Promote Rice Growth Research Articles

Effects of Azotobacter and Carbon Dioxide Concentrations on the Growth and Yield of Rice Plants Grown in Two Paddy Soils

Rice is an important staple crop influenced by rising CO2 and related climate change, but it is not well-known how N-fixing Azotobacter affects rice growth and yield under different CO2 concentrations. This study aimed to determine the effects of Azotobacter strains on the growth and yield of rice plants grown in two paddy soils under varying CO2 conditions. Rice plants inoculated with three Azotobacter strains were grown in a conventional rice soil (Dali) and an organic rice soil (Houlong) under 500 or 1000 ppm CO2. These three Azotobacter strains significantly increased the harvest index of rice plants grown in Dali soil under 1000 ppm CO2, but they did not significantly increase the harvest index for rice plants grown in Houlong soil under elevated CO2. Interestingly, only A. beijerinckii CHB 461 significantly promoted the thousand-grain weight of rice plants grown in both Dali and Houlong soils under elevated CO2. Dali soil had a high level of soil organic matter, exchangeable Ca and Mg, and available Cu and Zn, probably resulting in a better response of the rice plants to Azotobacter inoculation under elevated CO2. In conclusion, in the application of Azotobacter to promote rice growth and yield under future rising CO2 conditions, the soil properties and characteristics of Azotobacter strains may need to be considered.

Green synthesis of elephant manure-derived carbon dots and multifunctional applications: Metal sensing, antioxidant, and rice plant promotion

Carbon dots, the carbon nanomaterials, have been greatly developed for several applications including fluorescent sensors for metal ion detection, antioxidant activity, and plant growth promotion due to their excellent photophysical properties, non-toxicity, and high quantum yield. Therefore, this research focused on the synthesis of multifunctional carbon dots from elephant manure via green hydrothermal synthesis owing to its chemical composition of cellulose, hemicellulose, and lignin. The as-synthesized carbon dots exhibited blue fluorescence emission under UV light and the excitation wavelength-dependent fluorescence enhancement. Carbon dots could be further used as a “turn-off” fluorescence sensor for Hg2+ detection as a part of environmental monitoring. Furthermore, the as-synthesized carbon dots containing high phenolic content showed the antioxidant activity and promoted rice growth with an increase in the characteristic aroma compound (2-acetyl-1-pyrroline), confirmed by GC–MS analysis.

Identification of plant growth promoting antagonistic bacteria against blast disease of rice

This study aimed to isolate and identify plant growth-promoting bacteria from rhizosphere of rice plants that exhibit antagonistic properties against Magnaporthe oryzae, the causal agent of blast disease. Bacteria were isolated from the surface of rice leaves, stems, and soil attached to the roots. The antagonistic activity of the isolated bacteria was assessed using a dual culture method, and identities were determined through 16S rDNA sequencing. To evaluate their growth-promoting abilities, assays were conducted to measure indole acetic acid (IAA) production, siderophore secretion, hydrogen cyanide (HCN) production, and phosphate solubilization. The results revealed that Bacillus subtilis, identified as BDISO_01R, exhibited antagonistic behavior and the maximum inhibition of M. oryzae (81.00%) was obtained by bacterial isolate BDISO-01R. Additionally, eight bacterial isolates demonstrated IAA production, sixteen isolates produced siderophores, and nine isolates displayed phosphate solubilization capability. This research sheds light on the diverse microbial arsenal that can potentially promote rice growth while combating blast disease. Bangladesh J. Nuclear Agric, 37(1): 63-79, 2023

Transcriptomics and physiology reveal the mechanism of potassium indole-3-butyrate (IBAK) mediating rice resistance to salt stress

