Fixation Activity Research Articles

Research Progress on the Application of MOF and MOF‐Based Materials in Nitrogen Reduction

AbstractElectrocatalytic and photocatalytic nitrogen fixation have become new ways to achieve green nitrogen reduction because of their environmentally friendly and cost‐effective characteristics. At present, there has been an increasing curiosity about using metal‐organic frameworks (MOFs) for photocatalysis and electrocatalysis. However, electrocatalytic and photocatalytic ammonia production is still not practical for practical applications. Having a thorough understanding of nitrogen fixation is necessary for the advancement of practical applications and the development of highly efficient catalysts in the future. The catalytic nitrogen fixation activity of MOF itself is limited. By adjusting the exposure of active sites through low‐temperature calcination and solvent addition, the photogenerated carrier recombination is inhibited, and the adsorption and activation of N2 are enhanced, improving its performance in nitrogen fixation applications. This review examines the reported photocatalysts, electrocatalysts, and photoelectrocatalysts based on MOFs and their associated materials. The underlying mechanism for photocatalysis and electrocatalysis is elucidated. Additionally, an inclusive survey of MOFs and related materials as catalysts for nitrogen reduction reaction (NRR) is presented, with representative examples discussed. Finally, the research progress of MOF‐based catalytic nitrogen fixation materials is summarized and prospected.

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.

Degradation of Complex Carbon Sources in Organic Fertilizers Facilitates Nitrogen Fixation.

Biological nitrogen fixation is crucial for agriculture and improving fertilizer efficiency, but organic fertilizers in enhancing this process remain debated. Here, we investigate the impact of organic fertilizers on biological nitrogen fixation through experiments and propose a new model where bacterial interactions with complex carbon sources enhance nitrogen fixation. Field experiments showed that adding organic fertilizers increased the nitrogenase activity by 57.85%. Subculture experiments revealed that organic fertilizer addition enriched genes corresponding to complex carbon and energy metabolism, as well as nifJ involved in electron transfer for nitrogenase. It also enhanced bacterial interactions and enhanced connectors associated with complex carbon degradation. Validation experiments demonstrated that combinations increased nitrogenase activity by 2.98 times compared to the single. Our findings suggest that organic fertilizers promoted nitrogen fixation by enhancing microbial cooperation, improved the degradation of complex carbon sources, and thereby provided utilizable carbon sources, energy, and electrons to N-fixers, thus increasing nitrogenase activity and nitrogen fixation.

Bionic Design of Iron-Doped MoSe2 Catalyst for Efficient Nitrogen Fixation.

The catalytic system of biological nitrogen fixation in nature primarily relies on the "FeMo cofactor" within nitrogenase enzymes. Inspired by this natural structure, we have designed a bionic inorganic counterpart, iron-doped MoSe2, for the efficient electroreduction of dinitrogen to ammonia. The introduced Fe dopant significantly enhances nitrogen fixation activity of MoSe2. Furthermore, we constructed a heterostructure catalyst, the Fe-MoSe2/Mo2C with more versatile Mo valence states. The heterostructured electrocatalyst achieves an ammonia production rate of 3.38 μg cm-2 h-1, and a Faradaic efficiency of 30.8 %, which is ~5 fold higher than that of pristine MoSe2. This study presents a novel approach for designing bionic nitrogen fixation electrocatalysts.

Limited dependence on soil nitrogen fixation as subtropical forests develop

Soil nitrogen (N) fixation, driven by microbial reactions, is critical to support the entrance of nitrogen in nutrient poor and pioneer ecosystems. However, how and why N fixation and soil diazotrophs evolve as forests develop remain poorly understood. Here, we used a 60-year forest rewilding chronosequence and found that soil N fixation activity gradually decreased with increasing forest age, experiencing dramatic drops of 64.8% in intermediate stages and 93.0% in the oldest forests. Further analyses revealed loses in diazotrophic diversity and a significant reduction in the abundance of important diazotrophs (e.g., Desulfovibrio and Pseudomonas) as forest develops. This reduction in N fixation, and associated shifts in soil microbes, was driven by acidification and increases in N content during forest succession. Our results provide new insights on the life history of one of the most important groups of soil organisms in terrestrial ecosystems, with consequences for understanding the buildup of nutrients as forest soil develops.

