A Low‐Temperature Thin‐Film Encapsulation for Enhanced Stability of a Highly Efficient Perovskite Solar Cell

The stability of a perovskite solar cell (PSC) is enhanced significantly by applying a customized thin‐film encapsulation (TFE). The TFE is composed of a multilayer stack of organic/inorganic layers deposited by initiated chemical vapor deposition and atomic layer deposition, respectively, whose water vapor transmission rate is on the order of 10^?4 g m^?2 d^?1 at an accelerated condition of 38 °C and 90% relative humidity (RH). The TFE is optimized, taking into consideration various aspects of thermosensitive PSCs. Lowering the process temperature is one of the most effective methods for minimizing the thermal damage to the PSC during the monolithic integration of the TFE onto PSC. The direct deposition of TFE onto a PSC causes less than 0.3% degradation (from 18.5% to 18.2%) in the power conversion efficiency, while the long‐term stability is substantially improved; the PSC retains 97% of its original efficiency after a 300 h exposure to an accelerated condition of 50 °C and 50% RH, confirming the enhanced stability of the PSC against moisture. This is the first demonstration of a TFE applied directly onto PSCs in a damage‐free manner, which will be a powerful tool for the development of highly stable PSCs with high efficiency.     

Negligible‐Pb‐Waste and Upscalable Perovskite Deposition Technology for High‐Operational‐Stability Perovskite Solar Modules

An upscalable perovskite film deposition method combining raster ultrasonic spray coating and chemical vapor deposition is reported. This method overcomes the coating size limitation of the existing stationary spray, single‐pass spray, and spin‐coating methods. In contrast with the spin‐coating method (>90% Pb waste), negligible Pb waste during PbI₂ deposition makes this method more environmentally friendly. Outstanding film uniformity across the entire area of 5 cm × 5 cm is confirmed by both large‐area compatible characterization methods (electroluminescence and scattered light imaging) and local characterization methods (atomic force microscopy, scanning electron microscopy, photoluminescence mapping, UV–vis, and X‐ray diffraction measurements on multiple sample locations), resulting in low solar cell performance decrease upon increasing device area. With the FAPb(I_0.85Br_0.15)₃ (FA = formamidinium) perovskite layer deposited by this method, champion solar modules show a power conversion efficiency of 14.7% on an active area of 12.0 cm² and an outstanding shelf stability (only 3.6% relative power conversion efficiency decay after 3600 h aging). Under continuous operation (1 sun light illumination, maximum power point condition, dry N₂ atmosphere with <5% relative humidity, no encapsulation), the devices show high light‐soaking stability corresponding to an average T₈₀ lifetime of 535 h on the small‐area solar cells and 388 h on the solar module.     

Depositional fluxes and sources of particulate carbon and nitrogen in natural lakes and a young boreal reservoir in Northern Québec

We investigated the depositional trends of total particles, carbon and nitrogen in a newly created, 600-km² hydroelectric reservoir in Northern Québec, and compared the results with those observed in lakes of the surrounding region. We show that particulate fluxes exhibit a large degree of spatial heterogeneity in both the reservoir (68–548 mg POC m^?2 d^?1 and 5–33 mg PN m^?2 d^?1) and the natural lakes (30–150 mg POC m^?2 d^?1 and 3–12 mg PN m^?2 d^?1) and that on average, settling fluxes of the reservoir (211 ± 46 mg POC m^?2 d^?1 and 14 ± 3 mg PN m^?2 d^?1) exceeded lake deposition (79 ± 13 mg POC m^?2 d^?1 and 7 ± 1 mg PN m^?2 d^?1) by approximately two-fold. Our results also show that the nature of the organic matter reaching the sediments was significantly different between lakes and the reservoir, which can have consequences for benthic metabolism and the long-term storage. We found that sinking fluxes in the reservoir were mostly regulated by local morphological and hydrological conditions, with higher fluxes along or in the vicinity of the old riverbed (average 400 ± 73 mg POC m^?2 d^?1 and 24 ± 5 mg PN m^?2 d^?1) and lower fluxes in calmer zones such as side bays (average 106 ± 10 mg POC m^?2 d^?1 and 8 ± 1 mg PN m^?2 d^?1). In lakes, where settling fluxes were not linked to the trophy, or dissolved organic carbon, the actual nature of the sedimenting organic material was influenced by lake morphometry and the relative contribution of algal versus terrestrial sources. We conclude that re-suspension and erosion play a major role in shaping the reservoir sinking fluxes which explain both, the higher reservoir deposition and also some of the qualitative differences between the two systems. Despite all these differences, sinking particulate organic carbon fluxes were small and surprisingly similar relative to the surface carbon dioxide emissions in both the reservoir and lakes, representing approximately 16–17 % of the carbon efflux estimated for these same systems in 2008.     