BackgroundIBAK, as a plant growth regulator, has broad application prospects in improving crop resistance to abiotic stress.ResultsIn this study, the regulation mechanism of IBAK on rice was revealed by physiology and transcriptomics by spraying 80 mg·L−1 IBAK solution on rice leaves at the early jointing stage under salt stress. The results showed that spraying IBAK solution on leaves under salt stress could significantly increase K+ content, decrease Na+ content, increase net photosynthetic rate (Pn), and increase the activity of catalase (CAT) and the contents of glutathione (GSH) and soluble protein in rice leaves. Using IBAK under salt stress increased the expression of plant hormone signal transduction pathway-related genes LOC4332548 and LOC4330957, which may help rice to more effectively sense and respond to plant hormone signals and enhance resistance to salt stress. In addition, the photosynthesis pathway-related genes LOC4339270, LOC4327150, and LOC4346326 were upregulated after using IBAK under salt stress, and the upregulation of these genes may be beneficial to improve the efficiency of photosynthesis and increase the photosynthetic capacity of rice. Regarding starch and sucrose metabolism pathway, spraying IBAK on leaves could promote the expression of sucrose synthesis-related gene LOC4347800 and increase the expression of starch synthesis-related genes LOC4330709 and LOC4343010 under salt stress. Finally, IBAK spraying resulted in the upregulation of multiple 50 S and 30 S ribosomal protein genes in the ribosome pathway, which may increase protein synthesis, help maintain cell function, and promote rice growth and development.ConclusionThe results of this study revealed the mechanism of IBAK mediating resistance to salt stress in rice.

Rice foliar-adapted Pantoea species: Promising microbial biostimulants enhancing rice resilience against foliar pathogens, Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae

Foliar fungal blast and bacterial leaf blight have significant impacts on rice production, and their management through host resistance and agrochemicals has proven inadequate. To achieve their sustainable management, innovative approaches like leveraging the foliar microbiome, which collaborates with plants and competes against pathogens, are essential. In our study, we isolated three Pantoea strains (P. agglomerans Os-Ep-PPA-1b, P. vagans Os-Ep-PPA-3b, and P. deleyi Os-Ep-VPA-9a) from the rice phylloplane. These isolates exhibited antimicrobial action through their metabolome and volatilome, while also promoting rice growth. Our analysis, using Gas Chromatography-Mass Spectrometry (GC-MS), revealed the presence of various antimicrobial compounds such as esters and fatty acids produced by these Pantoea isolates. Inoculating rice seedlings with P. agglomerans and P. vagans led to increased root and shoot growth. Additionally, bacterized seedlings displayed enhanced immunocompetence, as evidenced by upregulated expressions of defense genes (OsEDS1, OsFLS2, OsPDF2.2, OsACO4, OsICS OsPR1a, OsNPR1.3, OsPAD4, OsCERK1.1), along with heightened activities of defense enzymes like Polyphenol Oxidase and Peroxidase. These plants also exhibited elevated levels of total phenols. In field trials, the Pantoea isolates contributed to improved plant growth, exemplified by increased flag-leaf length, panicle number, and grains per panicle, while simultaneously reducing the incidence of chaffy grains. Hypersensitivity assays performed on a model plant, tobacco, confirmed the non-pathogenic nature of these Pantoea isolates. In summary, our study underscores the potential of Pantoea bacteria in combatting rice foliar diseases. Coupled with their remarkable growth-promoting and biostimulant capabilities, these findings position Pantoea as promising agents for enhancing rice cultivation.

More effective than direct contact: Nano hydroxyapatite pre-treatment regulates the growth and Cd uptake of rice (Oryza sativa L.) seedlings

Cd contamination in rice urgently needs to be addressed. Nano hydroxyapatite (n-HAP) is an eco-friendly material with excellent Cd fixation ability. However, due to its own high reactivity, innovative application of n-HAP in the treatment of Cd contamination in rice is needed. In this study, we proposed a new application, namely n-HAP pre-treatment, which can effectively reduce Cd accumulation in rice and alleviate Cd stress. The results showed that 80 mg/L n-HAP pre-treatment significantly reduced Cd content in rice shoot by 35.1%. Biochemical and combined transcriptomic-proteomic analysis revealed the possible molecular mechanisms by which n-HAP pre-treatment promoted rice growth and reduced Cd accumulation. (1) n-HAP pre-treatment regulated gibberellin and jasmonic acid synthesis-related pathways, increased gibberellin content and decreased jasmonic acid content in rice root, which promoted rice growth; (2) n-HAP pre-treatment up-regulated gene CATA1 expression and down-regulated gene OsGpx1 expression, which increased rice CAT activity and GSH content; (3) n-HAP pre-treatment up-regulated gene OsZIP1 expression and down-regulated gene OsNramp1 expression, which reduced Cd uptake, increased Cd efflux from rice root cells.

