Rice Rhizosphere Soil Research Articles

Effects of elevated carbon dioxide (CO2)and ozone (O3)concentrations on ectoenzyme activities in rice rhizospheric soil.

Rising atmospheric carbon dioxide (CO2) and ozone (O3) concentrations are the main global change drivers. Soil ectoenzymes play an important role in maintaining soil ecosystem services. Exploring the responses of soil ectoenzymes to elevated CO2 and O3 concentrations is important for combating global climate change. In this study, we simulated elevated CO2 concentrations (+200 μmol·mol-1, eCO2), elevated O3 concentrations (0.04 μmol·mol-1, eO3), and their combination (eCO2+eO3) in open-top chambers (OTCs), and investigated the responses of rhizospheric soil ectoenzyme activities. The results showed that eCO2 significantly increased the β-D-Glucosidase (βG) activity by 73.0%, and decreased that of polyphenol oxidase (PHO), peroxidase (PEO), and acid phosphatase (AP) by 48.9%, 46.6% and 72.9% respectively, but did not affect that of cellulose hydrolase (CBH) and β-N-Acetylglucosaminidase (NAG). eO3 significantly reduced the activities of CBH and AP by 34.2% and 30.4%, respectively. The activities of PHO and AP were reduced by 87.3% and 32.3% under the eCO2+eO3 compared with the control, respectively. Results of the principal coordinate analysis, permutation multivariate analysis of variance and redundancy analysis showed that both elevated CO2 and O3 significantly affected soil ectoenzyme activities, with stronger effects of elevated CO2 than elevated O3. Root nitrogen content, root carbon to nitrogen ratio, soil microbial biomass carbon and nitrate nitrogen were the main drivers of soil ectoenzyme activities under elevated CO2 and O3. Elevated O3 could partially neutralize the effects of elevated CO2 on soil ectoenzyme activities. In conclusion, elevated CO2 and O3 restrained the activities of most soil ectoenzyme, suggesting that climate change would threat soil ecosystem services and functions in the agroecosystem.

Improvement of growth, yield and associated bacteriome of rice by the application of probiotic Paraburkholderia and Delftia.

Plant probiotic bacteria enhance growth and yield of crop plants when applied at the appropriate time and dose. Two rice probiotic bacteria, Paraburkholderia fungorum strain BRRh-4 and Delftia sp. strain BTL-M2 promote growth and yield of plants. However, no information is available on application of these two bacteria on growth, yield, and diversity and population of bacteriome in roots and rhizosphere soils of the treated rice plants. This study aimed to assess the effect of BRRh-4 and BTL-M2 application on growth, yield and bacteriome in roots and rhizosphere soil of rice under varying doses of N, P and K fertilizers. Application of BRRh-4 and BTL-M2 strains significantly (p < 0.05) increased seed germination, growth and yield of rice compared to an untreated control. Interestingly, the grain yield of rice by these bacteria with 50% less of the recommended doses of N, P, and K fertilizers were statistically similar to or better than the rice plants treated with 100% doses of these fertilizers. Targeted amplicon (16S rRNA) sequence-based analysis revealed significant differences (PERMANOVA, p = 0.00035) in alpha-diversity between the root (R) and rhizosphere soil (S) samples, showing higher diversity in the microbial ecosystem of root samples. Additionally, the bacteriome diversity in the root of rice plants that received both probiotic bacteria and chemical fertilizers were significantly higher (PERMANOVA, p = 0.0312) compared to the rice plants treated with fertilizers only. Out of 185 bacterial genera detected, Prevotella, an anaerobic and Gram-negative bacterium, was found to be the predominant genus in both rhizosphere soil and root metagenomes. However, the relative abundance of Prevotella remained two-fold higher in the rhizosphere soil metagenome (52.02%) than in the root metagenome (25.04%). The other predominant bacterial genera detected in the rice root metagenome were Bacillus (11.07%), Planctomyces (4.06%), Faecalibacterium (3.91%), Deinococcus (2.97%), Bacteroides (2.61%), and Chryseobacterium (2.30%). On the other hand, rhizosphere soil metagenome had Bacteroides (12.38%), Faecalibacterium (9.50%), Vibrio (5.94%), Roseomonas (3.40%), and Delftia (3.02%). Interestingly, we found the presence and/or abundance of specific genera of bacteria in rice associated with the application of a specific probiotic bacterium. Taken together, our results indicate that improvement of growth and yield of rice by P. fungorum strain BRRh-4 and Delftia sp. strain BTL-M2 is likely linked with modulation of diversity, structures, and signature of bacteriome in roots and rhizosphere soils. This study for the first time demonstrated that application of plant growth promoting bacteria significantly improve growth, yield and increase the diversity of bacterial community in rice.

