Changes In Carbon Fluxes Research Articles

Unexpected Consequences of River Engineering on the Carbon Cycle

AbstractRivers around the world have been heavily engineered, and these man‐made changes are affecting important biogeochemical cycles. Rivers play a key role in the global carbon cycle, by mobilizing organic carbon from land and delivering it to the oceans. River engineering techniques, like levees that prevent flooding, change the way carbon is cycled through rivers, but it is difficult to identify and quantify these changes. Shen et al. (2021) were able to quantify changes in river organic carbon fluxes induced by bank stabilization in the Mississippi River. The authors compared the age distribution of organic carbon in modern river sediment and old river sediment deposited before the construction of extensive levee systems. They found that bank stabilization significantly reduces the amount of time organic carbon spends in the river system before being exported to the Gulf of Mexico. As a result, less organic carbon is oxidized to CO2 and more organic carbon is exported to the ocean, ultimately reducing atmospheric CO2. This study highlights an important effect of anthropogenic activity on river carbon fluxes that should be considered in global carbon cycle models.

The soil Microbial Carbon Pump as a new concept for terrestrial carbon sequestration

Soil is a huge terrestrial carbon pool, which has higher carbon storage than the sum of atmospheric and terrestrial vegetation carbon. Small fluctuations in soil carbon pool can affect regional carbon flux and global climate change. As soil organic carbon plays key roles in soil carbon storage and sequestration, studying its composition, sources and stability mechanism is a key to deeply understand the functions of terrestrial ecosystem and how it will respond to climate changes. The recently-proposed concept of soil Microbial Carbon Pump (MCP) emphasizes the importance of soil microbial anabolism and its contributions to soil carbon formation and stabilization, which can be applied for elucidating the source, formation and sequestration of soil organic carbon. This article elaborates MCP-mediated soil carbon sequestration mechanism and its influencing factors, as well as representative scientific questions we may explore with the soil MCP conceptual framework.

Changes in soil properties and carbon fluxes following afforestation and agriculture in tropical forest

Anthropogenic land use change (LUC) affects soil quality and the global carbon (C) pool. Such LUC is a potential threat for forest ecosystems because it can alter soil biome and increases the emission of greenhouse gasses (GHGs). Here, we investigated the changes in soil quality and CO2 emission following afforestation of reclaimed coal mine land and agriculture land created in a tropical dry deciduous forest of Jharkhand, India. Soil samples were collected from afforested mined soil (AMS), agriculture soils (AGS), and the natural forest soils (NFS) and analyzed for physicochemical and biological properties. Soil infiltration rate and CO2 efflux were recorded in situ, and C balance and emission coefficient (Ci) were calculated to determine soil C dynamics.Our results demonstrated significant alteration in soil quality parameters (decreases/increases based on the individual parameter) in converted land use. Compared to NFS, soil organic carbon (SOC) stocks decreased by 84% in AMS and 50% in AGS, soil CO2 efflux increased by 35% in AGS and decreased by 43% in AMS, attributed to differences in vegetation and microbial activities among sites. Principal component analysis showed soil infiltration rate, total nitrogen, and clay content were highly influenced by the LUC and explicitly indicate soil quality. The 4-year old AMS was C negative and had a greater Ci value than AGS and NFS, probably due to the lesser vegetation cover and adverse soil properties. We concluded that the conversion of tropical forests to different lands altered soil quality that can be assessed using indicator parameters like soil infiltration rate, total nitrogen, and clay content. Such LUC tends to switch the forest from a sink to a source of CO2 whether the end use is afforestation or agriculture. However, land degradation due to surface mining activities had a greater impact on soil quality and C sequestration potential than agriculture.