Application of endophytic bacterium Bacillus velezensis BTR11 to control bacterial leaf blight disease and promote rice growth

BackgroundBacterial leaf blight (BLB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive pathogens responsible for severe yield losses in rice. Application of bacterial biocontrol agent (BCA) with plant growth promotion (PGP) abilities is a promising method that alternates current conventional practices to manage BLB disease and increase crop yield. Hence, this study aimed to isolate and identify BCA with PGP abilities from internal plant tissues and rhizosphere soil of healthy and Xoo-infected rice and evaluate their antagonistic and PGP properties under greenhouse and field conditions.ResultsA total of 14 bacterial isolates were isolated and presented in vitro antagonistic ability against the Xoo. The rice endophytic bacterium strain Bacillius velezensis (BTR11) had the highest antagonistic activity against the Xoo, produced indole acetic acid (IAA), and mineralized nutrients (K and P). The greenhouse experiment revealed that culture broth of strain BTR11 had a high protective effect (72.1%) against the BLB when applied at the protective-fighting mode, i.e., before and after the Xoo infection. Preliminary results of the field experiment showed that a protective effect against the bacterial blight disease was obtained as high as 75–85%, if the strain was used as an additive to the soil for the seedlings in combination with spraying when the disease began in the field. In addition, using the strain BTR11 also increased the rice yield to about 12% more than the un-treatment control.ConclusionsThe study showed a significant potential for the application of endophytic bacteria in controlling BLB disease, while stimulating plant growth, thus reducing the use of agrochemicals in rice cultivation.

Application Rates of Cricket Feces Influencing Soil Properties and Rice Yield in Soils of Different Moisture Contents

Background: Cricket feces is a potential high-quality soil amendment, but there is currently no established optimum rate for its application in paddy soils with varying moisture contents. This study therefore aimed to evaluate the effects of varied rates of cricket feces on soil properties, rice growth, and yield in paddy soils with differing moisture contents. Methods: Two study factors were evaluated: (i) the maximum water-holding capacity (WHCmax) and flooded soils, and (ii) cricket feces applied at rates of 0 (unamended), 3.125 (low), 6.25 (medium), and 12.5 (high) t/ha. Result: The total grain weight of rice in soil with WHCmax was 2.60, 4.33, 6.91, and 7.49 g/hill under the cricket feces from unamended to high rates, respectively, with no significant difference between the medium and high rates. Meanwhile, the total grain weight in flooded soil was 1.85, 4.02, 4.70, and 5.72 g/hill, respectively. Cricket feces increased the content of essential elements and decreased the acidity and toxicity of Al, Ca, and Na in the soil, thereby promoting rice growth and yield. The optimal application rates of cricket feces for rice in the WHCmax soil was determined to be the medium rate, while that in flooded soil was the high rate.

Immobilization of cadmium in paddy soil using a novel active silicon-potassium amendment: a field experimental study.

The rapid development of industrialization and agriculture has led to extensive environmental issues worldwide such as cadmium (Cd) pollution of paddy soils, posing a potential threat to environmental safety and food health. Therefore, there is an urgent need to reduce the Cd contents in paddy soils. In this study, a newly active silicon-potassium amendment was first prepared from potassium hydroxide-assisted potassium feldspar at a low temperature, and then was used to remediate a contaminated paddy soil by Cd over a long period. The obtained results demonstrated the effectiveness of the applied active silicon-potassium in promoting rice growth in the experimental field. In addition, soil pH values increased to 6.89-7.03, thus decreasing the bioavailability of Cd bioavailability by 8.61-13.7%. The soil enzyme activities and available nutrients (Si, Ca, Mg, N, and P) were also significantly increased. In particular, the Cd contents in the rice grains decreased from 0.279 to 0.179-0.194mg/kg following the application of the active silicon-potassium amendment, reaching the food crop standard level of China (< 0.2mg/kg). The detailed remediation mechanisms of the Cd-contaminated paddy soil involved several processes, including ion exchange, ligand complexation, electrostatic attraction, and precipitation. Overall, the active silicon-potassium material is a promising amendment for achieving effective control of Cd-contaminated paddy soils.

Hyphosphere microorganisms facilitate hyphal spreading and root colonization of plant symbiotic fungus in ammonium-enriched soil.