Effect of rice rhizospheric Trichoderma spp and fungicide for the management of brown spot disease of rice

Brown spot of rice caused by Bipolaris oryzae is of worldwide occurrence and is known to cause substantial quantitative and qualitative losses in grain yield. This disease was responsible for the epic 'Great Bengal Famine' in 1942-1943, resulting in the death of 4 million people. Studies were carried out to evaluate the effect of rice rhizospheric Trichoderma spp and fungicide for the management of brown spot disease of rice. A total of 20 isolates of Trichoderma spp were isolated from rice rhizospheric soil and screened by dual culture method in which three isolates Ti20, Ti19 and Ti16 showing maximum inhibition of 67.86%, 64.29% and 60.71% were selected for further test. Six fungicides viz., Hexaconazole, Propiconazole, Carbendazim + Mancozeb, Metalaxyl + Mancozeb, Carbendazim and Copper oxychloride were evaluated against B. oryzae by poison food technique, out of which Propiconazole, Hexaconazole and Copper oxychloride were selected and further tested for their compatibility with the selected Trichoderma spp was done. The most efficient and compatible Trichoderma sp with fungicide i.e., (Ti19 + Hexaconazole 5% SC) were selected for managing the disease in pot experiment with different treatment combinations i.e., seed treatment, seedling dip and foliar spray. Results under pot experiment showed that, seed treatment with Ti19 and Hexaconazole 5% SC recorded lowest disease severity of 3.70%, 7.41% and 11.11% at tillering, booting and milking stages respectively, with significantly higher yield of 28.27 g/pot as compared to untreated control pots.

Long-Term Chemical Fertilization Drove Beneficial Bacteria for Rice Soil to Move from Bulk Soil to the Rhizosphere

Overuse of chemical fertilizer (CF) causes damage to soil and the environment. To reveal the process of the response of crop rhizospheric and bulk soil fertility and the bacterial community to long-term CF conditions, CF application and nonfertilization (CK, control) treatments were used in a long-term (12-year) fertilization experiment. Long-term CF application significantly increased the soil organic matter, total nitrogen, and available phosphorus contents (p &lt; 0.05), increased the available nitrogen (AN) and potassium (AK) contents to varying degrees, and decreased the soil pH in both rice rhizospheric soil and bulk soil. In addition, the bacterial Shannon and Ace indices in rice rhizospheric soil under the CF treatment were all higher than those under the control (CK) treatment, and the bulk soil bacteria showed the opposite trend. The LEfSe results showed that unidentified_Gammaproteobacteria and Geobacter (genera) were significantly enriched in the rhizospheric and bulk soil of rice under the CK treatment, respectively. Gemmatimonadetes (phylum) and Nitrospirae (phylum) + Thiobacillus (genus) were significantly enriched in the rice rhizospheric and bulk soil under the CF treatment. Only AK and AN had strong positive correlations with soil bacteria. Long-term CF application accelerated the migration of soil bacteria from the bulk soil to the rhizosphere, thus improving soil fertility and nutrient cycling.

