Femtosecond formation dynamics of primary photoproducts of visual pigment rhodopsin

The coherent 11-cis-retinal photoisomerization dynamics in bovine rhodopsin was studied by femtosecond time-resolved laser absorption spectroscopy at 30-fs resolution. Femtosecond pulses of 500, 535, and 560 nm wavelength were used for rhodopsin excitation to produce different initial Franck-Condon states and relevant distinct values of the vibrational energy of the molecule in its electron excited state. Time evolution of the photoinduced rhodopsin absorption spectra was monitored after femtosecond excitation in the spectral range of 400–720 nm. Oscillations of the time-resolved absorption signals of rhodopsin photoproducts represented by photorhodopsin₅₇₀ with vibrationally-excited all-trans-retinal and rhodopsin₄₉₈ in its initial state with vibrationally-excited 11-cis-retinal were studied. These oscillations reflect the dynamics of coherent vibrational wave-packets in the ground state of photoproducts. Fourier analysis of these oscillatory components has revealed frequencies, amplitudes, and initial phases of different vibrational modes, along which the motion of wave-packets of both photoproducts occurs. The main vibrational modes established are 62, 160 cm⁻¹ and 44, 142 cm⁻¹ for photorhodopsin₅₇₀ and for rhodopsin₄₉₈, respectively. These vibrational modes are directly involved in the coherent reaction under the study, and their amplitudes in the power spectrum obtained through the Fourier transform of the kinetic curves depend on the excitation wavelength of rhodopsin.     

Nitrile‐Substituted QA Derivatives: New Acceptor Materials for Solution‐Processable Organic Bulk Heterojunction Solar Cells

The development of non‐fullerene‐based electron acceptors (especially organic molecules with sufficient absorption property within the solar spectrum region) for bulk‐heterojunction (BHJ) organic solar cells (OSCs) is an important issue for the achievement of high photoconversion efficiency. In this contribution, a new class of organic acceptors di‐cyan substituted quinacridone derivatives (DCN‐nCQA, n = 4, 6 and 8) for BHJ solar cells was designed and synthesized. DCN‐nCQA molecules possess facile synthesis, solution processability, visible and near‐IR light absorption and relatively stable characteristics. The DCN‐8CQA molecule exhibited a proper LUMO energy level (–4.1 eV), small bandgap (1.8 eV) and moderate electron mobility (10^?4 cm² V^?1 S^?1), suggesting that this molecule is an ideal acceptor material for the classical donor material regio‐regular poly (3‐hexylthiophene) (P3HT). A photovoltaic device with a structure of [ITO/PEDOT:PSS/P3HT:DCN‐8CQA/LiF/Al] displayed a power conversion efficiency of 1.57% and a fill factor of 57% under 100 mW cm^?2 AM 1.5G simulated solar illumination. The DCN‐nCQA molecules showed remarkable absorption in the region from 650 to 700 nm, where P3HT has a weak absorption promoting overlap with the solar spectrum and potentially improving the performance of the solar cell.     

DNA binding activity of Anabaena sensory rhodopsin transducer probed by fluorescence correlation spectroscopy

Anabaena sensory rhodopsin transducer (ASRT) is believed to be a major player in the photo-signal transduction cascade, which is triggered by Anabaena sensory rhodopsin. Here, we characterized DNA binding activity of ASRT probed by using fluorescence correlation spectroscopy. We observed clear decrease of diffusion coefficient of DNA upon binding of ASRT. The dissociation constant, K_D, of ASRT to 20?bp-long DNA fragments lied in micro-molar range and varied moderately with DNA sequence. Our results suggest that ASRT may interact with several different regions of DNA with different binding affinity for global regulation of several genes that need to be activated depending on the light illumination.     