Temporal Changes in Ozone Concentrations and Their Impact on Vegetation

Tropospheric concentrations of phytotoxic ozone (O3) have undergone a great increase from preindustrial 10–15 ppbv to a present-day concentration of 35–40 ppbv in large parts of the industrialised world due to increased emissions of O3 precursors including NOx, CO, CH4 and volatile organic compounds. The rate of increase in O3 concentration ranges between 1 ppbv per decade in remote locations of the Southern hemisphere and 5 ppbv per decade in the Northern hemisphere, where largest sources of O3 precursors are located. Molecules of O3 penetrating into the leaves through the stomatal apertures trigger the formation of reactive oxygen species, leading thus to the damage of the photosynthetic apparatus. Accordingly, it is assumed, that O3 increase reduces the terrestrial carbon uptake relative to the preindustrial era. Here we summarise the results of previous manipulative experiments in laboratory growth cabinets, field open-top chambers and free-air systems together with O3 flux measurements under natural growth conditions. In particular, we focus on leaf-level physiological responses in trees, variability in stomatal O3 flux and changes in carbon fluxes and biomass production in forest stands. As the results reported in the literature are highly variable, ranging from negligible to severe declines in photosynthetic carbon uptake, we also discuss the possible interactions of O3 with other environmental factors including solar radiation, drought, temperature and nitrogen deposition. Those factors were found to have great potential to modulate stomata openness and O3 fluxes.

Sediment trap-derived particulate matter fluxes in the oligotrophic subtropical gyre of the South Indian Ocean

Oligotrophic areas cover about 75% of the ocean's surface, and these ocean regions are predicted to expand under global warming scenarios. To evaluate impacts on global marine biogeochemical cycles and changes in ocean-atmosphere carbon fluxes, it is essential to understand particulate matter fluxes and determine the amount of organic carbon that is exported to the ocean's interior. The oligotrophic Indian Ocean subtropical gyre (IOSG) is one of the least explored ocean regions in terms of particulate matter fluxes. Sediment trap-based particulate matter fluxes determined during a 4-year time series provide new information on the nature of export fluxes, their controlling factors, and on the spatial and temporal variability of oceanic processes in the IOSG. Trap-averaged total mass fluxes (~9.8 ± 3.7 mg m−2 day−1), as well as particulate organic carbon (POC) fluxes (0.50 ± 0.15 mg m−2 day−1) measured at 500–600 m above bottom (2600–3500 m water depth) are among the lowest fluxes recorded worldwide. These low flux values are a result of strongly stratified and nutrient-depleted upper waters in the gyre. Such oligotrophic conditions lead to low primary production rates in a relatively homogeneous and isolated ocean region. Consequently, we observe an almost constant rain of POC fluxes in space and time, although minor variations in the net primary production (NPP) and in the sea surface temperature (SST) are seen in satellite surveys and model estimations. Factors contributing to the lack of seasonality in the POC fluxes are intense organic matter degradation, variations in the ocean mixed layer depth (OMLD), and impacts of physical mixing (surface wind stress, cyclonic eddies). Preliminary estimates indicate that the average POC export efficiency (ε = 0.03 ± 0.01) is extremely low in the IOSG. Assuming that the IOSG, as well as comparable ocean regions, will expand under climate warming conditions, it is of major importance to investigate POC export fluxes to the deep ocean in order to predict changes in the global carbon cycle during the next decades.

Carbon uptake and water vapor exchange in a pasture site in the Brazilian Cerrado

As Brazil becomes one of the largest agricultural and livestock producers, the expansion of cultivated pasture and crop areas in the Cerrado region is expected to cause significant changes in carbon and water vapor fluxes. While this change in land use promotes modifications in regional carbon uptake and water cycle, eddy covariance studies carried out in pasture areas in the Brazilian Cerrado remain scarce. The present study aimed to quantify the carbon uptake and water vapor exchange of these areas in the Brazilian Cerrado. The experimental site was installed in an area covered by Brachiaria sp. in Três Lagoas – MS, Brazil. Data were collected during two hydrological years (2016–2017 and 2017–2018). Pasture strongly acted as a carbon sink; its total accumulation reached −208.9 (±9.6) and −171.8 (±15.8) g C m−2 in the first and second hydrological years, respectively. Average evapotranspiration of 2.0 (±1.1) mm d−1 was observed in the two hydrological years. There was significant reduction in evapotranspiration at the pasture site during the driest months of the year (June and July), mainly in the second hydrological year, which recorded an average of 0.4 (±0.1) mm d−1. The lower recorded water availability in the soil led to the release of 86.7 g C m−2 (over 85 days) in the dry season of the second hydrological year. Ecosystem-level water use efficiency observed during the higher soil water deficit facilitated the survival of the grass. This information is the basis for further studies about the impact of climate change on carbon uptake and water vapor flux by cultivated and natural pasture; additionally, the present research will allow comparisons of carbon storage results to other ecosystems and to support studies of agrometeorological modeling.

