N2-fixing Ability Research Articles

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.

Effect of Three Different Nitrogen Rates and Three Rhizosphere N2- Fixing Bacteria on Growth, Yield and Quality of Peanuts

Raising prices of organic fertilizers, environmental relation of their usage and need for global foodstuff, placed a topic of universal interest in cultivation of legume plants for human nutrients and soil fertility supplementation. Three rates of N fertilizer were studied in the field: 0, 20 and 40 kg N/ha. Three bacterial strains were identified and inoculated in the experiment: Enterobacter asburiae (E. asburiae), Klebsiella quasipneumoniae (K. quasipneumoniae) and Enterobacter cloacae (E. cloacae). The soil samples were taken before and after experiment for chemical attributes analysis. The effect of N2 fertilizer and 3 bacterial strains was on soil chemical properties, yield components and yield of peanut plant. The results of present study showed that application of different N2 fertilizer rates was a little influence on the N2-fixing ability of rhizosphere bacteria, but high effect was significant at the peanut nodule number. In the 3 N fertilizer rates and 3 bacteria, which only had N2 fertilizer rate of 40 kg N/ha and E. asburiae significantly raised the maximum yield component and yield of peanut, while there was the lowest yield component and yield of peanut was observed in N fertilizer rate application of 0 kg N/ha and E. cloacae inoculation. The differences in rhizosphere bacterium strains between different N fertilizer rates was better than that caused by the nitrogen fertilizer amount. This could be due to the substantial improvement in soil chemical attributes at different soils, especially in, pH, OM and total N, as these significantly impacted the soil structure. HIGHLIGHTS Increasing pH, organic matter and total nitrogen of soil were statistically significantly different by 3 N2 fertilizer rates. There is a positive interaction between nitrogen rates and RNFB increasing yield of peanut. Number and weight of peanut nodules obtained the maximum value without applying N2 application compare to other treatments. The maximum yield components of peanut were inoculated with asburiae to compare with K. quasipneumoniae and E. cloacae and applied weight of 40 kg N/ha. The maximum yield of peanut was inoculated with asburiae to compare with K. quasipneumoniae and E. cloacae. GRAPHICAL ABSTRACT

Aplikasi Limbah Daun Trembesi (Samanea saman Jacq Merr) Sebagai Pupuk Hijau Terhadap Pertumbuhan Tanaman Bunga Matahari (Helianthus anuus L.)

The rain tree (Samanea saman) has the potential to become a green manure material for soil fertilizer due to its high biomass production and air N2 fixation ability. The research aims to determine the possibility of rain tree leaf waste being used as organic fertilizer in the construction of city parks without having to go through the previous composting process. The experiment was in polybags with four treatments namely (1) control with pure soil media, (2) addition of 20% volume of trembesi leaves composted, (3) adding 20% ​​volume of cocopeat growing media, and (4) adding 20% ​​volume of fresh rain tree leaves without composting. Experiment using sunflower plants as a representation of ornamental plants in the construction of city parks. The results showed that the application of composted rain tree leaves had the best effect on the growth and generative performance of sunflower plants compared to the application of fresh rain tree leaves without composting, comparison of cocopeat growing media and controls of pure soil media. The research findings will strengthen the recommendation that the application of organic matter to the soil should be through a composting or decomposition process first.

Protection of nitrogenase from photosynthetic O<sub>2</sub> evolution in Trichodesmium: methodological pitfalls and advances over 30 years of research

The Trichodesmium genus comprises some of the most abundant N2-fixing organisms in oligotrophic marine ecosystems. Since nitrogenase, the key enzyme for N2 fixation, is irreversibly inhibited upon O2 exposure, these organisms have to coordinate their N2-fixing ability with simultaneous photosynthetic O2 production. Although being the principal object of many laboratory and field studies, the overall process of how Trichodesmium reconciles these two mutually exclusive processes remains unresolved. This is in part due to contradictory results that fuel the Trichodesmium enigma. In this review, we sift through methodological details that could potentially explain the discrepancy between findings related to Trichodesmium's physiology. In doing so, we exhaustively contrast studies concerning both spatial and temporal nitrogenase protective strategies, with particular attention to more recent insights. Finally, we suggest new experimental approaches for solving the complex orchestration of N2 fixation and photosynthesis in Trichodesmium.

