Abstract
Tidal marshes sequester 11.4–87.0 Tg C yr
−1
globally, but climate change impacts can threaten the carbon capture potential of these ecosystems. Tidal marshes occur across a wide range of ...salinity, with brackish marshes (0.5–18 ppt (parts per thousand)) dominating global tidal marsh extents. A diverse mix of freshwater- and saltwater-tolerant plant and microbial communities has led researchers to predict that carbon cycling in brackish wetlands may be less sensitive to changes in salinity than fresh- or saltwater wetlands. Rush Ranch, a well-monitored brackish tidal wetland of the San Francisco Bay National Estuarine Research Reserve, experiences highly variable annual salinity regimes. Within a five-year period (2014–2018), Rush Ranch experienced particularly extreme drought-induced salinization during the 2014 and 2015 growing seasons. During drought years, tidal channel salinity rose from a 15 year baseline of 4.7 ppt to growing season peaks of 10.3 ppt and 12.5 ppt. Continuous eddy covariance data from 2014 to 2018 demonstrate that during drought summers, gross primary productivity (GPP) decreased by 24%, whereas ecosystem respiration remained similar among all five years. Stepwise linear regression revealed that salinity, not air temperature or tidal height, was the dominant driver of annual GPP. A random forest model trained to predict GPP based on environmental data from low salinity years (i.e. naive to salinization) significantly over predicted GPP in drought years. When growing season salinities were doubled, annual estimates of net ecosystem exchange of CO
2
decreased by up to 30%. These results provide ecosystem-scale evidence that increased salinity influences CO
2
fluxes dominantly through reductions in GPP. This relationship provides a starting point for incorporating the effect of changes in salinity in wetland carbon models, which could improve wetland carbon forecasting and management for climate resilience.
Integration of C₁ and C₂ Metabolism in Trees Jardine, Kolby J; Fernandes de Souza, Vinicius; Oikawa, Patty ...
International journal of molecular sciences,
09/2017, Letnik:
18, Številka:
10
Journal Article
Recenzirano
Odprti dostop
C₁ metabolism in plants is known to be involved in photorespiration, nitrogen and amino acid metabolism, as well as methylation and biosynthesis of metabolites and biopolymers. Although the flux of ...carbon through the C₁ pathway is thought to be large, its intermediates are difficult to measure and relatively little is known about this potentially ubiquitous pathway. In this study, we evaluated the C₁ pathway and its integration with the central metabolism using aqueous solutions of
C-labeled C₁ and C₂ intermediates delivered to branches of the tropical species
via the transpiration stream. Delivery of
Cmethanol and
Cformaldehyde rapidly stimulated leaf emissions of
Cmethanol,
Cformaldehyde,
Cformic acid, and
CO₂, confirming the existence of the C1 pathway and rapid interconversion between methanol and formaldehyde. However, while
Cformate solutions stimulated emissions of
CO₂, emissions of
Cmethanol or
Cformaldehyde were not detected, suggesting that once oxidation to formate occurs it is rapidly oxidized to CO₂ within chloroplasts.
C-labeling of isoprene, a known photosynthetic product, was linearly related to
CO₂ across C₁ and C₂ (
C₂acetate and 2-
Cglycine) substrates, consistent with reassimilation of C₁, respiratory, and photorespiratory CO₂. Moreover,
Cmethanol and
Cformaldehyde induced a quantitative labeling of both carbon atoms of acetic acid emissions, possibly through the rapid turnover of the chloroplastic acetyl-CoA pool via glycolate oxidation. The results support a role of the C₁ pathway to provide an alternative carbon source for glycine methylation in photorespiration, enhance CO₂ concentrations within chloroplasts, and produce key C₂ intermediates (e.g., acetyl-CoA) central to anabolic and catabolic metabolism.
