Changes In Carbon Fluxes Research Articles

High‐Latitude Eddy Covariance Temporal Network Design and Optimization

AbstractEcosystems at high latitudes are changing rapidly in response to climate change. To understand changes in carbon fluxes across seasonal to multi‐decadal timescales, long‐term in situ measurements from eddy covariance networks are needed. However, there are large spatiotemporal gaps in the high‐latitude eddy covariance network. Here we used the relative extrapolation error index in machine learning‐based upscaled gross primary production as a measure of network representativeness and as the basis for a network optimization. We show that the relative extrapolation error index has steadily decreased from 2001 to 2020, suggesting diminishing upscaling errors. In experiments where we limit site activity by either setting a maximum duration or by ending measurements at a fixed time those errors increase significantly, in some cases setting the network status back more than a decade. Our experiments also show that with equal site activity across different theoretical network setups, a more spread out design with shorter‐term measurements functions better in terms of larger‐scale representativeness than a network with fewer long‐term towers. We developed a method to select optimized site additions for a network extension, which blends an objective modeling approach with expert knowledge. This method greatly outperforms an unguided network extension and can compensate for suboptimal human choices. For the Canadian Arctic we show several optimization scenarios and find that especially the Canadian high Arctic and north east tundra benefit greatly from addition sites. Overall, it is important to keep sites active and where possible make the extra investment to survey new strategic locations.

Impact of Alaska atmospheric blocking on the carbon flux in the Northeast Pacific Ocean

The Northeast Pacific Ocean (NEP) is one of the important carbon sinks in the global ocean. The causes of carbon flux changes in this region have been widely studied, but the physical processes associated with large scale climate variability remain controversial primarily due to scarcity of spatially and temporally continuous observations. In this study, we constructed a high-resolution sea surface partial pressure of CO2 (pCO2) from satellite observations for the NEP from 2003 to 2020 using the machine learning based XGBoost model. By analyzing the interannual large-scale high-latitude atmospheric dynamics and ocean physical conditions over the NEP, we find that the CO2 flux density (FCO2) anomalies have a strong correlation with the Alaskan atmospheric blocking events. In the region north of 48°N, anomalous cyclones triggered by atmospheric blocking increased sea surface height (SSH), which reduced the replenishment of dissolved inorganic carbon (DIC) from deep seawater, leading to enhanced carbon uptake. By contrast, in the region south of 48°N, the increase in sea surface temperature (SST) triggered by atmospheric blocking reduced the solubility of CO2 in seawater, resulting in a decrease in regional carbon flux. These results provide new perspectives for better understanding and predicting the effects of high-latitude atmospheric dynamics on regional ocean carbon fluxes.

Carbon fluxes and water-use efficiency in a Pinus tabuliformis plantation in Northeast China and their relationship to drought

The impact of extreme weather events on carbon fluxes and water-use efficiency (WUE) in revegetated areas under water-limited conditions is poorly understood. We analyzed changes in carbon fluxes and WUE over three years of eddy-covariance measurements in a Pinus tabuliformis plantation in Northeast China to investigate carbon fluxes and WUE responses to drought events at different time scales. Mean annual net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (Re) were −368.48, 1042.42, and 673.94 g C m−2, respectively. Drought events increased NEE, as GPP was more sensitive to water stress than Re at different growing stages. Mean annual WUE was 2.46 g C kg−1 H2O, and plant phenology played a key role in WUE responses to drought. Water stress had negative and positive effects on daily WUE at the early and late growing stages, respectively, and daily WUE was generally insensitive to drought at the mid growing stage. A lagged effect existed in the carbon fluxes and WUE dynamics after drought events at various time scales. Water stress at the early growing stage was more important than that at other growing stages on annual carbon sequestration and WUE, as it dominated canopy growth in the current year. The annual mean normalized difference vegetation index controlled interannual variations in carbon fluxes and WUE in the plantation. Our findings contribute to the prediction of possible changes in carbon and water fluxes under climate warming in the afforested areas of Northeast China.