Changes in rice rhizosphere and bulk soil bacterial communities in the Doñana wetlands at different growth stages

The Doñana wetlands comprise an emblematic Mediterranean landscape protected as a UNESCO World Heritage Site. Some parts of these wetlands have been transformed into intensive rice cultivation areas, which are currently the most productive rice-growing areas in Europe. We examined the bacterial communities in these domesticated soils as they are key for plant health and productivity and have a strong influence on biochemical cycles. To identify the bacteria, we used metabarcoding analysis coupled with metabolic predictions and co-occurrence networks. This analysis was performed in the bulk and rhizosphere soils during different stages in the growing season. These soil compartments had a greater effect on the bacterial communities than the plant phenological stages. The diversity and richness of the bacterial population inhabiting the rhizosphere was much lower than that in the bulk soil, comprising taxa that were significantly more represented in this soil compartment, such as bacteria from the genus Hydrogenophaga, three genera from the order Rhizobiales, and unclassified genera from the families Desulfocapsaceae and Actinobacteria. Rhizosphere co-occurrence networks revealed a high number of negative connections, indicating unstable bacterial communities that may be highly influenced by biotic and abiotic factors. Rhizosphere networks mostly rely on two taxa belonging to the phyla Proteobacteria and Cyanobacteria, which are the predicted network hubs in this soil compartment. The bulk soil conserved high bacterial diversity and richness that was stable throughout the growth period of rice. Anaerobic bacteria from genera Marmoricola, the uncultured Gemmatimonadota bacteria SDR1034 terrestrial group, Anaerolinea, and the sulphur oxidizer, Thiobacillus were highly represented. This analysis provides valuable information for understanding bacterial diversity in the rhizosphere of rice cultivated in this region, which is critical for enhancing plant growth and productivity.

Appraise potassium chemistry and distribution patterns in tailing soil, India: Through quantity - Intensity relations and multi model statistical methods

Tailings are waste materials left behind after mineral extraction. Giridih district of Jharkhand, India has the second largest ore of mica mines in the country. This study evaluated the forms of potassium (K+) and quantity-intensity relationships in soils contaminated by tailings around the abundant mica mines. A total of 63 rice rhizosphere soil samples (8–10 cm depth) were collected from agricultural fields near 21 mica mines in the Giridih district at different distances: 10 m (zone 1), 50 m (zone 2), and 100 m (zone 3). The samples were collected to quantify various forms of potassium in the soil and characterize non-exchangeable K (NEK) reserves and Q/I isotherms. The semi-logarithmic release of NEK with continuous extractions suggests a decrease in release over time. Significant values of threshold K+ levels were observed in zone 1 samples. As K+ concentrations increased, the activity ratio (AReK) and its corresponding labile K+ (KL) concentrations decreased. The AReK, KL, and fixed K+ (KX) values were higher in zone 1 [AReK: 3.2 (mol L−1)1/2 × 10−4, KL: 0.058 cmol kg−1, and KX: 0.038 cmol kg−1), except for readily available K+ (K0) for zone 2 (0.028 cmol kg−1). The potential buffering capacity and K+ potential values were higher in zone 2 soils. In zone 1, Vanselow selectivity coefficients (KV) and Krishnamoorthy-Davis-Overstreet selectivity coefficients (KKDO) were higher, while Gapon constants were higher in zone 3. It was found that AReK was significantly correlated with K0, KL, K+ saturation, -ΔG, KV, and KKDO. Different statistical methods such as positive matrix factorization, self-organizing maps, geostatistics, and Monte Carlo simulation approaches were employed to predict soil K+ enrichment, source apportionment, distribution patterns, availability for plants, and contribution to soil K+ maintenance. Thus, this study significantly contributes to understanding K+ dynamics in mica mine soils and operational K+ management.

