Electron Transfer Reduction Research Articles

Proton-Coupled Electron-Transfer Reduction of Dioxygen: The Importance of Precursor Complex Formation between Electron Donor and Proton Donor.

The proton-coupled electron transfer (PCET) reaction has drawn extensive attention for its widespread occurrence in chemistry, biology, and materials science. The mechanistic studies via model systems such as tyrosine and phenol oxidation have gradually deepened the understanding of PCET reactions, which was widely accepted and applied to bond activation and transformation. However, direct PCET activation of nonpolar bonds such as the C-H bond, O2, and N2 has yet to be explored. Herein, we report that the interaction between electron donor and proton donor could overcome the barrier of direct O2 activation via a concerted electron-proton transfer mechanism. This work provides a new strategy for developing direct PCET activation of nonpolar bonds.

Carbon nanotubes accelerates the bio-induced vivianite formation

Vivianite widely existed in digested sludge and activated sludge as a potential phosphate resource recovered from wastewater treatment plants (WWTPs). As an important product of extracellular electron transfer (EET) and biological iron reduction, the production of vivianite can be enhanced by conductive materials. Carbon nanotubes (CNTs) with excellent electrical conductivity have been reported to promote electron transfer, which was applied in wastewater treatment to accelerate the degradation of the contaminants. However, the impact of CNTs on vivianite formation was barely reported. In this study, the iron reduction, vivianite recovery, and the biotoxicity of CNTs were investigated in order to determine the influence of CNTs towards the vivianite production. The enhancement of vivianite production after CNTs adding reached up to 17 % by promoting the electron transfer between dissimilative iron-reducing bacteria (DIRB) and Fe(III). However, at the initial stage (0–24 h), Fe(III) reduction efficiency decreased by 81 % after inoculating with sewage sludge, which was attributed to CNTs destroying of the cell membrane (as indicated by SEM, CLSM and AFM analysis). The biotoxicity of CNTs stimulated DIRB to secret extracellular polymeric substances (EPS) and form bio-flocs to resist the physical puncture. After 48 h, the proportion of living DIRB in 1000 mg/L CNTs batch increased to 98 %, which was 79 % higher than 12 h. As a result, the vivianite recovery of raw sewage with 1000 mg/L CNTs increased to 44 ± 1 %, which was 33 % higher than that in the CNT-0.

Construction and investigation of graphitic carbon nitride/expanded perlite composite photocatalyst with floating ability

Using melamine as the precursor of g-C3N4 and expanded perlite (EP) as the carrier, a kind of floating g-C3N4/expanded perlite composites (CN/EP-x, where x was denoted as 1, 2, 4 and 6, respectively, corresponding to the mass ratio of melamine to EP 1:2, 2:1, 4:1 and 6:1) were synthesized by cooperating wet-chemistry method with a unique heat treatment schedule, which aimed to enhance the g-C3N4 loading ratio and construct a tightly interface between g-C3N4 and EP. The phase composition, microstructure, element composition, optical property, etc. of the g-C3N4/EP composites were investigated, and their photocatalytic performances vs. the mass ratio of melamine to EP (loading ratio of g-C3N4) were evaluated through photo-degrading Rhodamine B (RhB) aqueous solution. It is found that g-C3N4 immobilized on the surface or embedded into the open pores of EP, which were beneficial to the interface bonding strength between g-C3N4 and EP. With the increasing of the mass ratio of melamine, the loading ratio of g-C3N4 in CN/EP-x composite increased gradually, and the specific surface area of the composite increased step by step but then dropped for CN/EP-6 composite owing to the intensified agglomeration of g-C3N4 particles. The photocatalytic performance of CN/EP-x composites also improved gradually and achieved the optimum for the CN/EP-4 composite, then reduced for the CN/EP-6 composite. CN/EP-4 composite (0.35 g) degraded 94 % of RhB molecules (10 mg/L, 100 mL) after visible light illumination for 120 min. The reduced band gap, improved separation efficiency of holes and electrons, enhanced photo-current response, reduced electron transfer resistance, as well as the enhanced specific surface area were responsible for the optimum photocatalytic performance of CN/EP-4 composite. Moreover, CN/EP-4 composite exhibited excellent floating performance, stability and reusability. After four degradation cycles, the removal rate of RhB by CN/EP-4 composite still achieved 83 %. This work will provide a new insight into synthesizing floating composite photocatalysts for the future practical application.