EPA reports a steady decline of US anthropogenic NO x emissions in 2005–2019 summers, while NO2 vertical column densities (VCDs) from the OMI satellite over large spatial domains have flattened since ...2009. To better understand the contributing factors to a flattening of the OMI NO2 trends, we investigate the role of soil and lightning NOx emissions on this apparent disagreement. We improve soil NO x emissions estimates using a new observation-based temperature response, which increases the linear correlation coefficient between GEOS-Chem simulated and OMI NO2 VCDs by 0.05–0.2 over the Central US. Multivariate trend analysis reveals that soil and lightning NO x combined emissions trends change from −3.95% a−1 during 2005–2009 to 0.60% a−1 from 2009 to 2019, thereby rendering the abrupt slowdown of total NO x emissions reduction. Non-linear inter-annual variations explain 6.6% of the variance of total NO x emissions. As background emissions become relatively larger with uncertain inter-annual variations, the NO2 VCDs alone at the national scale, especially in the regions with vast rural areas, will be insufficient to discern the trend of anthropogenic emissions.
Agricultural soils are important sources of greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O), as well as nitric oxide (NO), a precursor to tropospheric ozone. Management approaches that ...constrain these emissions can limit future warming and improve regional air quality, especially in high-temperature agroecosystems where soil emissions are high. Subsurface drip irrigation is a promising management solution that can limit emissions via targeted rhizosphere access to water and nitrogenous fertilizers. In complementary field studies in southern California, we compared per-yield irrigation and soil emissions in surface- and drip-irrigated field plots growing alfalfa (Medicago sativa L.) and sudangrass (Sorghum bicolor ssp. Sudanese), two forage crops with differing fertilizer requirements. For each study, we monitored soil temperature, moisture, and emission responses to irrigation in both spring and summer using a custom automated chamber array that recorded measurements every 30 minutes. We found that, compared to furrow irrigation, drip irrigation in sudangrass increased hay yield by 6% and per-yield soil CO2 emissions by 9% while it decreased irrigation demand by 49%, N2O emissions by 59%, and NO by 49%. In alfalfa, drip irrigation increased yield by 7% while decreasing irrigation by 1%, per-yield soil CO2 emissions by 59%, N2O by 38%, and NO by 20%. In both crops, differences between irrigation types were strongest in summer months, when high temperatures produced large pulses of N2O and NO in sudangrass and CO2 in alfalfa following flood irrigation relative to small pulses following drip irrigation. As agriculture intensifies in warmer climates, implementation of subsurface drip irrigation can help reduce the emission of soil emissions that affect Earth’s climate and regional air quality.
•Irrigation induced CO2, N2O, and NO pulses from high-temperature agricultural soils.•Subsurface drip irrigation reduced soil CO2, N2O, and NO emissions by up to 62%.•The strongest drip reductions for CO2 were in alfalfa and for N were in sudangrass.•Drip irrigation, compared to flood, weakened seasonal increases in soil emissions.
•Large-scale eddy-covariance flux datasets need to be used with footprint-awareness•Using a fixed-extent target area across sites can bias model-data integration•Most sites do not represent the ...dominant land-cover type at a larger spatial extent•A representativeness index provides general guidance for site selection and data use
Large datasets of greenhouse gas and energy surface-atmosphere fluxes measured with the eddy-covariance technique (e.g., FLUXNET2015, AmeriFlux BASE) are widely used to benchmark models and remote-sensing products. This study addresses one of the major challenges facing model-data integration: To what spatial extent do flux measurements taken at individual eddy-covariance sites reflect model- or satellite-based grid cells? We evaluate flux footprints—the temporally dynamic source areas that contribute to measured fluxes—and the representativeness of these footprints for target areas (e.g., within 250–3000 m radii around flux towers) that are often used in flux-data synthesis and modeling studies. We examine the land-cover composition and vegetation characteristics, represented here by the Enhanced Vegetation Index (EVI), in the flux footprints and target areas across 214 AmeriFlux sites, and evaluate potential biases as a consequence of the footprint-to-target-area mismatch. Monthly 80% footprint climatologies vary across sites and through time ranging four orders of magnitude from 103 to 107 m2 due to the measurement heights, underlying vegetation- and ground-surface characteristics, wind directions, and turbulent state of the atmosphere. Few eddy-covariance sites are located in a truly homogeneous landscape. Thus, the common model-data integration approaches that use a fixed-extent target area across sites introduce biases on the order of 4%–20% for EVI and 6%–20% for the dominant land cover percentage. These biases are site-specific functions of measurement heights, target area extents, and land-surface characteristics. We advocate that flux datasets need to be used with footprint awareness, especially in research and applications that benchmark against models and data products with explicit spatial information. We propose a simple representativeness index based on our evaluations that can be used as a guide to identify site-periods suitable for specific applications and to provide general guidance for data use.
