Nitrogen Fixation Rates Research Articles

Exploring microalgal nutrient-light synergy to enhance CO2 utilization and lipid productivity in sustainable long-term water recycling cultivation

In this work the effects of nutrient availability and light conditions on CO2 utilization and lipid production in Micractinium pusillum KMC8 is reported. The study investigated the ideal nitrogen concentrations for growth and nitrogen utilization in a 15% CO2 environment. Logistic and Gompertz models were employed to analyze the kinetics of KMC8 cell growth. Compared to 17.6 mmol L−1 control nitrogen, which generated 1.6 g L−1 growth, doubling and quadrupling nitrogen concentrations boosted biomass growth by 12.5% and 28.78%. At 8.6 mmol L−1 nitrogen, the growth decreased but lipid productivity increased to 18.62 mg L−1 day−1. At 70.6 mmol L−1 nitrogen, elevated nitrogen levels maintained an alkaline pH above 7 and enhanced CO2 mitigation, achieving 2.27% CO2 utilization efficiency. Nitrogen shows a positive correlation with higher rates of carbon and nitrogen fixation. The investigation extends to find out the influence of phosphorus and light conditions on microalgae. Increasing light intensity incrementally from 150 to 1200 μmol m−2 s−1 with more phosphorus increased biomass productivity by 85% (255 mg L-1 day−1) and lipid productivity by 2.5-fold (84.76 mg L-1 day−1), with 3.3% CO2 utilization efficiency compared to directly using 1200 μmol m−2 s−1. This study suggests a water recycling-fed batch cycle with gradual light feeding, which results in high CO2 fixation (1.1 g L−1 day−1), 7% CO2 utilization, and significant biomass and lipid productivity (577.23 and 150 mg L−1 day−1). This approach promotes lipid synthesis, maintains carbon fixation, and minimizes biomass loss, thus supporting sustainable bioenergy development in a circular bio-economy framework.

Nanotechnology in agriculture: A solution to global food insecurity in a changing climate?

Although the Green Revolution dramatically increased food production, it led to non- sustainable conventional agricultural practices, with productivity in general declining over the last few decades. Maintaining food security with a world population exceeding 9 billion in 2050, a changing climate, and declining arable land will be exceptionally challenging. In fact, nothing short of a revolution in how we grow, distribute, store, and consume food is needed. In the last ten years, the field of nanotoxicology in plant systems has largely transitioned to one of sustainable nano-enabled applications, with recent discoveries on the use of this advanced technology in agriculture showing tremendous promise. The range of applications is quite extensive, including direct application of nanoscale nutrients for improved plant health, nutrient biofortification, increased photosynthetic output, and greater rates of nitrogen fixation. Other applications include nano-facilitated delivery of both fertilizers and pesticides; nano-enabled delivery of genetic material for gene silencing against viral pathogens and insect pests; and nanoscale sensors to support precision agriculture. Recent efforts have demonstrated that nanoscale strategies increase tolerance to both abiotic and biotic stressors, offering realistic potential to generate climate resilient crops. Considering the efficiency of nanoscale materials, there is a need to make their production more economical, alongside efficient use of incumbent resources such as water and energy. The hallmark of many of these approaches involves much greater impact with far less input of material. However, demonstrations of efficacy at field scale are still insufficient in the literature, and a thorough understanding of mechanisms of action is both necessary and often not evident. Although nanotechnology holds great promise for combating global food insecurity, there are far more ways to do this poorly than safely and effectively. This review summarizes recent work in this space, calling out existing knowledge gaps and suggesting strategies to alleviate those concerns to advance the field of sustainable nano-enabled agriculture.

Modulating charge oriented accumulation via interfacial chemical-bond on In2O3/Bi2MoO6 heterostructures for photocatalytic nitrogen fixation

Photocatalytic nitrogen fixation presents an eco-friendly approach to converting atmospheric nitrogen into ammonia (NH3), but the process faces challenges due to rapid interface charge recombination. Here, we report an innovative charge transfer and oriented accumulation strategy using an In-O-Mo bond-modulated S-scheme heterostructure composed of In2O3/Bi2MoO6 (In/BMO) synthesized using a simple electrostatic assembly. The unique interfacial arrangement with optimal photocatalyst configuration (3 % In/BMO) enabled enhanced photogenerated electron separation and transfer, leading to a remarkable nitrogen fixation rate of approximately 150.9 μmol·gcat−1·h−1 under visible light irradiation. The performance of the photocatalyst was 9-fold and 27-fold higher than that of its pristine components, Bi2MoO6 and In2O3, respectively. The experimental and theoretical evaluation deemed interfacial In-O-Mo bonds crucial for rapid transfer and charge-oriented accumulation. Whereas the generated internal electric field drove the spatial separation and transfer of photo-generated electrons and holes, significantly enhancing the photocatalytic N2-to-NH3 conversion efficiency. The proposed work lays the foundation for designing S-scheme heterostructures with highly efficient interfacial bonds, offering a promising avenue for substantial improvements in photocatalytic nitrogen fixation.