Effects of dissolved organic matter on mercury speciation in rice rhizosphere amended with sulfur-rich biochar

Natural sulfur (S)-rich biochar (NRB) can be employed as an alternative for traditional S-modified biochar. However, the effect of dissolved organic matter (DOM) on mercury (Hg) speciation in rice rhizosphere soils under natural S-rich biochar application remains unclear. We conducted a pot experiment to study the effects of NRB application on the chemical composition and structure of DOM and the related speciation and availability of Hg in rice rhizosphere. Applying NRB significantly increased the concentration of methylmercury (MeHg) in the rhizosphere soils, which was enhanced with application frequency. This observation can be explained by MeHg immobilization in response to increasing S content in rice rhizosphere soils. We also observed increased molecular weight and functional group complexity of DOM, likely contributing to the decrease in MeHg mobility. Furthermore, the increase in pH and humification of DOM caused by S-rich biochar application generally reduced the concentrations of water-soluble and mercuric-sulfide fraction (easily-available Hg species) and organo-chelated fraction (potentially-available Hg species). Our findings highlight that the application of NRB can reduce the availability of MeHg in rice rhizosphere, thus providing a practical basis for reducing the potential risk of MeHg toxicity.

Impacts of 10 Years of Elevated CO2 and Warming on Soil Fungal Diversity and Network Complexity in a Chinese Paddy Field.

Climatic change conditions (elevated CO2 and warming) have been known to threaten agricultural sustainability and grain yield. Soil fungi play an important role in maintaining agroecosystem functions. However, little is known about the responses of fungal community in paddy field to elevated CO2 and warming. Herein, using internal transcribed spacer (ITS) gene amplicon sequencing and co-occurrence network methods, the responses of soil fungal community to factorial combinations of elevated CO2 (550 ppm), and canopy warming (+2 °C) were explored in an open-air field experiment for 10 years. Elevated CO2 significantly increased the operational taxonomic unit (OTU) richness and Shannon diversity of fungal communities in both rice rhizosphere and bulk soils, whereas the relative abundances of Ascomycota and Basidiomycota were significantly decreased and increased under elevated CO2, respectively. Co-occurrence network analysis showed that elevated CO2, warming, and their combination increased the network complexity and negative correlation of the fungal community in rhizosphere and bulk soils, suggesting that these factors enhanced the competition of microbial species. Warming resulted in a more complex network structure by altering topological roles and increasing the numbers of key fungal nodes. Principal coordinate analysis indicated that rice growth stages rather than elevated CO2 and warming altered soil fungal communities. Specifically, the changes in diversity and network complexity were greater at the heading and ripening stages than at the tillering stage. Furthermore, elevated CO2 and warming significantly increased the relative abundances of pathotrophic fungi and reduced those of symbiotrophic fungi in both rhizosphere and bulk soils. Overall, the results indicate that long-term CO2 exposure and warming enhance the complexity and stability of soil fungal community, potentially threatening crop health and soil functions through adverse effects on fungal community functions.

Long-term different fertilization regimes impact on the fate of root-derived C and microbial community structure in paddy soil

It is known that fertilization pattern could alter soil nutrient and organic matter status. However, it is still unclear how photosynthesized C is distributed in rice–rhizosphere soil-microbial system and its influencing factors due to fertilization pattern and subsequent changes in soil fertility. This study examined the allocation of rice photosynthetic C in rice–rhizosphere soil–microbial systems and the changes in microbial community under three long-term fertilizer regimes. Rice was grown in soils with 8-year history of no fertilizer, inorganic fertilizer (NPK) or NPK fertilizer plus cattle manure (NPK + CM), and was pulse–labelled with 13CO2 at rice tillering stage. The results showed that 13C incorporation in rice-rhizosphere soil system was the highest in the NPK + CM treatment, increased by 489% and 28.9% compared to unfertilized control and the NPK alone. In the >2 mm aggregate fraction, the 13C enrichment was higher in NPK + CM compared to no-fertilized control and NPK treatments. Total PLFA and PLFA groups contents in all aggregate size fractions were the greatest in the NPK + CM treatment. Partial least squares path modelling analysis revealed that microbial community in large macroaggregate (>2 mm) was significantly (P < 0.05) affected by root properties, while soil fertility had a significant (P < 0.01) impact on microbial community in microaggregate (<0.25 mm). The redundancy analysis showed that soil parameters except soil alkali-hydro nitrogen (AN) significantly impacted the soil microbial communities. Through canonical variation partitioning analysis, soil available K was the most important factor leading to variance (11.4%) in microbial community composition. On the other hand, soil pH significantly (P < 0.05) affected the distribution of 13C in microbe community. More than 20% of 13C was incorporated into G– and G+ bacteria across all treatments. Overall, it was observed the NPK fertilizer plus cattle manure treatment was most conducive to retain C from root exudates in the rice-rhizosphere soil-microbial system.

