Internal Cycling Research Articles

Biotinylation Assay to Determine LFA-1 Recycling in Motile T-Lymphocytes.

The cycles of internalization of the cell surface β2 integrin receptor lymphocyte function-associated antigen 1 (LFA-1) and its re-exposure on the plasma membrane are important for T-cell trafficking. Biotinylation of cells enables to measure surface expression of receptors, and after reducing surface biotin with reducing buffer, enables to measure the internalization of receptors. Here, by using biotin in combination with reducing buffer and recombinant intercellular adhesion molecule-1 (rICAM-1)-coated dishes and subsequent Western immunoblot analysis, we describe how to measure internalization of the LFA-1 receptor and its re-expression back to the cell surface in motile T-lymphocytes.

Spatial distribution of microbial biomass and residues across soil aggregate fractions at different elevations in the Central Austrian Alps

The distribution of microbial biomass and residues and their role in carbon (C) dynamics within soil aggregate fractions in the Alps are still poorly explored. We assessed the distribution of bacterial and fungal residues and their impact on the contribution of the microbial community to C dynamics within soil aggregate size fractions at different elevations. We sampled three sites located at different elevations (1300, 1600 and 2100 m a.s.l.) and subject to different temperature and precipitation regimes in the Central Austrian Alps. Fungal biomass and residues were higher in macro-aggregate fractions compared to micro-aggregates, as indicated by the ratios ergosterol/microbial biomass C and fungal C/bacterial C, suggesting a combined but discrete contribution of fungi and bacterial residues to soil aggregate formation. A greater contribution of microbial residues to soil organic C (SOC) in macro-aggregates demonstrates the importance of microbial residues for the soil organic matter pool's capacity to function as an active nutrient sink and source reservoir. The mid- and low-elevation spruce sites were dominated by fungi and higher aggregate stability, whereas the high-elevation grassland site exhibited a stronger bacterial community as indicated by fungal C/bacterial C ratio. In addition, greater proportions of fungal and bacterial residue in SOC at mid-elevation spruce and high-elevation grassland sites respectively, indicate differential role of fungi and bacteria in SOC sequestration. However, the observed changes in microbial community and residue contribution were mainly driven by variations in soil pH, C/N ratio and fine root biomass. Our findings indicate that fungi played a key role in the internal cycling of SOC and aggregate stability at the mid-elevation spruce site, while bacterial residues were successively activated and contributed increasingly to SOC sequestration at the high-elevation grassland site.

Regional differentiation of foliar N/Ca in Fagus americana and F. sylvatica on acid soils

Prolonged periods of air pollution depleted soil Ca and increased N supply in forests of Eastern North America and Central Europe. We compared a cool rural to a warm urban forest site to explore the geographic range of foliar N, Ca, and N/Ca on naturally regenerated saplings of American beech and European beech in Nova Scotia (Canada) and Saarland (Germany), respectively. Foliar N/Ca of beech saplings remained variable due to geo-climatic gradients and bio-climatic site factors, tight internal cycling of Ca, and varying pollution history. Our data suggest that deep and extreme soil Ca depletion renders climatic factors the drivers of foliar N/Ca in beech forests. Global warming will therefore amplify the potential risks of changing nutrient supply ratios in regions with a prolonged history of severe acid rain. Existing forest site classifications usually capture regional differentiation of climatic factors but often fail to assess impacts of acid rain history on foliar Ca that will be required for regional differentiation of foliar nutrient ratios on acid soils. However, homogenization of foliar Ca can be expected in regions with a history of severe acid rain.

Nutrients in Saltmarsh Soils Are Weakly Related to those in Adjacent Coastal Waters

Saltmarshes provide a broad range of high-value ecosystem services and can be sensitive to eutrophication, but elucidating such impacts at broad spatial scales demands a better understanding of the underlying nutrient linkages between saltmarsh soil and tidal waters. We used existing water quality data and field surveys of 15 saltmarshes across a broad trophic gradient of coastal waters, but similar biogeographic setting (in Ireland) to investigate if phosphorus and nitrogen pools in saltmarsh soils are related to those in tidal water across saltmarshes. We also investigated if the strength of such relationships is inversely related to ground elevation, which approximates the degree of tidal inundation. Plant-available phosphorus and nitrogen pools in soil were related to water nutrients, albeit only weakly. We did not find any support for the moderating influence of elevation, indicating that it may be obscured by internal cycling and external sources. We also found evidence for effect of birds on the saltmarsh nutrient pool. Saltmarsh soils are unlikely to serve as general sentinels of nutrient conditions in their corresponding water bodies and may need separate assessment criteria and management tools, which in turn require disentangling localised and whole-saltmarsh sources of variation in nutrient concentrations.

