbial Communities in Paddy Soil

Winter Drainage and Plastic Film Mulching Mitigate CH &lt;sub&gt;4&lt;/sub&gt; Emission by Regulating Function and Structure of Methanogenic Microbial Communities in Paddy Soil

Microbial community response to the toxic effect of pentachlorophenol in paddy soil amended with an electron donor and shuttle

Understanding the degradation of pentachlorophenol (PCP) by indigenous microorganisms stimulated by an electron donor and shuttle in paddy soil, and the influences of PCP/electron donor/shuttle on the native microbial community are important for biodegradation and ecological and environmental safety. Previous studies focused on the kinetics and the microbial actions of PCP degradation, however, the effects of toxic and antimicrobial PCP and electron donor/shuttle on the microbial community diversity and composition in paddy soil are poorly understood. In this study, the effects of PCP, an electron donor (lactate), and the electron shuttle (anthraquinone-2, 6-disulfonate, AQDS) on the microbial community in paddy soil were investigated. The results showed that the presence of PCP reduced the microbial diversity compared to the control during PCP degradation, while increased the microbial diversity was observed in response to lactate and AQDS. The addition of PCP stimulated the microorganisms involved in PCP dechlorination, including Clostridium, Desulfitobacterium, Pandoraea, and unclassified Veillonellaceae, which were dormant in raw soil without PCP stress. In all of the treatments with PCP, the addition of lactate or AQDS enhanced PCP dechlorination by stimulating the growth of functional groups involved in PCP dechlorination and by changing the microbial community during dechlorination process. The microbial community tended to be uniform after complete PCP degradation (28 days). However, when lactate and AQDS were present simultaneously in PCP-contaminated soil, lactate acted as a carbon source or electron donor to promote the activities of microbial community, and AQDS changed the redox potential because of the production of reduced AQDS. These findings enhance our understanding of the effect of PCP and a biostimulation method for PCP biodegradation in soil ecosystems at the microbial community level, and suggest the appropriate selection of an electron donor/shuttle for accelerating the bioremediation of PCP-contaminated soils.

The response of arsenic bioavailability and microbial community in paddy soil with the application of sulfur fertilizers

Arsenic (As) has been recognized as one of the most toxic metalloids present in the surface soil contaminating food chain and posing threat to human life. Sulfur (S) fertilizer is often supplied in paddy soil for rice growth, but its impact on As mobility and related bacteria remains poorly understood. In this study, a pot experiment was set up with two different types of sulfur treatments (element sulfur and Na2SO4) to evaluate the effect of sulfur fertilizers on As speciation in porewater, As fractions in soil, As accumulation in rice plants. Besides, rhizosphere bacterial composition and functional genes that might influence As mobility were also studied. The results revealed that the addition of 150 mg/kg Na2SO4 decreased As(III) and As(V) concentrations in soil porewater at maturation stage by 77% and 64%, respectively. With the same sulfur content, Na2SO4 was more effective than element sulfur. The addition of sulfur fertilizers promoted rice growth and reduced As accumulation in shoots, further reduced As translocation from root to above-ground parts by 39–59%. The addition of sulfur fertilizers had little effect on genes involved in As metabolism. However, the relative abundance of Fe(III) and sulfate reduction related genera increased with the addition of 150 mg/kg Na2SO4, consistent with the increase of Fe(III) reducing bacteria Geobacteraceae and sulfate reducing gene dsrA. The phenomenon likely influenced the decrease of As concentrations in soil porewater and rice uptake. The outcomes indicate that promoting Fe- and S- reducing bacteria in the rhizosphere by sulfur fertilizers may be one way to reduce As risk in the soil-rice system.

Non-target effect of bispyribac sodium on soil microbial community in paddy soil.

Bispyribac sodium is frequently used herbicide in the rice field. Though, it has been targeted to kill rice weeds, but its non-target effect on soil microbes in paddy soil was largely unknown. Therefore, in the present study, an attempt was made to assess the non-target effect of bispyribac sodium on alteration of functional variation of soil microbial community and their correlation with microbial biomass carbon (MBC) and soil enzymes. A microcosm experiment set up was made comprising three treatments viz., control (CON) (without application of bispyribac sodium), recommended dose of bispyribac sodium (35gha-1) (BS), and double the dose of BS (70gha-1) (DBS). Results indicated that the MBC and soil enzyme activities (dehydrogenase, alkaline phosphatase and urease) in BS and DBS-treated soil were significantly (p<0.05) declined from 1st to 30th day after application as compared to CON. Counts of heterotrophic bacteria, actinomycetes and fungal population were also decreased in BS and DBS-treated soil. The average well color development (AWCD) values derived from Biolog®ecoplates followed the order of DBS ˂ BS ˂ CON. Shannon index value was high (p≤0.05) in CON compared to soil-treated with BS and DBS. Principal component analysis (PCA) showed a clear distinction of the cluster of treatments between CON, BS and DBS. Biplot analysis and heatmap suggested that carboxylic compounds and amino acids showed positive response towards BS-treated soil, whereas phenolic compounds had positive correlation with DBS-treated soil. PCA analysis indicated that oligotrophs was rich in BS-treated paddy soil, whereas copiotrophs and asymbiotic nitrogen fixers were richer in DBS treatment. Overall, the present study revealed that application of recommended dose of BS and its double dose alter the soil microbial population, enzyme activities and functional microbial diversity in paddy soil.