Global climate response to idealized deforestation in CMIP6 models

Abstract. Changes in forest cover have a strong effect on climate through the alteration of surface biogeophysical and biogeochemical properties that affect energy, water and carbon exchange with the atmosphere. To quantify biogeophysical and biogeochemical effects of deforestation in a consistent setup, nine Earth system models (ESMs) carried out an idealized experiment in the framework of the Coupled Model Intercomparison Project, phase 6 (CMIP6). Starting from their pre-industrial state, models linearly replace 20×106 km2 of forest area in densely forested regions with grasslands over a period of 50 years followed by a stabilization period of 30 years. Most of the deforested area is in the tropics, with a secondary peak in the boreal region. The effect on global annual near-surface temperature ranges from no significant change to a cooling by 0.55 ∘C, with a multi-model mean of -0.22±0.21 ∘C. Five models simulate a temperature increase over deforested land in the tropics and a cooling over deforested boreal land. In these models, the latitude at which the temperature response changes sign ranges from 11 to 43∘ N, with a multi-model mean of 23∘ N. A multi-ensemble analysis reveals that the detection of near-surface temperature changes even under such a strong deforestation scenario may take decades and thus longer than current policy horizons. The observed changes emerge first in the centre of deforestation in tropical regions and propagate edges, indicating the influence of non-local effects. The biogeochemical effect of deforestation are land carbon losses of 259±80 PgC that emerge already within the first decade. Based on the transient climate response to cumulative emissions (TCRE) this would yield a warming by 0.46 ± 0.22 ∘C, suggesting a net warming effect of deforestation. Lastly, this study introduces the “forest sensitivity” (as a measure of climate or carbon change per fraction or area of deforestation), which has the potential to provide lookup tables for deforestation–climate emulators in the absence of strong non-local climate feedbacks. While there is general agreement across models in their response to deforestation in terms of change in global temperatures and land carbon pools, the underlying changes in energy and carbon fluxes diverge substantially across models and geographical regions. Future analyses of the global deforestation experiments could further explore the effect on changes in seasonality of the climate response as well as large-scale circulation changes to advance our understanding and quantification of deforestation effects in the ESM frameworks.

Authigenic Ferrimagnetic Iron Sulfide Preservation Due to Nonsteady State Diagenesis: A Perspective From Perseverance Drift, Northwestern Weddell Sea

AbstractWe document magnetic mineral diagenesis with high‐resolution magnetic susceptibility, hysteresis, isothermal remanent magnetization, and other rock magnetic measurements through a shallow sulfate‐methane transition (SMT) at Perseverance Drift—a high‐accumulation rate Holocene biosiliceous Antarctic marine sediment deposit. The structure of the SMT is defined with porewater measurements from the same core, allowing direct comparison. Dissolution of the detrital (titano)magnetite assemblage, with preferential dissolution of stochiometric magnetite, occurs in the upper SMT. Higher coercivity magnetic minerals dissolve more slowly, continuing to dissolve through the entire SMT and could be a source of ferric iron for microbial respiration following exhaustion of porewater sulfate, as suggested by accumulation of porewater ferrous iron below the SMT. Superparamagnetic ferrimagnetic mineral enrichment/depletion occurs in three phases through the SMT and is coupled tightly to the availability of dissolved ferrous iron relative to dissolved sulfide. High concentrations of authigenic remanence‐bearing iron sulfides, including greigite and hexagonal 3C pyrrhotite, which can be detected using remanence parameters but not in‐field concentration dependent parameters, accumulate in a transient horizon at the base of the SMT during this early diagenesis, where sulfide is present but limited relative to dissolved ferrous iron. Formation of this remanence‐bearing iron sulfide horizon is likely facilitated by continued iron reduction through the SMT. Nonsteady state perturbations that shift the porewater profile, such as changes in carbon flux or sedimentation rate, can lead to preservation of these transient horizons, much like well documented preservation of manganese oxide layers in marine sediments following similar shifts to porewater profiles.