A MAGIC concept for self-sustained, water-based, ultrafine particle counting

A self-sustaining, motion-tolerant, water-based condensation particle counter (CPC) has been designed, fabricated, and tested. Referred to as “MAGIC” for moderated aerosol growth with internal water cycling, the particle size response is similar to the 5-nm cut-point commercial CPCs. MAGIC is a laminar-flow instrument with three temperature stages: cool, warm, and cool. The middle warm-walled stage initiates the condensational growth and the final cool-walled stage maintains supersaturated conditions while recovering water vapor. By using a continuous wick throughout all three stages, the system recharges itself through a combination of water condensate from the sampled airstream and recovery of water vapor from the peak supersaturation region. A reservoir-less prototype system based on this concept was built and tested. Experiments show equal performance in any orientation, upright or inverted, and tolerance to tipping, shaking and vibrational shocks up to 5 g. Under mild ambient conditions, it provided multi-week operation without replenishing the wick.Copyright © 2018 American Association for Aerosol Research

Effect of organic matter on phosphorus adsorption and desorption in a black soil from Northeast China

Phosphorus (P) adsorption–desorption in soil is an important internal cycle related to soil fertility problems, as well as for determining the environmental fate of P. Soil organic matter (SOM) has been identified as an important factor affecting the adsorption–desorption of soil P through different mechanisms. In this study, humic acids were added to change the SOM content in black soil. Following an incubation period of 30 days, the changes in soil P adsorption–desorption capacity were studied. The results indicated that increased SOM led to increases in the soil available P and the P activation coefficient. All soil treatments fitted well with both Langmuir and Freundlich equations. The P adsorption and desorption characteristics were analyzed using the Langmuir equation as a local isotherm. The maximum adsorption capacity of P increased with the increase in SOM, but the P bonding energy and maximum buffering capacity first decreased, and then increased, with the lowest values obtained with a SOM content of 75.3 mg kg−1. Both the maximum desorption capacity of P and the ratio of soil P desorption showed a fluctuating trend, which were the greatest when the SOM content reached 75.3 g kg−1 in black soil, showing an improved ability to release P. Thus, the addition of organic matter could efficiently enhance P availability by reducing the strength of P adsorption and the maximum phosphate buffering capacity and increasing the desorption of P to some extent, with the greatest P availability obtained at a SOM content of 75.3 g kg−1.

The Internal Cycling of Zinc in the Ocean

AbstractThe internal cycling of zinc (Zn) in the ocean has been a longstanding mystery. Particularly puzzling is the strong correlation between Zn and silicate (SiO44−), but not phosphate (PO43−), even though Zn is involved with cell functions that regulate PO43− uptake and are unrelated to SiO44− uptake. To help solve this mystery, we use an artificial neural network to produce global maps of dissolved Zn, and then use a diagnostic model to infer rates of uptake and regeneration for Zn, SiO44−, and PO43−. We find that plankton in the Southern Ocean account for 62 (±32)% of global Zn uptake. The plankton Zn:PO43− uptake ratio increases by more than tenfold from the low latitudes to the Southern Ocean, a much larger range than expected from culture studies, suggesting controls from factors such as iron availability. Reconstruction of particulate Zn (PZn), phosphorus (PP), and biogenic silica (PSi) fluxes reveals that PZn remineralizes like PP, and not like PSi. However, a small flux of PZn into the deep ocean is not matched by an equivalent flux of PP, which is likely due to the combined effects of desorption of scavenged Zn and the input of hydrothermal Zn in the deep ocean. This small difference in the remineralization of PZn and PP, combined with the patterns of surface uptake, eliminates the correlation between Zn and PO43− in the deep ocean and causes a tight correlation between Zn and SiO44−. This coincidental correlation cannot be expected to hold for past and future states of the ocean.