Anthropogenic nitrogen inputs lead to a high ammonium (NH4+)/nitrate (NO3-) ratio in the soil, which restricts hyphal spreading of soil fungi. Access of symbiotic fungi to roots is a prerequisite for plant-fungal interactions. Hyphosphere bacteria protect fungi from environmental stress, yet the impact of hyphosphere bacteria on adaptation of host fungi to NH4+-enriched conditions remains unclear. By developing soil microcosm assays, we report that a plant-symbiotic fungus, Phomopsis liquidambaris, harbors specific hyphosphere bacteria that facilitate hyphal spreading and assist in the root colonization in NH4+-enriched soil. Genetic manipulation, 16S rRNA gene analysis and coinoculation assays revealed that the genus Enterobacter was enriched in the hyphosphere of NH4+-sensitive wild-type compared to NH4+-preferring nitrite reductase-deficient strain. The representative Enterobacter sp. SZ2-promoted hyphal spreading is only evident in nonsterilized soil. We further identified an increased abundance and diversity of ammonia-oxidizing archaea (AOA) and a synchronously decreased NH4+:NO3- ratio following SZ2 inoculation. Microbial supplementation and inhibitor assays showed that AOA-mediated reduction in NH4+:NO3- ratio is responsible for SZ2-enhanced fungal adaptation to NH4+-enriched conditions. The Ph. liquidambaris-Enterobacter-AOA triple interaction promoted rice growth in NH4+-enriched soil. Our study reveals the essential role of hyphosphere microorganism-based hyphal spreading in plant-fungal symbiosis establishment within nitrogen-affected agroecosystems.

Biofertilizer based on halotolerant microorganisms promotes the growth of rice plants and alleviates the effects of saline stress.

Long-term soil salinization easily contributes to soil hardness, soil nutrient imbalance, and soil microbial diversity reduction, resulting in low rice yields in the salinized fields, and microbial remediation is one of the important measures to improve salinized soil. To verify the effect of biofertilizer based on halotolerant microorganisms on promoting rice growth and alleviating saline stress, this study discussed the effects of biofertilizer on soil microbial diversity and community structure and analyzed the correlation between the formation of microbial community structure and soil nutrient factors in the salinized field. The result, in comparison with applying inorganic fertilizer (referred to as CK), showed that notably increased soil available nitrogen, available phosphorus, available potassium, and rice paddy yield (p < 0.05) and significantly decreased soil electrical conductivity (p < 0.05) were achieved via biofertilizer (referred to as G2). Additionally, the application of biofertilizer contributes to the increase in soil microbial diversity and reorganization of microbial community structure, and through the analysis of linear discriminant analysis effect size, a notable difference in relative abundance was found in 13 genera, 6 families, and 3 orders between the control group and experimental groups (p < 0.05), and by linear discriminant analysis, Desulfomonas was further identified as the differentiated indicator. The redundancy analysis showed that available phosphorus and cation exchange capacity were the key environmental factors that affected microbial community structure and composition. Through bacterial functional prediction, increased rhizosphere soil bacterial metabolism, enzyme activity, membrane transport, and other potential functions were achieved by applying biofertilizer. Therefore, the application of biofertilizer could significantly alleviate rice growth stress and increase nutrient supply capacity in saline soil. These findings provide theoretical support for soil microbial improvement technology in the salinized field.

Zinc supplementation and light intensity affect 2-acetyl-1-pyrroline (2AP) formation in fragrant rice

BackgroundImproving the yield and aroma content of fragrant rice is the focus of fragrant rice research. Light and Zinc (Zn) management generally cause regulations in the 2-acetyl-1-pyrroline (2AP) accumulation in fragrant rice. In addition, Zn promotes rice growth and improves rice yield, which has the potential to compensate for the negative impact of low light on fragrant rice yield. However, the potential of Zn to improve fragrant rice yield and 2AP content under shading conditions has not been verified.MethodsField experiments were conducted in the rice season (May–September) in 2019 to 2021. Two light i.e., normal light (NL) and low light (LL) and four Zn levels i.e., 0 kg Zn ha− 1 (N0), 1 kg Zn ha− 1 (Zn1), 2 kg Zn ha− 1(Zn2), and 3 kg Zn ha− 1 (Zn3), which applied at booting stage was set up. The grain yield, 2AP contents, Zn content in polished rice, photosynthesis related indicators, MDA content, antioxidant enzyme activity and the biochemical parameters related to 2AP formation were investigated.ResultsShading reduced yield by 8.74% and increased 2AP content by 24.37%. In addition, shading reduced net photosynthetic rate (Pn), superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and increased proline, γ-aminobutyric acid (GABA), and pyrroline-5-carboxylic acid (P5C), proline dehydrogenase (PDH), △1-pyrroline-5-carboxylic acid synthetase (P5CS), malondialdehyde (MDA). With increasing Zn application levels, yield, 2AP, Zn content in polished rice, Pn, proline, P5C, GABA, PDH, P5CS, SOD, CAT and POD increased, and MDA decreased. Significant Light and Zn interaction effect on 2AP content was detected, and both shading and increasing Zn application increased the 2AP content.ConclusionShading can increase the 2AP content but reduce the yield of fragrant rice. Increasing Zn application under shading conditions can further promote the biosynthesis of 2AP, but the effect of improving yield is limited.