Effect of Water Sources on the Growth Performance and Chlorophyll Content of Azolla pinnata R.Br.


 
 
 Azolla pinnata R.Br. is an aquatic fern that grows on the surface of water bodies. The unique quality of A. pinnata is its symbiotic relationship with a prokaryotic cyanobacterium (Anabaena azollae), which confers a high rate of nitrogen fixation. It is important to find the growing conditions of Azolla in different water sources for its optimum biomass production for different usages such as biofertilizers, animal feeds, water purification and biofuel production. This preliminary study was conducted to investigate the effect of water sources on the growth performance (shoot biomass, root biomass, root length), and the chlorophyll content of Azolla. Presence of Anabaena in Azolla fronds was monitored by light microscope and number of filaments were counted per leaflet. The experiment utilized three types of water sources (tap water as control (T1), lake water (T2) and cattle manure mixed tap water (T3), in plastic buckets with 40 cm in diameter and 25 cm in height. Each treatment was triplicated in a completely randomized design and total biomass was collected weekly. Data were statistically analyzed using Minitab 17. The highest biomass of Azolla was obtained in T3 from the first week until 8th week and it was higher from T1 and T2. The highest chlorophyll content was obtained in T3 (6.4 SPAD value) showed a significant difference from T1 and T2 (p<0.05). The dry weight of roots and root length in T1 showed a significant difference from T2 and T3 (p<0.05). The highest root length was observed as 5 cm in T1 indicating that roots may be in search of nutrients and the lowest root length was observed as 0.8 cm in T3 with high nutrient concentrations in water. The highest number of Anabaena was observed in the leaflet of Azolla fronds in T3 which in turn increase N content in Azolla plants. It reveals that application of cattle manure in tap water significantly affects the plant biomass and the chlorophyll content of Azolla. Further studies are needed to conduct in large scale growing facilities with different nutrient concentrations of water sources to find sustainable and optimum growing conditions for Azolla and the nutrient concentrations of the plants.
 Keywords: Azolla, Chlorophyll, Growth performance, Water sources
 
 

Insights into Genetic and Physiological Characteristics of Clover Rhizobia in Afghanistan Soils

Livestock production in Afghanistan highly relies on grazing and clover feed, which is a key component of pastures and forage crops. This study elucidated the genetic diversity of clover-nodulating rhizobia in different ecological regions and their effects on clover growth. A total of 57 rhizobia were isolated and their genetic diversities were studied through 16S rRNA and nifD genes. The isolates were inoculated to clover (Afghan local variety), to investigate the potential of nitrogen fixation and influences of clover growth. The 16S rRNA gene analysis showed two distinct groups of Rhizobium (94.7%) and Ensifer (5.3%) species. The nifD phylogenetic relationship revealed a high similarity to Rhizobium and a novel lineage group close to Rhizobium leguminosarum species. In the plant test, different genotypes significantly (p < 0.01) exhibited an increase in plant biomass production, compared to the un-inoculated plants. Among genotypes, the highest plant biomass was recorded in PC8 (1769.0 mg/plant) and PC9 (1409.2 mg/plant) isolates as compared to un-inoculated plants (144.0 mg/plant). Moreover, these isolates showed maximum nitrogen fixation rates of 8.2 and 6.5 µM/plant, respectively. These isolates were identified as the most promising rhizobial strains for developing biofertilizers in the context of Afghanistan.

Autochthonous carbon loading of macroalgae stimulates benthic biological nitrogen fixation rates in shallow coastal marine sediments.