Seawater Carbonate Chemistry Distributions Across the Eastern South Pacific Ocean Sampled as Part of the GEOTRACES Project and Changes in Marine Carbonate Chemistry Over the Past 20 Years

The US GEOTRACES Eastern Pacific Zonal Transect in 2013 provided an opportunity to complement studies of the sources, sinks, and internal cycling of trace elements and isotopes (TEIs) with observations of seawater carbon dioxide (CO2)–carbonate chemistry. Across the Peru-Tahiti section, very large horizontal gradients in surface/mixed layer dissolved inorganic carbon (DIC) and total alkalinity (TA) from the nutrient-rich, low-oxygen coastal upwelling region adjacent to Peru to the oligotrophic central Pacific. Near the coast of Peru, upwelling of CO2 rich waters from the oxygen deficient zone (ODZ) impinged at the surface with very high partial pressures of CO2 (pCO2; >800-1,200 µatm), and low pH (7.55 to 7.8). These waters were also undersaturated with respect to aragonite, a common calcium carbonate (CaCO3) mineral. These chemical conditions are not conducive to pelagic and shelf calcification, with shelf calcareous sediments vulnerable to CaCO3 dissolution, and to the future impacts of ocean acidification. A comparison to earlier data collected from 1991 to 1994 suggests that surface dissolved inorganic carbon (DIC) and pCO2 have increased by as much as 3% and 20%, respectively, while pH and saturation state for aragonite (Waragonite) have decreased by as much as 0.063 and 0.54, respectively. In intermediate waters (~200-500 m), dissolved oxygen has decreased (loss of up to -43 µmoles kg-1) and nitrate increased (gain of up to 5 µmoles kg-1) over the past twenty years and this likely reflects the westward expansion of the ODZ across the central Eastern South Pacific Ocean. Over the same period, DIC and pCO2 increased by as much as +45 µmoles kg-1 and +145 µatm, respectively, while pH and Waragonite decreased by -0.091 and -0.45, respectively. Such rapid change in pH and CO2–carbonate chemistry over the past twenty years has implications for changing the thermodynamics and solubility of intermediate water TEIs, but also for the marine ecosystem of the upper waters, especially for the vertically migrating community present in the eastern South Pacific.

Effects of Vessel and Water Temperatures on Direct Injection in Internal Combustion Rankine Cycle Engines

This study focused on the effects of vessel and water temperatures on direct injection in internal combustion Rankine cycle engines through experimental and numerical methods. First, a study was carried out with schlieren photography using a high-speed camera for simultaneous liquid–gas diagnoses. Water was directly injected into a constant-volume vessel that provided stable boundaries. We wrote a MATLAB program to calculate spray tip penetration and cone angle from the images. For the further extension of boundary conditions, a numerical model was established and calibrated in AVL-FIRE for the thorough analysis of injection characteristics. Both experimental and numerical results indicated that injection and vessel temperatures have different effects on spray tip penetration. An increase in injected water temperature leads to shorter spray tip penetration, while the spray tip penetration increases with increasing vessel temperature. However, increased injection and vessel temperatures can both decrease the spray cone angle. Moreover, the simulation results also suggested that heat conduction is a main factor in boosting evaporation under top dead center conditions. When the internal energy of water parcels surges, these parcels evaporate immediately. These results are helpful and crucial for internal combustion engines equipped with direct water injection technology.

Validation of a Universal Warming/Dilution Protocol for Frozen Embryo Transfers Independent of Vitrification Device/Cryoprotectant

