Fixation Ability Research Articles

Bioremediation of soils contaminated with nicosulfuron by the bacterial complex ES58

Nicosulfuron residues in soil can be harmful to the environment. In this study, acid-producing Klebsiella oxytoca ES5 and Klebsiella grimontii ES8 were isolated to construct the ES58 bacterial complex. The culture medium was optimized using response surface methodology, nicosulfuron degradation by ES58 reached 97.21% in 96h. The optimal degradation conditions were: temperature: 25℃, pH 6, initial nicosulfuron concentration: 50mgL-1 and inoculum volume: 2%. The two individual strains and the bacterial complex were tested for the ability of nitrogen fixation, phosphorus solubilization, potassium decomposition and iron carrier production. The results revealed that both strains and the bacterial complex had the ability to promote the growth, with bacterial complex being more capable than the two individual bacterial strains. After 28 d of bioremediation of nicosulfuron-contaminated soil by ES58, degradation rate of nicosulfuron was 90.84% in the unsterilized soil. Furthermore, the remediation process restored the activities of catalase, invertase, dehydrogenase and urease in the soil. The ES5-specific gene budA and ES8-specific gene ldh were detected in the soil at the 28th day. ES58 exhibited different effects on the growth indexes of nicosulfuron-sensitive crops. The study provides a novel strategy for nicosulfuron degradation effective by constructing and utilizing bacterial complex.

Immobilization mechanism of heavy metals by crystals and liquid phase during melting treatment of MSWI fly ash

Melting treatment has emerged as a promising technology for managing municipal solid waste incineration (MSWI) fly ash owing to its advantageous features of effective detoxification and volume reduction. The melting treatment of MSWI fly ash involves the immobilization of heavy metals by crystals and liquid phase. Herein, the immobilization mechanism of heavy metals (Cu, Pb and Cd) by the crystals and the liquid phase was investigated using melting experiments, thermodynamic calculations and density functional theory (DFT) calculations. Results demonstrate that the immobilization of heavy metals is influenced by a combination of factors: the reaction of heavy metals, physical encapsulation ability of the liquid phase and chemical fixation ability of both the crystals and the liquid phase. An increase in the content of SiO2 and Al2O3 promotes the conversion of heavy metals oxides into heavy metals chlorides. Furthermore, an increase in the content and polymerization degree of the liquid phase facilitates the physical encapsulation of heavy metals chlorides. The chemical fixation ability of the crystals and the liquid phase differs for Cu and Pb, while Cd cannot be immobilized through chemical fixation. To enhance the immobilization of heavy metals during melting treatment, the chemical composition of MSWI fly ash should be adjusted within the anorthite region of the ternary phase diagram. This study provides valuable insights into the immobilization mechanism of heavy metals by the crystals and the liquid phase during the melting treatment of MSWI fly ash.

Glucose addition in natural forest soils has higher biological nitrogen fixation capacity than other types of soils

Land use changes soil microbial and chemical properties, but the mechanism of biological nitrogen fixation under different land use patterns is rarely reported, so we used four types of soil: Natural forest soil (NS), healthy banana soil (HS), diseased banana soil (DS) and paddy soil (PS). Treatments included the control (CK), addition of glucose (G), addition of glucose and ammonium nitrate (GN), addition of banana straw (BS), addition of banana straw and ammonium nitrate (BSN), addition of banana root (BR), and addition of banana root and ammonium nitrate (BRN). The study found that the change of soil utilization types, glucose addition increased carbon dioxide emissions (Compared with the control, increased by 963.11%, 508.39%, 794.77% and 511.34%, respectively) and enhanced the ability of soil microbial nitrogen fixation. Importantly, natural forest soil microorganisms have a higher biological nitrogen fixation capacity compared to other types of soils. Glucose addition caused the accumulation of ammonium nitrogen (Compared with the control, increased by 426.08%, 934.21%, 420% and 1065.95%, respectively), indicating that microorganisms had higher utilization efficiency of soluble carbon and enhanced the biological nitrogen fixation capacity, and nitrogen addition caused the accumulation of ammonium nitrogen, thereby weakening the biological nitrogen fixation capacity. At the same time, glucose significantly increased the Fimicutes phylum (83.73%, 66.38%, 67.18% and 70.36%) and lowered the level of other bacterial phylums, thereby reducing the bacterial network structure, and the stability of the soil environment has decreased. Forest analysis showed that CO2 was an important factor in predicting the bacterial community structure of different soil types, an increase in CO2 content can predict drastic changes in the bacterial community. Bacteria at the Fimicutes phylum level preferred glucose, which may also have a negative effect on bacteria at the level of other phylums.