Metabolic Niches and Biodiversity: A Test Case in the Deep Sea Benthos

The great anthropogenic alterations occurring to carbon availability in the oceans necessitates an understanding of the energy requirements of species and how changes in energy availability may impact biodiversity. The deep oceans are characterized naturally by extremely low availability of chemical energy and are particularly vulnerable to changes in carbon flux from surface waters. Because the energetic requirements of an organism impact nearly every aspect of their ecology and evolution, we hypothesize that species are adapted to specific levels of carbon availability and occupy a particular metabolic niche. We test this hypothesis in deep-sea invertebrates specifically examining how energetic demand, axes of the metabolic niche, and geographic range size vary over gradients of chemical energy availability. We find that species with higher energetic expenditures, and ecologies associated with high energy demand, are located in areas with higher chemical energy availability. In addition, we find that range size and location of deep-sea species is determined by geographic patterns in chemical energy availability. Our findings indicate that deep-sea species are adapted to specific energy regimes, the metabolic niche can potentially link scales from individuals to ecosystems, and link adaptation to patterns in biogeography and biodiversity.

Spatial patterns and climate controls of seasonal variations in carbon fluxes in China's terrestrial ecosystems

Abstract Seasonal changes in CO2 exchange determine the strength and dynamics of the carbon budget in terrestrial ecosystems. Knowledge about seasonal and spatial variations in carbon fluxes (net ecosystem productivity (NEP), gross primary productivity (GPP), and ecosystem respiration (RE)) is thus essential to support accurate modeling of carbon flux dynamics. To the best of our knowledge, this study represents the first comprehensive evaluation of how carbon fluxes vary seasonally in different ecoregions in China. Using eddy covariance measurements from ChinaFLUX, we analyzed the spatial variations and climate controls of the phenological and physiological properties of NEP, GPP, and RE across China. Apart from the beginning and ending day of NEP (net carbon uptake), the phenological properties of the carbon fluxes varied significantly with latitude; however, there were no evident trends in the physiological properties of the carbon fluxes with latitude (apart from the annual values of GPP and RE, known as AGPP and ARE). The spatial variation in the physiological properties of GPP and RE was influenced by the precipitation patterns, while the spatial distribution of the phenological properties of GPP and RE was related to air temperature. Moreover, the spatial variation for the end of the growing season changed with the autumn mean soil temperatures. The factors that contributed to the spatial distribution in the annual NEP (ANEP) and annual GPP and RE (AGPP and ARE) were quite different. The mean daily GPP and RE were the main contributors to the spatial variations in AGPP and ARE, while the net carbon uptake period was the main contributor to the spatial variation in ANEP. In this study, we identified a series of ecological parameters and reference values for seasonal patterns that can be used to validate models that simulate changes in regional carbon fluxes.

Increased carbon uptake and water use efficiency in global semi-arid ecosystems

The semi-arid ecosystems dominate the inter-annual variability of the global carbon sink and the driving role of semi-arid ecosystems is becoming increasingly important. However, the impacts of climate change on the dynamics of carbon and water fluxes in global semi-arid ecosystems are still not well understood. We used a data-driven (or machine learning) approach, along with observations from a number of FLUXNET sites and spatially continuous satellite and meteorological data, to generate gridded carbon and water flux estimates for semi-arid regions globally, and then examined the magnitude, spatial patterns, and trends of carbon and water fluxes and their responses to climate change during the period 1982–2015. The average annual gross primary productivity (GPP), net ecosystem productivity (NEP), evapotranspiration (ET), and water use efficiency (WUE) were 628.6 g C m−2 yr−1, 9.6 g C m−2 yr−1, 463.1 mm yr−1, and 1.60 g C Kg−1 H2O, respectively. The climate conditions during the period 1982–2015 enhanced gross and net carbon uptake in global semi-arid regions. The spatially-averaged annual GPP, NEP, ET, and WUE in semi-arid regions showed significant increases both globally and regionally (Asia, Africa, and Australia). As with GPP and ET, WUE significantly increased in North America, Asia, Africa, and Australia. Australia was the most sensitive semi-arid region in terms of changes in carbon and water fluxes and their responses to climate. Semi-arid forests, shrublands, and savannas were net carbon sinks; croplands were minor carbon sources; grasslands were nearly carbon neutral. Overall, precipitation was the most important climate factor influencing the carbon and water fluxes; WUE in 40.9% of the semi-arid region was significantly influenced by precipitation. The global climate change is expected to influence global semi-arid ecosystems in many ways and our findings have implications for semi-arid ecosystem management and policy making.