Controls of the quantum yield and saturation light of isoprene emission in different‐aged aspen leaves

Leaf age alters the balance between the use of end‐product of plastidic isoprenoid synthesis pathway, dimethylallyl diphosphate (DMADP), in prenyltransferase reactions leading to synthesis of pigments of photosynthetic machinery and in isoprene synthesis, but the implications of such changes on environmental responses of isoprene emission have not been studied. Because under light‐limited conditions, isoprene emission rate is controlled by DMADP pool size (S_DMADP), shifts in the share of different processes are expected to particularly strongly alter the light dependency of isoprene emission. We examined light responses of isoprene emission in young fully expanded, mature and old non‐senescent leaves of hybrid aspen (Populus tremula x P. tremuloides) and estimated in vivo S_DMADP and isoprene synthase activity from post‐illumination isoprene release. Isoprene emission capacity was 1.5‐fold larger in mature than in young and old leaves. The initial quantum yield of isoprene emission (α_I) increased by 2.5‐fold with increasing leaf age primarily as the result of increasing S_DMADP. The saturating light intensity (Q_I90) decreased by 2.3‐fold with increasing leaf age, and this mainly reflected limited light‐dependent increase of S_DMADP possibly due to feedback inhibition by DMADP. These major age‐dependent changes in the shape of the light response need consideration in modelling canopy isoprene emission.     

Synthesis and luminescent properties of a novel bluish‐white afterglow phosphor,b‐Zn3(PO4)2:Hf4+

A new bluish‐white long‐lasting phosphorescent material, Hf⁴⁺‐doped b‐Zn₃(PO₄)₂, was prepared by the conventional high‐temperature solid‐state method. The photoluminescence (PL) spectrum reveals that it exhibits a strong blue emission band centred at 470 nm, with asymmetry on the long wavelength side; this material emits bluish‐white light and shows strong afterglow phosphorescence after it is excited with a 254 nm UV lamp. The phosphorescence lasts nearly 40 min in the light perception of the dark‐adapted human eye (0.32 mcd/m²). The possible phosphorescence mechanism is also analysed. Copyright © 2008 John Wiley & Sons, Ltd.     

Biomimetic MXene Textures with Enhanced Light‐to‐Heat Conversion for Solar Steam Generation and Wearable Thermal Management

2D materials are of particular interest in light‐to‐heat conversion, yet challenges remain in developing a facile method to suppress their light reflection. Herein, inspired by the black scales of Bitis rhinoceros, a generalized approach via sequential thermal actuations to construct biomimetic 2D‐material nanocoatings, including Ti₃C₂T_x MXene, reduced graphene oxide (rGO), and molybdenum disulfide (MoS₂) is designed. The hierarchical MXene nanocoatings result in broadband light absorption (up to 93.2%), theoretically validated by optical modeling and simulations, and realize improved light‐to‐heat performance (equilibrium temperature of 65.4 °C under one‐sun illumination). With efficient light‐to‐heat conversion, the bioinspired MXene nanocoatings are next incorporated into solar steam‐generation devices and stretchable solar/electric dual‐heaters. The MXene steam‐generation devices require much lower solar‐thermal material loading (0.32 mg cm^?2) and still guarantee high steam‐generation performance (1.33 kg m^?2 h^?1) compared with other state‐of‐the‐art devices. Additionally, the mechanically deformed MXene structures enable the fabrication of stretchable and wearable heaters dual‐powered by sunlight and electricity, which are reversibly stretched and heated above 100 °C. This simple fabrication process with effective utilization of active materials promises its practical application value for multiple solar–thermal technologies.     

The photobiology of Hydra’s periodic activity

Hydra’s response to a light pulse is a phase shift of the state of bioelectric activity correlated with the periodic shortening-elongation behaviour. The direction and absolute value of a phase shift depend on intensity, direction, application phase (along the periodic activity state), and wavelength of the light pulse. Repetitive pulses entrain the behavioural cycle. The period of the behavioural cycle depends on intensity and wavelength of steady background illumination; however, the light effect is not exerted isotropically along all the phases of the behavioural cycle. Inferences are drawn on light influence on the behaviour pacemaking mechanism. By using polyclonal antibodies against squid rhodopsin, an opsin-like protein has been identified in the ectodermal layer, presumably in sensory cells.     

