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In dinitrogen (N2) fixation chemistry, bimetallic end‐on bridging N2 complexes M(μ‐η1 : η1‐N2)M can split N2 into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)]2(μ‐N2)}0/1+/2+ (1–3) are incapable to cleave N2, in contrast to their Mo congeners. Remarkably, cross this series the N−N bond length of the N2 ligand and the N−N stretching frequency exhibit unprecedented nonmonotonic variations, and complexes 1 and 2 in both solid and solution states display rare thermally activated ligand‐mediated two‐center spin transitions, distinct from discrete dinuclear spin crossovers. In‐depth analyses using wave function based ab initio calculations reveal that the Cr‐N2‐Cr bonding in complexes 1–3 is distinguished by strong multireference character and cannot be described by solely one electron configuration or Lewis structure, and that all intriguing spectroscopic observations originate in their sophisticate multireference electronic structures. More critical is that such multireference bonding of complexes 1–3 is at least a key factor that contributes to their kinetic inertness toward N2 splitting. The mechanistic understanding is then used to rationalize the disparate reactivity of related 3d M(μ‐η1 : η1‐N2)M complexes compared to their 4d and 5d analogs. [ABSTRACT FROM AUTHOR]

In dinitrogen (N2) fixation chemistry, bimetallic end‐on bridging N2 complexes M(μ‐η1 : η1‐N2)M can split N2 into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)]2(μ‐N2)}0/1+/2+ (1–3) are incapable to cleave N2, in contrast to their Mo congeners. Remarkably, cross this series the N−N bond length of the N2 ligand and the N−N stretching frequency exhibit unprecedented nonmonotonic variations, and complexes 1 and 2 in both solid and solution states display rare thermally activated ligand‐mediated two‐center spin transitions, distinct from discrete dinuclear spin crossovers. In‐depth analyses using wave function based ab initio calculations reveal that the Cr‐N2‐Cr bonding in complexes 1–3 is distinguished by strong multireference character and cannot be described by solely one electron configuration or Lewis structure, and that all intriguing spectroscopic observations originate in their sophisticate multireference electronic structures. More critical is that such multireference bonding of complexes 1–3 is at least a key factor that contributes to their kinetic inertness toward N2 splitting. The mechanistic understanding is then used to rationalize the disparate reactivity of related 3d M(μ‐η1 : η1‐N2)M complexes compared to their 4d and 5d analogs. [ABSTRACT FROM AUTHOR]

In dinitrogen (N2) fixation chemistry, bimetallic end‐on bridging N2 complexes M(μ‐η1 : η1‐N2)M can split N2 into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)]2(μ‐N2)}0/1+/2+ (1–3) are incapable to cleave N2, in contrast to their Mo congeners. Remarkably, cross this series the N−N bond length of the N2 ligand and the N−N stretching frequency exhibit unprecedented nonmonotonic variations, and complexes 1 and 2 in both solid and solution states display rare thermally activated ligand‐mediated two‐center spin transitions, distinct from discrete dinuclear spin crossovers. In‐depth analyses using wave function based ab initio calculations reveal that the Cr‐N2‐Cr bonding in complexes 1–3 is distinguished by strong multireference character and cannot be described by solely one electron configuration or Lewis structure, and that all intriguing spectroscopic observations originate in their sophisticate multireference electronic structures. More critical is that such multireference bonding of complexes 1–3 is at least a key factor that contributes to their kinetic inertness toward N2 splitting. The mechanistic understanding is then used to rationalize the disparate reactivity of related 3d M(μ‐η1 : η1‐N2)M complexes compared to their 4d and 5d analogs. [ABSTRACT FROM AUTHOR]

In dinitrogen (N2) fixation chemistry, bimetallic end‐on bridging N2 complexes M(μ‐η1 : η1‐N2)M can split N2 into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)]2(μ‐N2)}0/1+/2+ (1–3) are incapable to cleave N2, in contrast to their Mo congeners. Remarkably, cross this series the N−N bond length of the N2 ligand and the N−N stretching frequency exhibit unprecedented nonmonotonic variations, and complexes 1 and 2 in both solid and solution states display rare thermally activated ligand‐mediated two‐center spin transitions, distinct from discrete dinuclear spin crossovers. In‐depth analyses using wave function based ab initio calculations reveal that the Cr‐N2‐Cr bonding in complexes 1–3 is distinguished by strong multireference character and cannot be described by solely one electron configuration or Lewis structure, and that all intriguing spectroscopic observations originate in their sophisticate multireference electronic structures. More critical is that such multireference bonding of complexes 1–3 is at least a key factor that contributes to their kinetic inertness toward N2 splitting. The mechanistic understanding is then used to rationalize the disparate reactivity of related 3d M(μ‐η1 : η1‐N2)M complexes compared to their 4d and 5d analogs. [ABSTRACT FROM AUTHOR]