Crosstalk between in situ root exudates and rhizobacteria to promote rice growth by selenium nanomaterials

Maximizing the potential of plant–microbe systems offers great opportunities to confront sustainability issues in agroecosystems. However, the dialog between root exudates and rhizobacteria remains largely unknown. As a novel nanofertilizer, nanomaterials (NMs) have significant potential to improve agricultural productivity due to their unique properties. Here, soil amendment with 0.1 mg·kg−1 selenium (Se) NMs (30–50 nm) significantly promoted rice seedling growth. Differences in root exudates and rhizobacteria were evident. At an earlier time point (3rd week), Se NMs increased the relative content of malic and citric acid by 15.4- and 8.1-fold, respectively. Meanwhile, the relative abundances of Streptomyces and Sphingomonas were increased by 164.6 % and 38.3 %, respectively. As the exposure time increased, succinic acid (40.5-fold) at the 4th week and salicylic acid (4.7-fold) and indole-3-acetic (7.0-fold) at the 5th week were enhanced, while Pseudomonas and Bacillus increased at the 4th (112.3 % and 50.2 %) and 5th weeks (190.8 % and 53.1 %), respectively. Further analysis indicated that (1) Se NMs directly enhanced the synthesis and secretion of malic and citric acids by upregulating their biosynthesis and transporter genes and then recruited Bacillus and Pseudomonas; (2) Se NMs upregulated the chemotaxis and flagellar genes of Sphingomonas for more interaction with rice plants, thereby promoting rice growth and stimulating root exudate secretion. This crosstalk of root exudates and rhizobacteria enhanced nutrient uptake, resulting in promoted rice growth. Our study offers insights into the crosstalk between root exudates and rhizobacteria by NMs and provides new insights into rhizosphere regulation in nano-enabled agriculture.

Identification, characteristics and rice growth promotion of a highly efficient cellulolytic bacterial strain, Cellulomonas iranensis ZJW-6, isolated from paddy soil in central China.

The microbial degradation of lignocellulose is the best way to treat straw, which has a broad application prospect. It is consistent with the idea of agricultural sustainable development and has an important impact on the utilization of biomass resources. To explore and utilize the microbial resources of lignocellulose degradation, 27 lignocellulose degrading strains were screened from 13 regions in China. ZJW-6 was selected because of its 49.6% lignocellulose weight loss rate. According to the theoretical analysis of the experimental results, the following straw degradation conditions were obtained by ZJW-6: nitrogen source input of 8.45 g/L, a pH of 8.57, and a temperature of 31.63°C, the maximum weight loss rate of rice straw could reach 54.8%. It was concluded that ZJW-6 belonged to Cellulomonas iranensis according to 16S rRNA-encoding gene sequence comparison and identification. ZJW-6 is a Gram-positive bacterium that grows slowly and has a small yellowish green colony. To explain the degradation mechanism of lignocellulose, the experiment of enzymatic properties of the strain was prepared and carried out. It was discovered that ZJW-6 has an excellent ability to degrade cellulose, hemicellulose, and lignin, with cellulose and hemicellulose loss rates reaching almost 50% in 4 days and lignin loss rates reaching nearly 30%. Furthermore, ZJW-6 demonstrated lignocellulose degradation under aerobic and anaerobic conditions, indicating the strain's broad application potential. ZJW-6 was found to be more effective than ordinary humic acid in improving rice soil (available phosphorus, available nitrogen, organic matter) and promoting rice growth in a rice pot experiment (increasing root-shoot ratio, root activity, chlorophyll content and net photosynthetic rate). ZJW-6 plays an important role in promoting the development and utilization of straw resources. It has important significance for the advancement of green agriculture.

Paenibacillus terrae NK3-4 regulates the transcription of growth-related and stress resistance-related genes in rice.