A Fruitful Decade of Organofluorine Chemistry: New Reagents and Reactions

A Fruitful Decade of Organofluorine Chemistry: New Reagents and Reactions

Unraveling the role of Ni13 catalyst supported on ZrO2 for CH4 dehydrogenation: The d-band electron reservoir

The activation of C–H bonds of CH4 is a key step for the conversion of methane to chemical commodities. Loading Ni onto ZrO2 is regarded as a relatively efficient way to harness the beneficial electronic property and the fine dispersion of the Ni catalyst for CH4 dissociation. Herein we demonstrate the crucial role of Ni13 catalyst supported on ZrO2 for the dissociation of CH4. The density functional theory (DFT) results show that the ZrO2 supported Ni13 stabilizes all species better and facilitates CH4 activation. The stepwise dehydrogenations of CH4 on Ni13-ZrO2(111) exhibits longer C–H bond lengths of ISs, lower Ea, and smaller displacements between the detaching H and the remaining CHx fragment in TSs. In addition, they are also thermodynamically more feasible. However, without the ZrO2 support on Ni13, the opposite results are obtained. Consequently, the ZrO2 modified Ni13 is more superior to the original Ni13 in CH4 dehydrogenation. The electronic analysis combining DFT calculations confirmed that the larger overlap between C 2p and Ni 3d, and the electron transfer of Ni→C cause the weaker C 2p–H 1s hybridization. In addition, the reduction of electron transfer of H→C leads to a stronger interaction between Ni and C along with a weak C–H bond. Hence, the ZrO2 support serves as the d-band electron reservoir at Ni13 and it is benefit to the activation of C–H bonds in CH4 dehydrogenation.

Neutron scattering maps the higher-order assembly of NADPH-dependent assimilatory sulfite reductase

Precursor molecules for biomass incorporation must be imported into cells and made available to the molecular machines that build the cell. Sulfur-containing macromolecules require that sulfur be in its S2− oxidation state before assimilation into amino acids, cofactors, and vitamins that are essential to organisms throughout the biosphere. In α-proteobacteria, NADPH-dependent assimilatory sulfite reductase (SiR) performs the final six-electron reduction of sulfur. SiR is a dodecameric oxidoreductase composed of an octameric flavoprotein reductase (SiRFP) and four hemoprotein metalloenzyme oxidases (SiRHPs). SiR performs the electron transfer reduction reaction to produce sulfide from sulfite through coordinated domain movements and subunit interactions without release of partially reduced intermediates. Efforts to understand the electron transfer mechanism responsible for SiR’s efficiency are confounded by structural heterogeneity arising from intrinsically disordered regions throughout its complex, including the flexible linker joining SiRFP’s flavin-binding domains. As a result, high-resolution structures of SiR dodecamer and its subcomplexes are unknown, leaving a gap in the fundamental understanding of how SiR performs this uniquely large-volume electron transfer reaction. Here, we use deuterium labeling, in vitro reconstitution, analytical ultracentrifugation (AUC), small-angle neutron scattering (SANS), and neutron contrast variation (NCV) to observe the relative subunit positions within SiR’s higher-order assembly. AUC and SANS reveal SiR to be a flexible dodecamer and confirm the mismatched SiRFP and SiRHP subunit stoichiometry. NCV shows that the complex is asymmetric, with SiRHP on the periphery of the complex and the centers of mass between SiRFP and SiRHP components over 100 Å apart. SiRFP undergoes compaction upon assembly into SiR’s dodecamer and SiRHP adopts multiple positions in the complex. The resulting map of SiR’s higher-order structure supports a cis/trans mechanism for electron transfer between domains of reductase subunits as well as between tightly bound or transiently interacting reductase and oxidase subunits.

Ion-pair reorganization regulates reactivity in photoredox catalysts.