Synergistic effect of bimetallic active sites on Ce doped NH2–MIL-125 for promoting photocatalytic conversion of nitrogen to NH3

Ammonia (NH3), one of the most abundant inorganic compounds in the world, is highly demanded in the international market. NH3 is mainly synthesized using Haber-Bosch technology, which severely pollutes the environment and consumes high quantities of energy. In this study, a series of Ce doped NH2–MIL-125 (Ce–NH2–MIL-125) was prepared using a one-step solvothermal method to assess the activity of photocatalytic nitrogen fixation. The applied light energy interval of Ce–NH2–MIL-125 was widened, and the establishment of a Ce–O–Ti chemical bond optimized the transport path of the photogenerated carriers. This excellent photoelectric performance represents a significant improvement in the separation capacity of the photogenerated electrons and holes in Ce–NH2–MIL-125. Doping with Ce resulted in the generation of dual active sites, Ti4+/Ti3+ and Ce4+/Ce3+, in NH2–MIL-125; additionally, the increase in the amount of Ti3+ was significantly higher than that of the initial NH2–MIL-125. The synergistic effect of the bimetallic active sites in Ce–NH2–MIL-125 accelerated the photocatalytic nitrogen fixation reaction. Under full spectrum radiation, the ammonia generation rate of NH2–MIL-125 was 10.6 µmol g−1 h−1. Ce–NH2–MIL-125–1.0 exhibited the highest capacity for nitrogen fixation; the highest ammonia formation rate was 39.4 µmol g−1 h−1. The photocatalytic activity of Ce–NH2–MIL-125–1.0 was 3.7 times higher than that of NH2–MIL-125. This study provides a reference for catalytic research on modified NH2–MIL-125.

Characterization of a novel root-associated diazotrophic rare PGPR taxa, Aquabacter pokkalii sp. nov., isolated from pokkali rice: new insights into the plant-associated lifestyle and brackish adaptation

Salinity impacts crop growth and productivity and lowers the activities of rhizosphere microbiota. The identification and utilization of habitat-specific salinity-adapted plant growth-promoting rhizobacteria (PGPR) are considered alternative strategies to improve the growth and yields of crops in salinity-affected coastal agricultural fields. In this study, we characterize strain L1I39T, the first Aquabacter species with PGPR traits isolated from a salt-tolerant pokkali rice cultivated in brackish environments. L1I39T is positive for 1-aminocyclopropane-1-carboxylate deaminase activity and nitrogen fixation and can promote pokkali rice growth by supplying fixed nitrogen under a nitrogen-deficient seawater condition. Importantly, enhanced plant growth and efficient root colonization were evident in L1I39T-inoculated plants grown under 20% seawater but not in zero-seawater conditions, identifying brackish conditions as a key local environmental factor critical for L1I39T-pokkali rice symbiosis. Detailed physiological studies revealed that L1I39T is well-adapted to brackish environments. In-depth genome analysis of L1I39T identified multiple gene systems contributing to its plant-associated lifestyle and brackish adaptations. The 16S rRNA-based metagenomic study identified L1I39T as an important rare PGPR taxon. Based on the polyphasic taxonomy analysis, we established strain L1I39T as a novel Aquabacter species and proposed Aquabacter pokkalii sp nov. Overall, this study provides a better understanding of a marine-adapted PGPR strain L1I39T that may perform a substantial role in host growth and health in nitrogen-poor brackish environments.