Mechanism research of elastic fixation promoting fracture healing based on proteomics and fracture microenvironment.

This study aimed to demonstrate the promoting effect of elastic fixation on fracture, and further explore its mechanism at the gene and protein expression levels. A closed tibial fracture model was established using 12 male Japanese white rabbits, and divided into elastic and stiff fixation groups based on different fixation methods. Two weeks after the operation, a radiograph and pathological examination of callus tissue were used to evaluate fracture healing. Then, the differentially expressed proteins (DEPs) were examined in the callus using proteomics. Finally, in vitro cell experiments were conducted to investigate hub proteins involved in this process. Mean callus volume was larger in the elastic fixation group (1,755 mm3 (standard error of the mean (SEM) 297)) than in the stiff fixation group (258 mm3 (SEM 65)). Pathological observation found that the expression levels of osterix (OSX), collagen, type I, alpha 1 (COL1α1), and alkaline phosphatase (ALP) in the callus of the elastic fixation group were higher than those of the stiff fixation group. The protein sequence of the callus revealed 199 DEPs, 124 of which were highly expressed in the elastic fixation group. In the in vitro study, it was observed that a stress of 200 g led to upregulation of thrombospondin 1 (THBS1) and osteoglycin (OGN) expression in bone marrow mesenchymal stem cells (BMSCs). Additionally, these genes were found to be upregulated during the osteogenic differentiation process of the BMSCs. Elastic fixation can promote fracture healing and osteoblast differentiation in callus, and the ability of elastic fixation to promote osteogenic differentiation of BMSCs may be achieved by upregulating genes such as THBS1 and OGN.

Study on combustion characteristics of crustacean biomass derived fuel coupled with in-situ capture of SO2 based on pulsed microwave radiation

Crustacean waste has great potential as fossil fuel substitution and efficient desulfurization to reduce pollutant emissions, but high moisture and poor quality restrict broad-scale utilization. This study used microwave radiation on crayfish shell to investigate the combustion characteristics and desulfurization effect in different atmospheres/pulse microwave cycle. Meanwhile, the structure evolution mechanism and molecular reaction pathways were revealed. The results show that crayfish shell derived fuel has a pleasurable combustion performance and sulfur fixation ability after microwave radiation in flue gas. The heat release of derived fuel increased by 29.9 % after five microwave cycle in flue gas, and activation energy decreased by 3.7 %. By contrast, the heat release increased by 17.4 % after five microwave cycle in inert gas, and activation energy increased by 39.3 %. Subsequently, the effect of microwave cycle times in flue gas on crayfish shell combustion and desulfurization performance was studied. The results show that the heat release of derived fuel gradually increases with microwave cycle. After seven microwave cycle, the derived fuel heat release and SO2 removal efficiency increased by 34.9 % and 44.4 %, respectively. The results establish the foundation for expanding the utilization pathway of crustacean waste and realizing the low-carbon energy transition.

A long-cycle-life reversible Li-CO2 battery enabled by engineering the active sites of graphene with Pd nanoparticles.