Seasonal variability of forest sensitivity to heat and drought stresses: A synthesis based on carbon fluxes from North American forest ecosystems.

Climate extremes such as heat waves and droughts are projected to occur more frequently with increasing temperature and an intensified hydrological cycle. It is important to understand and quantify how forest carbon fluxes respond to heat and drought stress. In this study, we developed a series of daily indices of sensitivity to heat and drought stress as indicated by air temperature (Ta ) and evaporative fraction (EF). Using normalized daily carbon fluxes from the FLUXNET Network for 34 forest sites in North America, the seasonal pattern of sensitivities of net ecosystem productivity (NEP), gross ecosystem productivity (GEP) and ecosystem respiration (RE) in response to Ta and EF anomalies were compared for different forest types. The results showed that warm temperatures in spring had a positive effect on NEP in conifer forests but a negative impact in deciduous forests. GEP in conifer forests increased with higher temperature anomalies in spring but decreased in summer. The drought-induced decrease in NEP, which mostly occurred in the deciduous forests, was mostly driven by the reduction in GEP. In conifer forests, drought had a similar dampening effect on both GEP and RE, therefore leading to a neutral NEP response. The NEP sensitivity to Ta anomalies increased with increasing mean annual temperature. Drier sites were less sensitive to drought stress in summer. Natural forests with older stand age tended to be more resilient to the climate stresses compared to managed younger forests. The results of the Classification and Regression Tree analysis showed that seasons and ecosystem productivity were the most powerful variables in explaining the variation of forest sensitivity to heat and drought stress. Our results implied that the magnitude and direction of carbon flux changes in response to climate extremes are highly dependent on the seasonal dynamics of forests and the timing of the climate extremes.

Seasonal and spatial changes in carbon and nitrogen fluxes estimated using 234Th:238U disequilibria in the North Pacific tropical and subtropical gyre

Particle dynamics are an essential component of global ocean biogeochemistry as they transport essential nutrients, carbon, and other reactive elements and compounds from the surface ocean to depth in the water column. The North Pacific Ocean is characterized by spatial and temporal variations in particle export mediated by a diverse food web and variations in environmental conditions, such as oxygenation. Here we explored temporal variability in the downward flux of particulate carbon (PC) and nitrogen (PN) using 238U234Th disequilibria, sediment traps and in situ pumps in winter, spring and summer at the time-series site Station ALOHA, a region characterized by a well-defined summer export pulse that influences the composition and structure of the biological community within the mesopelagic zone. We further explored spatial variability in PC and PN fluxes along a latitudinal gradient (17.5°-5°N x 150°W) that transitions from a low to high productivity region influenced by equatorial upwelling, with several stations further characterized by a shallow (~ 130 m) oxygen minimum zone. Winter PC and PN fluxes at 150 m at Station ALOHA were low, while summer and spring fluxes were significantly higher, coinciding with a seasonal export pulse associated with diazotrophs. PC and PN fluxes along the 155°W transect were also low at 150 m and similar to those measured at Station ALOHA in winter. At Station ALOHA zooplankton impart a greater influence over both small and large PC (and PN) fluxes in February relative to September or May, when heterotrophic bacteria play a proportionally larger role in particle remineralization and cycling. Along the transect stations, PC fluxes were too low to discern any clear trends with latitude, likely due to El Niño conditions at the time of sampling. Where vertical water column profiles of PC and PN fluxes were available, PC (and PN) fluxes were found to peak in the subsurface at 8°N (50 m) and 5°N (75 m) with zooplankton grazing and microbial remineralization following patterns similar to those found in February at Station ALOHA. Combined, these results support the hypothesis that small and large particles contribute to mesopelagic carbon demand depending on season, with smaller particles having greater contributions to mesopelagic food webs when surface derived particle export is low.