Engineering of a green‐light inducible gene expression system in Synechocystis sp. PCC6803

In order to construct a green‐light‐regulated gene expression system for cyanobacteria, we characterized a green‐light sensing system derived from Synechocystis sp. PCC6803, consisting of the green‐light sensing histidine kinase CcaS, the cognate response regulator CcaR, and the promoter of cpcG2 (P_cpcG2). CcaS and CcaR act as a genetic controller and activate gene expression from P_cpcG2 with green‐light illumination. The green‐light induction level of the native P_cpcG2 was investigated using GFPuv as a reporter gene inserted in a broad‐host‐range vector. A clear induction of protein expression from native P_cpcG2 under green‐light illumination was observed; however, the expression level was very low compared with P_trc, which was reported to act as a constitutive promoter in cyanobacteria. Therefore, a Shine‐Dalgarno‐like sequence derived from the cpcB gene was inserted in the 5′ untranslated region of the cpcG2 gene, and the expression level of CcaR was increased. Thus, constructed engineered green‐light sensing system resulted in about 40‐fold higher protein expression than with the wild‐type promoter with a high ON/OFF ratio under green‐light illumination. The engineered green‐light gene expression system would be a useful genetic tool for controlling gene expression in the emergent cyanobacterial bioprocesses.     

The effect of temperature on the formation and decay of the multiline EPR signal species associated with photosynthetic oxygen evolution

We have investigated the effects of temperature on the formation and decay of the light-induced multiline EPR signal species associated with photosynthetic oxygen evolution (Dismukes, G.C. and Siderer, Y. (1980) FEBS Lett. 121, 78–80). (1) The decay rate following illumination is temperature dependent: at 295 K the half-time of decay is about 40 s, at 253 K the half-time is approx. 40 min. (2) A single intense flash of light becomes progressively less effective in generating the multiline signal below about 240 K. (3) Continuous illumination is capable of generating the signal down to almost 160 K. (4) Continuous illumination after a preilluminating flash generates less signal above 200 K than at lower temperatures. Our results support the conclusion of Dismukes and Siderer that the S₂ state gives rise to this multiline signal; we find that the S₁ state can be fully advanced to the S₂ state at temperatures as low as 160 K. The S₂ state is capable of further advancement at temperatures above about 210 K, but not below that temperature.     

Circular dichroism of cattle rhodopsin and bathorhodopsin at liquid nitrogen temperatures

The photoevent in vision has been considered to be the conversion of rhodopsin to bathorhodopsin, which is caused by photoisomerization of the chromophoric retinal. Recently some objections were raised to this hypothesis. The reliability of the hypothesis was verified by measurement of circular dichroism of bathorhodopsin.The measurement of circular dichroism of rhodopsin extract (containing 66% or 75% of glycerol) at liquid nitrogen temperatures (?195°C) by a conventional spectropolarimeter induced an extraordinary large signal, owing to linear dichroism originated from conversion of rhodopsin to bathorhodopsin by the measuring light. The similar linear dichroism can be induced by irradiation of rhodopsin extract at ?195°C with polarized light or natural light. At photosteady state the linear dichroism disappeared.Circular dichroism spectrum of cattle rhodopsin displayed two positive peaks ([θ]_max = 80 800 degrees at 335 nm, and [θ]_max = 42 600 degrees at 500 nm) at ?195°C, whereas, bathorhodopsin displayed a positive peak ([θ]_max = 43 100 degrees at 334 nm) and a negative peak ([θ]_max = 163 000 degrees at 540 nm).The change of the positive sign to negative one at α-band of circular dichroism spectrum supports the hypothesis that the conversion of rhodopsin is due to rotation of the chromophoric retinal about C-11—12 double bond (‘photoisomerization model’).     