Li-CO2 batteries have been recognized as an emerging technology for energy storage systems owing to their high theoretical specific energy and environmentally friendly CO2 fixation ability. However, their development for applications requires a high energy efficiency and long cycle-life, this is currently limited to the formation of wide-bandgap insulator Li2CO3 during discharge. Here, nanoparticle Pd supported on reduced graphene oxide (rGO) is utilized as cathodes for Li-CO2 batteries, Pd nanoparticles as active centers significantly enhance CO2RR/CO2ER reaction activity, which can support the fast formation and decomposition of Li2CO3 in organic electrolytes and achieve a high discharge capacity of 7500 mAh g-1. It also performs remarkably high cycling stability of over 500 cycles with a long cycle-life of 5000 hours. The observed super electrochemical performance is attributable to the thick electrode design and uniform distribution of ultrafine catalyst nanoparticle Pd. When Li2CO3 is adsorbed on Pd particle, the Li-O bond in Li2CO3 will be elongated due to the interactions of two nucleophilic O atoms with Pd, resulting in a weakening of the Li-O bond and activation of Li2CO3. Our work suggests a way to design catalysts with high activity that can be used to activate the performance of Li-CO2 batteries.

Evaluation of heavy metal fixation ability from drilling waste of oil and gas wells using treated sugarcane bagasse

Evaluation of heavy metal fixation ability from drilling waste of oil and gas wells using treated sugarcane bagasse

Electrocatalytic ammonia synthesis on bimetallic AuPd porous structures

In industry, production of ammonia mainly relies on the intensive Haber-Bosch process, but it consumes high energy with low efficiency and generates a large number of green-house gases. Electrocatalytic nitrogen reduction reaction (ENRR), as an alternative method for fixing N2 under ambient conditions, provides a feasible strategy for sustainable development of N2 cycle storage and utilization of renewable energy. However, traditional nanocatalysts exhibit extremely poor ENRR performance due to low activity of the solid structure and intense hydrogen evolution reactions of single component. Herein, we design and prepare porous gold–palladium nanoalloys (pAuPdNs), which effectively enhance ENRR by the excellent catalytic activity of Au and the significant N2 fixation ability of Pd, as well as the nanoporous structure and synergistic effect between alloy components. The electrochemical results show the NH3 yield of the catalyst is as high as 43.6 μg·h−1·cm−2, and Faradaic efficiency reaches 43.8%, which are superior to the performances of most reported water-based ENRR electrocatalysts. Besides, the selectivity of 95% and stability also exhibit enhancement than numerous reported researches. As compared with solid alloy and porous Au or Pd structures, the superiority of pAuPdNs states the influence of alloying and porous structure. Hence pAuPdNs are proved to be the efficient, stable, and promising electrocatalysts for N2 reduction reaction at ambient temperature and atmospheric pressure.

Studying the spatiotemporal variations of the ecological network and carbon utilization efficiency in Southeast Tibet based on complex network theory

Currently, with the gradual advancement of urbanization and industrialization, ecological patches are severely fragmented and corridors are cut off, leading to the construction of regional ecological networks that can connect fragmented patches and corridors with regional characteristics. However, there is limited research on the relationship between ecological networks and Carbon Utilization Efficiency (CUE) based on complex network theory. This paper takes the ecologically fragile Southeast Tibet as the research area and investigates the variation patterns of CUE through the establishment of ecological spatial networks. The Graphab Model is employed to extract the ecological space network of Southeast Tibet. The Graphab Model integrates the complex network with the ecological space network to compute the topological index of ecological nodes and the overall ecological network. Later, MOD17A2HGF GPP and MOD17A2HGF PSNnet data from 2013 to 2021 are used as the primary data for calculating the CUE of ecological nodes. The connection between topological index and ecological nodes is analysed. The results indicate that, with interannual variations, ecological nodes dropped by 15, and the number of ecological galleries decreased by 7. However, the average values of various topological indices showed an increasing trend, suggesting that the ecological remediation items in Southeast Tibet have made some achievements. Nevertheless, the analysis of CUE in Southeast Tibet reveals a downward trend in the carbon fixation rate of vegetation in recent years. Through correlation analysis, it was found that the correlation between various topological indices and CUE was the lowest and insignificant in 2013, while from 2015 to 2021, all topological indices were significantly positively correlated with CUE. Through Principal Component Analysis (PCA), It is recommended to reduce and shorten redundant ecological corridors by aggregating small ecological patches and increasing stepping stone patches, and increase ecological galleries to enhance the carbon fixation ability of plants. This research lays a scientific foundation for addressing ecological issues, landscape patterns, and developing ecological networks in Southeast Tibet.