Macroalgae, commonly known as seaweed, are foundational species in coastal ecosystems and contribute significantly to coastal primary production globally. However, the impact of macroalgal decomposition on benthic biological nitrogen fixation (BNF) after deposition to the seafloor remains largely unexplored. In this study, we measure BNF rates at three different sites at the Big Fisherman's Cove on Santa Catalina Island, CA, USA, which is representative of globally distributed rocky bottom macroalgal habitats. Unamended BNF rates varied among sites (0.001-0.05 nmol N g-1 h -1) and were generally within the lower end of previously reported ranges. We hypothesized that the differences in BNF between sites were linked to the availability of organic matter. Indeed, additions of glucose, a labile carbon source, resulted in 2-3 orders of magnitude stimulation of BNF rates in bottle incubations of sediment from all sites. To assess the impact of complex, autochthonous organic matter, we simulated macroalgal deposition and remineralization with additions of brown (i.e., Macrocystis pyrifera and Dictyopteris), green (i.e., Codium fragile), and red (i.e., Asparagopsis taxiformis) macroalgae. While brown and green macroalgal amendments resulted in 53- to 520-fold stimulation of BNF rates-comparable to the labile carbon addition-red alga was found to significantly inhibit BNF rates. Finally, we employed nifH sequencing to characterize the diazotrophic community associated with macroalgal decomposition. We observed a distinct community shift in potential diazotrophs from primarily Gammaproteobacteria in the early stages of remineralization to a community dominated by Deltaproteobacteria (e.g., sulfate reducers), Bacteroidia, and Spirochaeta toward the latter phase of decomposition of brown, green, and red macroalgae. Notably, the nifH-containing community associated with red macroalgal detritus was distinct from that of brown and green macroalgae. Our study suggests coastal benthic diazotrophs are limited by organic carbon and demonstrates a significant and phylum-specific effect of macroalgal loading on benthic microbial communities.

Ultisol optimization strategy: the use of Tithonia compost and rice husk biochar to improve nodulation and promote soybean (Glycine max (L.) Merril) growth

This study aimed to investigate the optimization of Ultisol soil using biochar and compost to increase nodule formation and performance of soybeans. The trial was conducted at the Research and Teaching Farm, Faculty of Agriculture, University of Jambi, for six months from April through to October 2021. Three levels of compost (5 t ha-1, 10 t ha-1, and 15 t ha-1) were tested in combination with three levels of biochar (5 t ha-1, 10 t ha-1, and 15 t ha-1). A completely randomized design was employed with three replications. Each experimental unit consisted of 20 plants, and 25% of the population was taken as sample plants. Results indicated that the application of soil ameliorant in the form of Tithonia compost and biochar could increase soil pH and nutrient contents and reduce C/N ratio. Tithonia compost + biochar improved Ultisol productivity as indicated by increased nodule formation and soybean growth. The combination of Tithonia compost and biochar, each of 15 t ha-1, was the best combination for the optimization of Ultisol, which produced the highest biological nitrogen fixation rate and resulted in the best soybean growth.

Phosphorus availability regulates nitrogen fixation rate through a key diazotrophic assembly: Evidence from a subtropical Moso bamboo forest subjected to nitrogen application

Biological N fixation (BNF) is an important N input process for terrestrial ecosystems. Long-term N application increases the availability of N, but may also lead to phosphorus (P) deficiency or an imbalance between N and P. Here, we performed a 5-year N application experiment in a subtropical Phyllostachys heterocycla forest in site and a P application experiment in vitro to investigate the effect of N application on the BNF rate and its regulatory factor. The BNF rate, nifH gene, free-living diazotrophic community composition and plant properties were measured. We found that N application suppressed the BNF rate and nifH gene abundance, whereas the BNF rate in soils with added P was significantly higher overall than that in soils without added P. Moreover, we identified a key diazotrophic assembly (Mod#2), primarily comprising Bradyrhizobium, Geobacter, Desulfovibrio, Anaeromyxobacter, and Pseudodesulfovibrio, which explained 77 % of the BNF rate variation. There was a significant positive correlation between the Mod#2 abundance and soil available P, and the random forest results showed that soil available P is the most important factor affecting the Mod#2 abundance. Our findings highlight the importance of soil P availability in regulating the activities of key diazotrophs, and thus increasing P supply may help to promote N accumulation and primary productivity through facilitating the BNF process in forest ecosystems.