Tailoring defects in SrTiO3 by one step nanoarchitectonics for realizing photocatalytic nitrogen fixation in pure water.

Surface contamination of materials by nitrogenous impurities is a major problem that can bias the quantification of ammonia in photocatalytic N2 fixation reactions. In this work, SrTiO3 nanocubes were prepared by using a nitrogenous precursor and engineered with Ti3+ sites and oxygen vacancy defects in a one-step solvothermal approach. It was observed that the synthesized materials were containing surface nitrogenous impurities and therefore a rigorous cleaning procedure was adopted to eliminate them to the best extent. The contribution of unavoidable surface impurities was deduced in the form of adventitious NH3 by employing control experiments and a realistic photocatalytic NH3 generation was achieved. It was found that pristine SrTiO3 showed no photocatalytic activity, whereas one of the defected SrTiO3 materials showed the highest NH3 formation under natural sunlight in pure water, which was ascribed to the tuned defect sites, enhanced surface area and efficient separation of photogenerated charges. Based on the experimental results, a stringent protocol has been suggested for materials synthesis while working with nitrogenous precursors and for subsequent photocatalytic N2 fixation experiments. Thus, the present study provides a simple and affordable procedure for catalyst synthesis for the studied application and expands the scope of perovskite oxide materials to fabricate efficient photocatalysts for sustainable NH3 production.

Biotoxicity of NH4+ on Nostoc Sphaeroides (diazotrophic cyanobacteria) in paddy floodwater

In order to elucidate the toxicity of NH4+ on Nostoc Sphaeroides (commonly named GE-XIAN-MI in China, GXM), a diazotrophic cyanobacterium in paddy fields, this study investigated the growth, photosynthesis, N2-fixation, and oxidative-antioxidative characteristics of GXM under NH4+ stress in paddy floodwater. The results showed that the photosynthesis and the N2-fixing ability of GXM were inhibited by NH4+ at a concentration of 13.46 mg L-1 in paddy floodwater. The main target of NH4+ on photosystem II (PS II) of GXM was the electron donor side of react center. Oxygen evolution complex (OEC) was the secondary target of toxicity of NH4+ on PS II. The damage of PS II led to accumulation of ROS and resulted in oxidative damage on plasma membrane of GXM. Feedback inhibition and decrease of photosynthetic energy production may be the reasons for the decrease of N2-fixing ability of GXM under NH4+ stress. The results presented in this study suggest that high level of NH4+ loading may be a reason for the recession of GXM resource in paddy fields.

Unraveling Nitrogen Fixing Potential of Endophytic Diazotrophs of Different Saccharum Species for Sustainable Sugarcane Growth.

Sugarcane (Saccharum officinarum L.) is one of the world’s highly significant commercial crops. The amounts of synthetic nitrogen (N2) fertilizer required to grow the sugarcane plant at its initial growth stages are higher, which increases the production costs and adverse environmental consequences globally. To combat this issue, sustainable environmental and economic concerns among researchers are necessary. The endophytic diazotrophs can offer significant amounts of nitrogen to crops through the biological nitrogen fixation mediated nif gene. The nifH gene is the most extensively utilized molecular marker in nature for studying N2 fixing microbiomes. The present research intended to determine the existence of novel endophytic diazotrophs through culturable and unculturable bacterial communities (EDBCs). The EDBCs of different tissues (root, stem, and leaf) of five sugarcane cultivars (Saccharum officinarum L. cv. Badila, S. barberi Jesw.cv Pansahi, S. robustum, S. spontaneum, and S. sinense Roxb.cv Uba) were isolated and molecularly characterized to evaluate N2 fixation ability. The diversity of EDBCs was observed based on nifH gene Illumina MiSeq sequencing and a culturable approach. In this study, 319766 operational taxonomic units (OTUs) were identified from 15 samples. The minimum number of OTUs was recorded in leaf tissues of S. robustum and maximum reads in root tissues of S. spontaneum. These data were assessed to ascertain the structure, diversity, abundance, and relationship between the microbial community. A total of 40 bacterial families with 58 genera were detected in different sugarcane species. Bacterial communities exhibited substantially different alpha and beta diversity. In total, 16 out of 20 genera showed potent N2-fixation in sugarcane and other crops. According to principal component analysis (PCA) and hierarchical clustering (Bray–Curtis dis) evaluation of OTUs, bacterial microbiomes associated with root tissues differed significantly from stem and leaf tissues of sugarcane. Significant differences often were observed in EDBCs among the sugarcane tissues. We tracked and validated the plethora of individual phylum strains and assessed their nitrogenase activity with a culture-dependent technique. The current work illustrated the significant and novel results of many uncharted endophytic microbial communities in different tissues of sugarcane species, which provides an experimental system to evaluate the biological nitrogen fixation (BNF) mechanism in sugarcane. The novel endophytic microbial communities with N2-fixation ability play a remarkable and promising role in sustainable agriculture production.