A novel isolate of aerobic, mildly acidophilic methanotrophic bacteria, strain RX1T, was obtained from a subarctic Sphagnum peat bog in European Russia. Strain RX1T was represented by highly polymorphic, gram-negative, non-motile, encapsulated cells that possessed a particulate methane monooxygenase enzyme and grew on methane, methanol and acetate. Electron microscopy of ultrathin cell sections revealed stacks of intracytoplasmic membrane vesicles located on one side of a cell as characteristic for methanotrophs of the genus Methylocapsa. Strain RX1T was capable of fixing dinitrogen, belonged to the family Beijerinckiaceae, and was most closely related to the obligate methanotroph Methylocapsa acidiphila B2T (98.8% 16S rRNA gene sequence similarity and 92.2% of PmoA sequence identity). The genome of strain RX1T consisted of a 4.02 Mb chromosome and a 291 kb plasmid, and contained one rrn operon, one pmoCAB operon and about 3800 protein-coding genes. The average nucleotide identity between the genomes of strain RX1T and M. acidiphila B2T was 80.0%. Based on the distinct cell morphology, phenotypic and genotypic differences between strain RXT and earlier described members of the genus Methylocapsa, we propose to classify it as representing a novel species of this genus, M. polymorpha, with the type strain RX1T = VKM B-3754T = UQM 41806T. [ABSTRACT FROM AUTHOR]

The conversion of N2 to NH3 holds great importance due to the essential role of NH3 in fertilizer production, energy storage and the synthesis of key industrial chemicals. Development of novel methods for N2 transformation is a worthwhile goal and researchers have turned their attention to electrochemical N2 reduction as a potentially sustainable solution. The development of molecular electrocatalysts has gained considerable momentum over the last decades, and this review focuses on the advances and challenges in the field of molecular electrochemical nitrogen fixation and aims to inspire further research into the realm of nitrogen fixation chemistry from an electrochemical perspective. [ABSTRACT FROM AUTHOR]

Synthesising ammonia at low temperature and catalyst with high stability, selectivity and activity other than Haber Bosch process and enzymatic process is still a challenging task for chemists. Computational studies serve as a valuable tool for testing novel ideas in order to either realise a theoretically viable and practicably synthesizable catalyst or to identify more of the recognised catalysts both of which are important for the growth of this field. In this report, DFT calculations have been performed on a hypothetical Fe‐ imidazolyl‐pyridine complex to explore the potential of dinitrogen reduction to ammonia at optimum temperature and pressure using Fe bound Nitrogen as a catalyst and FLP‐H2 as a co‐catalyst. FLP acts as a hydrogen source which prevents the binding of H2 with metal centre. The computed Gibbs free energies of the elementary reactions revealed that the Fe bound nitrogen can act as a catalyst for activating and functionalising dinitrogen to yield NH3 and N2H2. [ABSTRACT FROM AUTHOR]

By applying the potassium salts of cyclopentadienyl‐phosphine ligands LK to CoCl2, the corresponding cobalt chlorides (1, LCoIICl) were prepared. By reducing complexes 1 with KHBEt3 under a N2 atmosphere, bridging end‐on complexes, LCoI−N2−CoIL (2 a and 2 b), were successfully obtained. 15N2‐labeled [15N2]‐2 a was prepared under 15N2/14N2 exchange in THF solution. LCoI−N2−CoIL complex 2 a could react with P4 molecules to release N2 and generate a Co−P4−Co moiety 4. Further reduction of complex 2 b led to cleavage of a P−C bond in the cyclopentadienyl‐phosphine ligand to provide novel μ‐PCy2‐bridged Co0−N2 complex 5. DFT calculations confirmed the experimental observations. [ABSTRACT FROM AUTHOR]