A Cost Analysis of Fully Solution‐Processed ITO‐Free Organic Solar Modules

Organic photovoltaics (OPVs) have become a potential candidate for clean and renewable photovoltaic productions. This work examines the current cost drivers and potential avenues to reduce costs for organic solar modules by constructing a comprehensive bottom‐up cost model. The direct manufacturing cost (MC) and the minimum sustainable price (MSP) for an opaque single solar module (SSM) (MC = 187 ¥ m^?2, MSP = 297 ¥ m^?2) and for a tandem solar module (MC = 224 ¥ m^?2, MSP = 438 ¥ m^?2) are analyzed in detail. Within this calculation, the most expensive layers and processing steps are identified and highlighted. Importantly, the low levelized cost of energy (LCOE) value for an SSM with a 10% power conversion efficiency in a 20‐year range from 0.185 to 0.486 ¥ kWh^?1, with a national average of 0.324 ¥ kWh^?1 in China under an average solar irradiance of 1200 kWh m^?2 year^?1. Moreover, the impact on the cost of alternative materials and constructions, process throughputs, module efficiency, and module lifetime, etc., is presented and avenues to further reduce the MSP and LCOE values are indicated. The analysis shows that OPVs can emerge as a competitive alternative to established power generation technologies if the remaining issues (e.g., active layer material cost, module efficiency, and lifetime) can be resolved.     

Low Substrate Temperature Encapsulation for Flexible Electrodes and Organic Photovoltaics

Encapsulation is of key importance to improve the stability and lifetime of organic conductors and devices, mainly in applications such as flexible electrodes or organic photovoltaics (OPV). Here, a single‐layer conformal encapsulation method is demonstrated via initiated chemical vapor deposition (iCVD) for organic conductor, poly (3,4‐ethylenedioxythiophene) (PEDOT). The accelerated degradation tests at 100 °C show that the conductivity of encapsulated PEDOT can be retained up to 17 times longer than that of the unencapsulated counterpart. PEDOT degradation and encapsulation mechanisms are also discussed. Furthermore, the versatility of the iCVD encapsulation on a top‐illuminated OPV architecture that can be used to produce low‐cost photovoltaics devices on various unconventional substrates (e.g., paper) is demonstrated. Unlike previous approaches of using solely water/oxygen barriers, the encapsulation effect of polymer films on OPV devices is improved by a thin layer capping of evaporated UV‐screening material, Cerium(IV) oxide (CeO₂) over the iCVD polymer layer. This bilayer encapsulation strategy efficiently slows the degradation of OPVs and represents a new method to encapsulate OPV and other organic devices.     

Spine influences on PAR interception, stem temperature, and nocturnal acid accumulation by cacti

Abstract. The influence of spines on nocturnal acid accumulation was examined for two Crassulacean acid metabolism plants, the barrel cactus Ferocactus acanthodes (Lemaire) Britton & Rose var. lecontei (Engelm.) Lindsay and the cylindropuntia Opuntia bigelovii Engelm. var. bigelovii. The ambient photo-synthetically active radiation (PAR) required for 90% saturation of nocturnal acid accumulation by O. bigelovii was 23 mol m^?2 d^?1 for stems that were 32% shaded by spines and 16 mol m^?2 d^?1 when the spines were removed. For F. acanthodes, 90% saturation occurred for an ambient PAR of 45 mol m^?2 d^?1 where the stem was 78% shaded by spines and 21 mol m^?2 d^?1 when the spines were removed. For comparison, the ambient PAR averaged 21 mol m^?2 d^?1 at various times of the year and stem positions for O. bigelovii fully exposed to solar irradiation. Although spines can reflect some PAR toward the stem surface, their presence decreases the PAR incident on the stem surface, thereby decreasing the nocturnal acid accumulation. For O. bigelovii, periodically removing the spines led to a 60% greater increase in stem volume over 2^1/2 years. The effect of variation in spine-shading on stem surface temperature was determined for F. acanthodes using computer simulations and an energy budget model. A substantial reduction in daytime stem temperatures and a smaller increase in night-time temperatures as the spine-shading increased had very little influence on nocturnal acid accumulation for both winter and summer days. Thus, the main effect of spines on the metabolism of cacti is apparently to reduce the PAR incident on the stem surface and thereby to reduce productivity.     