Objective Validate a universal warming/dilution approach for all vitrification (VTF) solutions associated with various device systems. Design Using a 2 × 2 factorial arrangement of treatments, 124 blastocysts derived from 363 research consented slow frozen embryos were vitrified in Glycerol/ethylene glycol (EG) solution (≥7.9M; I.C.E.) or a 15%DMSO/15%EG solution, and subsequently rapidly warmed and diluted by standard operating procedures (SOP) or a universal sucrose step-down dilution procedure (n = 31 embryos/group). Furthermore, we performed a retrospective analysis of our routine success with microSecure VTF (µS-VTF with Glycerol/EG)/warming to applying a universal sucrose dilution protocol, independent of vitrification device/solution, to blastocysts shipped in from outside facilities between 2015-2017. In validating our clinical approach, we contrasted live birth rates achieved in the latter groups (A and B, respectively; see Table) to outcomes reported in the 2015 CDC data, including the national average (C) and four local IVF labs/clinics (D-H). Materials and Methods All research blastocysts were vitrified by µS-VTF using solutions and dilution treatments described above. Conversely, all internal FET cycles implemented a standardized sucrose step-down dilution using I.C.E. diluents (T1 -T4; estimated to possess 1.0M, 0.5M, 0.25M and 0.125M sucrose concentrations; 3 min/step), independent of the VTF device/cryoprotectant, upon rapid warming and blastocyst isolation. All blastocysts underwent isotonic equilibration in Hepes buffered media for 5 min at 37°C before being in-vitro cultured until ET or research developmental assessment. Our live birth pregnancy rates for FETs (A,B; autologous oocytes, Results No statistical differences in survival or sustained development was observed between the combined dilution treatments of vitrified research blastocysts. SOP thawing (93.5%) or standard sucrose dilution (90.3%) outcomes were similar. Mean live births (see Table) following our universal sucrose dilution approach (B) revealed similar or improved outcomes to those reported in the 2015 CDC summary (C-G). The apparent reduced live birth success compared to µS-VTF (A) and a local group (H) is likely due to differences in embryo production (i.e., lab effect), not to a warming-dilution effect post-VTF. Conclusion A universal sucrose, step-down dilution approach has proven to be a simple, cost-effective and highly successful procedure in our treatment for vitrified blastocysts derived from outside IVF programs, thus alleviating the need to purchase and maintain various commercial thaw solutions. Disclosures MCS developed µS-VTF without any commercial interests. Funding None.

Experimental Study of Ion Current Signals and Characteristics in an Internal Combustion Rankine Cycle Engine Based on Water Injection

The internal combustion Rankine cycle (ICRC) engine utilizes pure oxygen as the oxidant instead of air during combustion to prevent the generation of nitrogen oxide emissions and lower the cost of CO2 recovery. To control combustion intensity and increase efficiency, water injection technology is implemented as it can increase the in-cylinder working fluid during combustion process. To further enhance the system thermal efficiency, the injected water is heated using coolant and waste heat before being directly injected into combustion chamber. The main challenge of controlling the ICRC engine is the interaction between water injection process and combustion stability. Ion current detection provides a potential solution of real-time detection of in-cylinder combustion status and water injection process simultaneously. In this paper, the characteristics of ion current signal in an ICRC engine were studied. The results indicate the ion current signal is primarily affected by the combination of trapped water vapor injected in the last cycle and in-cylinder combustion intensity. The water vapor contributes to the ionization reactions, which lead to enhanced ion current signals under water cycle. The ion current signal is capable of reflecting the operating conditions of the in-cylinder water injector. The phase of the ion current peak value has a linear relation as the water injection timing is delayed, and ion current detection technology has the potential to detect the combustion phase under different engine loads in an internal combustion Rankine cycle engine.

The Rise and Fall of CSR in Italian Local Government

CSR is an essential intangible business asset increasingly understood as a critical success factor in global markets. A new connotation of corporate responsibility, combined with a modern approach to CSR interpreted in a competitive key, can bring together economic and socio-environmental performance needs by providing adequate responses to a wide range of stakeholders. This, however, requires guaranteeing sustainability from an economic point of view as well as credibility in terms of the messages conveyed with the related communication tools. The Italian public sector has attempted to incorporate the managerial approach developed in the private sector, yet after a period of great attention to this issue, a gradual decline has manifested in the instruments supporting social responsibility and the importance they play in the internal programming, reporting, and communications cycle.

Molecular Signals of Heterogeneous Terrestrial Environments Identified in Dissolved Organic Matter: A Comparative Analysis of Orbitrap and Ion Cyclotron Resonance Mass Spectrometers