Z‐type heterojunction of graphene quantum dots/ g‐C 3 N 4 / BiOCl with excellent photocatalytic performance for nitrogen fixation

In this study, a Z-type g-C3N4/BiOCl composite was synthesized by a one-step hydrothermal technique with varying loading amounts of graphene quantum dots (GQDs) to investigate their photocatalytic activity of N2 fixation to NH3 under simulated solar light irradiation. Experimental results showed that the photocatalytic activity of as-prepared GQDs/g-C3N4/BiOCl (GCNB) was significantly higher than those of pure g-C3N4 and BiOCl, and the rate of NH3 formation reached 1773.8 μmol/(h·gcat), which was 7.3 and 5.2 times greater than those of pure g-C3N4 and BiOCl, respectively. After five cycles of experiments, the N2 fixation ability of GCNB did not decrease obviously, indicating that GCNB had high photocatalytic stability. The excellent photocatalytic performance of GCNB was attributed to the broad light absorption range of BiOCl/ultrathin g-C3N4 binary materials and the unique photoelectronic properties of GQDs, which were loaded to form Z-type heterojunctions with a strong redox capability. A Z-type composite photocatalytic mechanism was proposed in this paper, which could significantly improve the charge separation efficiency and maintain a good redox capability. This study could provide an effective method for designing Z-type composite catalysts with high photocatalytic activity. Highlights g-C3N4 can enhance photocatalytic activity by slowing down the recombination of electron-hole pairs. GQDs is an excellent electron transport material sandwiched between g-C3N4 and BiOCl. GQDs/g-C3N4/BiOCl composite material had the best performance of photocatalytic ammonia synthesis The fixation mechanism of N2 in Z-type heterojunction photocatalytic system was investigated.

Potential of N2-fixing endophytic bacteria isolated from maize roots as biofertiliser to enhance soil fertility, N uptake, and yield of Zea mays L. cultivated in alluvial soil in dykes

This study aimed to (i) select the endophytic bacteria from maize roots for their N2-fixing ability and (ii) evaluate the efficacy of potent indigenous bacterial strains on soil fertility, nitrogen (N) uptake, and growth and yield of maize. A total of 31 maize root samples were collected from An Giang province in Vietnam to isolate the bacteria. The pot experiment was conducted in nine treatments: (i) 100% N of the recommended fertiliser formula (RFF), (ii) 85% N of RFF, (iii) 70% N of RFF, (iv) 55% N of RFF, (v) 85% N of RFF plus a mixture of two potent strains of nitrogen-fixing endophytic bacteria (NFEB), (vi) 70% N of RFF plus a mixture of two potent strains of NFEB, (vii) 25% N of RFF plus a mixture of two potent strains of NFEB, (viii) 0% N of RFF plus a mixture of two potent strains of NFEB, and (ix) 0% N of RFF. The experiment was conducted in the greenhouse to collect soil and plant samples at harvest and observe their growth and agronomic parameters. The results showed that two acid-resistant endophytic bacterial strains were selected and identified as Enterobacter cloacae ASD-21 and E. cloacae ASD-48. At 85% N level, a mixture of the two endophytic bacteria strains was applied as biofertilisers and proved their ability to significantly enhance NH4+ content and N uptake, with an increase of 14.8 mg NH4+ kg-1 and 0.26 g N pot-1, respectively. A mixture of the two potent strains of NFEB produced higher values in plant height, stem diameter, cob length, and cob diameter compared to 100% N of RFF. It replaced 15% N of RFF but still maintained the maize grain yield

Transcriptomic profiling of nitrogen fixation and the role of NifA in Methylomicrobium buryatense 5GB1.