Cyclometalated and polypyridyl complexes of d6 metals are promising photoredox catalysts, using light to drive reactions with high kinetic or thermodynamic barriers via the generation of reactive radical intermediates. However, while tuning of their redox potentials, absorption energy, excited-state lifetime and quantum yield are well-known criteria for modifying activity, other factors could be important. Here we show that dynamic ion-pair reorganization controls the reactivity of a photoredox catalyst, [Ir[dF(CF3)ppy]2(dtbpy)]X. Time-resolved dielectric-loss experiments show how counter-ion identity influences excited-state charge distribution, evincing large differences in both the ground- and excited-state dipole moment depending on whether X is a small associating anion (PF6-) that forms a contact-ion pair versus a large one that either dissociates or forms a solvent-separated pair (BArF4-). These differences correlate with the reactivity of the photocatalyst toward both reductive and oxidative electron transfer, amounting to a 4-fold change in selectivity toward oxidation versus reduction. These results suggest that ion pairing could be an underappreciated factor that modulates reactivity in ionic photoredox catalysts.

Deferrivibrio essentukiensis sp. nov., gen. nov., a Representative of Deferrivibrionaceae fam. nov., Isolated from the Subsurface Aquifer of Caucasian Mineral Drinking Waters

The Yessentukskoye deposit of Caucasian mineral waters contains balneologically valuable drinking mineral water, which is extracted from the Upper Cretaceous 1 km subsurface aquifer and is almost unexplored by microbiologists. We have sampled this water via continuously operating production wells, characterized the phylogenetic diversity of its microbial community, and obtained enrichments of thermophilic iron reducers from the source aquifer. From the enrichments, a novel anaerobic thermophilic bacterium, reducing Fe(III) in the mineral ferrihydrite with acetate as the electron donor, was isolated into a pure culture. The novel isolate, designated as strain Es71-Z0220T belonging to Deferribacterales order, is thermophilic, neutrophilic, halotolerant, motile vibrio. It utilizes synthesized ferrihydrite, fumarate, nitrate or elemental sulfur as the electron acceptors with organic acids as the electron donors. The strain is incapable of soluble Fe(III) complexes reduction and fermentative growth. The draft genome assembly of strain Es71-Z0220T resulted in 65 contigs with a total size of ca. 2.3 Mb. On the basis of whole-genome phylogenetic reconstruction and physiological characterization, the novel isolate was considered to represent a novel family, genus and species for which the name Deferrivibrio essentukiensis gen. nov., sp. nov. is proposed. Genome analysis revealed key determinants of anaerobic respiration and carbon substrate utilization pathways in the organism with peculiarities related to putative Fe(III)-reducing electron transfer chain. Considering the revealed metabolic features of Deferrivibrio essentukiensis, the involvement of the organism in its subsurface environment in biogeochemical by carbon cycling by coupling the organic matter oxidation with Fe(III) minerals reduction is discussed.

Anthraquinone-2-Sulfonate as a Microbial Photosensitizer and Capacitor Drives Solar-to-N2O Production with a Quantum Efficiency of Almost Unity.

Semiartificial photosynthesis shows great potential in solar energy conversion and environmental application. However, the rate-limiting step of photoelectron transfer at the biomaterial interface results in an unsatisfactory quantum yield (QY, typically lower than 3%). Here, an anthraquinone molecule, which has dual roles of microbial photosensitizer and capacitor, was demonstrated to negotiate the interface photoelectron transfer via decoupling the photochemical reaction with a microbial dark reaction. In a model system, anthraquinone-2-sulfonate (AQS)-photosensitized Thiobacillus denitrificans, a maximum QY of solar-to-nitrous oxide (N2O) of 96.2% was achieved, which is the highest among the semiartificial photosynthesis systems. Moreover, the conversion of nitrate into N2O was almost 100%, indicating the excellent selectivity in nitrate reduction. The capacitive property of AQS resulted in 82-89% of photoelectrons released at dark and enhanced 5.6-9.4 times the conversion of solar-to-N2O. Kinetics investigation revealed a zero-order- and first-order- reaction kinetics of N2O production in the dark (reductive AQS-mediated electron transfer) and under light (direct photoelectron transfer), respectively. This work is the first study to demonstrate the role of AQS in photosensitizing a microorganism and provides a simple and highly selective approach to produce N2O from nitrate-polluted wastewater and a strategy for the efficient conversion of solar-to-chemical by a semiartificial photosynthesis system.