Changes in carbon flux and spectral reflectance of Sphagnum mosses as a result of simulated drought

AbstractSphagnum is an important peat‐forming genus, which aids the carbon sequestration of peatlands. Sphagnum is sensitive to drought; however, and it is uncertain how well it can recover from long periods without rainfall. Spectral reflectance can be used to assess Sphagnum desiccation damage, and we also tested whether it can be used to detect recovery. Different rainfall simulations were applied to two species of Sphagnum to assess the impact of drought on carbon function. After 80 days all samples were rewetted to assess recovery. The rainfall simulations included inputs analogous to actual precipitation at the field site (Forsinard Flows reserve, Northern Scotland), potential future changes in rainfall, and extended total drought. During the experiment gross primary productivity and respiration were measured. Photosynthesis decreased after approximately 30 days of continuous drought (i.e., days without rain). Spectral reflectance was measured to assess Sphagnum bleaching. The spectral absorption feature of Sphagnum associated with red light (around 650 nm) was affected by drought and did not recover after rewetting during the experimental period. No significant difference was found between the two Sphagnum species studied with respect to their photosynthesis or respiration, but there was a significant difference in optimum water content and spectral reflectance between the two. The results from this study suggest that Sphagnum carbon function is resilient to quite long drought periods, but once damage has occurred recovery is likely to be difficult. The spectral reflectance of Sphagnum can give useful information in assessing whether significant desiccation damage has occurred.

Application Of The Denitrification-Decomposition (DNDC) Model To Retrospective Analysis Of The Carbon Cycle Components In Agrolandscapes Of The Central Forest Zone Of European Russia

The retrospective dynamics of major components of the carbon cycle under land use changes in the Central Forest zone of European Russia was investigated. This area is known as one of the most important agricultural and economical regions of the country. We applied the process-based simulation model DNDC (DeNitrification-DeComposition) recommended by UNCCC and world widely used. In this study the DNDC model was parameterized for Russian arable soils using official statistical information and data taken from published sources. Three main carbon variables in agrolandscapes were modelled: soil organic carbon, soil respiration, and net ecosystem exchange over the period of 1990-2017. For the analysis six administrative regions were selected: three with unchanged (permanent) arable land structure (Kaluga, Moscow, and Yaroslavl), and other three with changed crop rotation (Kostroma, Smolensk, and Tver). All regions in the study are characterized by homogeneous soil cover and similar cultivated crops. The results of the modelling were verified using the data from field CO 2 fluxes observations in the European part of Russia. In growing season, the agrolandscapes function as a net carbon sink and accumulate C from the atmosphere into plant biomass. The dynamics of organic carbon in soil under growing crops depends on organic fertilizers in cultivation technologies, and if they aren’t inputted, soil loses carbon. During the last 30 years the cumulative rates of net ecosystem exchange and soil respiration had decreased mostly due to reduction of arable land area. CO 2 emission and soil organic carbon losses are the most important controls of land degradation. Based on the dynamic patterns of CO 2 fluxes, the regions of the Central Forest zone could be separated into two groups. The group with central location characterized by intensive soil respiration and high rate of accumulation of organic carbon in soil, whereas peripheral group characterized by losses of soil organic carbon and low rates of soil respiration. According to the modelling, within the period of observations the inter-annual changes of carbon fluxes are mainly controlled by rising air temperature and heat supply, variable precipitation, and increasing concentration of CO 2 in the atmosphere. Among human activity the most important are change of arable land area and decreasing amount of fertilizers.

Two‐Timescale Carbon Cycle Response to an AMOC Collapse

AbstractAtmospheric CO2 concentrations (pCO2) varied on millennial timescales in phase with Antarctic temperature during the last glacial period. A prevailing view has been that carbon release and uptake by the Southern Ocean dominated this millennial‐scale variability in pCO2. Here, using Earth System Model experiments with an improved parameterization of ocean vertical mixing, we find a major role for terrestrial and oceanic carbon releases in driving the pCO2 trend. In our simulations, a change in Northern Hemisphere insolation weakens the Atlantic Meridional Overturning Circulation (AMOC) leading to increasing pCO2 and Antarctic temperatures. The simulated rise in pCO2 is caused in equal parts by increased CO2 outgassing from the global ocean due to a reduced biological activity and changed ventilation rates, and terrestrial carbon release as a response to southward migration of the Intertropical Convergence Zone. The simulated terrestrial release of carbon could explain stadial declines in organic carbon reservoirs observed in recent ice core δ13C measurements. Our results show that parallel variations in Antarctic temperature and pCO2 do not necessitate that the Southern Ocean dominates carbon exchange; instead, changes in carbon flux from the global ocean and land carbon reservoirs can explain the observed pCO2 (and δ13C) changes.

