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1. Carbon isotope trends across a century of herbarium specimens suggest CO ₂ fertilization of C ₄ grasses

   https://doi.org/10.1111/nph.19868  

   del_Toro, Isa; Case, Madelon_F; Tyler_Karp, A.; Slingsby, Jasper_A; Staver, A_Carla (May 2024, New Phytologist)

   Summary Increasing atmospheric CO₂is changing the dynamics of tropical savanna vegetation. C₃trees and grasses are known to experience CO₂fertilization, whereas responses to CO₂by C₄grasses are more ambiguous.Here, we sample stable carbon isotope trends in herbarium collections of South African C₄and C₃grasses to reconstruct¹³C discrimination.We found that C₃grasses showed no trends in¹³C discrimination over the past century but that C₄grasses increased their¹³C discrimination through time, especially since 1950. These changes were most strongly linked to changes in atmospheric CO₂rather than to trends in rainfall climatology or temperature.Combined with previously published evidence that grass biomass has increased in C₄‐dominated savannas, these trends suggest that increasing water‐use efficiency due to CO₂fertilization may be changing C₄plant–water relations. CO₂fertilization of C₄grasses may thus be a neglected pathway for anthropogenic global change in tropical savanna ecosystems. 

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2. Biosystems Design to Accelerate C ₃ -to-CAM Progression

   https://doi.org/10.34133/2020/3686791  

   Yuan, Guoliang; Hassan, Md. Mahmudul; Liu, Degao; Lim, Sung Don; Yim, Won Cheol; Cushman, John C.; Markel, Kasey; Shih, Patrick M.; Lu, Haiwei; Weston, David J.; et al (October 2020, BioDesign Research)

   Global demand for food and bioenergy production has increased rapidly, while the area of arable land has been declining for decades due to damage caused by erosion, pollution, sea level rise, urban development, soil salinization, and water scarcity driven by global climate change. In order to overcome this conflict, there is an urgent need to adapt conventional agriculture to water-limited and hotter conditions with plant crop systems that display higher water-use efficiency (WUE). Crassulacean acid metabolism (CAM) species have substantially higher WUE than species performing C 3 or C 4 photosynthesis. CAM plants are derived from C 3 photosynthesis ancestors. However, it is extremely unlikely that the C 3 or C 4 crop plants would evolve rapidly into CAM photosynthesis without human intervention. Currently, there is growing interest in improving WUE through transferring CAM into C 3 crops. However, engineering a major metabolic plant pathway, like CAM, is challenging and requires a comprehensive deep understanding of the enzymatic reactions and regulatory networks in both C 3 and CAM photosynthesis, as well as overcoming physiometabolic limitations such as diurnal stomatal regulation. Recent advances in CAM evolutionary genomics research, genome editing, and synthetic biology have increased the likelihood of successful acceleration of C 3 -to-CAM progression. Here, we first summarize the systems biology-level understanding of the molecular processes in the CAM pathway. Then, we review the principles of CAM engineering in an evolutionary context. Lastly, we discuss the technical approaches to accelerate the C 3 -to-CAM transition in plants using synthetic biology toolboxes. 

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3. C ₃ plant carbon isotope discrimination does not respond to CO ₂ concentration on decadal to centennial timescales

   https://doi.org/10.1111/nph.17030  

   Stein, Rebekah A.; Sheldon, Nathan D.; Smith, Selena Y. (November 2020, New Phytologist)

   Summary Plant carbon isotope discrimination is complex, and could be driven by climate, evolution and/or edaphic factors. We tested the climate drivers of carbon isotope discrimination in modern and historical plant chemistry, and focus in particular on the relationship between rising [CO₂] over Industrialization and carbon isotope discrimination.We generated temporal records of plant carbon isotopes from museum specimens collected over a climo‐sequence to test plant responses to climate and atmospheric change over the past 200 yr (includingPinus strobus,Platycladus orientalis,Populus tremuloides,Thuja koraiensis,Thuja occidentalis,Thuja plicata,Thuja standishiiandThuja sutchuenensis). We aggregated our results with a meta‐analysis of a wide range of C₃plants to make a comprehensive study of the distribution of carbon isotope discrimination and values among different plant types.We show that climate variables (e.g. mean annual precipitation, temperature and, key to this study, CO₂in the atmosphere) do not drive carbon isotope discrimination.Plant isotope discrimination is intrinsic to each taxon, and could link phylogenetic relationships and adaptation to climate quantitatively and over ecological to geological time scales. 