Significant difference in the efficacies of silicon application regimes on cadmium species and environmental risks in rice rhizosphere

Silicon (Si) is commonly applied as base-fertilizer or foliar-topdressing to palliate the uptake-translocation-accumulation of cadmium (Cd) in rice through Si–Cd antagonism. However, little is known about the fate of Cd in rice rhizosphere soil and its eco-environmental effects under different Si treatments. Here, systematic works had been carried out to elucidate the Cd species, soil properties, and environmental risks in rice rhizosphere driven by different Si soil-fertilization regimes including CK (without Si-addition), TSi (added before transplanting stage), JSi (added at jointing stage), and TJSi (split into two equal parts, added half before transplanting and another half at jointing stage). Results showed that TJSi outperformed the rest of fertilization regimes. The solid-phase-Cd concentrations treated with TSi, TJSi and JSi were increased by 4.18%, 5.73% and 3.41%, respectively, when compared to CK. The labile Cd (F1+F2) proportion of TJSi was reduced by 16.30%, 9.30% and 6.78%, respectively, when compared to CK, TSi, and JSi. Simultaneously, the liquid-phase-Cd concentration was appreciably suppressed by TJSi throughout the rice lifecycle, while TSi mainly abated Cd dissociation during the vegetative period, and JSi attenuated it during the grain-filling stage. The mobility factor of Cd treated with TJSi was the lowest, which was significantly lower than that of TSi (9.30%) and JSi (6.78%), respectively. Similarly, the oral exposure risk of TJSi was reduced by 4.43% and 32.53%; and the food-chain exposure risk of TJSi was decreased by 13.03% and 42.78%. Additionally, TJSi was the most effective in promoting enzyme activities and nutrient content in rhizosphere soil. Overall, TJSi is more positive and sustainable than TSi and JSi in reconstructing Cd-contaminated rhizosphere environments and abating the environmental risks of Cd. Agronomic practices in Cd-contaminated paddy soils can be informed by applying Si-fertilizer separately before transplanting and at jointing stage to achieve soil welfare and food security.

Temporal transformation of indium speciation in rice paddy soils and spatial distribution of indium in rice rhizosphere

Indium is a potentially toxic element that could enter human food chains, including soil-rice systems. The submerged environment in rice paddy soil results in temporal and spatial variations in the chemical properties of the rice rhizosphere and bulk soils, expected to cause changes in indium's chemical speciation and consequently affect its bioavailability. Therefore, this study aimed to investigate indium speciation and fractionation in soils at different periods of rice growth under continuous submergence using X-ray absorption spectroscopy and a sequential extraction method. The predominant indium species were identified as indium-associated Fe hydroxide, and indium hydroxide and phosphate precipitates. The reductive dissolution of indium-associated Fe hydroxides led to the release of indium into the soil solution under continuous submergence of soils, and the released indium concentration decreased with time due to re-sorption and re-precipitation. Meanwhile, indium hydroxide was found to be the predominant species in rice rhizosphere using μ-X-ray absorption spectroscopy. The relative depletion of indium-associated Fe hydroxides in the rice rhizosphere was attributed to the low mobility of indium from bulk soil to rice rhizosphere and the root uptake of indium associated with Fe hydroxide around rice roots. Consequently, indium uptake by rice roots was lower during the reproductive and grain-ripening stage of rice growth. Understanding the behavior of indium will help develop a strategy to minimize uptake into crops in indium-contaminated paddy soils.