Isolation and Characterization of Azotobacter and Phosphate Solubilizing Bacterial Isolates

Isolation from 20 soil samples collected from rhizosphere of watermelon was done on Ashby's medium and Pikovskaya's agar media.8 Azotobacter and 6 Phosphate solubilizing bacteria PSB isolates were obtained from all samples. All the obtained isolates of Azotobacter sp and PSB were gram negative. On morphological study it was observed that, all Azotobacter isolates were motile and positive for KOH test. In case of PSB, the colony shapes of 4 obtained isolates were circular and irregular in 2. All the isolates showed smooth appearance on the media with white colony colour. The biochemical results for both Azotobacter spp and PSB revealed that, most of them were positive for methyl red test, catalase test, starch hydrolysis, gelatine hydrolase test, oxidase test and indol test. Out of eight Azotobacter isolates, Isolate 4 (Azob-1) showed highest (14.25 mg/ml) N fixing ability whereas, from of six PSB isolates, Isolate1 (PSB-1) showed highest solubilising index (4.13) therefore these two isolates were found most efficient in their roles and therefore recommended for use for field experiments.

Phytic Acid Modification Enhanced Cadmium Sorption and Immobilization of Sludge-based Hydrochar

Phytic acid-assisted sludge hydrothermal carbonization was employed to synthesize phytic acid-modified hydrochar via a one-step method. The surface morphology, pore structure, elemental composition, functional groups, and thermal stability of the phytic acid-modified hydrochar were characterized. Sorption kinetics and isotherm experiments were conducted to investigate the effects of humic acid, temperature, and pH on the sorption process of cadmium （Cd） onto the phytic acid-modified hydrochar. The Cd fixation ability was evaluated through soil passivation experiments. The results demonstrated that the surface of the phytic acid-modified hydrochar exhibited an abundance of phosphoric acid groups, enhanced electronegativity, and thermal stability. Furthermore, both the sorption rate and maximum sorption capacity for Cd increased by 1.88 times and 1.22 times compared to that in unmodified hydrochar, respectively, owing to the presence of phosphoric acid groups that enhanced complexation and electrostatic interaction with Cd. Elevated temperatures, higher pH values, and coexistence with humic acids were beneficial for enhancing Cd sorption onto phytic acid-modified hydrochar. When heavy metals such as Cu, Zn, and Pb coexisted, the sorption capacity of phytic acid-modified hydrochar for Cd was 0.77-6.88 times higher than that for other metals. Phyic acid-modified hydrochar exhibited excellent efficiency in fixing Cd （56.1%-81.l%）, mitigating the loss of available nutrients in soil and significantly increasing the AP content in the soil. In conclusion, the use of phytic acid-modified hydrochar could effectively remove Cd from water and serve as a promising soil amendment for stabilizing soil Cd content.

Engineering a Sinorhizobium meliloti Chassis with Monopartite, Single Replicon Genome Configuration.

Multipartite bacterial genomes pose challenges for genome engineering and the establishment of additional replicons. We simplified the tripartite genome structure (3.65 Mbp chromosome, 1.35 Mbp megaplasmid pSymA, 1.68 Mbp chromid pSymB) of the nitrogen-fixing plant symbiont Sinorhizobium meliloti. Strains with bi- and monopartite genome configurations were generated by targeted replicon fusions. Our design preserved key genomic features such as replichore ratios, GC skew, KOPS, and coding sequence distribution. Under standard culture conditions, the growth rates of these strains and the wild type were nearly comparable, and the ability for symbiotic nitrogen fixation was maintained. Spatiotemporal replicon organization and segregation were maintained in the triple replicon fusion strain. Deletion of the replication initiator-encoding genes, including the oriVs of pSymA and pSymB from this strain, resulted in a monopartite genome with oriC as the sole origin of replication, a strongly unbalanced replichore ratio, slow growth, aberrant cellular localization of oriC, and deficiency in symbiosis. Suppressor mutation R436H in the cell cycle histidine kinase CckA and a 3.2 Mbp inversion, both individually, largely restored growth, but only the genomic rearrangement recovered the symbiotic capacity. These strains will facilitate the integration of secondary replicons in S. meliloti and thus be useful for genome engineering applications, such as generating hybrid genomes.