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4. On the formation and the isomer specific detection of methylacetylene (CH ₃ CCH), propene (CH ₃ CHCH ₂ ), cyclopropane (c-C ₃ H ₆ ), vinylacetylene (CH ₂ CHCCH), and 1,3-butadiene (CH ₂ CHCHCH ₂ ) from interstellar methane ice analogues

   https://doi.org/10.1039/C8CP03921F  

   Abplanalp, Matthew J.; Góbi, Sándor; Kaiser, Ralf I. (March 2019, Physical Chemistry Chemical Physics)

   Pure methane (CH 4 ) ices processed by energetic electrons under ultra-high vacuum conditions to simulate secondary electrons formed via galactic cosmic rays (GCRs) penetrating interstellar ice mantles have been shown to produce an array of complex hydrocarbons with the general formulae: C n H 2n+2 ( n = 4–8), C n H 2n ( n = 3–9), C n H 2n−2 ( n = 3–9), C n H 2n−4 ( n = 4–9), and C n H 2n−6 ( n = 6–7). By monitoring the in situ chemical evolution of the ice combined with temperature programmed desorption (TPD) studies and tunable single photon ionization coupled to a reflectron time-of-flight mass spectrometer, specific isomers of C 3 H 4 , C 3 H 6 , C 4 H 4 , and C 4 H 6 were probed. These experiments confirmed the synthesis of methylacetylene (CH 3 CCH), propene (CH 3 CHCH 2 ), cyclopropane (c-C 3 H 6 ), vinylacetylene (CH 2 CHCCH), 1-butyne (HCCC 2 H 5 ), 2-butyne (CH 3 CCCH 3 ), 1,2-butadiene (H 2 CCCH(CH 3 )), and 1,3-butadiene (CH 2 CHCHCH 2 ) with yields of 2.17 ± 0.95 × 10 −4 , 3.7 ± 1.5 × 10 −3 , 1.23 ± 0.77 × 10 −4 , 1.28 ± 0.65 × 10 −4 , 4.01 ± 1.98 × 10 −5 , 1.97 ± 0.98 × 10 −4 , 1.90 ± 0.84 × 10 −5 , and 1.41 ± 0.72 × 10 −4 molecules eV −1 , respectively. Mechanistic studies exploring the formation routes of methylacetylene, propene, and vinylacetylene were also conducted, and revealed the additional formation of the 1,2,3-butatriene isomer. Several of the above isomers, methylacetylene, propene, vinylacetylene, and 1,3-butadiene, have repeatedly been shown to be important precursors in the formation of polycyclic aromatic hydrocarbons (PAHs), but until now their interstellar synthesis has remained elusive. 

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5. Resolving the Carbon‐Climate Feedback Potential of Wetland CO ₂ and CH ₄ Fluxes in Alaska

   https://doi.org/10.1029/2022GB007524  

   Ma, Shuang; Bloom, A. Anthony; Watts, Jennifer D.; Quetin, Gregory R.; Donatella, Zona; Euskirchen, Eugénie S.; Norton, Alexander J.; Yin, Yi; Levine, Paul A.; Braghiere, Renato K.; et al (September 2023, Global Biogeochemical Cycles)

   Abstract Boreal‐Arctic regions are key stores of organic carbon (C) and play a major role in the greenhouse gas balance of high‐latitude ecosystems. The carbon‐climate (C‐climate) feedback potential of northern high‐latitude ecosystems remains poorly understood due to uncertainty in temperature and precipitation controls on carbon dioxide (CO₂) uptake and the decomposition of soil C into CO₂and methane (CH₄) fluxes. While CH₄fluxes account for a smaller component of the C balance, the climatic impact of CH₄outweighs CO₂(28–34 times larger global warming potential on a 100‐year scale), highlighting the need to jointly resolve the climatic sensitivities of both CO₂and CH₄. Here, we jointly constrain a terrestrial biosphere model with in situ CO₂and CH₄flux observations at seven eddy covariance sites using a data‐model integration approach to resolve the integrated environmental controls on land‐atmosphere CO₂and CH₄exchanges in Alaska. Based on the combined CO₂and CH₄flux responses to climate variables, we find that 1970‐present climate trends will induce positive C‐climate feedback at all tundra sites, and negative C‐climate feedback at the boreal and shrub fen sites. The positive C‐climate feedback at the tundra sites is predominantly driven by increased CH₄emissions while the negative C‐climate feedback at the boreal site is predominantly driven by increased CO₂uptake (80% from decreased heterotrophic respiration, and 20% from increased photosynthesis). Our study demonstrates the need for joint observational constraints on CO₂and CH₄biogeochemical processes—and their associated climatic sensitivities—for resolving the sign and magnitude of high‐latitude ecosystem C‐climate feedback in the coming decades. 

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