Key message: The proportional contribution of endophytic and phyllospheric diazotrophs to tree N nutrition can be quantified by 15N techniques. Observations of vigorous growth of Pinus spp. on unreclaimed gravel mining sites, together with measured net nitrogen (N) gains of 50 kg N ha–1 y–1 in sand culture, indicate the importance of alternative N sources when soil organic matter (SOM) cannot meet plant demand. Non-nodulated trees can respond positively to inoculation with N2 fixing bacteria under conditions of low N supply, suggesting that non-nodular symbiotic N2 fixation can make a significant contribution to tree nutrition, a well-established pathway for cereals, forage grasses and some industrial crops in N-limited environments. We reviewed the literature where non-isotopic approaches and techniques based on stable (15N) and radioactive (13N) tracers were used to estimate the relative contribution of endophytic and phyllospheric N2 fixation to the N economies of non-nodulated trees. The principal avenue of enquiry has so far involved determination of the response of trees to inoculation with diazotrophic bacteria. There is a need to obtain in situ measurements of the reliance of non-leguminous trees on endophytic and phyllospheric N2 fixation under a range of environmental and edaphic conditions. Current methodological obstacles have to be overcome to meet this challenge. Future research directions are suggested. [ABSTRACT FROM AUTHOR]

The ability of non-nodulating pioneer plants on newly exposed glacial till to obtain atmospheric N2 was investigated using both acetylene reduction assay (ARA) and 15N2 gas incorporation methods. Plant tissues were also examined for the presence of endophytic diazotrophic bacteria using high-throughput nifH amplification sequencing. Both ARA and 15N2 gas incorporation demonstrated that non-nodulating pioneer plants can obtain atmospheric N2, but the amount was highly variable depending on the plant organ, with clearly higher values in leaves relative to twigs and roots. High-throughput amplification sequencing of nifH genes indicated that a great variety of diazotrophic communities developed in pioneer plant tissues under primary succession. The N2 fixation rate (based on both 15N2 incorporation and ARA) was not directly linked to the abundance of any specific diazotrophs, but was correlated with the Chao1 index and the number of observed species, suggesting that different diazotrophs jointly accounted for N2 fixation activity. Our results highlight that non-nodulating pioneer plants may acquire N through endophytic N2-fixing bacteria as a supplement for other potential N sources in oligotrophic environments in early stages of primary succession following glacier retreat. [ABSTRACT FROM AUTHOR]

The potential effects of carbonaceous nanomaterials (CNMs) on agricultural plants are of concern. However, little research has been performed using plants cultivated to maturity in soils contaminated with various CNMs at different concentrations. Here, we grew soybean for 39 days to seed production in soil amended with 0.1, 100, or 1000 mg kg-1 of either multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), or carbon black (CB) and studied plant growth, nodulation, and dinitrogen (N2) fixation potential. Plants in all CNM treatments flowered earlier (producing 60% to 372% more flowers when reproduction started) than the unamended controls. The low MWCNT-treated plants were shorter (by 15%) with slower leaf cover expansion (by 26%) and less final leaf area (by 24%) than the controls. Nodulation and N2 fixation potential appeared negatively impacted by CNMs, with stronger effects at lower CNM concentrations. All CNM treatments reduced the whole-plant N2 fixation potential, with the highest reductions (by over 91%) in the low and medium CB and the low MWCNT treatments. CB and GNPs appeared to accumulate inside nodules as observed by transmission electron microscopy. CNM dispersal in aqueous soil extracts was studied to explain the inverse dose-response relationships, showing that CNMs at higher concentrations were more agglomerated (over 90% CNMs settled as agglomerates >3 μm after 12 h) and therefore proportionally less bioavailable. Overall, our findings suggest that lower concentrations of CNMs in soils could be more impactful to leguminous N2 fixation, owing to greater CNM dispersal and therefore increased bioavailability at lower concentrations.

Intercropping is commonly used in low-input systems but could also be a strategy for higher input systems. Three ratios of substitutive oat–pea intercrops were tested on a fertile soil in eastern Austria with application of a low nitrogen (N) fertiliser rate (6 g N m−2) versus an unfertilised control to assess the effect of intercropping and low N fertilisation on dinitrogen fixation (NFIX). The above-ground dry matter (AGDM) and N yield of intercrops increased with N fertilisation, but the increase occurred only in oat, while pea was not affected by N fertilisation. Pure pea stands and intercrops with high pea share resulted in N sparing in the soil at harvest, as the soil mineral N was higher than in pure oat. Half of the applied amount of N was recovered by the AGDM of crops and half remained in the soil at harvest. The NFIX per unit area was highest in pure pea. Intercropping considerably reduced NFIX, especially in intercrops with low pea share. NFIX per unit of AGDM of pea, however, was neither affected by intercropping nor by N fertilisation. Consequently, a low amount of N fertilisation of oat–pea intercrops on a fertile soil can increase overall performance of the system through increasing the performance of oat without impairing that of pea.