Simultaneous Phenol Removal and Resource Recovery from Phenolic Wastewater by Electrocatalytic Hydrogenation.

Efficient pollutants removal and simultaneous resource recovery from wastewater are of great significance for sustainable development. In this study, an electrocatalytic hydrogenation (ECH) approach was developed to selectively and rapidly transform phenol to cyclohexanol, which possesses high economic value and low toxicity and can be easily recovered from the aqueous solution. A three-dimensional Ru/TiO2 electrode with abundant active sites and massive microflow channels was prepared for efficient phenol transformation. A pseudo-first-order rate constant of 0.135 min-1 was observed for ECH of phenol (1 mM), which was 34-fold higher than that of traditional electrochemical oxidation (EO). Both direct electron transfer and indirect reduction by atomic hydrogen (H*) played pivotal roles in the hydrogenation of phenol ring. The ECH technique also showed excellent performance in a wide pH range of 3-11 and with a high concentration of phenol (10 mM). Moreover, the functional groups (e.g., chloro- and methyl-) on phenol showed little influence on the superiority of the ECH system. This work provides a novel and practical solution for remediation of phenolic wastewater as well as recovery of valuable organic compounds.

Pt Particle Size Affects Both the Charge Separation and Water Reduction Efficiencies of CdS-Pt Nanorod Photocatalysts for Light Driven H2 Generation.

Decreasing the metal catalyst size into nanoclusters or even single atom is an emerging direction of developing more efficient and cost-effective photocatalytic systems. Because the catalyst particle size affects both the catalyst activity and light driven charge separation efficiency, their effects on the overall photocatalytic efficiency are still poorly understood. Herein, using a well-defined semiconductor-metal heterostructure with Pt nanoparticle catalysts selectively grown on the apexes of CdS nanorods (NRs), we study the effect of the Pt catalyst size on light driven H2 generation quantum efficiency (QEH2). With the increase of the Pt catalyst size from 0.7 ± 0.3 to 3.0 ± 0.8 nm, the QEH2 of CdS-Pt increases from 0.5 ± 0.2% to 38.3 ± 5.1%, by nearly 2 orders of magnitude. Transient absorption spectroscopy measurement reveals that the electron transfer rate from the CdS NR to the Pt tip increases with the Pt diameter following a scaling law of d5.6, giving rise to the increase of electron transfer efficiency at larger Pt sizes. The observed trend can be understood by a simplified kinetic model that assumes the overall efficiency is the product of the quantum efficiencies of charge separation (including hole transfer, electron transfer, and hole scavenging) and water reduction steps, and for CdS-Pt NRs, the quantum efficiencies of electron transfer and water reduction steps increase with the Pt sizes. Our findings suggest the importance of improving the quantum efficiencies of both charge separation and catalysis in designing efficient semiconductor-metal hybrid photocatalysts, especially in the regime of small metal particle sizes.

Dinitrogen Binding Relevant to FeMoco of Nitrogenase: Clear Visualization of σ‐Donation and π‐Backdonation from Deformation Electron Densities around Carbon/Silicon‐Iron Site