Cultivated Grassland Types Differently Affected Carbon Flux Downstream of the Yellow River

Cultivated grasslands are an important part of grassland ecosystems and have been proven to be major carbon sinks, then playing an important role in the global carbon balance. The effect of cultivated grassland type (Medicago sativa, Triticum aestivum, Secale cereale, and Vicia villosa grasslands) on carbon flux (including net ecosystem CO2 exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP)) downstream of the Yellow River was studied via the static chamber technique and a portable photosynthetic system. Bare land was used as a control. The results showed that the four cultivated grassland types were mainly carbon sinks, and bare land was a carbon source. The cultivated grassland types significantly affected carbon flux. The average NEE and GEP of the grassland types were in the following order from high to low: Medicago sativa, Secale cereale, Triticum aestivum, and Vicia villosa grassland. Stepwise regression analysis showed that among all measured environmental factors, soil pH, soil bulk density (BD), soil organic carbon (SOC), and soil microbial carbon (MBC) were the main factors affecting CO2 flux. The combined influence of soil BD, SOC, and pH accounted for 77.6% of the variations in NEE, while soil BD, SOC, and MBC collectively explained 79.8% of changes in ER and 72.9% of the changes in GEP. This finding indicates that Medicago sativa grassland is a cultivated grassland with a high carbon sink level. The changes in carbon flux were dominated by the effects of soil physicochemical properties.

The influence patterns of carbon flux in different climatic zones in China —Based on the complex network approach

Research on ecosystem carbon flux can provide important methodological and strategic support for climate change mitigation. The existing studies focus on the calculation of carbon flux, ignoring the intertwined effects between regions. The quantification and analysis of the interaction patterns of carbon flux is crucial for understanding the global carbon cycle process, forecasting and coping with climate change. In this study, carbon flux network model sequences are established based on complex network theory using carbon flux data spanning from December 1, 2005, to November 30, 2020. The time delay effect is introduced to accurately quantify the influence patterns of carbon flux within climate zones across China. The findings indicate that the probability distribution function of the link weights during the various seasons of each year exhibits a bimodal distribution with distinct positive and negative components. The delay probability distribution function reveals the significant impact of delay effects, which are especially pronounced and mostly significant long-term lag effects in nodes with negative weights. Further, the results of the interactions of carbon flux among climate zones demonstrate that changes in carbon flux in the plateau and southern temperate regions have either positive or negative impacts on other climate zones. Therefore, controlling carbon flux changes in these climatic zones can effectively optimize the distribution of carbon flux. The modeling framework and results presented in this paper provide useful insights for the regulation and distribution optimization of carbon flux in China.

Dynamics of carbon and water vapor fluxes in three typical ecosystems of Heihe River Basin, Northwestern China

Understanding the dynamics of carbon and water vapor fluxes in arid inland river basin ecosystems is essential for predicting and assessing the regional carbon-water budget amid climate change. However, studies aiming to unravel the mechanisms driving the variations and coupling process of regional carbon-water budget in a changing environment in arid regions are limited. Here, we used the eddy covariance technique to analyze the relationship between CO2 and H2O fluxes in three typical ecosystems across the upper, middle, and lower reaches of an arid inland river basin in Northwestern China. Our results showed that all ecosystems acted as carbon sinks, with the alpine swamp meadow, cropland, and desert shrubland sequestrating −300.2 ± 0.01, −644.8 ± 2.9, and − 203.7 ± 22.5 g C m−2 yr−1, respectively. Air temperature (Ta) primarily controlled daily gross primary productivity (GPP) and net ecosystem CO2 exchange (NEE) in the irrigated cropland during the growing season, while soil temperature (Ts) and vapor pressure deficit (VPD) regulated these parameters in the alpine swamp meadow and desert shrubland. Additionally, Ta and net radiation (Rn) controlled daily evapotranspiration (ET) in cropland, while Ts and Rn regulated ET at other sites. Consequently, carbon and water vapor fluxes of all three ecosystems tended to be energy-limited during the growing season. The differential responses of carbon and water vapor fluxes in the upper, middle, and lower reaches of these ecosystems to biophysical factors determined their distinct coupling and variations in water use efficiency. Notably, the desert shrub ecosystem in the lower reach of the basin maintained a stable balance between carbon gain and water loss, indicating adaptation to aridity. This study provides valuable insights into the underlying mechanisms behind the changes in carbon and water vapor fluxes and water-use efficiency in arid river basin ecosystems.