Simplified method for the synthesis of efficient Ohm-Schottky heterojunction photocatalysts for hydrogen evolution reaction and nitrogen fixation

Multifunctional semiconductor photocatalyst with Ohmic-Schottky contact heterojunctions for hydrogen evolution reaction (HER) and nitrogen fixation (NF) were constructed by modifying CdS with bimetallic Co2xNi2(1-x)P (xCNP) and thin layer Ti3C2 (TLTC) containing -Ox rich functional groups. Under the optimal conditions (2 % 0.2CNP@CdS/2% TLTC), it yielded a hydrogen evolution rate of up to 1.72 mmol h−1 and a nitrogen fixation rate of 656.82 μmol L−1 h−1, corresponding to an apparent quantum efficiency (AQE) of 59.81 %. The remarkable HER and NF properties can be attributed to the improved electron transfer efficiency of the double transition metal and the improved surface N2/NH3 adsorption energy. The construction of Ohmic-Schottky contact heterojunctions reduced the HER overpotential and improved the separation efficiency of the photogenerated carriers.

Effect of moss removal on soil multifunctionality during vegetation restoration in subtropical ecosystems

Mosses are multifunctional communities that are increasingly recognized as potential and sustainable resources to restore degraded ecosystems. However, available information is limited on the influence of mosses on soil multifunctionality during vegetation restoration in subtropical ecosystems. We investigated the effects of mosses on soil multifunctionality and four single functions in three vegetation restoration approaches (monoculture plantations, monoculture forage grasses and intercropping of trees and forage grasses) by conducting a moss removal and retention experiment. Moss removal decreased soil multifunctionality and the single functions of nutrient provisioning, water retention and plant–microbe symbiosis, particularly in monoculture plantations, in the 0–5 cm soil layer. Moss removal decreased the phospholipid fatty acid abundance of soil microbes (e.g., bacteria, Gram-negative bacteria and general fungi) in the 2–5 cm soil layer but had nonsignificant effects on the nematode community. Random forest analysis showed that moss properties were more important factors than the soil physicochemical, microbial and nematode properties linked to soil multifunctionality. Moss properties (diversity, thickness, biomass, carbon and nitrogen concentrations, carbon to nitrogen ratio, biological nitrogen fixation rate and saturated water absorption content) were positively associated with soil multifunctionality, nutrient provisioning, water retention and plant–microbe symbiosis. These findings highlight the importance of preserving mosses to maintain soil multifunctionality during vegetation restoration in degraded subtropical ecosystems, especially in monoculture plantations.

Nitrogen fixation rates in the Guinea Dome and the equatorial upwelling regions in the Atlantic Ocean

AbstractBiological nitrogen fixation is a key process balancing the loss of combined nitrogen in the marine nitrogen cycle. Its relevance in upwelling or high nutrient regions is still unclear, with the few available studies in these regions of the ocean reporting rates that vary widely from below detection limit to > 100 nmol N L−1 d−1. In the eastern tropical Atlantic Ocean, two open ocean upwelling systems are active in boreal summer. One is the seasonal equatorial upwelling, where the residual phosphorus associated with aged upwelled waters is suggested to enhance nitrogen fixation in this season. The other is the Guinea Dome, a thermal upwelling dome. We conducted two surveys along 23° W across the Guinea Dome and the Equator from 15° N to 5° S in September 2015 and August–September 2016 with high latitudinal resolution (20–60 nm between stations). The abundance of Trichodesmium colonies was characterized by an Underwater Vision Profiler 5 and the total biological nitrogen fixation in the euphotic layer was measured using the 15N2 technique. The highest abundances of Trichodesmium colonies were found in the area of the Guinea Dome (9°–15° N) with a maximum of 3 colonies L−1 near the surface. By contrast, colonies were almost absent in the Equatorial band between 2° N and 5° S. The highest nitrogen fixation rate was measured at the northern edge of the Guinea Dome in 2016 (ca. 31 nmol N L−1 d−1). In this region, where diazotrophs thrived on a sufficient supply of both phosphorus and iron, a patchy distribution was unveiled by our increased spatial resolution scheme. In the Equatorial band, rates were considerably lower, ranging from below detection limit to ca. 4 nmol N L−1 d−1, with a clear difference in magnitude between 2015 (rates close to zero) and 2016 (average rates around 2 nmol N L−1 d−1). This difference seemed triggered by a contrasting supply of phosphorus between years. Our study stresses the importance of surveys with sampling at fine-scale spatial resolution, and shows unexpected high variability in the rates of nitrogen fixation in the Guinea Dome, a region where diazotrophy is a significant process supplying new nitrogen into the euphotic layer.