AbstractDinitrogen (N2) binding and electron transfer reduction of N2 to ammonia (NH3) by the FeMoco cofactor of the nitrogenase enzyme are captivating. They are a part of the textbook for general chemistry. The nature of N2 bonding by reduced FeMoco is speculated based on the experimental evidence. The inorganic core MoFe7S9C1− possesses a Fe6(μ6‐C4−) unit. The mode of N2‐binding at one of the Fe‐centers of the elusive Fe6(μ6‐C4−) unit and the role of light element C4− is intriguing. In the past, the mode of N2‐binding and the kinetics of N2 reduction have been studied by spectroscopic and other tools. Herein, we report on the energy decomposition analysis coupled with natural orbital for chemical valence (EDA‐NOCV) calculations/analyses to shed light on the deeper insight of the N2 binding and especially on the influence of the C‐atom of previously reported Fe‐complexes with an EP3 donor set (E=C, Si). The role of the C‐atom in the iron‐carbon site has been studied by elaboration with deformation electron densities. The intrinsic interaction energy of the bond between Fe and N2 and pairwise orbital interactions between them have been quantitatively estimated. The influence of σ‐donation of three phosphine ligands and their effects on the Fe−N2 bond have been thoroughly studied.

Dynamic Pt-OH-·H2O-Ag species mediate coupled electron and proton transfer for catalytic hydride reduction of 4-nitrophenol at the confined nanoscale interface.

Generally, the catalytic transformation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) at heterogeneous metal surfaces follows a Langmuir-Hinshelwood (L-H) mechanism when sodium borohydride (NaBH4) is used as the sacrificial reductant. Herein, with Pt-Ag bimetallic nanoparticles confined in dendritic mesoporous silica nanospheres (DMSNs) as a model catalyst, we demonstrated that the conversion of 4-NP did not pass through the direct hydrogen transfer route with the hydride equivalents being supplied by borohydride via the bimolecular L-H mechanism, since Fourier transform infrared (FTIR) spectroscopy with the use of isotopically labeled reactants (NaBD4 and D2O) showed that the final product of 4-AP was composed of protons (or deuterons) that originated from the solvent water (or heavy water). Combined characterization by X-ray photoelectron spectroscopy (XPS), 1H nuclear magnetic resonance (NMR) and the optical excitation and photoluminescence spectrum evidenced that the surface hydrous hydroxide complex bound to the metal surface (also called structural water molecules, SWs), due to the space overlap of p orbitals of two O atoms in SWs, could form an ensemble of dynamic interface transient states, which provided the alternative electron and proton transfer channels for selective transformation of 4-NP. The cationic Pt species in the Ag-Pt bimetallic catalyst mainly acts as a dynamic adsorption center to temporally anchor SWs and related reactants, and not as the active site for hydrogen activation.

In-situ synthesis of porous ZnO nanosphere/reduced graphene oxide (ZnO@rGO) composite for structural, optical and electrochemical properties

ZnO nanospheres wrapped with reduced graphene oxide sheets were successfully synthesized using an in-situ technique, and their structural, morphological, optical, and electrochemical properties were characterized. The hexagonal wurtzite phase of the nanoparticles was confirmed by XRD analysis. Ultraviolet–Visible Absorption Spectroscopy showed a decrease in the band gap energy values of the composite in comparison to pure ZnO. The photoluminescence study reveals that the ultraviolet emission of the ZnO@rGO composite was significantly increased whereas the defect-related visible emission was quenched compared to pure ZnO, which is thought to be due to the reduction of defect states and possible electron transfer between reduced graphene oxide and ZnO. Then the synthesized samples were utilized for electrochemical performance. The electrochemical tests reveal the ZnO@rGO composite shows a high specific capacitance of 846F/g, which is nearly 2.3 times higher than that of ZnO. Furthermore, this supercapacitor electrode exhibits excellent cycle life with a specific capacitance ∼96% of the initial value after 1000 cycles. According to the findings, the hybrid material is an attractive electrode material for high-performance supercapacitor applications.

Electrochemically activated carbon-halogen bond cleavage and C-C coupling monitored by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy.

The electroreductive cleavage of carbon-halogen bonds has attracted increasing attention in both electrosynthesis and pollution remediation. Herein, by employing the in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique, we have successfully investigated the electroreductive dehalogenation process of aryl halides with the thiol group on a smooth Au electrode in aqueous solution at different pH values. The obtained potential-dependent Raman spectra directly reveal a mixture of the reduction products 4,4'-biphenyldithiol (BPDT) and thiophenol (TP). The conversion ratios of the C-Cl and C-Br bonds at pH = 7 are 37% and 55%, respectively. Furthermore, quantitative analysis of the intensity variations of ν(C-Cl), ν(C-Br) and aromatic ν(CC) stretching modes suggests electroreductive dehalogenation via both direct electron transfer reduction and electrocatalytic hydrodehalogenation. Molecular evidence for the C-C cross coupling process through TP reaction with benzene free radical intermediates is found at negative potentials, which leads to the increasing selectivity of biphenyl products.