Methanotrophs capable of converting C1-based substrates play an important role in the global carbon cycle. As one of the essential macronutrient components in the medium, the uptake of nitrogen sources severely regulates the cell's metabolism. Although the feasibility of utilizing nitrogen gas (N2) by methanotrophs has been predicted, the mechanism remains unclear. Herein, the regulation of nitrogen fixation by an essential nitrogen-fixing regulator (NifA) was explored based on transcriptomic analyses of Methylomicrobium buryatense 5GB1. A deletion mutant of the nitrogen global regulator NifA was constructed, and the growth of M. buryatense 5GB1ΔnifA exhibited significant growth inhibition compared with wild-type strain after the depletion of nitrate source in the medium. Our transcriptome analyses elucidated that 22.0% of the genome was affected in expression by NifA in M. buryatense 5GB1. Besides genes associated with nitrogen assimilation such as nitrogenase structural genes, genes related to cofactor biosynthesis, electron transport, and post-transcriptional modification were significantly upregulated in the presence of NifA to enhance N2 fixation; other genes related to carbon metabolism, energy metabolism, membrane transport, and cell motility were strongly modulated by NifA to facilitate cell metabolisms. This study not only lays a comprehensive understanding of the physiological characteristics and nitrogen metabolism of methanotrophs, but also provides a potentially efficient strategy to achieve carbon and nitrogen co-utilization.Key points• N2 fixation ability of M. buryatense 5GB1 was demonstrated for the first time in experiments by regulating the supply of N2.• NifA positively regulates nif-related genes to facilitate the uptake of N2 in M. buryatense 5GB1.• NifA regulates a broad range of cellular functions beyond nif genes in M. buryatense 5GB1.

Topographical influences on foliar nitrogen concentration and stable isotope composition in a Mediterranean-climate catchment

Nitrogen (N) oligotrophication is increasing globally across terrestrial ecosystems and manifested in decreasing nitrogen concentration ([N]) and changes in the stable nitrogen isotope composition (δ15N) of foliage. Heterogeneity in plant nitrogen sources makes it challenging to detect the effects of N oligotrophication even at a small catchment scale with complex topography. Understanding the spatial and temporal variation of foliar δ15N and [N] at such a scale is required to develop useful ecological indicators and monitoring methods to support catchment management with a potential N oligotrophication problem. This study examined spatial and high-resolution temporal variation of foliar δ15N and [N] and their influencing factors in ten trees grouped by Eucalyptus and Acacia in a native forest vegetation catchment. Over 16 sampling campaigns within a 12-month period, foliar δ15N and [N] increased in Eucalyptus but were constant in the N2-fixing Acacia. The higher foliar [N] and δ15N in Acacia reflected its N2-fixation ability. Topographic flow accumulation area (NDVI) explained 46% (77%) of spatial variation in dry-season Eucalyptus foliar δ15N ([N]). For Eucalyptus, foliar δ15N was higher at the downslope than the upslope locations, but no hillslope location differences were observed for foliar [N]. These results suggest that in the non-N2-fixing Eucalyptus, seasonal water stress related nitrogen availability may be reflected in foliar δ15N rather than foliar [N]. As such, foliar δ15N of non-N2-fixing plants potentially is a more sensitive indicator of seasonal or topographical N availability than foliar [N].

Chloride-ion-directed synthesis of plate-like Cu2O mesocrystals for effective nitrogen fixation.