In-situ synthesis and enhanced photocatalytic nitrogen fixation property of novel NiS/g-C3N4 heterostructure photocatalysts with nitrogen vacancy

Rapid recombination of the photo-generated charge carriers leads to the poor photocatalytic nitrogen fixation property of pristine graphite-like carbon nitride (g-C3N4). To enhance the photocatalytic performance of g-C3N4, nickel sulfide (NiS) nanoparticles were anchored onto the surface of g-C3N4 by using the in-situ decomposition-thermal polymerization method in this work. The incorporation of NiS cocatalyst expanded the absorption range, enhanced the efficiency of separating photo-generated charge carriers, reduced the band gap from 2.78 eV to 2.47 eV, increased the specific surface area 7.1 m2·g−1 to 19.5 m2·g−1, and enlarged the photo-current density, which can inhibit the recombination of photo-generated charge carriers. Furthermore, the emergence of the nitrogen vacancy occurred during the in-situ synthetic process as a result of the thermal decomposition of thioacetamide hydrolysate, thereby leading to an enhancement in the photocatalytic nitrogen fixation efficiency. The results of the nitrogen fixation experiment demonstrated that 13 % NiS/g-C3N4 exhibited the highest activity, with a photocatalytic nitrogen fixation rate of 8.15 mg/L. This rate is 7.6 times greater than that of pure g-C3N4, which can be attributed to several factors, including a higher separation rate of photogenerated electrons, a larger specific surface area, a wider range of responsiveness to visible light, and the presence of the nitrogen vacancy.

Composition and distribution of diazotrophs in the Baltic Sea

Nitrogen (N2) fixation rates in the brackish Baltic Sea are among the highest per unit of area in the world. However, beyond the filamentous heterocyst-forming cyanobacteria, knowledge about the composition and distribution of N2-fixing microbes (diazotrophs) is limited. To address this, we investigated nitrogenase gene (nifH) composition and expression at coastal (<10 km offshore) and offshore (>10 km offshore) stations, at surface (avg. 1.8 m) and at depth (avg. 24 m) and in free-living (0.2–3.0 μm) and particle-associated size fractions (>3 μm). Surprisingly, nifH genes affiliated with Pseudanabaena and non-cyanobacterial diazotrophs (NCDs) dominated the composition whereas filamentous heterocyst-forming cyanobacteria accounted for almost 80% of the nifH transcripts. Salinity had a minor influence on the composition, but Aphanizomenon and Nodularia showed increased relative nifH gene expression at low and higher salinity, respectively. Pseudanabaena only accounted for up to 5% of the nifH transcripts and nifH gene expression by Candidatus Atelocyanobacterium thalassa (sublineage UCYN-A2) was mainly observed in the most saline western part of the Baltic. The only notable expression by NCDs (up to 15% of nifH transcripts at a given station) coincided with an upwelling event at the southern coast and was largely accounted for by a Pseudomonas-like nifH phylotype, recurrently found in the Baltic Sea. NCD relative abundances were dominant in coastal stations, presumably driven by sediment resuspension as evidenced by higher turbidity and DOC levels and the recovery of sediment diazotrophs in the pelagic zone. This study reveals the heterogeneity of the composition and activity of diazotrophs in the Baltic Sea, and underscores the need for future N2 fixation studies that include coastal and offshore Baltic waters.

Nitrogen fixation in different termite lineages and diets

Abstract Nitrogen fixation is often cited as an important nitrogen source for termites. However, the rate of nitrogen fixation between experiments and termite species is highly variable due to termite diversity and sampling limitations. New evidence suggests that subterranean termites (Coptotermes formosanus Shiraki) (Blattodea, Rhinotermitidae) seek alternative dietary nitrogen sources for colony growth and development. This study compares N2 fixation rates and nitrogenase gene expression rates to a diverse assemblage of feeding groups. It was observed that nitrogenase expression was much higher in one-piece nesting termites from the family Kalotermitidae which lack access to soil. On the other hand, subterranean termites from the family Rhinotermitidae fix nitrogen at much lower rates, not differing from ambient nitrogenase activity in soil.