Fluorescent organo-antimony compounds as precursors for syntheses of redox-active trimeric and dimeric alkali metal antimonides: an insight into electron transfer reduction processes.

(Tip)2SbCl (1, Tip = 2,4,6-triisopropylphenyl) has been utilized as a precursor for the synthesis of the distibane (Tip)4Sb2 (4) via one-electron reduction using KC8. The two-electron reduction of 1 and 4 afforded the novel trinuclear antimonide cluster [K3((Tip)2Sb)3(THF)5] (6). Changing the reducing agent from KC8 to a different alkali metal resulted in the solid-state isolation of corresponding stable dimeric alkali metal antimonides with the general formula [M2((Tip)2Sb)2(THF)p-x(tol)x] (M = Li (14), Na (15), Cs (16)). In this report, different aspects of the various reducing agents [K metal, KC8, and [K2(Naph)2(THF)]] used have been studied, correlating the experimental observations with previous reports. Additional reactivity studies involving 1 and AgNTf2 (Tf = trifluoromethanesulfonyl) afforded the corresponding antimony cation (Tip)2Sb+NTf2- (19). The Lewis acidic character of 19 has been unambiguously proved via treatment with Lewis bases to produce the corresponding adducts 20 and 21. Interestingly, the precursors 1 and 4 have been observed to be highly luminescent, emitting green light under short-wavelength UV radiation. All the reported compounds have been characterized via NMR, UV-vis, mass spectrometry, and single-crystal X-ray diffraction analysis. Cyclic voltammetry (CV) studies of 1 in THF showed possible two electron reduction, suggesting the in situ generation of the corresponding radical-anion intermediate 1˙- and its subsequent conversion to the monomeric intermediate (Tip)2Sb- (5) upon further reduction. 5 undergoes oligomerization in the solid state to produce 6. The existence of 1˙- was proved using electron paramagnetic resonance (EPR) spectroscopy in solution. CV studies of 6 suggested its potential application as a reducing agent, which was further proved via the conversion of Tip-PCl2 to trimeric (Tip)3P3 (17), and cAACP-Cl (cAAC = cyclic alkyl(amino)carbene) to (cAAC)2P2 (18) and 4, utilizing 6 as a stoichiometric reducing agent.

Evidence of synergistic electrocatalysis at a cobalt oxide–graphene interface through nanochemical mapping of scanning transmission X-ray microscopy

Free-standing graphene membranes are a promising candidate for use as in-situ environmental windows in X-ray (electron) microscopy. In this study, graphene membranes were used as the working electrode, and cobalt nanoparticles (Co-NPs) were grown directly on top of the graphene through electrochemical deposition for interfacial variation. The electronic structure and the chemical bonding states of the Co-NPs and the graphene materials were examined by using the high spatial resolution and element-specific properties of scanning transmission X-ray microscopy. X-ray absorption spectra of C, O, and Co revealed that the Co-NP size increased in accordance with the oxidation state (Co0/2+/3+), depending on the configuration of carbon bonding (C–C/C–OH/HO–C=O/O–C(O)–O/C=O–like state). We conducted a spectral comparison of the dipped graphene and the electrodeposited Co–graphene sample, which revealed an increase in C–OH formation before Co-NPs growth. In addition to electron transfer and electrochemical reduction, the oxidation evolution from C–OH to HO–C=O (or a defect) and the O–C(O)–O (or C=O) state paralleled the increase in Co-NPs size. We curve-fitted the results to demonstrate the reduction in chemical structure from mixing Co2+/3+ to Co3+/2+/0, and to explain the interfacial modulation and the unique metal Co0 layer on the surface of the Co-NPs. Our results provide information for the design of a reliable graphene window and offer an example for the interpretation of experimental X-ray (electron) microscopy.