Cobalt Polypyridyl Complexes as Transparent Solution‐Processable Solid‐State Charge Transport Materials

Charge transport materials (CTMs) are traditionally inorganic semiconductors or metals. However, over the past few decades, new classes of solution‐processable CTMs have evolved alongside new concepts for fabricating electronic devices at low cost and with exceptional properties. The vast majority of these novel materials are organic compounds and the use of transition metal complexes in electronic applications remains largely unexplored. Here, a solution‐processable solid‐state charge transport material composed of a blend of [Co(bpyPY4)](OTf)₂ and Co(bpyPY4)](OTf)₃ where bpyPY4 is the hexadentate ligand 6,6′‐bis(1,1‐di(pyridin‐2‐yl)ethyl)‐2,2′‐bipyridine and OTf^? is the trifluoromethanesulfonate anion is reported. Surprisingly, these films exhibit a negative temperature coefficient of conductivity (dσ/dT) and non‐Arrhenius behavior, with respectable solid‐state conductivities of 3.0 S m^?1 at room temperature and 7.4 S m^?1 at 4.5 K. When employed as a CTM in a solid‐state dye‐sensitized solar cell, these largely amorphous, transparent films afford impressive solar energy conversion efficiencies of up to 5.7%. Organic–inorganic hybrid materials with negative temperature coefficients of conductivity generally feature extended flat π‐systems with strong π–π interactions or high crystallinity. The lack of these features promotes [Co(bpyPY4)](OTf)_{2+ x} films as a new class of CTMs with a unique charge transport mechanism that remains to be explored.     

CO2 Supersaturation and Net Heterotrophy in a Tropical Estuary (Cochin, India): Influence of Anthropogenic Effect

Carbon biogeochemistry of a tropical ecosystem (The Cochin Estuary, India) undergoing increased human intervention was studied during February (premonsoon), April (early monsoon) and September (monsoon) 2005. The Cochin estuary sustains high levels of pCO₂ (up to 6000 μatm) and CO₂ effluxes (up to 274 mmolC m^?2 d^?1) especially during monsoon. A first-order estimate of the carbon mass balance shows that net production of dissolved inorganic carbon is an order of magnitude higher than the net loss of dissolved and particulate organic carbon from the estuary. This imbalance is attributed to the organic inputs to the estuary through anthropogenic supplies. The bacteria-mediated mineralization of organic matter is mainly responsible for the build-up of pCO₂ and increased CO₂ emission to the atmosphere indicating heterotrophy. The linear correlation between excess CO₂ and apparent oxygen utilization indicates respiration as the chief mechanism for CO₂ supersaturation. An increase in the net negative ecosystem production (–ve NEP) between premonsoon (?136 mmolC m^?2 d^?1 or ?376 MgC d^?1) and monsoon (?541 mmolC m^?2 d^?1 or ?1500 MgC d^?1) is supported by a corresponding increase in O₂ influxes from 17 mmol O₂ m^?2 d^?1 (126 MgC d^?1) to ?128 mmol O₂ m^?2 d^?1 (?946 MgC d^?1) and CO₂ emissions from 65 mmolC m^?2 d^?1 (180 MgC d^?1) to 267 mmolC m^?2 d^?1 (740 MgC d^?1). There is a significant north-south gradient in metabolic rates and CO₂ fluxes attributable to the varying flow patterns and anthropogenic inputs into the estuary. The study reveals that the Cochin estuary, a previously autotrophic (CO₂ sink) system, has been transformed to a heterotrophic (CO₂ source) system following rapid urbanization and industrialization. Moreover, the export fluxes from the Cochin estuary appear to be quite important in sustaining net heterotrophy in the southeastern Arabian Sea.     