Sea Surface pCO2 Response to Typhoon “Wind Pump” and Kuroshio Intrusion in the Northeastern South China Sea

The Luzon Strait (LS) is a key region for estimating carbon sources and sinks in the South China Sea (SCS) and is highly influenced by the Kuroshio Current (KC) and typhoons. Understanding the variations in the sea surface partial pressure of carbon dioxide (pCO2-sw) under the combined effects of typhoons and KC in this region is crucial for estimating local and regional changes in ocean carbon flux. Based on valuable in situ pCO2-sw and remote sensing data, this study aimed to reveal the temporal variations and the physical mechanisms of pCO2-sw variations under the comprehensive effects of both typhoons and Kuroshio Intrusion (KI) in the LS. One week after the passage of the tropical cyclone (TC) Nanmadol, the concentration in the pCO2-sw and the influencing mechanisms varied in three different regions (W1–W3) on Transect A (120°E). In the region dominated by SCS waters (W1), the average pCO2-sw increased by 5.1 μatm after TC, which was mainly due to the TC “Wind Pump” inducing strong vertical mixing, which brought dissolved inorganic carbon (DIC)-rich deeper water up to the surface. In the region affected by KC (W2 and W3), pCO2-sw decreased after the TC (−8.2 μatm and −1.8 μatm, respectively) with TC-enhanced KI because the invasion of lower pCO2-sw of Kuroshio waters inhibited the TC-induced upwelling. More significant TC-induced upwelling (W3) would alleviate the decrease in pCO2-sw caused by the TC-enhanced KI. This study is a rare case providing a better understanding of the variations in pCO2-sw under TC-enhanced KI, which provides support for regional climate change prediction and carbon flux estimation in the western boundary current regions.

Study on the intracellular adaptative mechanism of Acidithiobacillus caldus MTH-04 to NaCl stress

To understand the adaptive mechanism of bioleaching microorganism Acidithiobacillus caldus MTH-04, its physiology and metabolic changes at the transcriptional level were systemically studied. The results of growth curves, SO42− content, pH and flow cytometry analyses indicated that the higher the NaCl concentration, the more the strain was inhibited. The transcriptome response of A. caldus to elevated NaCl concentrations included changes in carbon flux, elevated glutathione synthesis, alterations in cell wall and membrane composition, the down-regulation in genes involved in flagellar synthesis and rotation, the reduced energy generation through sulfur oxidation, and the up-regulation in genes involved in DNA and protein repair. Based on the transcriptome results, the effects of proline and glutathione on NaCl adaptation in A. caldus were analyzed separately. We found that either the exogenous addition of proline and glutathione or the intracellular overexpression of the enzymes responsible for the synthesis of these two substances contributed to the enhancement of the adaptive capacity of A. caldus under NaCl stress. The findings offer insight into the design of chloride-based techniques for the bioprocessing of minerals.

Assessing the Reliability of Global Carbon Flux Dataset Compared to Existing Datasets and Their Spatiotemporal Characteristics

Land carbon fluxes play a critical role in ecosystems, and acquiring a comprehensive global database of carbon fluxes is essential for understanding the Earth’s carbon cycle. The primary methods of obtaining the spatial distribution of land carbon fluxes include utilizing machine learning models based on in situ measurements, estimating through satellite remote sensing, and simulating ecosystem models. Recently, an innovative machine learning product known as the Global Carbon Flux Dataset (GCFD) has been released. In this study, we assessed the reliability of the GCFD by comparing it with existing data products, including two machine learning products (FLUXCOM and NIES (National Institute for Environmental Studies)), two ecosystem model products (TRENDY and EC-LUE (eddy covariance–light use efficiency model)), and one remote sensing product (Global Land Surface Satellite), on both site and global scales. Our findings indicate that, in terms of average absolute difference, the spatial distribution of the GCFD is most similar to the NIES product, albeit with slightly larger discrepancies compared to the other two types of products. When using site observations as the benchmark, gross primary production (GPP), respiration of ecosystem (RECO), and net ecosystem exchange of machine learning products exhibit higher R2 (ranging from 0.57 to 0.85, 0.53–0.79, and 0.31–0.70, respectively) compared to model products and remote sensing products. Furthermore, we analyzed the spatial and temporal distribution characteristics of carbon fluxes in various regions. The results demonstrate an upward trend in both GPP and RECO over the past two decades, while NEE exhibits an opposite trend. This trend is particularly pronounced in tropical regions, where higher GPP is observed in tropical, subtropical, and oceanic climate zones. Additionally, two remote sensing variables that influence changes in carbon fluxes, i.e., fraction absorbed photosynthetically active radiation and leaf area index, exhibit relatively consistent spatial and temporal characteristics. Overall, our study can provide valuable insights into different types of carbon flux products and contribute to understanding the general features of global carbon fluxes.