Molybdenum dinitrogen complexes supported by monodentate arylsilylamido ligand, [Ar(Me3Si)N]3MoN2Mg(THF)2[N(SiMe3)Ar] (5) and [Ar(Me3Si)N]3MoN2SiMe3 (6) (Ar = 3,5-Me2C6H3) were synthesized and structurally characterized, and proved to be effective catalysts for the disproportionation of cyclohexadienes and isomerization of terminal alkenes. The 1H NMR spectrum suggested that the bridging nitrogen ligand remains intact during the catalytic reaction, indicating possible catalytic ability of the Mo-N=N motif. [ABSTRACT FROM AUTHOR]

Reef-building corals generally thrive in nutrient-poor tropical waters, where among other elements, nitrogen (N) availability often limits primary productivity. In addition to their close association with endosymbiotic dinoflagellates of the family Symbiodiniaceae, enabling an effective use and retention of dissolved inorganic nitrogen (DIN), scleractinian corals have developed strategies to acquire new N: (1) They can ingest N-rich sediment particles and preys (from picoplankton to macro-zooplankton) via heterotrophy, including diazotrophs [plankton fixing dinitrogen (N2) and releasing part of this nitrogen—Diazotroph-Derived N (DDN)—in seawater], a pathway called “heterotrophic nutrition on diazotrophs”; (2) Symbiotic diazotrophs located in the coral holobiont have the molecular machinery to fix N2, a pathway called “symbiotic N2 fixation”. Here we used the 15N2 isotopic labeling in a series of incubations to investigate the relative contribution of each of these DDN transfer pathways in three worldwide distributed coral species: Acropora muricata, Galaxea fascicularis, and Pocillopora damicornis. We show that N provision via “symbiotic N2 fixation” is negligible compared to that obtained via “heterotrophic nutrition on diazotrophs,” with DDN assimilation rates about a thousand times lower for P. damicornis and G. fascicularis, or assimilation rates via “symbiotic N2 fixation” almost nil for A. muricata. Through heterotrophic feeding on planktonic diazotrophs, only G. fascicularis and P. damicornis can successfully obtain N and fulfill a large part of their N requirements (DDN asimilation rates: 0.111 ± 0.056 and 0.517 ± 0.070 μg N cm–2 h–1 in their Symbiodiniaceae, respectively). Whereas this contribution is again negligible for A. muricata. They also largely consume the picoplankton that likely benefit from this DDN (Prochlorococcus and Synechococcus cells; respectively, 2.56 ± 1.57 104 and 2.70 ± 1.66 104 cell h–1 cm–2 for G. fascicularis; 3.02 ± 0.19 105 and 1.14 ± 0.79 104 cell h–1 cm–2 for P. damicornis). The present study confirms the different dependencies of the three tested species regarding heterotrophy, with P. damicornis and G. fascicularis appearing highly efficient at capturing plankton, while A. muricata, considered as mainly autotroph, does not rely on these food resources to meet its N and energy needs.

Recent research suggests that nitrogen (N) cycling microbes are important for coral holobiont functioning. In particular, coral holobionts may acquire bioavailable N via prokaryotic dinitrogen (N2) fixation or remove excess N via denitrification activity. However, our understanding of environmental drivers on these processes in hospite remains limited. Employing the strong seasonality of the central Red Sea, this study assessed the effects of environmental parameters on the proportional abundances of N cycling microbes associated with the hard corals Acropora hemprichii and Stylophora pistillata. Specifically, we quantified changes in the relative ratio between nirS and nifH gene copy numbers, as a proxy for seasonal shifts in denitrification and N2 fixation potential in corals, respectively. In addition, we assessed coral tissue-associated Symbiodiniaceae cell densities and monitored environmental parameters to provide a holobiont and environmental context, respectively. While ratios of nirS to nifH gene copy numbers varied between seasons, they revealed similar seasonal patterns in both coral species, with ratios closely following patterns in environmental nitrate availability. Symbiodiniaceae cell densities aligned with environmental nitrate availability, suggesting that the seasonal shifts in nirS to nifH gene abundance ratios were probably driven by nitrate availability in the coral holobiont. Thereby, our results suggest that N cycling in coral holobionts probably adjusts to environmental conditions by increasing and/or decreasing denitrification and N2 fixation potential according to environmental nitrate availability. Microbial N cycling may, thus, extenuate the effects of changes in environmental nitrate availability on coral holobionts to support the maintenance of the coral–Symbiodiniaceae symbiosis.