Transcriptional, metabolic, physiological and developmental responses to nitrogen limitation in switchgrass (Panicum virgatum)

Sustainable switchgrass production (Panicum virgatum) as a bioenergy crop hinges partly on efficiently using soil macronutrients, especially nitrogen (N). In this study, switchgrass plants were grown under four different N conditions (6.0 mM KNO3, N-replete control; 2.0 mM, mild limitation; 0.6 mM, moderate limitation; and 0.2 mM, severe limitation). Subsequently, the physiological, metabolic, and transcriptomic responses of switchgrass roots and shoots to N limitation were determined.Moderate N limitation marked a tipping point for large changes in plant growth, root-to-shoot ratio, root system architecture (root surfaces and specific root length - SRL) and total nitrogen content. Integrating metabolic data and transcriptomic analyses revealed that N limitation reduced switchgrass photosynthetic capacity and carbon(C)-fixation activities. Our results indicate that switchgrass balances C-fixation with N-assimilation and N transport and recycles N-compounds by rerouting C-flux from glycolysis, the oxidative branch of the pentose phosphate pathway (OPPP), and from the tricarboxylic acid (TCA) cycle in an organ-specific manner. The energy and reduction power so generated, and C-skeletons appear to be directed towards N uptake, biosynthesis of energy storage compounds with high C/N ratio such as sucrose, non-N-containing lipids, and various branches of secondary metabolism. Taken together, the findings of this study provide new insights into how switchgrass plants adapt to N limitation.

Regulating concentration of surface oxygen vacancies in Bi2MoO6/Bi-MOF for boosting photocatalytic ammonia synthesis

Surface oxygen vacancies (OVs) engineering has been widely adopted as an effective strategy to enhance photocatalytic performance. At present, photocatalytic systems capable of precisely regulating surface OVs concentrations, which could help illuminate the effects of the surface OVs concentration on N2 fixation activity, are still scarce. Herein, bismuth-based metal organic framework (Bi-MOF) was loaded onto the surface of Bi2MoO6 (BMO) as an operable platform, and the OVs concentration in the Bi-MOF component of BMO/Bi-MOF could be regulated by reduction of bismuth ions therein. Experimental results confirm that optimum construction of OVs in the Bi-MOF promotes the photoelectrons transfer from BMO to Bi-MOF, facilitating the activation of N2 at OVs. Consequently, the optimized catalyst shows superior performance in NH3 production, which reaches 125.78 μmol h−1 g−1, 21.4 higher than that of BMO. This work underline the significance of regulating surface OVs concentration, providing inspiration for the development of efficient OVs-modified photocatalysts.

Assessment of Plant-Growth Promoting Potential of Bacteria Isolated from Amazonian Black Pepper Roots

Purpose: In the Amazon, farmers use chemical fertilizers on a large scale to meet the nutritional requirements of some crops. Plant-growth promoting bacteria (PGPB) offer a sustainable alternative to enhance crop productivity. This study aimed to prospect novel PGPB from Amazonian black pepper (Piper nigrum L.) roots. Methods: Bacterial isolates were obtained from plant roots, evaluated for their biofertilizing potential, and the most promising strain was selected for genome sequencing. Taxonomic classification was based on 16 S rRNA gene sequencing. ACC deaminase activity, phosphate solubilization, and nitrogen fixation were assessed. Genome sequencing was performed using the Ion GeneStudio S5 platform. Results: The 20 isolates were affiliated to Enterobacter (7 isolates), Klebsiella (4 isolates), Kosakonia (5 isolates), Bacillus (2 isolates), and two unclassified bacteria. Seven isolates were positive for ACC deaminase activity, while four were positive for the presence of the nifH gene. Nitrogenase gene was found only in Kosakonia isolates. Ninety isolates were able to solubilize phosphate. The isolate Pn16 was the most promising and presented a genome of 6,432,985 bp, GC content of 55%, 6,465 Coding Sequences, 10 Symbiotic Islands, 28 biosynthetic gene clusters, and several genes involved in plant-growth promotion such as phoU-pstSCAB-phoBR, oqxAB, ipdC, speADEGF, nifHDK. Conclusions: We were able to isolate a bacterium with potential for biofertilization. Based on phylogeny and Average Nucleotide Identity, we propose the classification of the Pn16 isolate as Kosakonia pseudosacchari Pn16.