Horizontal variability and diurnal fluctuation of soil respiration in corn and soybean rows

This study evaluated the horizontal variability and diurnal fluctuation of soil respiration to accurately capture changes in carbon flux during agricultural production in Lishu County, Jilin Province, China. Corn (Zea mays L.) and soybean (Glycine max L.) were planted with 60-cm row spacing in 2020. The soil respiration rate (SRR) was measured at 2-hour intervals on July 1, August 1, and September 25 using a portable, closed chamber at five positions, P0, P15, P30, P45, and P60, denoting specific distances from the crop rows. The SRR between crop rows was affected both by dates and fields with the coefficient of variation ranging between 7.1 and 37.7%. The SRR at P45 was closest to the mean SRR, with a relative deviation of 0.09–4.85% on July 01 and August 01 in corn and soybean fields. On September 25, the optimal position to measure SRR was between P45 and P60. The sampling dates influenced the optimal time for measuring SRR but were mostly concentrated between 9:00 and 11:00 (24-hour clock) for corn and between 11:00 and 13:00 for soybean. The root biomass of crop rows and diurnal soil temperature were the main factors affecting horizontal variability and diurnal fluctuation of SRR, respectively. We recommend an SRR sampling strategy at P45 between 9:00 and 11:00 for corn and between 11:00 and 13:00 for soybean to decrease the effects of horizontal variability and diurnal fluctuation of SRR.

THE NUMERICAL ANALYSIS OF MIXING DEPTH AND THE THICKNESS OF BBL CONSIDERING THE SUBMERGED AQUATIC VEGETATION AND WIND STRESS

Mangrove forests, salt marshes, and seagrass meadows have a vital role in mitigating global warming (Duarte et al.,2013). They contribute about 50 percent of carbon burial in ocean sediments (Duarte et al., 2013). On the other hand, submerged aquatic vegetations (SAVs) significantly affect the mixing depth (the thickness of the upper layer), resulting in a change in carbon flux with the atmosphere. According to the numerical simulations in the previous studies, mixing depth becomes larger with increasing SAV's density and decreasing SAV’s height (Herb et al., 2005, Vilas et al., 2017). On the other hand, Coates et al. (2009) indicated that wind stress was not crucial for mixing depth in SAV’s meadow since it did not change the vertical turbulent kinetic energy (TKE) profile, except in the thin surface layer, thus mixing depth became similar even though wind speed varied under the effect of SAVs (Coates et al., 2009). In addition, it is crucial to estimate the thickness of the benthic boundary layer (BBL) because dissolved inorganic carbon elucidates from bottom sediments, affecting carbon flux. Therefore, we aim to clarify how wind stress impacts the mixing depth and thickness of BBL with SAVs.