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Nature‐based Climate Solutions (NbCS) are managed alterations to ecosystems designed to increase carbon sequestration or reduce greenhouse gas emissions. While they have growing public and private ...support, the realizable benefits and unintended consequences of NbCS are not well understood. At regional scales where policy decisions are often made, NbCS benefits are estimated from soil and tree survey data that can miss important carbon sources and sinks within an ecosystem, and do not reveal the biophysical impacts of NbCS for local water and energy cycles. The only direct observations of ecosystem‐scale carbon fluxes, for example, by eddy covariance flux towers, have not yet been systematically assessed for what they can tell us about NbCS potentials, and state‐of‐the‐art remote sensing products and land‐surface models are not yet being widely used to inform NbCS policymaking or implementation. As a result, there is a critical mismatch between the point‐ and tree‐scale data most often used to assess NbCS benefits and impacts, the ecosystem and landscape scales where NbCS projects are implemented, and the regional to continental scales most relevant to policymaking. Here, we propose a research agenda to confront these gaps using data and tools that have long been used to understand the mechanisms driving ecosystem carbon and energy cycling, but have not yet been widely applied to NbCS. We outline steps for creating robust NbCS assessments at both local to regional scales that are informed by ecosystem‐scale observations, and which consider concurrent biophysical impacts, future climate feedbacks, and the need for equitable and inclusive NbCS implementation strategies. We contend that these research goals can largely be accomplished by shifting the scales at which pre‐existing tools are applied and blended together, although we also highlight some opportunities for more radical shifts in approach.
Many state‐of‐the‐art tools and approaches for quantifying ecosystem carbon pools and fluxes have not yet been systematically applied to assess or monitor Nature‐based climate solutions (NbCS). Here, we outline steps for using the best‐available science to create robust NbCS assessments that are informed by ecosystem‐scale observations, and which consider concurrent biophysical impacts, future climate feedbacks, and the need for equitable and inclusive implementation.
Abstract
EPA reports a steady decline of US anthropogenic NO
x
emissions in 2005–2019 summers, while NO
2
vertical column densities (VCDs) from the OMI satellite over large spatial domains have ...flattened since 2009. To better understand the contributing factors to a flattening of the OMI NO
2
trends, we investigate the role of soil and lightning NO
x
emissions on this apparent disagreement. We improve soil NO
x
emissions estimates using a new observation-based temperature response, which increases the linear correlation coefficient between GEOS-Chem simulated and OMI NO
2
VCDs by 0.05–0.2 over the Central US. Multivariate trend analysis reveals that soil and lightning NO
x
combined emissions trends change from −3.95% a
−1
during 2005–2009 to 0.60% a
−1
from 2009 to 2019, thereby rendering the abrupt slowdown of total NO
x
emissions reduction. Non-linear inter-annual variations explain 6.6% of the variance of total NO
x
emissions. As background emissions become relatively larger with uncertain inter-annual variations, the NO
2
VCDs alone at the national scale, especially in the regions with vast rural areas, will be insufficient to discern the trend of anthropogenic emissions.