Heterodera glycines HG type 1.2.5.7 causes a decrease in soybean (Glycine max [L.] Merr.) nitrogen fixation and growth variables

ABSTRACT Soybean cyst nematode (SCN), Heterodera glycines, HG type 1.2.5.7 is the most virulent and widespread SCN biotype in the southern states of the USA, but its effect on soybean (Glycine max [L.] Merr.) nitrogen fixation (NF) activity and growth is not well documented. The objectives of this study were to: (1) measure the impact of HG type 1.2.5.7 on NF activity during the early vegetative stage of three soybean genotypes and (2) compare the impact on soybean leaf and root development, and plant growth. The NF activity of two susceptible (S) genotypes (“Ellis” and “Williams 82”) and one resistant (R) genotype (PI 88,788), subjected to a 10,000-egg treatment, was measured using an in-situ flow-through acetylene reduction assay. The average NF activity of the soybean genotypes was decreased by SCN activity. Time points assessment showed that the NF activity was differently impacted among the genotypes. Based on the measured values, the NF activity was decreased by 30% in SCN infected plants of Williams 82 but that of PI 88,788 and Ellis was affected. Likewise, soybean leaf color and leaf area were affected by SCN infection, but there was no impact on root length and root area. These results showed that SCN HG type 1.2.5.7 can exhibit varying negative impact on NF and shoot growth of S soybean genotypes, while R genotypes may be unaffected. Thus, indicating genetic resistance continues to be a critical tool for the management of the SCN.

Inhibition of Verticillium Wilt in Cotton through the Application of Pseudomonas aeruginosa ZL6 Derived from Fermentation Residue of Kitchen Waste.

To isolate and analyze bacteria with Verticillium wilt-resistant properties from the fermentation residue of kitchen wastes, as well as explore their potential for new applications of the residue. A total of six bacterial strains exhibiting Verticillium wilt-resistant capabilities were isolated from the biogas residue of kitchen waste fermentation. Using a polyphasic approach, strain ZL6, which displayed the highest antagonistic activity against cotton Verticillium wilt, was identified as belonging to the Pseudomonas aeruginosa. Bioassay results demonstrated that this strain possessed robust antagonistic abilities, effectively inhibiting V. dahliae spore germination and mycelial growth. Furthermore, P. aeruginosa ZL6 exhibited high temperature resistance (42°C), nitrogen fixation, and phosphorus removal activities. Pot experiments revealed that P. aeruginosa ZL6 fermentation broth treatment achieved a 47.72% biological control effect compared to the control group. Through activity tracking and protein mass spectrometry identification, a neutral metalloproteinase (Nml) was hypothesized as the main virulence factor. The mutant strain ZL6ΔNml exhibited a significant reduction in its ability to inhibit cotton Verticillium wilt compared to the strain P. aeruginosa ZL6. While the inhibitory activities could be partially restored by a complementation of nml gene in the mutant strain ZL6CMΔNml. This research provides a theoretical foundation for the future development and application of biogas residue as biocontrol agents against Verticillium wilt and as biological preservatives for agricultural products. Additionally, this study presents a novel approach for mitigating the substantial amount of biogas residue generated from kitchen waste fermentation.