Unveiling the bathypelagic zone with an acoustic vertical profiler

There is a growing interest in the study of mesopelagic and bathypelagic species due to their implication in the active carbon flux and climate change. Underwater acoustics is one of the most efficient methods to study such widely distributed communities. However, there are several challenges among which the reduced spatial resolution with depth for vessel-mounted echosounders stands out. The increase in sampling volume with range precludes observation of fine structures within the scattering layers or the study of less-aggregated organisms far from the transducer face. Echosounders are thus increasingly being deployed in alternative platforms that get the transducer close to the layers of interest. We present here the comparison between two active acoustic platforms used to analyse mesopelagic and bathypelagic species: a vessel-mounted EK60 scientific echosounder and a 6000 m depth rated Acoustic Zooplankton Fish Profiler (AZFP) attached to a CTD rosette. Both systems depicted similar vertical distributions and scattering at 38 kHz for the main scattering layers recorded around the Canary Islands but the finer vertical resolution of the AZFP discerned a series of sub-layers within them that differed in scattering, avoidance and sparsity. The availability of high frequencies at depth also provided further insights on the frequency response of those layers. However, the horizontal orientation of the AZFP created sidelobe artefacts close to the surface and bottom that limit its use in those areas. Signal-to-noise ratio of the AZFP system in the bathypelagic zone also precludes applying echointegration analysis at those depths or outside the denser scattering layers. Finally, the visualization of horizontal or temporal patterns such as migration or mesoscale features is limited to a coarse resolution using data from closely spaced successive stations. New challenges encountered with vertically-deployed echosounders and recommendations for their use are pointed out. Although no scattering layers were detected in the bathypelagic zone, this study unveils an area never before recorded acoustically.

Consequences of elevated CO2 on soil acidification, cation depletion, and inorganic carbon: A column-based experimental investigation

The anthropogenic release of atmospheric CO2 affects soil nutrient cycling through varied biogeochemical processes. Cation depletion from exchange sites, carbonate mineral dissolution, and subsequent changes in organic and inorganic carbon flux are growing concerns for soil health and sustainability. Particularly, the effects of acid deposition on soil pH and soil health under changing global carbon flux is poorly understood. To estimate the magnitude and effects of pH change across different soil profiles, the depth-wise response of soil cations, pH, and soil inorganic carbon (SIC) to varying CO2 levels was investigated using column-leachate experiments. Six soils, representing acidic, neutral, and alkaline pH, were exposed to different CO2 enrichments (100%, 10%, 1%, and Control) of water percolate for 30 days. Analysis of the column leachates revealed that the base cations (Ca, Mg, Na) were higher initially than on day 30, while Si leaching increased with time. The pH in leachates tended to attain an equilibrium state with time under CO2 saturation, indicating the buffering capacity of alkaline and neutral soils. Evaluation of the soil before and after the experiments showed that the solid SIC, such as carbonate minerals and any dissolved SIC components (e.g., carbonate, bicarbonate ions) entrained in the pore space increased, whereas the potential cation exchange capacity (PCEC) decreased in all soils. This trend was especially prominent for alkaline soils at 100% CO2 enrichment. Over the short-term study, the SIC showed minimal response to varying CO2 enrichment conditions in neutral and acidic soils. The altered cation concentrations in the leachates suggest that under long-term exposure to elevated CO2, a deficiency of cationic essential plant nutrients such as Ca2+, Mg2+, and K+ is likely, especially with low buffering capacity and primary mineral content. In contrast, an increase in nutrient solubility and elemental toxicity (e.g., Al3+ Mn) can be observed in the short term. The initial soils with greater ECEC experienced an increased SIC leaching in the shorter term and suggested potential deposition in deeper layers. The resultant SIC loss might be amplified in arid to semi-arid soils with low SIC and affect soil health.

Responses of fine-root biomass and production to drying depend on wetness and site nutrient regime in boreal forested peatland

IntroductionPeatlands are terrestrial-carbon hotspots, where changes in carbon pools and fluxes potentially caused by drying or warming may have significant feedbacks to climate change. In forested peatlands, fine-root biomass (FRB), and production (FRP) are important carbon pools and fluxes, but they and their depth distribution and plant functional type (PFT) composition are poorly known.MethodsWe studied the effects of persistent water-table level (WTL) drawdown on these characteristics in four forested boreal peatland site types that varied in soil nutrient and WTL regimes, ground vegetation and tree stand characteristics. Each site type was represented by a pair of one undrained and one drained site. Two pairs were nutrient-poor, Scots pine dominated sites, one very wet and one relatively dry in their undrained condition. The other two pairs were nutrient-rich, Norway spruce dominated sites, again one wetter and one drier in the undrained condition. FRB was estimated by separating and visually identifying roots from soil cores extending down to 50 cm depth. FRP was estimated using ingrowth cores covering the same depth, and the separated roots were identified using infrared spectroscopy.Results and discussionBoth FRB and FRP varied widely both within and among the different types of boreal forested peatland. In FRB, the clearest differences were seen in the two originally wettest sites, nutrient-poor tall-sedge pine fen and nutrient-rich herb-rich spruce swamp: FRB was smaller in the drained site compared to the undrained site in the pine fen, but the opposite was true in the spruce swamp. FRP was generally higher in the nutrient-poor, pine-dominated sites than the nutrient-rich, spruce-dominates sites. The depth distribution of FRB was more superficial than that of FRP, except for the most nutrient-rich spruce swamp. Tree and shrub roots dominated both FRB and FRP, except for the undrained pine fen, where graminoids and forbs dominated. Even there, these PFTs were replaced by trees and shrubs at the drained site. Site wetness and nutrient regime both thus clearly regulated FRB and FRP of the forested peatland site types studied, and both need to be considered when making any generalizations.