Cuprous oxide (Cu2O) mesocrystals, which are composed of numerous nanocrystals with a common crystallographic orientation, are supposed to possess superior photocatalytic abilities than the normal constructions, but very few of them have been reported to date. In this work, plate-like Cu2O mesocrystals were successfully fabricated via a facile one-pot wet chemical strategy. Unlike the commonly used polymers or small molecules, chloride ions (Cl-) were employed as structure-directing agents and played the main role in the Cu2O mesocrystal formation. The formation mechanism was interpreted as follows: the presence of Cl- inhibited the formation of CuO and Cu by forming the intermediate product CuCl, which was further hydrolyzed to Cu2O nanocrystals. Cl- tended to adsorb on the (111) facets of the formed Cu2O nanocrystals and stabilize them. Then the Cu2O nanocrystals were aligned side by side through the unabsorbed side faces, leading to mutual nanocrystals orientation and crystallographic lock-in, facilitating the formation of plate-like Cu2O mesocrystals. The polymer, polyacrylamide (PAM), also promoted the mesocrystals formation by serving as a stabilizer and fixed the crystallographic orientation of the Cu2O nanocrystals during their orderly stacking process. The plate-like Cu2O mesocrystals showed a long decay time and pronounced performance toward the visible-light-driven photocatalytic reduction of N2 into NH3. This research may stimulate in-depth investigations into the exploration of new synthetic methods for the design and construction of novel mesocrystals.

Isolation and characterization of nitrogen-fixing bacteria from soil sample in Dhaka, Bangladesh

Biological nitrogen (N2) fixation is very essential for limiting the growth of plants and agricultural crops. The present study was conducted to potentially isolate N2-fixing bacteria from garden soil sample at Stamford University Bangladesh, Siddeswari, Dhaka. Here, we used culture-dependent method to perform this experiment. Firstly, we collected garden soil sample, diluted and inoculated in N2-free Jensen’s media by maintaining the aseptic procedure. We obtained 5 different colonies from soil samples. We cultured the isolates in N2-free Jensen’s media containing bromothymol blue (BMB) and also, in Yeast Extract Mannitol Agar (YEMA) media containing congo red to confirm nitrogen fixation capacity. We collected the colony characteristics of all the isolates. Only 1A isolate showed good growth after 24 h of incubation among all the isolates. We performed ammonification test with Nessler reagent to confirm N2-fixing ability for our selected isolates. The 1A isolate was positive in ammonification test. Culture, microscopy and biochemical tests were performed to identify isolate 1A. This isolate was presumptively identified as Azotobacter sp. In the present study, Azotobacter sp. that was isolated from the soil sample was found to be a potential N2-fixing bacterium. Isolate 1A can be used for N2-fixation to boost production of crops. Stamford Journal of Microbiology, Vol.11 (1) 2021: 11-13

Cultivable Endophytic Bacteria in Seeds of Dongxiang Wild Rice and Their Role in Plant-Growth Promotion

Dongxiang wild rice (Oryza rufipogon Griff.) germplasm is a precious resource for the improvement of agronomic traits in rice. Rice seeds also harbor a diverse endophytic bacterial community, and their interactions with their hosts and each other can influence plant growth and adaptability. Here, we investigated the community composition of cultivable endophytic bacteria obtained from the surface-sterilized seeds of Dongxiang wild rice and screened them for plant growth-promoting traits. Phylogenetic analysis of 16S rRNA gene sequences indicated that the 47 isolates were affiliated with five classes and 13 discrete genera, and Bacillus and Microbacterium predominated. Evaluations of plant growth promoting (PGP) traits showed that 45 endophytic bacteria isolates produced between 3.37 and 90.11 μg mL−1 of Indole-3-acetic acid (IAA), with the highest yield of 90.11 μg mL−1 (Fse28). Further, 37 of the isolates were able to solubilize mineral phosphate, while 28 other isolates had the ability of N2-fixation, 17 isolates possessed 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity with the highest yield of 20.72 μmol mg−1 protein h−1 (Fse35), and 17 isolates were also able to produce siderophores. The two strains Fse28 and Fse35 had multiple PGP traits that significantly improved the agronomic traits (root length, shoot length, dry matter, and chlorophyll content) of cultivated rice seedlings. Our results illustrate the rich diversity of seed endophytic bacteria in Dongxiang wild rice and their potential for developing novel efficient bioinoculants to enhance soil fertility and favor seedling growth.