Irradiance optimization of outdoor microalgal cultures using solar tracked photobioreactors

Photosynthetic activity and temperature regulation of microalgal cultures (Chlorella vulgaris and Scenedesmus obliquus) under different irradiances controlled by a solar tracker and different cell densities were studied in outdoor flat panel photobioreactors. An automated process control unit regulated light and temperature as well as pH value and nutrient concentration in the culture medium. CO₂ was supplied using flue gas from an attached combined block heat and power station. Photosynthetic activity was determined by pulse amplitude modulation fluorometry. Compared to the horizontal irradiance of 55 mol photons m^?2 d^?1 on a clear day, the solar tracked photobioreactors enabled a decrease and increase in the overall light absorption from 19 mol photons m^?2 d^?1 (by rotation out of direct irradiance) to 79 mol photons m^?2 d^?1 (following the position of the sun). At biomass concentrations below 1.1 g cell dry weight (CDW) L^?1, photoinhibition of about 35 % occurred at irradiances of ≥1,000 μmol photons m^?2 s^?1 photosynthetic active radiation (PAR). Using solar tracked photobioreactors, photoinhibition can be reduced and at optimum biomass concentration (≥2.3 g CDW L^?1), the culture was irradiated up to 2,000 μmol photons m^?2 s^?1 to overcome light limitation with biomass yields of 0.7 g CDW mol photons^?1 and high photosynthetic activities indicated by an effective quantum yield of 0.68 and a maximum quantum yield of 0.80 (F _v/F _m). Overheating due to high irradiance was avoided by turning the PBR out of the sun or using a cooling system, which maintained the temperature close to the species-specific temperature optima.     

Effects of organic matter availability on the life history and production of a top vertebrate predator (Plethodontidae: Gyrinophilus palleucus) in two cave streams

1. Surface ecosystems provide the primary source of organic matter to many cave communities. Variation in the strength of connectivity to the surface suggests that some caves may be more resource‐limited than others. To test this, we examined diet, prey availability and production of an obligate cave salamander Gyrinophilus palleucus (Plethodontidae), a top predator, in two south‐eastern U.S.A. caves with different levels of organic matter (Tony Sinks cave, 165 g AFDM m^?2; Bluff River cave, 62 g AFDM m^?2). 2. We quantified density, biomass, growth rate, production and diet of G. palleucus monthly for 21 months. Diet composition, differences in prey communities and seasonal patterns in prey consumption were also analysed. 3. Salamander density, biomass and secondary production were significantly greater in the high organic matter cave (0.10 m^?2, 0.18 g AFDM m^?2, 0.12 g AFDM m^?2 year^?1) than in the low organic matter cave (0.03 m^?2, 0.03 g AFDM m^?2, 0.01 g AFDM m^?2 year^?1). Although growth rates were not statistically different between the two cave salamander populations, low recaptures probably influenced this result. 4. Isopoda prey were the major contributor to salamander production in the high organic matter cave (69%). In the low organic matter cave, production was provided by isopods (41%) and oligochaetes (20%). The lower number of prey taxa contributing to salamander production in the high organic matter cave suggests the ability to forage more selectively. 5. The differences in foraging strategy, density, biomass and secondary production were probably related to differences in the strength of surface connectivity, which controls organic matter supply. Links between basal resource level and top predator performance show the importance of bottom‐up limitation in the food webs of caves and other detritus‐based ecosystems.     

Composition Engineering in Doctor‐Blading of Perovskite Solar Cells

Organic–inorganic halide perovskite (OIHP) solar cells with efficiency over 18% power conversion efficiency (PCE) have been widely achieved with lab scale spin‐coating method which is however not scalable for the fabrication of large area solar panels. The PCEs of OIHP solar cells made by scalable deposition methods, such as doctor‐blading or slot‐die coating, have been lagging far behind than spin‐coated devices. In this study the authors report composition engineering in doctor‐bladed OIHP solar cells with p–i–n planar heterojunction structure to enhance their efficiency. Phase purer OIHP thin films are obtained by incorporating a small amount of cesium (Cs⁺) and bromine (Br^?) ions into perovskite precursor solution, which also reduces the required film formation temperature. Pinhole free OIHP thin films with micrometer‐sized grains have been obtained assisted by a secondary grain growth with added methylammonium chloride into the precursor solution. The OIHP solar cells using these bladed thin films achieved PCEs over 19.0%, with the best stabilized PCE reaching 19.3%. This represents a significant step toward scalable manufacture of OIHP solar cells.     