Terrestrial dissolved organic matter (DOM) interlinks large carbon reservoirs of soils, sediments and marine environments but remains largely uncharacterized on the molecular level. Fourier Transform Mass Spectrometry (FTMS) has proven to be a powerful technique to reveal DOM chemodiversity and potential information encrypted therein. State-of the art FT-ICR MS (Ion Cyclotron Resonance) instruments are yet inaccessible for most researchers. To evaluate the performance of the most recent Orbitrap analyzer as a more accessible alternative, we compared our method to an established 15 Tesla FT-ICR MS on a diverse suite of 17 mainly terrestrial DOM samples regarding 1) ion abundance patterns, 2) differential effects of DOM type on information loss, and 3) derived biogeochemical information. We show that the Orbitrap provides similar information as FT-ICR MS, especially for compound masses below 400 m/z, and is mainly limited by its actual resolving power rather than its sensitivity. Ecosystems that are dominated by inputs of plant-derived material, like DOM from soil, bog, lake and rivers, showed remarkably low average mass to charge ratios, making them also suitable for Orbitrap measurements. The additional information gained from FT-ICR MS was highest in heteroatom-rich (N, S, P) samples from systems dominated by internal cycling, like DOM from groundwater and the deep sea. Here FT-ICR MS detected 37% more molecular formulae and 11% higher ion abundance. However, the overall information content, which was analyzed by multivariate statistical methods, was comparable for both data sets. Mass spectra-derived biogeochemical trends, for example the decrease of DOM aromaticity during the passage through terrestrial environments, were retrieved by both instruments. We demonstrate the growing potential of the Orbitrap as an alternative FTMS analyzer in the context of challenging analyses of DOM complexity, origin and fate.

Determination of the copper isotope composition of seawater revisited: A case study from the Mediterranean Sea

A new technique for the determination of dissolved copper isotope composition (δ65Cu) of seawater was applied to examine copper sources and internal cycling in the Mediterranean Sea along the GEOTRACES GA04N transect. A succession of chelating resin with nitrilotriacetic acid functional groups and strong base anion exchange resin, together with optimization of the multi-collector inductively coupled plasma mass spectrometry set-up allowed to isolate copper from seawater matrix and to measure the 65Cu/63Cu ratios in seawater with an external precision of 0.06‰ (2 s.d.). This method was first applied for inter-comparison measurements to surface and deep waters sampled at the Bermuda Atlantic Time-Series station (BATS) in the North Atlantic Ocean during the GEOTRACES Intercalibration Cruise 1. Disparities in δ65Cu reported here and in the literature over these samples showed a need to investigate whether a new inter-comparison sample should be decided upon, or whether the use of UV-oxidation can also affect the measurement of δ65Cu. We also measured total dissolved Cu concentration ([dCu]T) and δ65Cu for 12 stations in the Mediterranean Sea. The δ65Cu distribution showed significant variations in the euphotic zone, at the Chl a maximum and at bottom depths. Copper isotope ratios ranged from +0.21‰ to +0.76‰ (±0.06‰, 2 s.d.), yielding an average of +0.51‰ (±0.20‰, 2 s.d.; n = 96) for the Mediterranean Sea. A strong zonation between natural aerosol deposition to the South and anthropogenic aerosol deposition to the North was seen in the sample set (Dulaquais et al. 2017; Gerringa et al. 2017; Rolison et al. 2015). Natural dust deposits seemed to draw δ65Cu toward lower values and deeper in the euphotic zone whereas the impact of anthropogenic aerosols seemed restricted to an increase in [dCu]T. At the Chl a maximum, δ65Cu showed significant increase which we attributed to scavenging on and/or uptake by phytoplankton. The isotope signature of Cu sources to the Mediterranean Sea was also investigated and we inferred a significant source of isotopically heavy Cu in the Gibraltar area, potentially originating from a release of Cu sulfide leached in the mining area of Southern Spain (i.e. Iberian Pyrite Belt) in rivers and transported to the Mediterranean Sea in surface by seasonal water mass circulation. Conversely, marine sediments appear to be a source of isotopically-light Cu to deep waters. This study provides new hints on the use of copper isotopes to study sources and sinks of Cu in seawater. This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

«New Angarstroy» as a Project of Non-Raw Materials Integration of Economies of Russia and China

The article is dedicated to the project «New Angarstroy» (Baikal-Amur Superindustrial Complex) which is being developed, first of all, to meet the needs of the development of the Russian economy, as well as in the context of non-raw material cooperation of Russia, China, Mongolia and other countries. The authors explain the expediency of the transition from a raw-material model of economic integration of Russia and China to a non-raw material one. They outline the «New Angarstroy» project, a key part of which is the organization of the largest metallurgical production of national scale, including a high-quality full-cycle ferrous metallurgy (with iron direct reduction and electrometallurgy) and titanium-magnesium industry. Particular attention is paid to the analysis of the transport component of the project as the railway transport plays an important role of in the functioning of the technological flow-stage scheme of the superindustrial complex, the enormous scale of the planned production and, accordingly, the transported cargoes, certain limited capacity of the main Siberian railways. It is planned to organize the transportation of products in the internal production cycle of the Baikal-Amur Superindustrial Complex according to the pendulum principle; the authors identified the need to implement large-scale programs for the radical modernization of the Trans-Siberian Railway and the Baikal-Amur Mainline and the entire Siberian railway system. They describe the benefits of constructing the railway connection of the Transsib and BAM by the Mogzon - Novy Uoyan line with the goal of ensuring effective transition of products of «New Angarstroy» across the external international pendulum - Central Russia - Northeast China.