The authors compare Community Earth System Model results to marine observations for the 1990s and examine climate change impacts on biogeochemistry at the end of the twenty-first century under two future scenarios (Representative Concentration Pathways RCP4.5 and RCP8.5). Late-twentieth-century seasonally varying mixed layer depths are generally within 10 m of observations, with a Southern Ocean shallow bias. Surface nutrient and chlorophyll concentrations exhibit positive biases at low latitudes and negative biases at high latitudes. The volume of the oxygen minimum zones is overestimated.The impacts of climate change on biogeochemistry have similar spatial patterns under RCP4.5 and RCP8.5, but perturbation magnitudes are larger under RCP8.5. Increasing stratification leads to weaker nutrient entrainment and decreased primary and export production (>30% over large areas). The global-scale decreases in primary and export production scale linearly with the increases in mean sea surface temperature. There are production increases in the high nitrate, low chlorophyll (HNLC) regions, driven by lateral iron inputs from adjacent areas. The increased HNLC export partially compensates for the reductions in non-HNLC waters (~25% offset). Stabilizing greenhouse gas emissions and climate by the end of this century (as in RCP4.5) will minimize the changes to nutrient cycling and primary production in the oceans. In contrast, continued increasing emission of CO2 (as in RCP8.5) will lead to reduced productivity and significant modifications to ocean circulation and biogeochemistry by the end of this century, with more drastic changes beyond the year 2100 as the climate continues to rapidly warm.

Intercropping is commonly used in low-input systems but could also be a strategy for higher input systems. Three ratios of substitutive oat–pea intercrops were tested on a fertile soil in eastern Austria with application of a low nitrogen (N) fertiliser rate (6 g N m−2) versus an unfertilised control to assess the effect of intercropping and low N fertilisation on dinitrogen fixation (NFIX). The above-ground dry matter (AGDM) and N yield of intercrops increased with N fertilisation, but the increase occurred only in oat, while pea was not affected by N fertilisation. Pure pea stands and intercrops with high pea share resulted in N sparing in the soil at harvest, as the soil mineral N was higher than in pure oat. Half of the applied amount of N was recovered by the AGDM of crops and half remained in the soil at harvest. The NFIX per unit area was highest in pure pea. Intercropping considerably reduced NFIX, especially in intercrops with low pea share. NFIX per unit of AGDM of pea, however, was neither affected by intercropping nor by N fertilisation. Consequently, a low amount of N fertilisation of oat–pea intercrops on a fertile soil can increase overall performance of the system through increasing the performance of oat without impairing that of pea. [ABSTRACT FROM AUTHOR]

In dinitrogen (N 2 ) fixation chemistry, bimetallic end-on bridging N 2 complexes M(μ-η 1  : η 1 -N 2 )M can split N 2 into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)] 2 (μ-N 2 )} 0/1+/2+ (1-3) are incapable to cleave N 2 , in contrast to their Mo congeners. Remarkably, cross this series the N-N bond length of the N 2 ligand and the N-N stretching frequency exhibit unprecedented nonmonotonic variations, and complexes 1 and 2 in both solid and solution states display rare thermally activated ligand-mediated two-center spin transitions, distinct from discrete dinuclear spin crossovers. In-depth analyses using wave function based ab initio calculations reveal that the Cr-N 2 -Cr bonding in complexes 1-3 is distinguished by strong multireference character and cannot be described by solely one electron configuration or Lewis structure, and that all intriguing spectroscopic observations originate in their sophisticate multireference electronic structures. More critical is that such multireference bonding of complexes 1-3 is at least a key factor that contributes to their kinetic inertness toward N 2 splitting. The mechanistic understanding is then used to rationalize the disparate reactivity of related 3d M(μ-η 1  : η 1 -N 2 )M complexes compared to their 4d and 5d analogs., (© 2024 Wiley-VCH GmbH.)

• A new NPZD modelling software package for estuarine systems was developed. • Transport between spatial boxes is calculated by a coupled FEM model. • The model is capable to output all types of process dynamic, including N 2 -fixation. Introducing ESTAS-AQUABC, a new software tool designed for modelling nutrient cycles and eutrophication in highly-eutrophic estuaries. Our focus on replicating intense cyanobacteria blooms and N2-fixation sets us apart from other estuary models. We account for N2-fixation by cyanobacteria, the inorganic carbon cycle, non-conservative alkalinity, and pH calculations through CO2SYS integration. AQUABC also includes ammonia-stripping at high pH in its kinetic sub-model. ESTAS-AQUABC uses box modelling approach where the fluxes between boxes are calculated by a hydrodynamical model, in our case the SHYFEM model. This approach is robust, especially when field data for calibration is scarce, saving computational time. While our model accurately reproduced pelagic N2-fixation rates, inorganic nutrient dynamics were less precise, mainly due to the absence of bentho-pelagic exchange processes. ESTAS-AQUABC provides a useful tool to investigate nutrient retention from land to open sea, which could be important to mitigate eutrophication in estuarine systems and the adjacent coastal areas. [ABSTRACT FROM AUTHOR]