Engineering the productivity of recombinant Escherichia coli for limonene formation from glycerol in minimal media

The efficiency and productivity of cellular biocatalysts play a key role in the industrial synthesis of fine and bulk chemicals. This study focuses on optimizing the synthesis of (S)‐limonene from glycerol and glucose as carbon sources using recombinant Escherichia coli. The cyclic monoterpene limonene is extensively used in the fragrance, food, and cosmetic industries. Recently, limonene also gained interest as alternative jet fuel of biological origin. Key parameters that limit the (S)‐limonene yield, related to genetics, physiology, and reaction engineering, were identified. The growth‐dependent production of (S)‐limonene was shown for the first time in minimal media. E. coli BL21 (DE3) was chosen as the preferred host strain, as it showed low acetate formation, fast growth, and high productivity. A two‐liquid phase fed‐batch fermentation with glucose as the sole carbon and energy source resulted in the formation of 700 mg L_org^–1 (S)‐limonene. Specific activities of 75 mU g_cdw^–1 were reached, but decreased relatively quickly. The use of glycerol as a carbon source resulted in a prolonged growth and production phase (specific activities of ≥50 mU g_cdw^–1) leading to a final (S)‐limonene concentration of 2,700 mg L_org^–1. Although geranyl diphosphate (GPP) synthase had a low solubility, its availability appeared not to limit (S)‐limonene formation in vivo under the conditions investigated. GPP rerouting towards endogenous farnesyl diphosphate (FPP) formation also did not limit (S)‐limonene production. The two‐liquid phase fed‐batch setup led to the highest monoterpene concentration obtained with a recombinant microbial biocatalyst to date.     

New Na‐Ion Solid Electrolytes Na4−xSn1−xSbxS4 (0.02 ≤ x ≤ 0.33) for All‐Solid‐State Na‐Ion Batteries

Sulfide Na‐ion solid electrolytes (SEs) are key to enable room‐temperature operable all‐solid‐state Na‐ion batteries that are attractive for large‐scale energy storage applications. To date, few sulfide Na‐ion SEs have been developed and most of the SEs developed contain P and suffer from poor chemical stability. Herein, discovery of a new structural class of tetragonal Na_4?xSn_1?xSb_xS₄ (0.02 ≤ x ≤ 0.33) with space group I4₁/acd is described. The evolution of a new phase, distinctly different from Na₄SnS₄ or Na₃SbS₄, allows fast ionic conduction in 3D pathways (0.2–0.5 mS cm^?1 at 30 °C). Moreover, their excellent air stability and reversible dissolution in water and precipitation are highlighted. Specifically, TiS₂/Na–Sn all‐solid‐state Na‐ion batteries using Na_3.75Sn_0.75Sb_0.25S₄ demonstrates high capacity (201 mA h (g of TiS₂)^?1) with excellent reversibility.     

An FTIR study on the structure of the oxygen-evolving Mn-cluster of Photosystem II in different spin forms of the S2 state

The S₂ state of the oxygen-evolving Mn-cluster of Photosystem II (PS II) is known to have different forms that exhibit the g =2 multiline and g = 4.1 EPR signals. These two spin forms are interconvertible at > 200 K and the relative amplitudes of the two signals are dependent on the species of cryoprotectant and alcohol contained in the medium. Also, it was recently found that the mutiline form can be converted to the g = 4.1 form by absorption of near-infrared light by the Mn-cluster itself at around 150 K [Boussac et al. (1996) Biochemistry 35: 6984–6989]. We have used light-induced Fourier transform infrared (FTIR) difference spectroscopy to study the structural difference in these two S₂ forms. FTIR difference spectra for S₂/S₁ as well as for S₂Q_A ^-/S₁Q_A measured at cryogenic temperatures using PS II membranes in the presence of various cryoprotectants, and monohydric alcohols did not show any specific differences except for intensities of amide I bands, which were larger when ethylene glycol or glycerol was present in addition to sucrose. This result was interpreted due to more flexible movement of the protein backbones upon S₂ formation with a higher cryoprotectant content. Light-induced difference spectra measured at 150 K using either blue light without near-infrared light or red plus near-infrared light also did not show any detectable difference. In addition, a different spectrum upon near-infrared illumination at 150 K of the PS II sample in which the S₂ state had been photogenerated at 200 K exhibited no meaningful signals. These results indicate that the two S₂ forms that give rise to the multiline and g = 4.1 signals have only minor differences, if any, in the structures of amino-acid ligands and polypeptide backbones. This conclusion suggests that conversion between the two spin states is caused by a spin-state transition in the Mn(III) ion rather than valence swapping within the Mn-cluster that would considerably affect the vibrations of ligands.This revised version was published online in October 2005 with corrections to the Cover Date.     