Paenibacillus terrae NK3-4 is a plant growth-promoting rhizobacterium. In this study, the effects of NK3-4 on rice growth and gene transcription were determined. The results indicated that a seed soaking treatment and a pre-germination seed treatment using NK3-4 promoted rice growth, especially spraying rice seedlings with NK3-4 increased the root number and root length by 34.2% and 34.1%, respectively. Moreover, NK3-4 induced the differential transcription of genes annotated with gene ontology (GO) terms; the number of up-regulated genes was 4.38-times higher than the number of down-regulated genes. The NK3-4 treatment induced the differential transcription of genes in 1794 GO functional groups, with 1531 functional groups containing up-regulated genes. Specific growth-related genes up-regulated by NK3-4 are involved in biological processes, including responses to auxin, hormone biosynthesis, cellular component biogenesis, root system development, and other functions. Furthermore, stress resistance-related genes were up-regulated, some of which encode WRKYs, NPK1-related protein kinase, NPR1-like 4, CaM-like proteins, MYBs, ERFs, TIFYs, NACs, EL5s, PR1s, PR2, PR8, PODs, and PAD4. Considered together, these findings imply that NK3-4 may promote plant growth and enhance stress resistance by regulating gene expression, making it a potentially useful microbe for regulating rice growth and stress resistance.

Effects of rice blast biocontrol strain Pseudomonas alcaliphila Ej2 on the endophytic microbiome and proteome of rice under salt stress.

Soil salinity is a prevalent environmental stress in agricultural production. Microbial inoculants could effectively help plants to alleviate salt stress. However, there is little knowledge of the biocontrol strain Pseudomonas alcaliphila Ej2 mechanisms aiding rice plants to reduce the adverse effects caused by salt stress. We performed integrated field and greenhouse experiments, microbial community profiling, and rice proteomic analysis to systematically investigate the Ej2 mechanism of action. The results displayed that biocontrol strain Ej2 increased shoot/root length and fresh/dry weight compared with control under salt stress. Meanwhile, strain Ej2 has the ability to control rice blast disease and promote rice growth. Furthermore, the microbial community analysis revealed that the alpha-diversity of Ej2-inoculated plants was higher than the control plants, expect the Shannon index of the bacterial microbiome and the Ej2-inoculated samples clustered and separated from the control samples based on beta-diversity analysis. Importantly, the enriched and specific OTUs after Ej2 inoculation at the genus level were Streptomyces, Pseudomonas, Flavobacterium, and Bacillus. Moreover, we observed that Ej2 inoculation influenced the rice proteomic profile, including metabolism, plant-pathogen interactions, and biosynthesis of unsaturated fatty acids. These results provide comprehensive evidence that Ej2 inoculation induced the rice endophytic microbiome and proteomic profiles to promote plant growth under salt stress. Understanding the biocontrol strain effects on the endophytic microbiome and rice proteomics will help us better understand the complex interactions between plants and microorganisms under salt stress. Furthermore, unraveling the mechanisms underlying salt tolerance will help us more efficiently ameliorate saline soils.

Co-inoculation of antagonistic Bacillus velezensis FH-1 and Brevundimonas diminuta NYM3 promotes rice growth by regulating the structure and nitrification function of rhizosphere microbiome.

Microbial inoculation with plant growth-promoting microorganisms (PGPMs) is one of the most promising technologies to solve the current global challenges. Co-inoculants is more efficient and stable than mono-inoculants. However, the growth promoting mechanism of co-inoculants in complex soil system is still poorly understood. In this study, the effects on rice, soil and the microbiome of the mono-inoculant Bacillus velezensis FH-1 (F) and Brevundimonas diminuta NYM3 (N) and the co-inoculant FN obtained in previous works were compared. Correlation analysis and PLS-PM were used to explore the primary mechanism of different inoculants promoting rice growth. We hypothesized that inoculants promoted plant growth (i) by themselves, (ii) by improving soil nutrient availability or (iii) by regulating the rhizosphere microbiome in complex soil system. We also assumed that different inoculants had different ways of promoting plant growth. The results showed that FN significantly promoted rice growth and nitrogen absorption and slightly increased soil total nitrogen and microbial network complexity compared with F, N and the control (CK). B. velezensis FH-1 and B. diminuta NYM3 interfered with each other's colonization in FN. FN increased the complexity of the microbial network compared to F and N. The bacterial community of FN was quite different from CK and N, while the fungal community was not significantly different from other treatments. The species and functions enriched or inhibited by FN are part of F. The correlation analysis and PLS-PM results showed that inoculants (F/N/FN) promoted the growth of rice mainly by regulating the rhizosphere microbiome rather than by themselves or by improving soil nutrient availability. Co-inoculant FN promotes rice growth specifically by enhancing microbial nitrification function through enriching related species compared with F or N. This may provide theoretical guidance for the construction and application of co-inoculants in the future.