Repeated inoculation of antimony resistant bacterium reduces antimony accumulation in rice plants

Applying beneficial bacteria in rice rhizosphere to manage heavy metal behaviour in soil-plant system is a promising strategy. However, colonization/domination of exogenous bacteria in rhizosphere soils remains a challenge. In this study, a bacterium Ochrobactrum anthropi, which showed the potential of transforming soluble SbIII into Sb2O3 mineral, was repeatedly inoculated into the rice rhizosphere weekly throughout the rice growth period, and the colonization of this bacterium in rice rhizosphere soils and its effect on Sb accumulation in rice plants were investigated. Results showed that repeated inoculants changed the native bacterial community in rhizosphere soils in comparison with the control, but the inoculated O. anthropi was not identified as an abundant species. With weekly inoculation, the decrease in Sb in rice roots and straws was maintained throughout the rice growth period, with decrease percentages ranging from 36 to 49% and 33–35%. In addition, decrease percentages of Sb in husks and grains at the maturing stage obtained 34 and 37%, respectively. Furthermore, the XRD identified the formation of valentinite (Sb2O3) on rice root in inoculation treatment, and the decrease percentages in aqueous SbIII in rhizosphere were 53–100% through the growth period. It demonstrated that weekly inoculants performed their temporary activity of valentinite formation, and reduced Sb accumulation in rice plants efficiently. This study suggests that regardless of successful colonization, repeated inoculation of beneficial bacteria is an option to facilitate the positive effects of inoculated bacteria in the management of heavy metal behaviour.

Burkholderia gladioli strain KJ-34 exhibits broad-spectrum antifungal activity.

Plant pathogens are one of the major constraints on worldwide food production. The antibiotic properties of microbes identified as effective in managing plant pathogens are well documented. Here, we used antagonism experiments and untargeted metabolomics to isolate the potentially antifungal molecules produced by KJ-34. KJ-34 is a potential biocontrol bacterium isolated from the rhizosphere soil of rice and can fight multiple fungal pathogens (i.e. Ustilaginoidea virens, Alternaria solani, Fusarium oxysporum, Phytophthora capsica, Corynespora cassiicola). The favoured fermentation conditions are determined and the fermentation broth treatment can significantly inhibit the infection of Magnaporthe oryzae and Botryis cinerea. The fermentation broth suppression ratio is 75% and 82%, respectively. Fermentation broth treatment disrupted the spore germination and led to malformation of hyphae. Additionally, we found that the molecular weight of antifungal products were less than 1000 Da through semipermeable membranes on solid medium assay. To search the potentially antifungal molecules that produce by KJ-34, we used comparative and bioinformatics analyses of fermentation broth before and after optimization by mass spectrometry. Untargeted metabolomics analyses are presumed to have a library of antifungal agents including benzoylstaurosporine, morellin and scopolamine. These results suggest that KJ-34 produced various biological control agents to suppress multiple phytopathogenic fungi and showed a strong potential in the ecological technologies of prevention and protection.

Changes in the activities of key enzymes and the abundance of functional genes involved in nitrogen transformation in rice rhizosphere soil under different aerated conditions

Soil microorganisms play important roles in nitrogen transformation. The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods (continuous flooding (CF), continuous flooding and aeration (CFA), and alternate wetting and drying (AWD)). The abundances of amoA ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), nirS, nirK, and nifH genes; and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering (S1), heading (S2), and ripening (S3) stages. We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon (MBC) and soil microbial biomass nitrogen (MBN), with the concentration of soil nitrate and ammonium nitrogen. The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments. AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong. During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively. The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively. The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase. All the above indicators were positively correlated with soil MBC and MBN. In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2. Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.