The impact of bacillus sp. NTLG2-20 and reduced nitrogen fertilization on soil properties and peanut yield

The excessive use of nitrogen (N) fertilizers has led to farmland degradation and reduced crop yields. To address this drawback, reducing the amount of nitrogen fertilizer and Bacillus sp. NTLG2-20 inoculant are the optimal cultivation method. The impact of different N rates (0, 20, and 40 kg ha-1) combined with the Bacillus sp. NTLG2-20 inoculant on soil chemical properties, growth, development, and peanut yield was designed in the field in Phuoc Hung commune, An Phu district from May to August 2023. The field experiment was designed with 6 treatments and 4 replications. The research results showed that different N rates adequately augmented soil chemical traits such as pH, cation exchange capacity (CEC), soil organic matter (SOM), total N, available phosphorous (AP), and exchangeable potassium (EK). Furthermore, different N fertilizers rates combined with Bacillus sp. NTLG2-20 inoculant adequately augmented plant height, number of leaves, total chlorophyll, nodulous number and weight per groundnut plant. Reducing N fertilizer application by 50% (20 kg N ha-1) was the optimal N reduction rate when combined with the Bacillus sp. NTLG2-20, which resulted in 17.6% higher peanut yield compared to no N application and no difference compared to 100% of recommended N application (P<0.01)). Bacillus sp. NTLG2-20 inoculant increased peanut yield by 19.6% when compared to no Bacillus sp. NTLG2-20 inoculant (P<0.01). Nitrogen – fixing ability of Bacillus sp. NTLG2-20 promoted peanut yield and reduced fifty percentage of the N fertilizer application. Bacillus sp. NTLG2-20 is the promising species for the production of biological fertilizer in the future.

Evolutionary history and root trait coordination predict nutrient strategy in tropical legume trees.

Plants express diverse nutrient use and acquisition traits, but it is unclear how trait combinations at the species level are constrained by phylogeny, trait coordination, or trade-offs in resource investment. One trait - nitrogen (N) fixation - is assumed to correlate with other traits and used to define plant functional groups, despite potential confounding effects of phylogeny. We quantified growth, carbon metabolism, fixation rate, root phosphatase activity (RPA), mycorrhizal colonization, and leaf and root morphology/chemistry across 22 species of fixing and nonfixing tropical Fabaceae trees under common conditions. Belowground trait variation was high even among closely related species, and most traits displayed a phylogenetic signal, including N-fixation rate and nodule biomass. Across species, we observed strong positive correlations between physiological traits such as RPA and root respiration. RPA increased ~ fourfold per unit increase in fixation, supporting the debated hypothesis that N-fixers 'trade' N for phosphatases to enhance phosphorus acquisition. Specific root length and root N differed between functional groups, though for other traits, apparent differences became nonsignificant after accounting for phylogenetic nonindependence. We conclude that evolutionary history, trait coordination, and fixation ability contribute to nutrient trait expression at the species level, and recommend explicitly considering phylogeny in analyses of functional groupings.

Competition between mixo‐ and heterotrophic ciliates under dynamic resource supply