A novel real-time TMAO detection method based on microbial electrochemical technology

Trimethylamine N-oxide (TMAO) is considered to be a novel biomarker of cardiovascular diseases. However, the traditional TMAO detection method has failed to meet the requirements of real-time and point-of-care tests. Herein, a novel TMAO detection method based on microbial electrochemical technology is established, which realizes the direct conversion of TMAO concentration into electrical signals. Attached Shewanella loihica PV-4 was first proven to be capable of simultaneous inward extracellular electron transfer and TMAO reduction. The TMAO detection method showed a wide linear range of 0 to 250 μM, a high sensitivity of 23.92 μA/mM, and a low limit of detection of 5.96 μM. In addition, the TMAO detection process was accomplished within 600 s, with an acceptable accuracy of 90% in the real serum, showing high feasibility in clinical applications.

Anaerobic primed CO2 and CH4 in paddy soil are driven by Fe reduction and stimulated by biochar

Soil C inputs and its priming effect (PE) are important in regulating soil C accumulation and mitigating climate change; however, the factors that control the direction and intensity of PE remains unclear. Soil C accumulation is strongly affected by the reductive iron status in paddy fields, while the addition of organic substances increases the emission of certain gases (CO2/CH4) under the PE, contributing to climate change. Here, we elucidated the mechanism by which Fe reduction, measured by Fe(II) production, regulates PE for CO2 and CH4 in paddy soils. Specifically, we quantified PE induced by 13C-labeled straw in anaerobic paddy soil, augmented by ferrihydrite and/or biochar, over 150 days in a laboratory experiment. The PE of CO2 was initially negative (−15.3 to −41.5 mg C kg−1) before 20 days of incubation and subsequently became positive. PE intensity for both gases depended on ferrihydrite or biochar application. Straw+biochar had the highest PEs (CO2, 116.5 mg C kg−1; CH4, 309.4 mg C kg−1), while straw+ferrihydrite produced the lowest PEs (CO2, 41.3 mg C kg−1; CH4, 107.8 mg C kg−1). Fe reduction was approximately three times higher with straw+ferrihydrite than with straw alone and was further stimulated by additional biochar. Thus, biochar appeared to accelerate Fe reduction, destabilize mineral-bound organic C, and increase nutrient availability to microbes. Enhanced microbial C and N mining led to a positive PE for CO2. Cumulative PE for CH4 was 2–3 times higher than that for CO2, indicating conversion via methanogenesis. Biochar acted as an electron shuttle, increasing Fe reduction and stimulating interspecies electron transfer, and increased CH4 production. Therefore, Fe reduction and biochar jointly increased PE intensity for CH4. In conclusion, water and fertilizer management of paddy soil could contribute toward mitigating climate change.

Light potentials of photosynthetic energy storage in the field: what limits the ability to use or dissipate rapidly increased light energy?

The responses of plant photosynthesis to rapid fluctuations in environmental conditions are critical for efficient conversion of light energy. These responses are not well-seen laboratory conditions and are difficult to probe in field environments. We demonstrate an open science approach to this problem that combines multifaceted measurements of photosynthesis and environmental conditions, and an unsupervised statistical clustering approach. In a selected set of data on mint (Mentha sp.), we show that ‘light potentials’ for linear electron flow and non-photochemical quenching (NPQ) upon rapid light increases are strongly suppressed in leaves previously exposed to low ambient photosynthetically active radiation (PAR) or low leaf temperatures, factors that can act both independently and cooperatively. Further analyses allowed us to test specific mechanisms. With decreasing leaf temperature or PAR, limitations to photosynthesis during high light fluctuations shifted from rapidly induced NPQ to photosynthetic control of electron flow at the cytochrome b6f complex. At low temperatures, high light induced lumen acidification, but did not induce NPQ, leading to accumulation of reduced electron transfer intermediates, probably inducing photodamage, revealing a potential target for improving the efficiency and robustness of photosynthesis. We discuss the implications of the approach for open science efforts to understand and improve crop productivity.