Bacterial volatile organic compounds (VOCs) promote growth and induce metabolic changes in rice.

Plant growth-promoting bacteria (PGPB) represent an eco-friendly alternative to reduce the use of chemical products while increasing the productivity of economically important crops. The emission of small gaseous signaling molecules from PGPB named volatile organic compounds (VOCs) has emerged as a promising biotechnological tool to promote biomass accumulation in model plants (especially Arabidopsis thaliana) and a few crops, such as tomato, lettuce, and cucumber. Rice (Oryza sativa) is the most essential food crop for more than half of the world's population. However, the use of VOCs to improve this crop performance has not yet been investigated. Here, we evaluated the composition and effects of bacterial VOCs on the growth and metabolism of rice. First, we selected bacterial isolates (IAT P4F9 and E.1b) that increased rice dry shoot biomass by up to 83% in co-cultivation assays performed with different durations of time (7 and 12 days). Metabolic profiles of the plants co-cultivated with these isolates and controls (without bacteria and non-promoter bacteria-1003-S-C1) were investigated via 1H nuclear magnetic resonance. The analysis identified metabolites (e.g., amino acids, sugars, and others) with differential abundance between treatments that might play a role in metabolic pathways, such as protein synthesis, signaling, photosynthesis, energy metabolism, and nitrogen assimilation, involved in rice growth promotion. Interestingly, VOCs from IAT P4F9 displayed a more consistent promotion activity and were also able to increase rice dry shoot biomass in vivo. Molecular identification by sequencing the 16S rRNA gene of the isolates IAT P4F9 and E.1b showed a higher identity with Serratia and Achromobacter species, respectively. Lastly, volatilomes of these and two other non-promoter bacteria (1003-S-C1 and Escherichia coli DH5α) were evaluated through headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. Compounds belonging to different chemical classes, such as benzenoids, ketones, alcohols, sulfide, alkanes, and pyrazines, were identified. One of these VOCs, nonan-2-one, was validated in vitro as a bioactive compound capable of promoting rice growth. Although further analyses are necessary to properly elucidate the molecular mechanisms, our results suggest that these two bacterial isolates are potential candidates as sources for bioproducts, contributing to a more sustainable agriculture.

Translocation and metabolism of tricresyl phosphate in rice and microbiome system: Isomer-specific processes and overlooked metabolites

Tricresyl phosphate (TCP) is extensively used organophosphorus flame retardants and plasticizers that posed risks to organisms and human beings. In this study, the translocation and biotransformation behavior of isomers tri-p-cresyl phosphate (TpCP), tri-m-cresyl phosphate (TmCP), and tri-o-cresyl phosphate (ToCP) in rice and rhizosphere microbiome was explored by hydroponic exposure. TpCP and TmCP were found more liable to be translocated acropetally, compared with ToCP, although they have same molecular weight and similar Kow. Rhizosphere microbiome named microbial consortium GY could reduce the uptake of TpCP, TmCP, and ToCP in rice tissues, and promote rice growth. New metabolites were successfully identified in rice and microbiome, including hydrolysis, hydroxylated, methylated, demethylated, methoxylated, and glucuronide- products. The methylation, demethylation, methoxylation, and glycosylation pathways of TCP isomers were observed for the first time in organisms. What is more important is that the demethylation of TCPs could be an important and overlooked source of triphenyl phosphate (TPHP), which broke the traditional understanding of the only manmade source of toxic TPHP in the environment. Active members of the microbial consortium GY during degradation were revealed and metagenomic analysis indicated that most of active populations contained TCP-degrading genes. It is noteworthy that the strains and function genes in microbial consortium GY that responsible for TCP isomers’ transformation were different. These results can improve our understanding of the translocation and transformation of organic pollutant isomers in plants and rhizosphere microbiome.

Solubilization by nematode-controlling Trichoderma of nutrients to promote rice growth, yield and phosphorus content

Solubilization by nematode-controlling Trichoderma of nutrients to promote rice growth, yield and phosphorus content