Corals are associated with dinitrogen (N2)-fixing bacteria that potentially represent an additional nitrogen (N) source for the coral holobiont in oligotrophic reef environments. Nevertheless, the few studies investigating the assimilation of diazotrophically derived nitrogen (DDN) by tropical corals are limited to a single scleractinian species (i.e., Stylophora pistillata). The present study quantified DDN assimilation rates in four scleractinian and three soft coral species from the shallow waters of the oligotrophic Northern Red Sea using the 15N2 tracer technique. All scleractinian species significantly stimulated N2 fixation in the coral-surrounding seawater (and mucus) and assimilated DDN into their tissue. Interestingly, N2 fixation was not detected in the tissue and surrounding seawater of soft corals, despite the fact that soft corals were able to take up DDN from a culture of free-living diazotrophs. Soft coral mucus likely represents an unfavorable habitat for the colonization and activity of diazotrophs as it contains a low amount of particulate organic matter, with a relatively high N content, compared to the mucus of scleractinian corals. In addition, it is known to present antimicrobial properties. Overall, this study suggests that DDN assimilation into coral tissues depends on the presence of active diazotrophs in the coral’s mucus layer and/or surrounding seawater. Since N is often a limiting nutrient for primary productivity in oligotrophic reef waters, the divergent capacity of scleractinian and soft corals to promote N2 fixation may have implications for N availability and reef biogeochemistry in scleractinian versus soft coral-dominated reefs.

Corals are associated with dinitrogen (N2)-fixing bacteria that potentially represent an additional nitrogen (N) source for the coral holobiont in oligotrophic reef environments. Nevertheless, the few studies investigating the assimilation of diazotrophically derived nitrogen (DDN) by tropical corals are limited to a single scleractinian species (i.e., Stylophora pistillata). The present study quantified DDN assimilation rates in four scleractinian and three soft coral species from the shallow waters of the oligotrophic Northern Red Sea using the 15N2 tracer technique. All scleractinian species significantly stimulated N2 fixation in the coral-surrounding seawater (and mucus) and assimilated DDN into their tissue. Interestingly, N2 fixation was not detected in the tissue and surrounding seawater of soft corals, despite the fact that soft corals were able to take up DDN from a culture of free-living diazotrophs. Soft coral mucus likely represents an unfavorable habitat for the colonization and activity of diazotrophs as it contains a low amount of particulate organic matter, with a relatively high N content, compared to the mucus of scleractinian corals. In addition, it is known to present antimicrobial properties. Overall, this study suggests that DDN assimilation into coral tissues depends on the presence of active diazotrophs in the coral's mucus layer and/or surrounding seawater. Since N is often a limiting nutrient for primary productivity in oligotrophic reef waters, the divergent capacity of scleractinian and soft corals to promote N2 fixation may have implications for N availability and reef biogeochemistry in scleractinian versus soft coral-dominated reefs. [ABSTRACT FROM AUTHOR]

In the Arabian Sea (AS), spatiotemporal nutrient limitation patterns of primary production and the possible role of nutrient inputs from the atmosphere are still not well understood. Using a biogeochemical model forced by modeled aerosol deposition, we show that without high atmospheric iron inputs through dust deposition during the summer monsoon, primary production over the AS would be reduced by half. Atmospheric iron deposition also supports most of the nitrogen fixation over the AS. However, our ocean biogeochemistry modeling results suggest that dinitrogen fixation constitutes a negligible fraction of the primary production. Finally, we show that atmospheric inputs of nitrogen, mostly from anthropogenic activities in India, have a negligible impact on primary production. Plain‐Language summary: Phytoplankton are microscopic organisms that live in watery environments such as the ocean. Like land plants, phytoplankton need nutrients to survive, develop, and reproduce. In the surface ocean, nutrients come from one of several pathways: from the depths of the ocean, from the rivers, and from the atmosphere. In the Arabian Sea, there are two important sources of nutrients for the organisms living in the surface layer of the ocean: the nutrient‐rich waters coming from below, which occurs along the coast of the Arabian Peninsula, and the desert dust deposited from above. In this study, we show that neither source brings all the necessary nutrients nor brings enough nutrients. Both of these types of inputs are required to understand the distribution of the phytoplankton. If there was no dust deposition in the Arabian Sea, these organisms that represent the first link in the ocean food chain would be half as abundant as they are currently. Key Points: Atmospheric iron deposition is essential to sustain the high levels of productivity during the summer monsoonNitrogen fixation remains low despite large iron depositionAtmospheric deposition of nitrogen and phosphorus plays a negligible role [ABSTRACT FROM AUTHOR]