Impermeable Charge Transport Layers Enable Aqueous Processing on Top of Perovskite Solar Cells

Several applications of perovskite solar cells (PSCs) demand a semitransparent top electrode to afford top‐illumination or see‐through devices. Transparent conductive oxides, such as indium tin oxide (ITO), typically require postdeposition annealing at elevated temperatures, which would thermally decompose the perovskite. In contrast, silver nanowires (AgNWs) in dispersions of water would be a very attractive alternative that can be deposited at ambient conditions. Water is environmentally friendly without safety concerns associated with alcohols, such as flammability. Due to the notorious moisture sensitivity of lead‐halide perovskites, aqueous processing of functional layers, such as electrodes, on top of a perovskite device stack is elusive. Here, impermeable electron transport layers (ETLs) are shown to enable the deposition of semitransparent AgNW electrodes from green aqueous dispersions on top of the perovskite cell without damage. The polyvinylpyrrolidone (PVP) capping agent of the AgNWs is found to cause a work–function shift and an energy barrier between the AgNWs and the adjacent ETL. Thus, a high carrier density (≈10¹⁸ cm^?3) in the ETL is required to achieve well‐behaved J/V characteristics free of s‐shapes. Ultimately, semitransparent PSCs are demonstrated that provide an efficiency of 17.4%, which is the highest efficiency of semitransparent p‐i‐n perovskite solar cells with an AgNW top electrode.     

Organic Carbon Degradation in Anoxic Organic-Rich Shelf Sediments: Biogeochemical Rates and Microbial Abundance

Identifying and explaining bottlenecks in organic carbon mineralization and the persistence of organic matter in marine sediments remain challenging. This study aims to illuminate the process of carbon flow between microorganisms involved in the sedimentary microbial food chain in anoxic, organic-rich sediments of the central Namibian upwelling system, using biogeochemical rate measurements and abundances of Bacteroidetes, Gammaproteobacteria, and sulfate-reducing bacteria at two sampling stations. Sulfate reduction rates decreased by three orders of magnitude in the top 20 cm at one sampling station (280 nmol cm^?3 d^?1 – 0.1 nmol cm^?3 d^?1) and by a factor of 7 at the second station (65 nmol cm^?3 d^?1 – 9.6 nmol cm^?3 d^?1). However, rates of enzymatic hydrolysis decreased by less than a factor of three at both sampling stations for the polysaccharides laminarin (23 nmol cm^?3 d^?1– 8 nmol cm^?3 d^?1 and 22 nmol cm^?3 d^?1– 10 nmol cm^?3 d^?1) and pullulan (11 nmol cm^?3 d^?1– 4 nmol cm^?3 d^?1 and 8 nmol cm^?3 d^?1– 6 nmol cm^?3 d^?1). Increasing imbalance between carbon turnover by hydrolysis and terminal oxidation with depth, the steep decrease in cell specific activity of sulfate reducing bacteria with depth, low concentrations of volatile fatty acids (less than 15 μM), and persistence of dissolved organic carbon, suggest decreasing bioavailability and substrate limitation with depth.     

Optimization of Electrodeposited p‐Doped Sb2Te3 Thermoelectric Films by Millisecond Potentiostatic Pulses

A systematic optimization of p‐type Sb₂Te₃ thermoelectric films made by potentiostatic electrodeposition on Au and stainless steel substrates is presented. The influence of the preparative parameters of deposition voltage, concentration, and the deposition method are investigated in a nitric acid solution. As a postdeposition step, the influence of annealing the films is investigated. The use of a potential‐controlled millisecond‐pulsed deposition method could improve both the morphology and the composition of the films. The samples are characterized in terms of composition, crystallinity, Seebeck coefficient, and electrical resistivity. Pulsed‐deposited films exhibit Seebeck coefficients of up to 160 μV K^?1 and an electrical conductivity of 280 S cm^?1 at room temperature, resulting in power factors of about 700 μW m^?1 K^?2. After annealing, power factors of maximum 852 μW m^?1 K^?2 are achieved. Although the annealing of DC‐deposited films significantly increased the power factor, they do not reach the values of the pulsed‐deposited films in the preannealing state. Structural analysis is performed with X‐ray diffraction and shows the crystalline structure of Sb₂Te₃ films. The performance is tuned by annealing of deposited films up to 300 °C under He atmosphere while performing in‐situ X‐ray diffraction and resistivity measurements. The chemical analysis of the films is performed by inductively coupled plasma optical emission spectroscopy (ICP‐OES) as well as scanning electron microscope energy dispersive X‐ray analysis (SEM‐EDX).     