A link between rhodopsin and disc membrane cyclic nucleotide phosphodiesterase. Action spectrum and sensitivity to illumination.

Frog (Rana pipiens) rod outer segment disc membranes contain guanosine 3',5'-cyclic monophosphate phosphodiesterase (EC 3.1.4.1.c) which, in the presence of ATP, is stimulated 5- to 20-fold by illumination. The effectiveness of monochromatic light of different wavelengths in activating phosphodiesterase was examined. The action spectrum has a maximum of 500 nm, and the entire spectrum from 350 to 800 nm closely matches the absorption spectrum of rhodopsin, which is apparently the pigment which mediates the effects of light on phosphodiesterase activity. trans-Retinal alone does not mimic light. Half-maximal activation of the phosphodiesterase occurs with a light exposure which bleaches 1/2000 of the rhodopsins. Half-maximal activation can also be achieved by mixing 1 part of illuminated disc membranes in which the rhodopsin is bleached with 99 parts of unilluminated membranes. Regeneration of bleached rhodopsin by addition of 11-cis-retinal is illuminated disc membranes reverses the ability of these membranes to activate phosphodiesterase in unilluminated membranes. If the rhodopsin regenerated by 11-cis-retinal is illuminated again, it regains the ability to activate phosphodiesterase. These studies show that the levels of cyclic nucleotides in vetebrate rod outer segments are regulated by minute amounts of light and clearly indicate that rhodopsin is the photopigment whose state of illumination is closely linked to the enzymatic activity of disc membrane phosphodiesterase.     

Factors underlying genotypic differences in the induction of photosynthesis in soybean [Glycine max (L.) Merr.]

Crop leaves are subject to continually changing light levels in the field. Photosynthetic efficiency of a crop canopy and productivity will depend significantly on how quickly a leaf can acclimate to a change. One measure of speed of response is the rate of photosynthesis increase toward its steady state on transition from low to high light. This rate was measured for seven genotypes of soybean [Glycine max (L.) Merr.]. After 10 min of illumination, cultivar ‘UA4805’ (UA) had achieved a leaf photosynthetic rate (P_n) of 23.2 μmol · m^?2 · s^?1, close to its steady‐state rate, while the slowest cultivar ‘Tachinagaha’ (Tc) had only reached 13.0 μmol · m^?2 · s^?1 and was still many minutes from obtaining steady state. This difference was further investigated by examining induction at a range of carbon dioxide concentrations. Applying a biochemical model of limitations to photosynthesis to the responses of P_n to intercellular CO₂ concentration (C_i), it was found that the speed of apparent in vivo activation of ribulose‐1:5‐bisphosphate carboxylase/oxygenase (Rubisco) was responsible for this difference. Sequence analysis of the Rubisco activase gene revealed single nucleotide polymorphisms that could relate to this difference. The results show a potential route for selection of cultivars with increased photosynthetic efficiency in fluctuating light.     

Standard metabolism and growth dynamics of laboratory‐reared larvae of Sardina pilchardus

This study provides the first measurements of the standard respiration rate (R_S) and growth dynamics of European sardine Sardina pilchardus larvae reared in the laboratory. At 15° C, the relationship between R_S (µl O₂ individual^?1 h^?1) and larval dry mass (M_D, µg) was equal to: R_S = 0·0057(±0·0007, ± s.e.)·M_D^{0·8835(±0·0268)}, (8–11% M_D day^?1). Interindividual differences in R_S were not related to interindividual differences in growth rate or somatic (Fulton's condition factor) or biochemical‐based condition (RNA:DNA).     