The Impacts of Phosphorus-Containing Compounds on Soil Microorganisms of Rice Rhizosphere Contaminated by Lead

The cost effectiveness of using exogenous phosphorus to remediate heavy metals in soil, which would alter the structure of the soil microbial community, had been widely acknowledged. In the present study, phospholipid fatty acid (PLFA) technology was taken as the breakthrough point, and rhizosphere soil microorganisms in different growth stages (jointing stage and maturity stage) of Minghui 86 (MH) and Yangdao No.6 (YD) rice were taken as the research objects. As revealed by the results, the rhizosphere soil microorganisms of MH and YD had distinct sensitivities to exogenous phosphorus and had a certain inhibitory effect on MH and YD enhancement. The sensitivity of rice root soil microorganisms to exogenous phosphorus also varied in different growth stages of rice. Bacteria were the dominant microorganism in the soil microbial community of rice roots, and the gain of exogenous phosphorus had a certain impact on the structure of the two soil microbial communities. Through analysis of the microbial community characteristics of MH rice and YD soil after adding exogenous phosphorus, further understanding was attained with respect to the effect of exogenous phosphorus on the microbial community characteristics of rice rhizosphere soil and the impact thereof on ecological functions.

Zinc application facilitates the turnover of organic phosphorus in rice rhizosphere soil by modifying microbial communities

Zinc application facilitates the turnover of organic phosphorus in rice rhizosphere soil by modifying microbial communities

Higher pH is associated with enhanced co-occurrence network complexity, stability and nutrient cycling functions in the rice rhizosphere microbiome.

The rice rhizosphere microbiota is crucial for crop yields and nutrient use efficiency. However, little is known about how co-occurrence patterns, keystone taxa and functional gene assemblages relate to soil pH in the rice rhizosphere soils. Using shotgun metagenome analysis, the rice rhizosphere microbiome was investigated across 28 rice fields in east-central China. At higher pH sites, the taxonomic co-occurrence network of rhizosphere soils was more complex and compact, as defined by higher average degree, graph density and complexity. Network stability was greatest at medium pH (6.5 < pH < 7.5), followed by high pH (7.5 < pH). Keystone taxa were more abundant at higher pH and correlated significantly with key ecosystem functions. Overall functional genes involved in C, N, P and S cycling were at a higher relative abundance in higher pH rhizosphere soils, excepting C degradation genes (e.g. key genes involved in starch, cellulose, chitin and lignin degradation). Our results suggest that the rice rhizosphere soil microbial network is more complex and stable at higher pH, possibly indicating increased efficiency of nutrient cycling. These observations may indicate routes towards more efficient soil management and understanding of the potential effects of soil acidification on the rice rhizosphere system.

The Impact of Different Planting Systems on the Bacterial Diversity of Rice Cultivated in Saline Soil Based on 16S rRNA Gene-Based Metagenomic Insights

Soil salinity is considered to be a major impediment to the production of rice among other abiotic stresses. In this study, 16S rRNA Illumina amplicon sequencing was performed to characterise the halophilic communities entrapped in rice rhizosphere soil cultivated in different planting systems (conventional, aerobic and System of Rice Intensification (SRI)) under saline conditions. The physicochemical properties and urease, soil dehydrogenase, alkaline phosphatase and arylsulphatase activity of soil samples were evaluated to understand their influence on the bacterial communities of the soil. Electrical conductivity (EC) of soil was lower in SRI soil samples, while the available major soil nutrients (nitrogen, phosphorous and potassium) content and soil enzyme activities such as dehydrogenase, alkaline phosphatase, urease and arylsulphatase were higher. A total of 2,516,700 reads were generated by amplicon sequencing of the hypervariable V3–V4 regions of bacterial 16S rRNA gene and were clustered into 273,447 OTU operational taxonomic units. The total number of Operational Taxonomic Units (OTUs) was higher in the conventional soil samples compared to the SRI and aerobic soil samples. Metagenomic analysis revealed that Proteobacteria was the most dominant phyla in all the planting systems followed by Actinobacteria, Firmicutes and Chloroflexi. The alpha diversity index was higher in conventional soil samples compared to other samples and more species diversity was found in SRI soil samples. KEGG analysis revealed that bacterial communities in different soil samples showed varied functional properties. The bacterial diversity of saline soil in this study can be utilised to identify microbial communities with biotechnological potential that can be employed for plant growth promotion in saline environments.