AbstractThe outcome of species competition strongly depends on the traits of the competitors and associated trade‐offs, as well as on environmental variability. Here, we investigate the relevance of consumer trait variation for species coexistence in a ciliate consumer–microalgal prey system under fluctuating regimes of resource supply. We focus on consumer competition and feeding traits, and specifically on the consumer's ability to overcome periods of resource limitation by mixotrophy, that is, the ability of photosynthetic carbon fixation via algal symbionts in addition to phagotrophy. In a 48‐day chemostat experiment, we investigated competitive interactions of different heterotrophic and mixotrophic ciliates of the genera Euplotes and Coleps under different resource regimes, providing prey either continuously or in pulses under constant or fluctuating light, entailing periods of resource depletion in fluctuating environments, but overall providing the same amount of prey and light. Although ultimate competition results remained unaffected, population dynamics of mixotrophic and heterotrophic ciliates were significantly altered by resource supply mode. However, the effects differed among species combinations and changed over time. Whether mixotrophs or heterotrophs dominated in competition strongly depended on the genera of the competing species and thus, species‐specific differences in the minimum resource requirements that are associated with feeding on shared prey, nutrient uptake, light harvesting, and access to additional resources such as bacteria. Potential differences in the curvature of the species' resource‐dependent growth functions may have further mediated the species‐specific responses to the different resource supply modes. Overall, our study demonstrates that genus‐ or species‐specific traits other than that related to nutritional mode may override the relevance of acquired phototrophy by heterotrophs in competitive interactions, and that the potential advantage of photosynthetic carbon fixation of symbiont‐bearing mixotrophs in competition with pure heterotrophs may differ greatly among different mixotrophs, playing out under different environmental conditions and depending on the specific requirements of the species. Complex trophic interactions determine the outcome of competition, which can only be understood by taking on a multidimensional trait perspective.

Power of seeds: exploring the growth boosting potential of endophytes

Insect pests on agricultural crops cause biotic stress, resulting in enormous yield losses. Nowadays, microbial insecticides for insect pests have been explored to overcome insect resistance and environmental hazards caused by chemical insecticides. Bacillus thuringiensis (Bt) is known as the most successful microbial insecticide globally, but its commercial application is limited due to its vulnerability to abiotic factors. To overcome these factors, the establishment of Bt as an endophyte in maize plants by seed treatment has been proposed. So, for that reason, the present study aimed to investigate the effect of seed endophytic bacteria in maize on Bt isolates and vice versa. Furthermore, the study was also carried out to assess the antibiotic resistance of these bacteria as well as their role in plant growth promotion. A total of 12 maize seed endophytic bacterial isolates were used for this study. In that, seven isolates belong to the Bacillus genus, two to the Staphylococcus genus, and one each from Paenibacillus, Pantoea, and Enterobacter. No antagonistic effect of seed endophytes was observed against Bt strains. Five isolates had the ability to solubilize phosphate and potassium, seven showed zinc solubilization, and all the isolates showed nitrogen fixation ability. Thus, these seed endophytic bacteria can be explored as potential bio-inputs for improving plant growth, and their harmonizing effect on Bt has been found to be promising for the establishment of Bt as an endophyte in maize plants.

Microbial Protein Production Using Lignocellulosic Biomass (Switchgrass) and Klebsiella oxytoca M5A1—A Nitrogen Fixer

The expanding global population has increased the demand for sustainable protein sources, and microbial protein (MP) has emerged as a promising alternative. However, conventional carbon (glucose) and nitrogen (ammonia, urea) sources needed for MP production pose environmental and economic issues. This study aims to produce protein using lignocellulosic biomass (LCB) as a carbon source and the nitrogen fixation ability of Klebsiella oxytoca M5A1 as a nitrogen source. The study investigates the pretreatment of LCB (switchgrass), enzymatic hydrolysis, protein quantification, nitrogen fixation, glucose utilization and organic acids production. K. oxytoca M5A1 harnessed free nitrogen from the atmosphere and used abundant, cheap glucose from LCB to produce MP and organic acids as by-products. Protein production occurred in two phases: first within the initial 8 h and secondly, within the last 16 h. The highest protein concentration was at 40 h, with approximately 683.46 µg/mL protein content. High-performance liquid chromatography system (HPLC) analysis revealed a dynamic profile of glucose utilization and organic acids (Lactic acid, Propionic acid, Acetic acid, and Succinic acid) production. K. oxytoca M5A1 exhibited an early high rate of glucose consumption, and conversion to organic acids, that were later used for second-phase protein production. The acids profile revealed intra-conversion from one acid to another via metabolic pathways (glycolysis and tricarboxylic acid cycle). Overall, leveraging LCB and the nitrogen-fixing ability of K. oxytoca M5A1 for MP production offers an eco-friendly and cost-effective alternative to traditional protein sources, contributing to a sustainable circular economy.