Conversion of tropical forests to smallholder rubber and oil palm plantations impacts nutrient leaching losses and nutrient retention efficiency in highly weathered soils

Abstract. Conversion of forest to rubber and oil palm plantations is widespread in Sumatra, Indonesia, and it is largely unknown how such land-use conversion affects nutrient leaching losses. Our study aimed to quantify nutrient leaching and nutrient retention efficiency in the soil after land-use conversion to smallholder rubber and oil palm plantations. In Jambi province, Indonesia, we selected two landscapes on highly weathered Acrisol soils that mainly differed in texture: loam and clay. Within each soil type, we compared two reference land uses, lowland forest and jungle rubber (defined as rubber trees interspersed in secondary forest), with two converted land uses: smallholder rubber and oil palm plantations. Within each soil type, the first three land uses were represented by 4 replicate sites and the oil palm by three sites, totaling 30 sites. We measured leaching losses using suction cup lysimeters sampled biweekly to monthly from February to December 2013. Forests and jungle rubber had low solute concentrations in drainage water, suggesting low internal inputs of rock-derived nutrients and efficient internal cycling of nutrients. These reference land uses on the clay Acrisol soils had lower leaching of dissolved N and base cations (P= 0.01–0.06) and higher N and base cation retention efficiency (P < 0.01–0.07) than those on the loam Acrisols. In the converted land uses, particularly on the loam Acrisol, the fertilized area of oil palm plantations showed higher leaching of dissolved N, organic C, and base cations (P < 0.01–0.08) and lower N and base cation retention efficiency compared to all the other land uses (P < 0.01–0.06). The unfertilized rubber plantations, particularly on the loam Acrisol, showed lower leaching of dissolved P (P=0.08) and organic C (P < 0.01) compared to forest or jungle rubber, reflecting decreases in soil P stocks and C inputs to the soil. Our results suggest that land-use conversion to rubber and oil palm causes disruption of initially efficient nutrient cycling, which decreases nutrient availability. Over time, smallholders will likely be increasingly reliant on fertilization, with the risk of diminishing water quality due to increased nutrient leaching. Thus, there is a need to develop management practices to minimize leaching while sustaining productivity.

Experimental evidence reveals impact of drought periods on dissolved organic matter quality and ecosystem metabolism in subalpine streams

AbstractSubalpine streams are predicted to experience lower summer discharge following climate change and water extractions. In this study, we aimed to understand how drought periods impact dissolved organic matter (DOM) processing and ecosystem metabolism of subalpine streams. We mimicked a gradient of drought conditions in stream‐side flumes and evaluated implications of drought on DOM composition, gross primary production, and ecosystem respiration. Our experiment demonstrated a production and release of DOM from biofilms and leaf litter decomposition at low discharges, increasing dissolved organic carbon concentrations in stream water by up to 50%. Absorbance and fluorescence properties suggested that the released DOM was labile for microbial degradation. Dissolved organic carbon mass balances revealed a high contribution of internal processes to the carbon budget during low flow conditions. The flumes with low discharge were transient sinks of atmospheric CO2 during the first 2 weeks of drought. After this autotrophic phase, the metabolic balance of these flumes turned heterotrophic, suggesting a nutrient limitation for primary production, while respiration remained high. Overall our experimental findings suggest that droughts in subalpine streams will enhance internal carbon cycling by transiently increasing primary production and more permanently respiration as the drought persists. We propose that the duration of a drought period combined with inorganic nutrient availability are key variables that determine if more carbon is respired in situ or exported downstream.

Novel Autotrophic Organisms Contribute Significantly to the Internal Carbon Cycling Potential of a Boreal Lake.