Migration and Transformation of Arsenic in Rice and Soil under Different Nitrogen Sources in Polymetallic Sulfide Mining Areas.

Nitrogen (N) fertilizer affects the migration and transformation of arsenic (As) in soil and rice. We conducted pot experiments and studied the effects of 0.1, 0.2, and 0.4 g∙kg−1 N levels of NH4Cl, (NH4)2SO4, and NH4NO3 fertilizers on the As bioavailability in the As-contaminated inter-rhizosphere soil and As accumulation in the rice organs. The results showed that the concentration of bioavailable As in the rice rhizosphere soil was significantly negatively correlated with pH under the 0.4 g∙kg−1 N level of each fertilizer. At the same N level, while the As concentration was maturity stage > tillering stage in rice stems and leaves treated with NH4Cl and (NH4)2SO4, it was the opposite in roots. This suggests that the transfer of As from roots to stems and leaves mainly occurs in the late stage of rice growth under the condition of only NH4+-N fertilizer applying. The As concentration in rice aboveground organ (grains and stems–leaves) decreased with the increasing N application under the same N fertilizer treatment condition during the mature stage. In addition, the As concentration in rice grains treated with (NH4)2SO4 was the lowest. This result indicated that SO42− and NH4+-N had a significant synergistic inhibition on the As accumulation in rice grains. It was concluded that appropriate (NH4)2SO4 levels for As-contaminated paddy soils with high sulfur (S) contents would obtain rice grains with inorganic As concentrations below 0.2 mg·kg−1.

Effects of nitrogen application after abrupt drought-flood alternation on rice root nitrogen uptake and rhizosphere soil microbial diversity

Abrupt drought-flood alternation is a frequent meteorological disaster that occurs during the summer in southern China. This study sought to clarify the composition of the bacterial community in the rhizosphere soil of rice under nitrogen (N) application after abrupt drought-flood alternation and to provide more basic data for understanding N absorption by the roots system under N application after abrupt drought-flood alternation. The activity of N metabolism enzymes and the N content and N accumulation in various organs improved under N application after abrupt drought-flood alternation. Between the T1_N and T1 comparison groups, 1758 differentially expressed genes were identified, including 1027 upregulated and 731 downregulated genes. Transcriptomic GO and KEGG analyses indicated that nitrate assimilation, response to bacterium, defence response to bacterium, and N compound metabolic processes were enriched. At the phylum level, Proteobacteria, Acidobacteria, Nitrospirota, and Gemmatimonadota were the dominant flora. The root glutamine synthetase activity was significantly negatively correlated with Nitrospirota. Nitrospirota is a key taxon regulating rice root N absorption under N application after abrupt drought-flood alternation. N application after abrupt drought-flood alternation promoted the rapid recovery ability of plants and improved the microbial environment in rice. This study preliminarily clarified the role of microorganisms in the root uptake of rice under N application after abrupt drought-flood alternation. • This study was subjected to RNA-seq and 16S rRNA gene technology. • Abrupt drought-flood alternation changed rice rhizosphere soil microbial environment. • The nitrospirota of T1_N is the dominant flora at the phylum level. • Response to bacterium, nitrogen compound metabolic processes were enriched between T1_N and T1.