Assessment of spectroscopic parameters of solvated Eu(dmh)3phen organometallic complex in various basic and acidic solvents

We report on the comprehension of novel europium activated hybrid organic Eu(dmh)₃phen (Eu: europium, dmh: 2,6‐dimethyl‐3,5‐heptanedione, phen: 1,10 phenanthroline) organo‐metallic complexes, synthesized at different pH values by the solution technique. Photo physical properties of these complexes in various basic and acidic solvents were probed by UV–vis optical absorption and photoluminescence (PL) spectra. Minute differences in optical absorption peaks with variable optical densities were encountered with the variation in solvent from basic (chloroform, toluene, tetrahydrofuran) to acidic (acetic acid) media, revealing bathochromic shift in the absorption peaks. The PL spectra of the complex in various acidic and basic organic solvents revealed the position of the emission peak at 613 nm irrespective of the changes in solvents whereas the excitation spectrum almost matched with that of the UV–vis absorption data. The optical density was found to be maximum for the complex with pH 7.0 whereas it gradually decreased when pH was lowered to 6.0 or raised to 8.0 at an interval of 0.5, demonstrating its pH sensitive nature. Several spectroscopic parameters related to probability of transition such as absorbance A(λ), Napierian absorption coefficient α(λ), molecular absorption cross‐section σ(λ), radiative lifetime (τ₀) and oscillator strength (f) were calculated from UV–vis spectra. The relative intensity ratio (R‐ratio), calculated from the emission spectra was found to be almost the same in all the organic solvents. The optical energy gap, calculated for the designed complexes were found to be well in accordance with the ideal acceptance value of energy gap of the emissive materials used for fabrication of red organic light‐emitting diode (OLED). The relation between Stoke's shift and solvent polarity function was established by Lippert–Mataga plot. This remarkable independence of the electronic absorption spectra of Eu complexes on the nature of the solvent with unique emission wavelength furnishes its potential to serve as a red light emitter for solution processed OLEDs, display panels and solid‐state lighting.     

Low-temperature modulation of the redox properties of the acceptor side of photosystem II: photoprotection through reaction centre quenching of excess energy

Although it has been well established that acclimation to low growth temperatures is strongly correlated with an increased proportion of reduced Q_A in all photosynthetic groups, the precise mechanism controlling the redox state of Q_A and its physiological significance in developing cold tolerance in photoautotrophs has not been fully elucidated. Our recent thermoluminescence (TL) measurements of the acceptor site of PSII have revealed that short‐term exposure of the cyanobacterium Synechococcus sp. PCC 7942 to cold stress, overwintering of Scots pine (Pinus sylvestris L.), and acclimation of Arabidopsis plants to low growth temperatures, all caused a substantial shift in the characteristic T_M of S₂Q_B^– recombination to lower temperatures. These changes were accompanied by much lower overall TL emission, restricted electron transfer between Q_A and Q_B, and in Arabidopsis by a shift of the S₂Q_A^–‐related peak to higher temperatures. The shifts in recombination temperatures are indicative of a lower activation energy for the S₂Q_B^– redox pair and a higher activation energy for the S₂Q_A^– redox pair. This results in an increase in the free‐energy gap between P680⁺Q_A^– and P680⁺Pheo^– and a narrowing of the free energy gap between Q_A and Q_B electron acceptors. We propose that these effects result in an increased population of reduced Q_A (Q_A^–), facilitating non‐radiative P680⁺Q_A^– radical pair recombination within the PSII reaction centre. The proposed reaction centre quenching could be an important protective mechanism in cyanobacteria in which antenna and zeaxanthin cycle‐dependent quenching are not present. In herbaceous plants, the enhanced capacity for dissipation of excess light energy via PSII reaction centre quenching following cold acclimation may complement their capacity for increased utilization of absorbed light through CO₂ assimilation and carbon metabolism. During overwintering of evergreens, when photosynthesis is inhibited, PSII reaction centre quenching may complement non‐photochemical quenching within the light‐harvesting antenna when zeaxanthin cycle‐dependent energy quenching is thermodynamically restricted by low temperatures. We suggest that PSII reaction centre quenching is a significant mechanism enabling cold‐acclimated organisms to acquire increased resistance to high light.     