Mitochondrial Driving Forces and Metabolic Resilience

Evidence supporting a causal link between mitochondrial performance and disease risk has been bolstered by the advent and application of state‐of‐the‐art multi‐omics molecular profiling technologies, such as genomics, proteomics and metabolomics. Although these are powerful tools that can produce provocative molecular signatures of disease, they still do not tell us how well (or not) mitochondria resident in specific tissues are able to maintain the free energy of ATP hydrolysis (ΔGATP, i.e. ATP:ADP ratio)–the energetic currency that powers normal cell and organ function. Thus, we came to recognize that progress toward deciphering the precise role of mitochondria in the disease process requires sophisticated approaches that can assess changes in carbon flux and bioenergetics in intact mitochondria working to regenerate ATP, and maintain ΔGATP, in the context of physiologically relevant energy demands and thermodynamic constraints (i.e. backpressure). To this end, we developed a new multiplexed assay platform for interrogating respiratory kinetics and thermodynamics under multiple substrate and energetic conditions. Unlike conventional respirometry methods, the new platform permits comprehensive assessment of respiratory fluxes (JO2) and energy transduction, which refers to the transfer of energy in carbon fuels–to electron potential energy (NAD(P)H/NAD+ redox)–to membrane potential–to ΔGATP. Importantly, these assays are performed in the context of dynamic extramitochondrial ATP:ADP concentrations (i.e. ΔGATP) that are precisely controlled within a (near) physiologic range. In simple terms, our diagnostic assays mimic an exercise “stress test” by evaluating how well a given population of mitochondria, fueled by specific mixtures of carbon substrates, responds to a graded energetic challenge. We have been combining this platform with mass spectrometry‐based metabolomics and proteomics to evaluate mitochondrial remodeling, and corresponding changes in respiratory power and efficiency, in response to a variety of nutritional and genetic maneuvers. This seminar will discuss new insights pertaining to the interplay between mitochondrial driving forces and metabolic resilience.Support or Funding InformationSupported by grants from NIDDK and NHLBI.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Carbon and evapotranspiration dynamics of a non-native perennial grass with biofuel potential in the southern U.S. Great Plains

Old world bluestem cultivar WW-B Dahl [Bothriochloa bladhii (Retz.), S. T. Blake] is a non-native perennial C4 bunch grass with biofuel production potential grown predominantly in the Southern U.S. Great Plains. Although this is a popular introduced grass cultivar, data on carbon fluxes and evapotranspiration (ET) from this warm-season grass is rare. In this study, the eddy covariance method was used to measure CO2 and ET from an established stand of bluestem for three years (2013–2015). Year 2015 had the highest gross primary production (GPP; 1358 ± 143 g C m−2) followed by 2014 (1250 ± 31 g C m−2) and 2013 (1024 ± 91 g C m−2). The average loss of GPP as ecosystem respiration (Reco) was 76%. Annual NEE sums were -302 ± 15 g C m−2 in 2013, -265 ± 41 g C m-2 in 2014, and -287 ± 32 g C m−2 in 2015. Results from this study show that the NEE in grasslands in years with normal precipitation that is well distributed may not vary from years with above-normal precipitation. This is because precipitation enhances Reco along with carbon uptake, which may result in lower net carbon uptake in perennial grasslands in higher precipitation years than normal precipitation years. Gross primary production showed a linear relationship with ET (R2 = 0.90) and above ground biomass (R2 = 0.74). Only 26% of the GPP was allocated to above ground biomass indicating a higher allocation of carbon to below ground biomass. The water use efficiency of bluestem (2.9 g C kg-1 of water) matched well with that of native prairies and other dedicated biomass crops grown in the Southern Great Plains. As the demand for cellulosic biofuels is increasing, results from field experiments quantifying seasonal changes in carbon fluxes and ET could be important in understanding the contributions of large-scale production of novel biomass crops to regional carbon and hydrologic cycles.