Optimizations of Pulsed Plated p and n‐type Bi2Te3‐Based Ternary Compounds by Annealing in Different Ambient Atmospheres

This work presents a comprehensive study of the fabrication and optimization of electrodeposited p‐ and n‐type thermoelectric films. The films are deposited on Au and stainless steel substrates over a wide range of deposition potentials. The influence of the preparative parameters such as the composition of the electrolyte bath and the deposition potential are investigated. Furthermore, the p‐doped (Bi_xSb_1‐x)₂Te₃ and the n‐doped Bi₂(Te_xSe_1‐x)₃ films are annealed for a period of about 1 h under helium and under tellurium atmosphere at 250 °C for 60h. Annealing in He already leads to significant improvements in the thermoelectric performance. Furthermore, due to the equilibrium conditions during the process, annealing in Te atmosphere leads to a strongly improved film composition, charge carrier density and mobility. The Seebeck coefficients increase to values up to +182 μV K^?1 for p‐doped and–130 μV K^?1 for n‐doped materials at room temperature. The power factors also exhibit improvements with 1320 μW m^?1 K^?2 and 820 μW m^?1 K^?2 for p‐doped and n‐doped films, respectively. Additionally, in‐situ XRD measurements performed during annealing of the films up to 600K under He atmosphere show stepwise improvements of the crystal structure leading to the improvements in thermoelectric parameters. The thermal conductivity is between 1.2 W m^?1 K^?1 and 1.0 W m^?1 K^?1.     

Comparison of RNA- and DNA-based bacterial communities in a lab-scale methane-degrading biocover

Methanotrophs must become established and active in a landfill biocover for successful methane oxidation. A lab-scale biocover with a soil mixture was operated for removal of methane and nonmethane volatile organic compounds, such as dimethyl sulfide (DMS), benzene (B), and toluene (T). The methane elimination capacity was 211?±?40 g?m^?2 d^?1 at inlet loads of 330–516 g?m^?2 d^?1. DMS, B, and T were completely removed at the bottom layer (40–50 cm) with inlet loads of 221.6?±?92.2, 99.6?±?19.5, and 23.4?±?4.9 mg m^?2 d^?1, respectively. The bacterial community was examined based on DNA and RNA using ribosomal tag pyrosequencing. Interestingly, methanotrophs comprised 80 % of the active community (RNA) while 29 % of the counterpart (DNA). Types I and II methanotrophs equally contributed to methane oxidation, and Methylobacter, Methylocaldum, and Methylocystis were dominant in both communities. The DNA vs. RNA comparison suggests that DNA-based analysis alone can lead to a significant underestimation of active members.     

Soil N and C trace gas fluxes and microbial soil N turnover in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary

During two intensive field campaigns in summer and autumn 2004 nitrogen (N₂O, NO/NO₂) and carbon (CO₂, CH₄) trace gas exchange between soil and the atmosphere was measured in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N₂O emission rates were 1.5 μg N m⁻² h⁻¹ in summer and 3.4 μg N m⁻² h⁻¹ in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m⁻² h⁻¹) as compared to summer (6.0 μg N m⁻² h⁻¹). However, as NO₂ deposition rates continuously exceeded NO emission rates (−9.7 μg N m⁻² h⁻¹ in summer and −18.3 μg N m⁻² h⁻¹ in autumn), the forest soil always acted as a net NO _x sink. The mean value of CO₂ fluxes showed only little seasonal differences between summer (81.1 mg C m⁻² h⁻¹) and autumn (74.2 mg C m⁻² h⁻¹) measurements, likewise CH₄uptake (summer: −52.6 μg C m⁻² h⁻¹; autumn: −56.5 μg C m⁻² h⁻¹). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N₂O/CH₄ soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO_{2 resp} ΔO_{2 resp}⁻¹) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg⁻¹ SDW d⁻¹) and autumn measurements (0.89 μg N kg⁻¹ SDW d⁻¹). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg⁻¹ SDW d⁻¹) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg⁻¹ SDW d⁻¹). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N₂O emissions and negatively correlated with CH₄ uptake, whereas soil CO₂ emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn.     