Circadian disruption decreases gluconeogenic flux in late-gestation, nonlactating dairy cows

Cattle exposed to shifts in light-dark phases during late pregnancy develop hypoglycemia and insulin resistance. Our objective was to investigate if differences in liver carbon flux for gluconeogenesis were driving circadian-disrupted metabolic alterations in glucose homeostasis, and relate changes in carbon flux to hepatic gene expression. We hypothesized circadian disruption would decrease hepatic carbon flux for glucose synthesis. Milking was ceased in late-gestation Holstein cows (n = 8) at 60 d before expected calving (BEC), and animals were assigned to either a control (n = 4) or a phase-shifted (PS; n = 4) group. From d 35 to 21 BEC both groups of cows were exposed to 16 h of light and 8 h of dark, but for the PS, light was shifted forward 6 h every 3 d. On d 21 BEC, liver biopsies were collected, subdivided, and incubated in 1.0 mM [U-13C] propionate for 2 h. Total RNA was isolated from a separate liver sample and used for RNA-sequencing analysis. Postincubation 13C mass isotopologue distribution was determined for aspartate, serine, alanine, and glutamate and used to calculate metabolic flux ratios. Enrichment of serine to enrichment of aspartate ratio (eSer:eAsp) was lower for PS (0.75 ± 0.02) cows compared with control (0.81 ± 0.04), indicating a reduction in carbon flux toward glucose for PS animals. eSer:eAsp ratio was negatively correlated to propionyl-CoA carboxylase (PCCB; r = −0.79) and succinate dehydrogenase subunit D (SDHD; r = −0.82). These relationships indicate that when dairy cattle are exposed to circadian disruption during late gestation, propionate carbon is preferentially used for energy rather than gluconeogenesis.

Coastal upwelling drives ecosystem temporal variability from the surface to the abyssal seafloor

Long-term biological time series that monitor ecosystems across the ocean's full water column are extremely rare. As a result, classic paradigms are yet to be tested. One such paradigm is that variations in coastal upwelling drive changes in marine ecosystems throughout the water column. We examine this hypothesis by using data from three multidecadal time series spanning surface (0 m), midwater (200 to 1,000 m), and benthic (~4,000 m) habitats in the central California Current Upwelling System. Data include microscopic counts of surface plankton, video quantification of midwater animals, and imaging of benthic seafloor invertebrates. Taxon-specific plankton biomass and midwater and benthic animal densities were separately analyzed with principal component analysis. Within each community, the first mode of variability corresponds to most taxa increasing and decreasing over time, capturing seasonal surface blooms and lower-frequency midwater and benthic variability. When compared to local wind-driven upwelling variability, each community correlates to changes in upwelling damped over distinct timescales. This suggests that periods of high upwelling favor increase in organism biomass or density from the surface ocean through the midwater down to the abyssal seafloor. These connections most likely occur directly via changes in primary production and vertical carbon flux, and to a lesser extent indirectly via other oceanic changes. The timescales over which species respond to upwelling are taxon-specific and are likely linked to the longevity of phytoplankton blooms (surface) and of animal life (midwater and benthos), which dictate how long upwelling-driven changes persist within each community.