The northern Red Sea experiences strong annual differences in environmental conditions due to its relative high-latitude location for coral reefs. This allows the study of regulatory effects by key environmental parameters (i.e., temperature, inorganic nutrient, and organic matter concentrations) on reef primary production and dinitrogen (N2) fixation, but related knowledge is scarce. Therefore, this study measured environmental parameters, primary production and N2 fixation of phytoplankton groups in the water overlying a coral reef in the Gulf of Aqaba. To this end, we used a comparative approach between mixed and stratified water column scenarios in a full year of seasonal observations. Findings revealed that inorganic nutrient concentrations were significantly higher in the mixed compared to the stratified period. While gross photosynthesis and N2 fixation rates remained similar, net photosynthesis decreased from mixed to stratified period. Net heterotrophic activity of the planktonic community increased significantly during the stratified compared to the mixed period. While inorganic nitrogen (N) availability was correlated with net photosynthesis over the year, N2 fixation only correlated with N availability during the mixed period. This emphasizes the complexity of planktonic trophodynamics in northern Red Sea coral reefs. Comparing mixed and stratified planktonic N2 fixation rates with those of benthic organisms and substrates revealed a close seasonal activity similarity between free-living pelagic and benthic diazotrophs. During the mixed period, N2 fixation potentially contributed up to 3% of planktonic primary production N demand. This contribution increased by ca. one order of magnitude to 21% during the stratified period. Planktonic N2 fixation is likely a significant N source for phytoplankton to maintain high photosynthesis under oligotrophic conditions in coral reefs, especially during stratified conditions.

The northern Red Sea experiences strong annual differences in environmental conditions due to its relative high-latitude location for coral reefs. This allows the study of regulatory effects by key environmental parameters (i.e., temperature, inorganic nutrient, and organic matter concentrations) on reef primary production and dinitrogen (N2) fixation, but related knowledge is scarce. Therefore, this study measured environmental parameters, primary production and N2 fixation of phytoplankton groups in the water overlying a coral reef in the Gulf of Aqaba. To this end, we used a comparative approach between mixed and stratified water column scenarios in a full year of seasonal observations. Findings revealed that inorganic nutrient concentrations were significantly higher in the mixed compared to the stratified period. While gross photosynthesis and N2 fixation rates remained similar, net photosynthesis decreased from mixed to stratified period. Net heterotrophic activity of the planktonic community increased significantly during the stratified compared to the mixed period. While inorganic nitrogen (N) availability was correlated with net photosynthesis over the year, N2 fixation only correlated with N availability during the mixed period. This emphasizes the complexity of planktonic trophodynamics in northern Red Sea coral reefs. Comparing mixed and stratified planktonic N2 fixation rates with those of benthic organisms and substrates revealed a close seasonal activity similarity between free-living pelagic and benthic diazotrophs. During the mixed period, N2 fixation potentially contributed up to 3% of planktonic primary production N demand. This contribution increased by ca. one order of magnitude to 21% during the stratified period. Planktonic N2 fixation is likely a significant N source for phytoplankton to maintain high photosynthesis under oligotrophic conditions in coral reefs, especially during stratified conditions. [ABSTRACT FROM AUTHOR]

Abstract: The import of nitrogen via dinitrogen fixation supports primary production, particularly in the oligotrophic ocean; however, to what extent dinitrogen fixation influences primary production, and the role of specific types of diazotrophs, remains poorly understood. We examined the relationship between primary production and dinitrogen fixation together with diazotroph community structure in the oligotrophic western and eastern South Pacific Ocean and found that dinitrogen fixation was higher than nitrate‐based new production. Primary production increased in the middle of the western subtropical region, where the cyanobacterium Trichodesmium dominated the diazotroph community and accounted for up to 7.8% of the phytoplankton community, and the abundance of other phytoplankton taxa (especially Prochlorococcus) was high. These results suggest that regenerated production was enhanced by nitrogen released from Trichodesmium and that carbon fixation by Trichodesmium also contributed significantly to total primary production. Although volumetric dinitrogen fixation was comparable between the western and eastern subtropical regions, primary production in the western waters was more than twice as high as that in the eastern waters, where UCYN‐A1 (photoheterotroph) and heterotrophic bacteria were the dominant diazotrophs. This suggests that dinitrogen fixed by these diazotrophs contributed relatively little to primary production of the wider community, and there was limited carbon fixation by these diazotrophs. Hence, we document how the community composition of diazotrophs in the field can be reflected in how much nitrogen becomes available to the wider phytoplankton community and in how much autotrophic diazotrophs themselves fix carbon and thereby influences the magnitude of local primary production. [ABSTRACT FROM AUTHOR]

