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Attributing Past Carbon Fluxes to CO 2 and Climate Change: Respiration Response to CO 2 Fertilization Shifts Regional Distribution of the Carbon Sink
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ABSTRACT Photosynthesis is the largest flux of carbon between the atmosphere and Earth's surface and is driven by enzymes that require nitrogen, namely, ribulose‐1,5‐bisphosphate (RuBisCO). Thus, photosynthesis is a key link between the terrestrial carbon and nitrogen cycle, and the representation of this link is critical for coupled carbon‐nitrogen land surface models. Models and observations suggest that soil nitrogen availability can limit plant productivity increases under elevated CO2. Plants acclimate to elevated CO2by downregulating RuBisCO and thus nitrogen in leaves, but this acclimation response is not currently included in land surface models. Acclimation of photosynthesis to CO2can be simulated by the photosynthetic optimality theory in a way that matches observations. Here, we incorporated this theory into the land surface component of the Energy Exascale Earth System Model (ELM). We simulated land surface carbon and nitrogen processes under future elevated CO2conditions to 2100 using the RCP8.5 high emission scenario. Our simulations showed that when photosynthetic acclimation is considered, photosynthesis increases under future conditions, but maximum RuBisCO carboxylation and thus photosynthetic nitrogen demand decline. We analyzed two simulations that differed as to whether the saved nitrogen could be used in other parts of the plant. The allocation of saved leaf nitrogen to other parts of the plant led to (1) a direct alleviation of plant nitrogen limitation through reduced leaf nitrogen requirements and (2) an indirect reduction in plant nitrogen limitation through an enhancement of root growth that led to increased plant nitrogen uptake. As a result, reallocation of saved leaf nitrogen increased ecosystem carbon stocks by 50.3% in 2100 as compared to a simulation without reallocation of saved leaf nitrogen. These results suggest that land surface models may overestimate future ecosystem nitrogen limitation if they do not incorporate leaf nitrogen savings resulting from photosynthetic acclimation to elevated CO2.more » « less
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More than 90% of the world’s hydrogen (H2) is produced from fossil fuel sources, which requires energy-intensive separation and purification to produce high-purity H2fuel and to capture the carbon dioxide (CO2) by-product. While membranes can decarbonize H2/CO2separation, their moderate H2/CO2selectivity requires secondary H2purification by pressure swing adsorption. Here, we report hyperselective carbon molecular sieve hollow fiber membranes showing H2/CO2selectivity exceeding 7000 under mixture permeation at 150°C, which is almost 30 times higher than the most selective nonmetallic membrane reported in the literature. The membrane is able to maintain an ultrahigh H2/CO2selectivity over 1400 under mixture permeation at 400°C. Pore structure characterization suggests that highly refined ultramicropores are responsible for effectively discriminating the closely sized H2and CO2molecules in the hyperselective carbon molecular sieve membrane. Modeling shows that the unprecedented H2/CO2selectivity will potentially allow one-step enrichment of fuel-grade H2from shifted syngas for decarbonized H2production.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2022GB007478