Soil organic carbon storage following conversion from cropland to grassland on sites differing in soil drainage and erosion history

Changing soil use from cropland to grassland influences organic carbon storage in a highly complex way. This includes the root/shoot allocation, the root depth distribution, the incorporation of shoot biomass and lateral organic carbon fluxes, by erosion and removal of harvested carbon, and finally the aeration by tillage. An experiment was designed allowing resampling a number of soils 18 yr after conversion to grassland (either pasture or meadow or set-aside) only 20 cm apart from the original sampling to exclude site variation. Before conversion to grassland the cropland was prone to erosion, with a mean lateral carbon flux during 20 yr prior to conversion of 13 t ha−1. Harvest had removed another 29 t ha−1 of carbon at eroding sites. Colluvial carbon inputs had been up to 18 t ha−1 while harvest had removed 38 t ha−1 at colluvial sites. The carbon fluxes by erosion were negligible during the 18 yr period after conversion. After conversion the carbon losses by harvest also ceased at set-aside grassland and pastures while the net losses on meadows were 45 t ha−1. Conversion to grassland significantly changed depth functions of carbon, stones, bulk density and porosity. Despite the large changes in carbon fluxes, carbon stocks did only change significantly within 18 yr under poorly drained, gleyic soils. Well-aerated soils did not show a significant increase in SOC stocks. This was even true for heavily eroded soils, where conversion from cropland to grassland (without erosion) should foster dynamic replacement of SOC. The widespread drainage of wet grassland soils prior to conversion to cropland thus can cause a large release of carbon, while an influence of tillage by either increasing aeration or erosion could not be detected in this study. Therefore, fostering carbon sequestration by conversion of cropland to grassland requires restoring former draining conditions.

Records of carbon and sulfur cycling during the Silurian Ireviken Event in Gotland, Sweden

Abstract Early Silurian (∼431 Ma) carbonate rocks record a ca. 4.5‰ positive excursion in the stable isotopic composition of carbonate carbon (δ13Ccarb). Associated with this isotopic shift is a macroevolutionary turnover pulse known as the ‘Ireviken Event’. The onset of this carbon isotope excursion is commonly associated with a shallowing-upward facies transition that may have been accompanied by climatic change, as indicated by a parallel positive shift (∼0.6‰) in the stable isotopic composition of carbonate oxygen (δ18Ocarb). However, the relationships among carbon cycle perturbations, faunal turnover, and environmental changes remain enigmatic. Here we present a suite of new isotopic data across the Ireviken Event from multiple sections in Gotland, Sweden. These samples preserve no systematic change in δ18Ocarb but show positive excursions of equal magnitude in both carbonate (δ13Ccarb) and organic (δ13Corg) carbon. In addition, the data reveal a synchronous perturbation in sulfur isotope ratios, manifest as a ca. 7‰ positive excursion in carbonate-associated sulfate (δ34SCAS) and a ca. 30‰ positive excursion in pyrite (δ34Spyr). The increase in δ34Spyr values is accompanied by a substantial, concomitant increase in stratigraphic variability of δ34Spyr. The relatively constant offset between the δ13Ccarb and δ13Corg excursions throughout the Ireviken Event could be attributed to increased organic carbon burial, or possibly a change in the isotopic composition of CO2 sources from weathering. However, a positive correlation between carbonate abundance and δ13Ccarb suggests that local to regional changes in dissolved inorganic carbon (DIC) during the shallowing-upward sequence may have been at least partly responsible for the observed excursion. The positive excursion recorded in δ34SCAS suggests a perturbation of sufficient magnitude and duration to have impacted the marine sulfate reservoir. An inverse correlation between CAS abundance and δ34SCAS supports the notion of decreased sulfate concentrations, at least locally, consistent with a concomitant increase in pyrite burial. A decrease in the offset between δ34SCAS and δ34Spyr values during the Ireviken Event suggests a substantial reduction in the isotopic fractionations (epyr) expressed during microbial sulfur cycling and pyrite precipitation through this interval. Decreased epyr and the concomitant increase in stratigraphic variation in δ34Spyr are typical of isotope systematics observed in modern shallow-water environments, associated with increased closed-system behavior and/or oxidative sedimentary reworking during early sediment diagenesis. While the isotopic trends associated with the Ireviken Event have been observed in multiple locations around the globe, many sections display different magnitudes of isotopic change, and moreover, are typically associated with local facies changes. Due to the stratigraphic coherence of the carbon and sulfur isotopic and abundance records across the Ireviken Event, and their relationship to changes in local depositional environment, we surmise that these patterns more closely reflect biogeochemical processes related to deposition and lithification of sediment than global changes in carbon and sulfur burial fluxes.