In situ construction of Fe substituted palygorskite/FeS2 heterostructure for full-spectrum photocatalytic nitrogen fixation

The innovation of cost-effective ammonia synthesis under mild condition to replace traditional Haber-Bosch process remains a grand challenge. In this work, partial cations in one-dimensional clay palygorskite (Pal) were substituted by Fe ions to achieve lattice reconstruction, followed by in situ precipitation of FeS2 nanoparticles using a microwave hydrothermal method. The band gap of Fe-modified Pal was largely reduced with the perseverance of its original crystal structure. As the Fe content exceeded 20 wt%, excess Fe ions on the surface of Fe-Pal reacted with sulfide ions to form iron sulfide (FeS2), which owned narrow bandgap (1.3 eV) responsive in near infrared (NIR) light. The presence of abundant sulfur vacancies (Sv) as well as Fe species served as nitrogen adsorption and activation center, which promoted the adsorption of N2 and weakened the NN triple bond. A Z-scheme heterostructure can be formed between Fe-Pal and FeS2 intermediated by Sv, improving the adsorption range of solar light and enhancing the redox potential for N2 reduction. The optimized 40 wt% Fe-Pal exhibited remarkable N2 fixation ability in a wide spectrum, providing a new perspective for cost-effective photocatalytic nitrogen fixation.

Phenetic Characterization of Nitrogen Fixing Azotobacter from Rhizospheric Soil of Southern Rajasthan

The present research was conducted to characterize the indigenous plant growth promoting (PGP) Azotobacter strains isolated from plant root interface of semi-arid regions of Rajasthan (India) and to study their potential to be used as bio-fertilizers. A total of 172 Azotobacter strains were isolated, purified and based on the morphological test i.e. gram staining, pigmentation, cyst formation, fluorescence etc, broadly classified as Azotobacter. Further the secluded strains were examined for biochemical analysis and plant growth promoting characters. All the isolates showed different biochemical characteristics and significant PGP traits. IAA activity of the Azotobacter strains ranges from 54.5-6000 µg/mL. Ammonia, HCN and siderophore was produced by 92.4%, 78.4% and 80.23% of the total isolates respectively. Solubilization of phosphate was observed in 97.6% of the total isolates. These strains were also characterized for qualitative and quantitative N2 fixation abilities and the result indicated that 114 strains showed positive results on nitrogen free malate agar medium (NFMM) containing bromothymol blue (BTB) and able to produce 18.93-475.6 N-moles C2H4 mg protein−1 h−1 of acetylene reduced by Azotobacter strains. In vitro pot studies revealed that the selected native Azotobacter strains having high ARA results significantly increase the plant growth characters. Shoot length, root length, root number and chlorophyll content and leaf number increases by 45.62%, 17.60%, 97.49%, 49.69% and 27.83% respectively in pot inoculated with AZO23-3 as compared to control. These effective strains can further be utilized for development of effective microbial formulations.

Planting season and date of harvest effect on biomass production and nitrogen contribution of Crotalaria juncea L. 'Tropic Sun' in southwestern

Sunn hemp (Crotalaria juncea L.) is a fast-growing, multipurpose legume of high N2 fixation ability, and an option for use in improving the fertility of degraded tropical soils. The objective of this study was to compare the effects of two planting seasons and three harvest dates on biomass yield (DMY) and N accumulation in the vegetative material of sunn hemp Tropic Sun'. Sunn hemp was seeded at the Lajas Agricultural Experimental Substation of the University of Puerto Rico in a Mollisol soil (San Antón Series) at a density of 7 kg/ha in May and October, and harvested at 84, 121, and 177 days after planting (DAP). The 177 DAP date proved to be not feasible because of previous senescence of the plants from the October planting; therefore, it was excluded from the analysis. Planting in May rather than October and harvesting at 121 DAP rather than 84 DAP resulted in higher DMY (kg/ha) (7,248 vs. 5,975 and 7,946 vs. 5,277, respectively). However, only the difference between planting seasons was significant (P < 0.05). The same tendencies were observed in N accumulation (kg/ha), means of 126.55 vs. 105.09 and 120.65 vs. 110.99, respectively, but without differences at P = 0.05. No interactions (P > 0.05) were detected between seasons of planting and date of harvest in these two dependent variables. Differences (P < 0.05) were found in N content of plant tissue, the upper canopy mean surpassing that of the lower canopy (2.12 vs. 1.00%). The highest crude protein content of 16.05% was found in the upper canopy for the May planting. These results suggest that sunn hemp has good potential as a cover crop and green manure in the Lajas region, and that summer planting is preferable.