English

Millets are becoming popular due to special features of high nutrition, low inputs, and climate resiliency. While major crops like wheat, rice &amp; maize are exhaustive, resource-loving, and susceptible. There is a need for crop diversification &amp; potential millets to be adapted for sustainability. Faisalabad is the grain belt of Punjab, Pakistan, but only one millet crop, pearl millet, is being cultivated for grain purposes. An alternate crop, foxtail millet study was designed, and 200 exotic accessions of different origins were acquired from the USDA. Germination behavior at optimal controlled temperatures (18 °C, 25°C, 32°C, and 39 °C) was tested, best germination was observed at 32 °C, and 135 out of 200 accessions germinated at ≥80%. These accessions were initially screened for germination strength (G%, G50, MGT, U, GI, Z, and CVG), seedling vigor (SL, RL, SFW, SDW), and preliminary yield tests in the greenhouse, then evaluated under three different field locations of varied soil environments. Principle component analysis (PCA) was performed, and 14 clusters of accessions were sorted out using hierarchical clustering. The high-yielding accessions were selected from each cluster and sown at three different locations/soil environments in the Faisalabad, i.e., 1- ARA, UAF (fertile, low irrigated), 2= DFP, UAF (salt-affected soil), 3= JKA, CJF (fertile, well-irrigated). Results were statistically analyzed &amp; graphically represented using project R for statistical computing. Accessions A73-IN and A101-IN produced the highest grain yield of 3504 kg ha-1 and 2667 kg ha-1 respectively, and a biomass accumulation of 8 t ha-1 at the location JKA, CJF. Yield-related results under low irrigation &amp; saline soil were also significant, however, overall, 69% of yield was reduced in the saline and 67% in low irrigated fields. It was concluded that accessions of Indian origin may be adapted under Faisalabad climate and an additional inquiry into abiotic stresses is required to discover suitable genotypes

Nitrogen fixation under the interaction of Kuroshio and upwelling in the northeastern South China Sea

Diazotrophic organisms are vulnerable to physical dynamic processes. However, the interactions and mechanisms of multiple dynamic processes on nitrogen fixation remain unclear. This study aimed to investigate one of these interactions; we conducted field investigations and bioassay experiments in the northeastern South China Sea, which faces the Kuroshio current and coastal upwelling. Using 15N tracer and molecular biology methods, we found that the eastern Guangdong upwelling, having high phosphorus and a lower N:P ratio, had higher nitrogen fixation rates as well as a higher abundance of diazotrophic cyanobacteria Trichodesmium spp. and UCYN-A compared with nonupwelling area. Additionally, a higher abundance of diazotrophic cyanobacteria occurred near the bottom of the euphotic zone along the shelf break that was affected by the Kuroshio current. Field incubation experiments confirmed that phosphorus increased the nitrogen fixation rates and stimulated the growth of cyanobacteria in the area affected by upwelling. Taken together, our results indicated that warmer surface water with a high N:P ratio likely mixed with upwelled phosphorus-rich water containing diazotrophic cyanobacteria, which were transported by the intensified Kuroshio current under the influence of the 2015/16 El Niño. This mixing then triggered a high abundance of diazotrophic cyanobacteria. These findings provide new insights into how the interaction of multiple dynamic processes can regulate nitrogen fixation.

PHYTOREMEDIATION OF PARTS CONTAMINATED WITH ISOPROTURONE, TRANSGENIC OILY BEANS

The widespread use of isoproturon [IPU] can lead to severe environmental pollution and threats to environmental functions. In this study, the PDMAB IPU bacterial n-demethylase gene was transported and expressed in fat pea chloroplast [Glycine Max L. 'Zhonghuang13']. Transgenic fat bean pods showed significant resistance to PPU and demethylated PPU to the phytotoxic 3-[4 - isopropylphenyl]-1-methylurea [MDIPU] metabolite in vivo. Transgenic fat bean pods removed 98% and 84% MPU from water and soil in 5 and 14 days respectively, accumulating fewer MPU in plant tissues compared to wild type [WT]. MPs showed higher rates of symbiotic nitrogen fixation in transgenic fat peas under stress [total biomass o f nodules and higher nitrogenase activity] and a more stable community of rhizosphere bacteria than WT. However, intensive use and accumulation of toxic herbicides can negatively affect the symbiosis of legumes. Thirty different herbicides and environmental pollutants have affected signaling between plants and rhizobias, delayed node formation, and reduced biological nitrogen fixation in vitro [Fox et al., 2007]. This study developed a transgenic [TS] oil bean that is capable of effectively removing PPU from the growing environment and restoring the high symbiotic ability to fix nitrogen under PPU stress, and provides new insight into the interaction between rhizospheric microorganisms and legumes under herbicidal stress.