Soil respiration in six temperate forests in China

Scaling soil respiration (R_S), the major CO₂ source to the atmosphere from terrestrial ecosystems, from chamber‐based measurements to ecosystems requires studies on variations and correlations of R_S from various biomes and across geographic regions. However, few studies on R_S are available for Chinese temperate forest despite the importance of this forest in the national and global carbon budgets. In this study, we conducted 18‐month R_S measurements during 2004–2005 in six temperate forest types, representing the typical secondary forest ecosystems across various site conditions in northeastern China: Mongolian oak (Quercus mongolica Fisch.), aspen‐birch (Populous davidiana Dode and Betula platyphylla Suk.), mixed deciduous (no dominant tree species), hardwood (dominated by Fraxinus mandshurica Rupr., Juglans mandshurica Maxim., and Phellodendron amurense Rupr.) forests, Korean pine (Pinus koraiensis Sieb. et Zucc.) and Dahurian larch (Larix gmelinii Rupr.) plantations. Our specific objectives were to: (1) explore relationships of R_S against soil temperature and water content for the six forest ecosystems, (2) quantify annual soil surface CO₂ flux and its relations to belowground carbon storage, (3) examine seasonal variations in R_S and related environmental factors, and (4) quantify among‐ and within‐ecosystem variations in R_S. The R_S was positively correlated to soil temperature in all forest types, and was significantly influenced by the interactions of soil temperature and water content in the pine, larch, and mixed deciduous forests. The sensitivity of R_S to soil temperature at 10 cm depth (Q₁₀) ranged from 2.61 in the oak forest to 3.75 in the aspen‐birch forests. The Q₁₀ tended to increase with soil water content until reaching a threshold, and then decline. The annual R_S for the larch, pine, hardwood, oak, mixed deciduous, and aspen‐birch forests averaged 403, 514, 781, 785, 786, and 813 g C m^?2 yr^?1, respectively. The annual R_S of the broadleaved forests was 72% greater than that of the coniferous forests. The annual R_S was positively correlated to soil organic carbon (SOC) concentration at O horizon (R²=0.868) and total biomass of roots <0.5 cm in diameter (R²=0.748). The coefficient of variation (CV) of R_S among forest types averaged 25% across the 18‐month measurements. The CV of R_S within plots varied from 20% to 27%, significantly (P<0.001) greater than those among plots (9–15%), indicating the importance of the fine‐scaled heterogeneity in R_S. This study emphasized that variations in soil respiration and potential sampling bias should be appropriately tackled for accurate soil CO₂ flux estimates.     

Parsing redox potentials of five ferredoxins found within Thermotoga maritima

Most organisms contain multiple soluble protein‐based redox carriers such as members of the ferredoxin (Fd) family, that contain one or more iron–sulfur clusters. The potential redundancy of Fd proteins is poorly understood, particularly in connection to the ability of Fd proteins to deliver reducing equivalents to members of the “radical SAM,” or S‐adenosylmethionine radical enzyme (ARE) superfamily, where the activity of all known AREs requires that an essential iron–sulfur cluster bound by the enzyme be reduced to the catalytically relevant [Fe₄S₄]¹⁺ oxidation state. As it is still unclear whether a single Fd in a given organism is specific to individual redox partners, we have examined the five Fd proteins found within Thermotoga maritima via direct electrochemistry, to compare them in a side‐by‐side fashion for the first time. While a single [Fe₄S₄]‐cluster bearing Fd (TM0927) has a potential of ?420 mV, the other four 2x[Fe₄S₄]‐bearing Fds (TM1175, TM1289, TM1533, and TM1815) have potentials that vary significantly, including cases where the two clusters of the same Fd are essentially coincident (e.g., TM1175) and those where the potentials are well separate (TM1815).