Legume rhizodeposition promotes nitrogen fixation by soil microbiota under crop diversification

Biological nitrogen fixation by free-living bacteria and rhizobial symbiosis with legumes plays a key role in sustainable crop production. Here, we study how different crop combinations influence the interaction between peanut plants and their rhizosphere microbiota via metabolite deposition and functional responses of free-living and symbiotic nitrogen-fixing bacteria. Based on a long-term (8 year) diversified cropping field experiment, we find that peanut co-cultured with maize and oilseed rape lead to specific changes in peanut rhizosphere metabolite profiles and bacterial functions and nodulation. Flavonoids and coumarins accumulate due to the activation of phenylpropanoid biosynthesis pathways in peanuts. These changes enhance the growth and nitrogen fixation activity of free-living bacterial isolates, and root nodulation by symbiotic Bradyrhizobium isolates. Peanut plant root metabolites interact with Bradyrhizobium isolates contributing to initiate nodulation. Our findings demonstrate that tailored intercropping could be used to improve soil nitrogen availability through changes in the rhizosphere microbiome and its functions.

Nitrogen Fixing Activity of Endophytic Bacteria Associated with Kalanchoe pinnata (Lam.) and its effect on Zea mays

ABSTRACT: Nitrogen is essentially required for the plant growth as well as productivity. Plants take nitrogen in the form of ammonia or nitrate either from soil or fertilizer. There are nitrogen fixing bacteria plays a vital role to supply atmospheric nitrogen to plants where plants do not obtain from soil. Apart from soil bacteria, endophytic bacteria which living inside the plant tissues can improve crop productivity and soil health sustainably through biological nitrogen fixation and act as a potential replacement for chemical fertilizers in agriculture. This study was conducted to determine the nitrogen fixing activity of isolated endophytic bacteria from Kalanchoe pinnata (Lam.). The isolated endophytes were subjected to molecular confirmation and evaluated for ammonia production, Acetylene Reduction Assay (ARA), nif gene amplification and analysis of growth parameters in Zea mays using pot culture assay. The data were analyzed using SPSS ver.16. In this study, Bacillus thuringiensis, Bacillus paranthracis, Staphylococcus xylosus and Bacillus cereus were isolated from the leaves of Kalachoe pinnata (Lam). They were confirmed using 16SrRNA sequencing. All the endophytic bacteria were positive for ammonia production and ARA. The percentage of nitrogen produced was 32.8 % (B. thuringiensis), 65.7% (B. paranthracis), 80.7% (S. xylosus) and 45.2% (B. cereus).The presence of nif gene was confirmed through the PCR amplification of a 550-580bp fragment of the gene. Pot culture assay of Zea mays were observed with significant improvement in S. xylosus followed by B. paranthracis inoculated pots. The presence of the nitrogenase enzyme and the nif gene in these endophytic bacteria allows them to fix atmospheric nitrogen to meet plant nitrogen demands, resulting in a symbiotic relationship with agricultural crops.

Graphene quantum dots enhance the biological nitrogen fixation by up-regulation of cellular metabolism and electron transport

Graphene quantum dots (GQDs) are useful nanomaterials of excellent water solubility, biocompatibility and optical stability for various applications. In this study, we achieved the nitrogen fixation activity enhancement of autogenous azotobacters (Azotobacter vinelandii) by GQDs and revealed its mechanism. GQDs (1–10 mg/L) accelerated the logarithmic growth phase of A. vinelandii, making bacteria enter the plateau earlier. Biocompatible GQDs did not cause cell death and oxidative damage of A. vinelandii. The expression levels of metabolism and nitrogen fixation related genes were significantly up-regulated by GQDs, thereby enhancing the activity of nitrogenase. The nitrogen fixation activity of A. vinelandii reached 471.7 % of the control upon the exposure to GQDs. The intracellular polyhydroxyalkanoate vesicles were consumed to provide energy for nitrogen fixation, which involved with a chain reaction of carbohydrate metabolism, lipid metabolism, and energy metabolism pathways accompanied by significant increases in electron transfer rate. The synergistic effect of GQDs on A. vinelandii further facilitated the augmentation of soil nitrogen content in Qinghai-Tibet Plateau. Our results provided an effective approach to enhance the biological nitrogen fixation by GQDs.