Integrating local polarization in hydrogen bonded organic frameworks for efficient photocatalytic nitrogen fixation

Elaborately designing stabilized hydrogen-bonded organic frameworks (HOFs) with higher charge transfer rate and abundant active sites for efficient photocatalytic nitrogen fixation are urgent and challenging. Herein, a micromolecular hydrogen-based triazole unit integrated into rigid perylene diimide based hydrogen-bonded organic framework (NPDI) has been elaborately designed. Experimental and theoretical results demonstrate that the flexibility and polar micromolecular group embedded in rigid framework not only stabilized HOFs frameworks, but also enhanced the local polarization, electron delocalization and the built-in electric field of HOFs, which greatly promotes exciton dissociation and the carrier transfer. Fortunately, NPDI has excellent photocatalytic nitrogen fixation rate (179 µmol h−1 g−1) and near-infrared NH4+ yield in pure water under ambient conditions. Our work offers deep insights into molecular level regulation for rationally designing efficient HOFs.

Reframing the contribution of pelagic Sargassum epiphytic N2 fixation.

Though nitrogen fixation by epiphytic diazotrophs on pelagic Sargassum has been recognized for decades, it has been assumed to contribute insignificantly to the overall marine nitrogen budget. This six-year study reframes this concept through long-term measurements of Sargassum community nitrogen fixation rates, and by extrapolating mass-specific rates to a theoretical square meter portion of Sargassum mat allowing for comparison of these rates to those of other marine and coastal diazotrophs. On 24 occasions from 2015 to 2021, rates of nitrogen fixation were measured using whole fronds of Sargassum collected from the western edge of the Gulf Stream off Cape Hatteras, North Carolina. Across all dates, mass-specific rates ranged from 0 to 37.77 μmol N g-1 h-1 with a mean of 4.156 μmol N g-1 h-1. Extrapolating using a mat-specific density of Sargassum, these rates scale to a range of 0 to 30,916 μmol N m-2 d-1 and a mean of 3,697 μmol N m-2 d-1. Quantifying this community's rates of nitrogen fixation over several years captured the sometimes-extreme variability in rates, characteristic of marine diazotrophs, which has not been reported in the literature to date. When these measurements are considered alongside estimates of the density of pelagic Sargassum, rates of nitrogen fixation by Sargassum's epiphytic diazotrophs rival that of their coastal macrophyte and planktonic counterparts. Given Sargassum's wide and expanding geographic range, the results of this study suggest this community may contribute reactive nitrogen on a meaningful, basin-wide scale, which merits further study.

High site elevation enhanced nitrogen fixation and the stability of diazotrophic community in planted Sonneratia apetala mangrove sediments

Site elevation was decisive in determining effective mangrove restoration, and nitrogen availability was a decisive factor for mangrove growth and development. The biological nitrogen fixation conducted by diazotrophs was responsible for 40–60 % of the nitrogen demand of mangrove ecosystems, and the nitrogen dynamics of mangrove forests were primarily correlated with stand age. Understanding how site elevation affects sediment diazotrophs and their variation across stand age was critical for site selection for mangrove restoration and evaluating the functional rehabilitation and primary productivity of mangrove wetlands. Diazotrophic community and nitrogen fixation rate (NFR) in mangrove sediments with depth were compared among 12-year and 18-year-old S. apetala mangrove forests planted under high (H18) and low site elevations (L18 and L12), respectively. The results indicated the sediment nutrient pools (e.g., TOC, TN, and TS) and NFR in mangrove sediments followed an increasing trend with increased site elevation over time (H18 > L18 > L12), and NFR weakly increased with sediment depth. Moreover, the diazotrophic community structure was both elevation- and age-dependent. The relative abundance of the dominant diazotrophic group Desulfuromonadales (belonged to sulfate-reducing bacteria, SRB) decreased with increasing site elevation, while another SRB group Syntrophobacterales showed an opposite trend. Moreover, network analyses revealed more stable and less complicated networks in sediments with higher site elevation, which followed a similar trend with NFR by H18 > L18 > L12. This study provided new perspectives on the microbe-based assessment of mangrove functional restoration from the viewpoint of both diazotrophic communities and NFR. From this perspective, high site elevation had a higher nutrient pool, NFR, and diazotrophic community stability, which should be recommended for mangrove restoration in the future, and long-term rehabilitation would benefit the ecological functional (nitrogen fixation) restoration.