Redox behaviors of monomeric and dimeric titanocenes, [Cp2TiCl2] ( 1) and [(Cp2TiCl)2] ( 2), were investigated in two different types of ionic liquid (IL) with non-coordinating and coordinating anions, 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)- trifluorophosphate (Pyr4FAP) and 1-butyl-1-methylpyrrolidinium triflate (Pyr4OTf), respectively. UV-vis/NIR spectra obtained during the electrochemical reduction of 1 revealed that it was converted to 2 in the ILs through the formation of [Cp2TiCl] ( 3). In Pyr4OTf, 3 was coordinated with the OTf anion in the η1-O mode, during the electrochemical reductions of Ti(IV/III) process, whereas 3 was not coordinated by the FAP anion in Pyr4FAP. Additionally, electrochemical NH3 synthesis was carried out in a solid polymer electrolyte cell by using a gas diffusion electrode coated with Pyr4FAP or Pyr4OTf containing titanocenes. The electrochemical reduction using 2 in Pyr4FAP at −1.5 V (vs. Ag/AgCl) gave a high yield (34 % at 29.9 C) of NH3 per Ti ion. The electrochemical reduction using 1 in Pyr4OTf gave a 6.8 % yield of NH3 per Ti ion at 20 °C. These findings indicate that the use of an IL with a non-coordinating anion such as FAP contributes to the coordination and reduction of N2 to titanocenes. [ABSTRACT FROM AUTHOR]

Biogeochemical implications of global imbalance between the rates of marine dinitrogen (N2) fixation and denitrification have spurred us to understand the former process in the Arabian Sea, which contributes considerably to the global nitrogen budget. Heterotrophic bacteria have gained recent appreciation for their major role in marine N budget by fixing a significant amount of N2. Accordingly, we hypothesize a probable role of heterotrophic diazotrophs from the 15N2 enriched isotope labeling dark incubations that witnessed rates comparable to the light incubations in the eastern Arabian Sea during spring 2010. Maximum areal rates (8 mmol N m−2 d−1) were the highest ever observed anywhere in world oceans. Our results suggest that the eastern Arabian Sea gains ~92% of its new nitrogen through N2 fixation. Our results are consistent with the observations made in the same region in preceding year, i.e., during the spring of 2009.

Sustainable agriculture demands reduced input of man-made nitrogen (N) fertilizer, yet N2 fixation limits the productivity of crops with heterotrophic diazotrophic bacterial symbionts. We investigated floating ferns from the genus Azolla that host phototrophic diazotrophic Nostoc azollae in leaf pockets and belong to the fastest growing plants. Experimental production reported here demonstrated N-fertilizer independent production of nitrogen-rich biomass with an annual yield potential per ha of 1200 kg-1 N fixed and 35 t dry biomass. 15N2 fixation peaked at noon, reaching 0.4 mg N g-1 dry weight h-1. Azolla ferns therefore merit consideration as protein crops in spite of the fact that little is known about the fern's physiology to enable domestication. To gain an understanding of their nitrogen physiology, analyses of fern diel transcript profiles under differing nitrogen fertilizer regimes were combined with microscopic observations. Results established that the ferns adapted to the phototrophic N2-fixing symbionts N. azollae by (1) adjusting metabolically to nightly absence of N supply using responses ancestral to ferns and seed plants; (2) developing a specialized xylem-rich vasculature surrounding the leaf-pocket organ; (3) responding to N-supply by controlling transcripts of genes mediating nutrient transport, allocation and vasculature development. Unlike other non-seed plants, the Azolla fern clock is shown to contain both the morning and evening loops; the evening loop is known to control rhythmic gene expression in the vasculature of seed plants and therefore may have evolved along with the vasculature in the ancestor of ferns and seed plants. [ABSTRACT FROM AUTHOR]

Keywords: cobalt; dinitrogen activation; dinitrogen fixation; P4 activation EN cobalt dinitrogen activation dinitrogen fixation P4 activation 1 1 1 12/06/22 20221201 NES 221201 B Cobalt dinitrogen complexes b supported by cyclopentadienyl-phosphine ligands and their reactivities are described. Cover Feature: Cobalt Cyclopentadienyl-Phosphine Dinitrogen Complexes (Chem. Eur. J. 67/2022) Cobalt, dinitrogen activation, dinitrogen fixation, P4 activation. [Extracted from the article]