Plant responses to elevated CO2 under competing hypotheses of nitrogen and phosphorus limitations.

The future ecosystem carbon cycle has important implications for biosphere-climate feedback. The magnitude of future plant growth and carbon accumulation depends on plant strategies for nutrient uptake under the stresses of nitrogen (N) versus phosphorus (P) limitations. Two archetypal theories have been widely acknowledged in the literature to represent N and P limitations on ecosystem processes: Liebig's Law of the Minimum (LLM) and the Multiple Element Limitation (MEL) approach. LLM states that the more limiting nutrient controls plant growth, and commonly leads to predictions of dramatically dampened ecosystem carbon accumulation over the 21st century. Conversely, the MEL approach recognizes that plants possess multiple pathways to coordinate N and P availability and invest resources to alleviate N or P limitation. We implemented these two contrasting approaches in the E3SM model, and compiled 98 in situ forest N or P fertilization experiments to evaluate how terrestrial ecosystems will respond to N and P limitations. We find that MEL better captured the observed plant responses to nutrient perturbations globally, compared with LLM. Furthermore, LLM and MEL diverged dramatically in responses to elevated CO2 concentrations, leading to a two-fold difference in CO2 fertilization effects on Net Primary Productivity by the end of the 21st century. The larger CO2 fertilization effects indicated by MEL mainly resulted from plant mediation on N and P resource supplies through N2 fixation and phosphatase activities. This analysis provides quantitative evidence of how different N and P limitation strategies can diversely affect future carbon and nutrient dynamics.

Effect of nitrogen fixation enhancing type SEN1 gene on soybean growth

ABSTRACT It is well known that the growth of legumes is greatly affected not only by fertilizer nitrogen but also by fixed nitrogen by symbiosis with rhizobia. We have reported that a polymorphism in SEN1, which is essential for nitrogen fixation in Lotus japonicus, could be used to enhance nitrogen fixation and plant growth. In this study, we examined whether the same strategy could be applied to Glycine max. Sequencing of orthologs of the LjSEN1 gene in 38 soybean cultivars revealed that the polymorphism occurred at Glyma.08g076300. We defined the standard sequence that most of the cultivars retained as Peking type SEN1, and the mutated sequence found in Enrei as Enrei type SEN1. To investigate the effect of genotype differences, we generated near-isogenic lines by crossing Enrei with Fukuyutaka, which has Peking type SEN1, and analyzed their characteristics. The results showed that Enrei type enhanced nitrogen fixation activity and promoted plant growth. Since soybean SEN1 has been reported to be a homolog of vacuolar iron transporter-like protein, we investigated the iron content in the nodules. In the result, the iron content in the nodules of Enrei type was significantly higher than that of Peking type. Iron is known to be present in the active center of nitrogenase, and the high iron content may have contributed to the increased nitrogen fixation activity. These results suggest that Enrei type SEN1 is a nitrogen fixation enhancing gene and that introduction of Enrei type SEN1 may reduce nitrogen fertilizer application and increase yield.

S-scheme homojunction and activate site engineering over TiO2 for highly efficient photocatalytic nitrogen fixation

The presence of efficient catalytic active sites and an ample supply of electrons are the two indispensable factors for achieving photocatalytic nitrogen fixation. Herein, the Fe-doped TiO2 S-scheme anatase/rutile homojunction (F-T-A/R) was synthesized as a brilliant photocatalyst for photocatalytic nitrogen fixation from N2 to NH3 under ambient atmosphere. The optimized F-T-A/R photocatalyst (A/R = 98:2, Fe-2 wt%) exhibits an unprecedented NH3 generation rate of 358 μmol gcat-1h−1 in water solvent and under simulated solar light irradiation. Experimental and theoretical studies reveal that the constructed S-scheme homojunction in F-T-A/R is conducive to fluent charge separation and adequate supply of electrons on rutile with higher nitrogen fixing activity, while the tuned local electronic structure of oxygen vacancy with Fe doping is engineered to strengthen active sites, synergistically enhancing the photocatalytic nitrogen fixation.