Phenetic and Molecular Diversity of Nitrogen Fixating Plant Growth Promoting Azotobacter Isolated from Semiarid Regions of India

In the present study, 24 Azotobacter strains were isolated from soils of different areas of southern Rajasthan and characterized at biochemical, functional, and molecular levels. The isolated Azotobacter strains were gram negative and cyst forming when viewed under the microscope. These strains were also screened for their plant growth promoting activities and the ability of these isolates to survive under abiotic stress conditions viz. salt, pH, temperature, and drought stress. All the isolates showed IAA, siderophore, HCN, and ammonia production, whereas seven Azotobacter strains showed phosphate solubilization. Amplified Ribosomal DNA Restriction Analysis (ARDRA) revealed significant diversity among Azotobacter strains and the dendrogram obtained differentiated twenty-four of the strains into two major clusters at a similarity coefficient of 0.64. Qualitative and quantitative N2 fixation abilities of these strains were also detrained, and the amounts of acetylene reduced by Azotobacter strains were in the range of 1.31 to 846.56 nmol C2H4 mg protein−1 h−1. The strains showing high nitrogen fixation ability with multiple PGP activities were selected for further pot studies, and these Azotobacter strains significantly increased the various plant growth parameters of maize plantlets. Furthermore, the best Azotobacter isolates were subjected to 16S rRNA sequencing and confirmed their identities as Azotobacter sp. The indigenous Azotobacter strains with multiple PGP activities could be further used for commercial production.

In situ synthesis of hierarchical nitrogen-doped MoS2 microsphere with an excellent visible light-driven photocatalytic nitrogen fixation ability

A photocatalyst of high-performance hierarchical nitrogen-doped MoS2 (N-MoS2) microsphere was fabricated by an in situ hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB). The as-prepared N-MoS2 microsphere was self-assembled by extremely thin interleaving petals, where CTAB acts as a nucleation site for the formation of the interleaving petals due to the strong interaction between CTA+ and [Formula: see text]. N-MoS2 showed higher N2 fixation ability (101.2 [Formula: see text] mol/g(cat)h) than the non-doped MoS2 under the visible light irradiation, and the improved photocatalytic activity could be ascribed to that the doped N narrows the band gap, and the surface reflecting and scattering effect caused by the hierarchical structure enhance the light adsorption. The trapping experiment of active species was also investigated to evaluate the role of photogenerated electrons in the photocatalytic reaction process. Meanwhile, the possible mechanism for the formation and excellent photocatalytic performance of N-MoS2 microsphere were also presented.

Enhanced H2 production with efficient N2-fixation by fructose mixotrophically grown Anabaena sp. PCC 7120 strain disrupted in uptake hydrogenase

To explore the potential of a model filamentous cyanobacterium Anabaena sp. PCC 7120 for solar based biohydrogen production, an inactivated uptake hydrogenase ΔHupL strain was used in combination with fructose induced N2-fixing ability of the cells. The results revealed that fructose supports N2-fixing and H2-metabolism in ΔHupL strain. Cells showed an increase in growth rate, pigment content, and the formation of mature heterocysts within 6 h after growing under light-fructose mixotrophic condition. Upon supplementation of optimum fructose concentration at 60 mM, the cells grown for 24 h showed a 3.1-fold increase of nitrogenase activity in conjunction with an increase of nifD expression, with increased electron flow from utilization of fructose through the oxidative pentose phosphate pathway. Nitrogenase rather than bidirectional hydrogenase was likely responsible for the fructose mediated increase of H2-production. The maximum H2-production rate of ΔHupL strain under fructose mixotrophic growth was 101.33 μmolH2 mg chl a−1 h−1, accounting for a 4.7-fold increase compared to wild type under the same condition. Overall results indicated that fructose supplementation enabled Anabaena sp. PCC 7120 strain ΔHupL to increase N2-fixation leading to an enhanced H2-production.