Compost amendment to rangelands is a proposed nature‐based climate solution to increase plant productivity and soil carbon sequestration. However, it has not been evaluated using quasicontinuous ...ecosystem‐scale measurements. Here, we present the first study to utilize eddy covariance and footprint partitioning to monitor carbon exchange in a grassland with and without compost amendment, monitoring for 1 year before and 1 year after treatment. Compost amendment to an annual California grassland was found to enhance net ecosystem removal of carbon. Our study confirmed that compost‐amended grasslands, similar to nonamended grasslands, are net carbon sources to the atmosphere; however, the amendment appears to be slowing down the rate at which these ecosystems lose carbon by 0.71 Mg C ha−1 per growing season. Digital repeated imagery of the canopy revealed that compost‐amended grasslands experienced an earlier green‐up, resulting in an overall longer growing season by >60 days. Notably, we did not detect significantly higher amounts of soil carbon in compost‐amended soils. High variability in soil carbon demands greater sampling replication in future studies. A longer growing season and higher productivity are hypothesized to be a result of greater availability of macronutrients and micronutrients in the top layer of soil (specifically nitrogen, phosphorus, and zinc).
Plain Language Summary
Previous research in California rangelands has shown that spreading a single thin layer of compost on grasslands can improve plant growth and therefore help to store more carbon in the soil. However, this previous research was constrained to small research plots. This is the first study that continuously monitored how compost affects the flow of carbon into and out of the grassland across multiple acres using a technique called eddy covariance. Our study confirmed that grasslands that receive compost have overall higher productivity or photosynthesis compared to control grasslands. Soil measurements found significantly elevated nutrients in the top layer of soil, specifically nitrogen, phosphorus, and zinc. Further, this was the first study to continuously take digital pictures to understand how compost affects the life cycles of grassland ecosystems. Examining these images revealed that the compost extended the growing season of the grasslands by >60 days. We hypothesize that the compost added essential nutrients to the soil that allowed the grasses to have a longer growing season and have higher productivity, confirming earlier studies that compost amendment to grasslands may be a viable approach for mitigating climate change.
Key Points
A compost amendment to a grazed CA grassland enhanced gross primary productivity, due to an earlier green‐up and longer growing season
Soil nitrogen, phosphorus, and zinc were significantly elevated in surface soils following compost amendment
Changes in phenology highlight the importance of scale‐emergent processes associated with nature‐based climate solutions
The aquatic landscapes of the Sacramento–San Joaquin Delta (hereafter, the Delta) and Suisun Bay represent both a significant past and future soil carbon stock. Historical alterations of hydrologic ...flows have led to depletion of soil carbon stocks via emissions of carbon dioxide (CO2), and loss of elevation as a result of subsidence. Optimizing ecosystem hydrology in the Delta and Suisun Bay could both reduce and reverse subsidence while also providing significant opportunities for climate mitigation and adaptation. Emissions of greenhouse gases (GHGs)—notably CO2, methane (CH4 ), and nitrous oxide (N2O)—contribute to global warming at different rates and intensities, requiring GHG accounting and modeling to assess the relative benefits of management options. Decades of data collection, model building, and map development suggest that past and current management actions have both caused—and can mitigate—losses of soil carbon. We review here the magnitude of potential GHG offsets, management options that may be achievable, and trade-offs of carbon storage under different land management. Using a land-use/land-cover framework to assess these management options, we describe the potential of three interventions (impoundment to reverse subsidence, agricultural management, and tidal reintroduction and/or maintained connectivity), both in acreage and radiative balance to clarify their relative influence on the region’s GHG balance today and in relation to its millennial history. From floodplains to farming to floating aquatic vegetation, we find specific scalable strategies to manage hydrology that can alter regional GHG balance. Preservation of soil carbon stocks and restoration of net atmospheric CO2 fluxes into soils are the primary route to net negative emissions in the Delta and Suisun Bay, with CH4 emission management occurring in a supporting role. Over a 40-year horizon of climate-mitigation markets, the resilience of different aquatic habitats introduces the most uncertainty, from expected and unexpected hydrologic changes associated with land, ocean, and operational water flows.
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