In situ community transcriptomics illuminates CO2-fixation potentials and supporting roles of phagotrophy and proton pump in plankton in a subtropical marginal sea.

Lineage-wise physiological activities of plankton communities in the ocean are important but challenging to characterize. Here, we conducted whole-assemblage metatranscriptomic profiling at continental shelf and slope sites in the South China Sea to investigate carbon fixation potential in different lineages. RuBisCO expression, the proxy of Calvin carbon fixation (CCF) potential, was mainly contributed by Bacillariophyta, Chlorophyta, Cyanobacteria, and Haptophyta, which was differentially affected by environmental factors among lineages. CCF potential exhibited positive or negative correlations with phagotrophy gene expression, suggesting phagotrophy possibly enhances or complements CCF. Our data also reveal significant non-Calvin carbon fixation (NCF) potential, as indicated by the active expression of genes in all five currently recognized NCF pathways, mainly contributed by Flavobacteriales, Alteromonadales, and Oceanospirillales. Furthermore, in Flavobacteriales, Alteromonadales, Pelagibacterales, and Rhodobacterales, NCF potential was positively correlated with proton-pump rhodopsin (PPR) expression, suggesting that NCF might be energetically supported by PPR. The novel insights into the lineage-differential potential of carbon fixation, widespread mixotrophy, and PPR as an energy source for NCF lay a methodological and informational foundation for further research to understand carbon fixation and the trophic landscape in the ocean.IMPORTANCEMarine plankton plays an important role in global carbon cycling and climate regulation. Phytoplankton and cyanobacteria fix CO2 to produce organic compounds using solar energy and mainly by the Calvin cycle, whereas autotrophic bacteria and archaea may fix CO2 by non-Calvin cycle carbon fixation pathways. How active individual lineages are in carbon fixation and mixotrophy, and what energy source bacteria may employ in non-Calvin carbon fixation, in a natural plankton assemblage are poorly understood and underexplored. Using metatranscriptomics, we studied carbon fixation in marine plankton with lineage resolution in tropical marginal shelf and slope areas. Based on the sequencing results, we characterized the carbon fixation potential of different lineages and assessed Calvin- and non-Calvin- carbon fixation activities and energy sources. Data revealed a high number of unigenes (4.4 million), lineage-dependent differential potentials of Calvin carbon fixation and responses to environmental conditions, major contributors of non-Calvin carbon fixation, and their potential energy source.

Fe-Bi dual sites regulation of Bi2O2.33 nanosheets to promote photocatalytic nitrogen fixation activity

In the process of photocatalytic ammonia synthesis, efficient activation of nitrogen molecules constitutes a fundamental challenge. During the N2 activation, the close interdependence between the acceptance and donation of electron results in their mutual limitation, leading to high energy barrier for N2 activation and unsatisfactory photocatalytic performance. This work decoupled the electron acceptance and donation processes by constructing Fe-Bi dual active sites, resulting in enhancing N2 activation through the high electron trapping ability of Fe3+ and strong electron donating ability of Bi2+. The photocatalytic nitrogen reduction efficiency of 3%Fe/Bi2O2.33 (118.71 μmol gcat−1h−1) is 5.3 times that of Bi2O2.33 (22.41 μmol gcat−1h−1). In-situ Fourier transform infrared (In situ FTIR) spectroscopy and density functional theory (DFT) calculations manifest that Fe3+-Bi2+ dual active sites work together to promote nitrogen adsorption and activation, and the reaction path is more inclined toward alternate hydrogenation path. N2 adsorption and activation properties are optimized by heteronuclear bimetallic active sites, which offers a new way for the rational design of nitrogen-fixing photocatalysts.