Effects of Semi‐Film and Full‐Film Mulching on Soybean Growth, Biological Nitrogen Fixation and Grain Yield

ABSTRACTSoybean film mulching has shown promise in maintaining consistent and high yields in semi‐arid regions. However, the specific impacts of full‐film and semi‐film mulching on soybean growth, root nodule traits and grain yield are poorly understood. This 2‐year study (2021–2022) investigates the effects of full‐film and semi‐film mulching on soil moisture, soybean growth and yield. Our findings revealed that semi‐film mulching increased soybean yield by 18.12% compared to full‐film mulching, averaged across 2 years. Furthermore, the semi‐film treatment significantly enhanced biological nitrogen fixation ability, increasing root nodule numbers by 24.81%–33.43%, compared to full‐film mulching. This improvement also positively affected soybean quality, with crude protein content increasing by 5.89% in 2021 and 4.14% in 2022 compared to full‐filming. Moreover, semi‐film mulching helped maintain soil moisture and temperature during later soybean growth stages. There findings suggest that semi‐film mulching is a viable agricultural strategy for soybean cultivation in semi‐arid regions, improving soybean quality and efficiency while promoting environmental sustainability.

Combined dynamic transcriptome and flavonoid metabolome reveal the role of Mo nanoparticles in the nodulation process in soybean

Symbiotic nitrogen fixation can reduce the impact of agriculture on the environment by reducing fertilizer input. The rapid development of nanomaterials in agriculture provides a new prospect for us to improve the biological nitrogen fixation ability of leguminous crops. Molybdenum is an important component of nitrogenase, and the potential application of MoO3NPs in agriculture is largely unexplored. In this study, on the basis of verifying that MoO3NPs can improve the nitrogen fixation ability of soybean, the effects of MoO3NPs on the symbiotic nitrogen fixation process of soybean were investigated by using dynamic transcriptome and targeted metabolome techniques. Here we showed that compared with conventional molybdenum fertilizer, minute concentrations of MoO3NPs (0.01–0.1 mg kg−1) could promote soybean growth and nitrogen fixation efficiency. The nodules number, fresh nodule weight and nitrogenase activity of 0.1 mg kg−1 were increased by 17 %, 14 % and 27 %, and plant nitrogen accumulation increased by 17 %. Compared with conventional molybdenum fertilizer, MoO3NPs had a greater effect on apigenin, kaempferol and other flavonoid, and the expression of nodulation related genes such as ENOD93, F3'H. Based on WGCNA analysis, we identified a core gene GmCHS9 that was positively responsive to molybdenum and was highly expressed during MoO3NPs induced nodulation. MoO3NPs could improve the nitrogen fixation ability of soybean by promoting the secretion of flavonoids and the expression of key genes. This study provided a new perspective for the nano-strengthening strategy of nodules development and flavonoid biosynthesis by molybdenum.

Nitrogen fixation of different seasons and parts of seagrass Enhalus acoroides in Xincun Bay, northern South China Sea

In coastal ecosystems, the nitrogen fixation of seagrasses is crucial. However, the nitrogen fixation rates of seagrasses can vary spatially and temporally, especially in tropical regions. To investigate the nitrogen fixation rates of Enhalus acoroides, we used principal component analysis to examine the rates of nitrogen fixation in the roots, rhizome, and leaves of E. acoroides during the southwest monsoon (July) and the northeast season (October and January), respectively. The results showed that the nitrogen fixation rates in all three parts of E. acoroides were significantly higher during the southwest monsoon period compared to the northeast period. The rates of nitrogen fixation in the leaves of E. acoroides were found to be higher than in the roots and rhizomes. The difference in nitrogen fixation between the various parts of E. acoroides was highly significant (p<0.01). The nitrogen fixation activity of E. acoroides was significantly affected by temperature, as determined by principal component analysis. The spatial variations observed in different regions of E. acoroides were influenced by environmental factors in addition to the temperature-driven seasonal changes. The results suggest that temperature plays a vital role in the nitrogen fixation ability of E. acoroides.