Exogenous addition of putrescine enhanced lipid accumulation in Tetradesmus obliquus for increased biodiesel productivity

Microalgae can continuously convert carbon dioxide into biofuels as a typical organism of biological carbon fixation. This study investigated the effects of exogenous putrescine on lipid accumulation, algal growth, and transcriptional metabolism of Tetradesmus obliquus. The results showed that the content of neutral lipids increased by 2.26-fold after short-term stress of putrescine, and the total lipids increased to 355.51 mg/g. Furthermore, the transcriptomic analysis reveals that putrescine treatment plays a dramatic role in photosynthetic electron transport, carbon metabolism, and signal transduction pathways, and the purpose of lipid accumulation was achieved by influencing the changes in cell carbon flux and physiological functions. Altogether, this study demonstrates for the first time that putrescine treatment has a positive effect on lipid accumulation through unprecedented regulation of key metabolic nodes and provides theoretical support for the industrial biodiesel production of microalgae.

Attributing Past Carbon Fluxes to CO2 and Climate Change: Respiration Response to CO2 Fertilization Shifts Regional Distribution of the Carbon Sink

AbstractOver the past century, increased atmospheric CO2 concentrations have enhanced photosynthesis through CO2 fertilization across the globe. However, the increased growth has also led to greater respiration rates—both from vegetation (autotrophic respiration) and through the breakdown of plant litter and soil organic matter (heterotrophic respiration). The resulting change in carbon flux—and its spatial distribution—that can be attributed to increasing CO2 and climate change remains unknown. We used the Carbon Data Model Framework, a model‐data fusion system that assimilates global observations from satellites and other sources to create an ensemble of observationally constrained carbon cycle representations, to determine the photosynthesis and respiration fluxes that can be attributed to increased atmospheric CO2 and associated climate change from 1920 to 2015. Across the globe, the response of photosynthesis and respiration to atmospheric CO2 dominates their response to climate alone. The regional distribution of the carbon sink attributable to climate change and CO2 is strongly influenced by the 'loss ratio of carbon gained'—the fraction of enhanced photosynthesis that is lost to respiration. While the wet tropics' attributable photosynthesis flux is 1.4 times larger than that of the temperate region, the attributable flux of net carbon uptake is actually 1.25 larger in the temperate region, due to the wet tropics' greater heterotrophic respiration response to enhanced plant growth. At the global scale, the loss ratio of carbon gained is 83 ± 0.6%. Our results highlight the importance of the respiration responses to enhanced plant growth in regulating the land carbon sink.

Decoupling of land-use net carbon flux, economic growth, and population change in China.

In the process of China's modernization, promoting the sustainable development of resource-based cities is a major strategic issue and it has now also become a worldwide issue. This study uses the coupling model to validate the coupling relationship between China's land-use net carbon flux and economic growth and population change during 2009-2017. The study for the first time draws the conclusion that the coupling degree among the three is getting lower, the correlation is gradually weaker, and the independent relationship is becoming more and more prominent. Utilizing the Tapio decoupling model, we obtained the weak decoupling conclusion that the economic growth rate is higher than the growth rate of the land-use net carbon flux, while negative decoupling of sprawl is where the rate of population growth is less than the rate of net land-use carbon flux growth.

The metabolic sensitivity of hydrogen isotope fractionation differs between plant compounds

Hydrogen stable isotope analyses (δ2H) of plant derived organic compounds are a useful tool for ecological, environmental, and palaeoclimatological research. However, during organic compound synthesis, variable biosynthetic 2H-fractionation has been suggested to occur as a result of changes in plant carbon fluxes. So far, inference has been based on examining the δ2H patterns of plant compounds along environmental gradients, among plant species, and between plant organs. In an alternative approach, we used four plant species with four different types of mutations that cause impaired starch synthesis to assess whether variability in carbon metabolism affects the biosynthetic 2H-fractionation during cellulose, phytol, and acetogenic lipid synthesis. We found that mutants with impaired starch synthesis always had higher cellulose and phytol δ2H values compared to the wild type. By contrast, 2H-fractionation during acetogenic lipid biosynthesis generally did not show strong metabolic sensitivity. We rationalise these differences by considering the biosynthetic pathway of each compound and the likely source of the variable isotope fractionation. In different organic compounds, the sensitivity of variable biosynthetic 2H-fractionation to changes in C-metabolism depends on incorporation of specific H atoms from precursor molecules. As such, we determined that the similar increase in cellulose and phytol δ2H values as an effect of impaired starch synthesis most likely originates in triose-phosphates.