A closed solar photobioreactor for cultivation of microalgae under supra-high irradiance: basic design and performance

An account is given of the setting up and use of a novel type of closed tubular photobioreactor at the Academic and University Centre in Nove Hrady, Czech Republic. This "penthouse-roof" photobioreactor was based on solar concentrators (linear Fresnel lenses) mounted in a climate-controlled greenhouse on top of the laboratory complex combining features of indoor and outdoor cultivation units. The dual-purpose system was designed for algal biomass production in temperate climate zone under well-controlled cultivation conditions and with surplus solar energy being used for heating service water. The system was used to study the strategy of microalgal acclimation to supra-high solar irradiance, with values as much as 3.5 times the ambient value, making the approach unique. The cultivation system proved to be fully functional with sufficient mixing and cooling, efficient oxygen stripping and light tracking. Experimental results (measurement of the maximum photochemical yield of PSII and non-photochemical quenching) showed that the cyanobacterium Spirulina (= Arthrospira) platensis cultivated under sufficient turbulence and biomass density was able to acclimate to irradiance values as high as 7 mmol photon m^–2 s^–1. The optimal biomass concentration of Spirulina cultures in September ranged between 1.2 to 2.2 g L^–1, which resulted in a net productivity of about 0.5 g L^–1 d^–1 corresponding to a biomass yield of 32.5 g m^–2 d^–1 (based on the minimum illuminated surface area of the photobioreactor).     

Uptake of inorganic and organic nutrient species during cultivation of a Chlorella isolate in anaerobically digested dairy waste

A natural assemblage of microalgae from a facultative lagoon system treating municipal wastewater was enriched for growth in the effluents of an anaerobic digester processing dairy waste. A green microalga with close resemblance to Chlorella sp. was found to be dominant after multiple cycles of sub‐culturing. Subsequently, the strain (designated as LLAI) was isolated and cultivated in 20× diluted digester effluents under various incident light intensities (255–1,100 µmoles m^?2 s^?1) to systematically assess growth and nutrient utilization. Our results showed that LLAI production increased with increasing incident light and a maximum productivity of 0.34 g L^?1 d^?1 was attained when the incident irradiance was 1,100 µmoles m^?2 s^?1. Lack of growth in the absence of light indicated that the cultures did not grow heterotrophically on the organic compounds present in the medium. However, the cultures were able to uptake organic N and P under phototrophic conditions and our calculations suggest that the carbon associated with these organic nutrients contributed significantly to the production of biomass. Overall, under high light conditions, LLAI cultures utilized half of the soluble organic nitrogen and >90% of the ammonium, orthophosphate, and dissolved organic phosphorus present in the diluted waste. Strain LLAI was also found to accumulate triacylglycerides (TAG) even before the onset of nutrient limitation and a lipid productivity of 37 mg‐TAG L^?1 d^?1 was measured in cultures incubated at an incident irradiance of 1,100 µmoles m^?2 s^?1. The results of this study suggest that microalgae isolates from natural environments are well‐suited for nutrient remediation and biomass production from wastewater containing diverse inorganic and organic nutrient species. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1336–1342, 2016     

Major changes in forest carbon and nitrogen cycling caused by declining sulphur deposition

Sulphur (S) and nitrogen (N) deposition are important drivers of the terrestrial carbon (C) and N cycling. We analyzed changes in C and N pools in soil and tree biomass at a highly acidified spruce site in the Czech Republic during a 15 year period. Total S deposition decreased from 5 to 1.1 g m^?2 yr^?1 between 1995 and 2009, whereas bulk N deposition did not change. Over the same period, C and N pools in the Oa horizon declined by 116 g C and 4.2 g N m^?2 yr^?1, a total decrease of 47% and 42%, respectively. This loss of C and N probably originated from organic matter (OM) that had accumulated during the period of high acid deposition when litter decomposition was suppressed. The loss of OM from the Oa horizon coincided with a substantial leaching (1.3 g N m^?2 yr^?1 at 90 cm) in the 1990s to almost no leaching (<0.02 g N m^?2 yr^?1) since 2006. Forest floor net N mineralization also decreased. This had consequences for spruce needle N concentration (from 17.1 to 11.4 mg kg^?1 in current needles), an increase in litterfall C/N ratio (from 51 to 63), and a significant increase in the Oi + Oe horizon C/N ratio (from 23.4 to 27.3) between 1994 and 2009/2010. Higher forest growth and lower canopy defoliation was observed in the 2000s compared to the 1990s. Our results demonstrate that reducing S deposition has had a profound impact on forest organic matter cycling, leading to a reversal of historic ecosystem N enrichment, cessation of nitrate leaching, and a major loss of accumulated organic soil C and N stocks. These results have major implications for our understanding of the controls on both N saturation and C sequestration in forests, and other ecosystems, subjected to current or historic S deposition.