ABSTRACTOxygen-stratified lakes are typical for the boreal zone and also a major source of greenhouse gas emissions in the region. Due to shallow light penetration, restricting the growth of phototrophic organisms, and large allochthonous organic carbon inputs from the catchment area, the lake metabolism is expected to be dominated by heterotrophic organisms. In this study, we test this assumption and show that the potential for autotrophic carbon fixation and internal carbon cycling is high throughout the water column. Further, we show that during the summer stratification carbon fixation can exceed respiration in a boreal lake even below the euphotic zone. Metagenome-assembled genomes and 16S profiling of a vertical transect of the lake revealed multiple organisms in an oxygen-depleted compartment belonging to novel or poorly characterized phyla. Many of these organisms were chemolithotrophic, potentially deriving their energy from reactions related to sulfur, iron, and nitrogen transformations. The community, as well as the functions, was stratified along the redox gradient. The autotrophic potential in the lake metagenome below the oxygenic zone was high, pointing toward a need for revising our concepts of internal carbon cycling in boreal lakes. Further, the importance of chemolithoautotrophy for the internal carbon cycling suggests that many predicted climate change-associated fluctuations in the physical properties of the lake, such as altered mixing patterns, likely have consequences for the whole-lake metabolism even beyond the impact to the phototrophic community.

NetCycle+: A Framework for Collective Evolution Inference in Dynamic Heterogeneous Networks

Collective inference has attracted considerable attention in the last decade, where the response variables within a group of instances are correlated and should be inferred collectively, instead of independently. Previous works on collective inference mainly focus on exploiting the autocorrelation among instances in a static network during the inference process. There are also approaches on time series prediction, which mainly exploit the autocorrelation within an instance at different time points during the inference process. However, in many real-world applications, the response variables of related instances can co-evolve over time and their evolutions are not following a static correlation across time, but are following an internal life cycle . In this paper, we study the problem of collective evolution inference , where the goal is to predict the values of the response variables for a group of related instances at the end of their life cycles. This problem is extremely important for various applications, e.g., predicting fund-raising results in crowd-funding and predicting gene-expression levels in bioinformatics. This problem is also highly challenging because different instances in the network can co-evolve over time and they can be at different stages of their life cycles and thus have different evolving patterns. Moreover, the instances in collective evolution inference problems are usually connected through heterogeneous information networks (HINs for short), which involve complex relationships among the instances interconnected by multiple types of links. We propose an approach, called NetCycle+ , by incorporating information from both the correlation among related instances and their life cycles. Furthermore, in order to study the deep dependencies between nodes in the network, we extend the graph convolution model into our algorithm. We compared our approach with existing methods of collective inference and time series analysis on two real-world networks. The results demonstrate that our proposed approach can improve the inference performance by considering the autocorrelation through networks and the life cycles of the instances.

Deposition and Fate of Mercury in Litterfall, Litter, and Soil in Coniferous and Broad‐Leaved Forests

AbstractMercury dynamics in the process of litter decomposition is crucial to understanding the atmospheric mercury deposition to soils in the forest catchments. This work aimed to quantify mercury internal biogeochemical cycling and the fractionation process in a coniferous forest and a broad‐leaved forest in southwest China. Annual deposition fluxes of total mercury (THg) and methylmercury (MeHg) via litterfall were 40.5 and 0.10 μg/m2 in the coniferous forest and were 90.9 and 0.34 μg/m2 in the broad‐leaved forest, respectively. The litterfall biomass was the most influential factor resulting in the higher mercury input in the broad‐leaved forest. During the one‐year incubation, THg and MeHg mass in the decomposing litter increased 49 and 444% in the coniferous forest compared to those in the broad‐leaved forest, respectively. Methylation has increased the risk of MeHg mobilization to aquatic and soil ecosystems during litter decomposition. Additionally, higher mercury deposition flux but lower accumulation in the broad‐leaved forest resulted in similar mercury content in the coniferous forest soils. Six mercury fractions were determined by sequential extraction for the decomposing litter, while MeHg concentrations were statistically significantly correlated to water soluble and salt soluble fractions. The residual mercury fraction accounted for over 90% of the THg and increased with litter decomposition. During the last half of the litter decomposition, the ratio of residual fraction significantly increased, while the sum of the other ratios reduced, which indicated that litter dynamics in the internal forests stabilized the mercury in organic soils during litter decomposition.