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Remnant forest patches within agricultural landscapes may play an underappreciated role in tropical carbon storage. Understanding their carbon storage contribution will inform land-use policies to balance economic production with forest-based climate mitigation strategies, especially in tropical developing countries where agriculture dominates. This study quantified and compared carbon stocks of five biomass pools (overstorey, understorey, litter, roots, and soil) using 54 nested plots established in nine pairs of remnant forest patches and adjacent banana (Musa spp.) agroecosystems in Bukidnon, Southern Philippines. Results showed that forest patches stored most carbon in the overstorey layer (65-75%) followed by roots (18-22%), litter (5-8%) and understorey layers (< 2%). Banana agroecosystems stored more carbon in the pseudostems and litter layer with 40-45% and 45-50% of the total biomass carbon, respectively, while roots had only 8-10%. The absence of understorey vegetation in banana plantations may indicate the intensive nature of management practices in this agroecosystem. Forest patches stored significantly higher carbon in the overstorey (77.06 ± 69.71 Mg C ha −1 ), understorey (1.24 ± 0.44 Mg C ha −1 ), and roots (20.43 ± 17.23 Mg C ha −1 ). Interestingly, litter carbon was higher in banana agroecosystems (20.40 ± 12.15 Mg C ha −1 ) than in forest patches (7.67 ± 3.43 Mg C ha −1 ) likely due to the practice of leaving banana residues after harvest. Total biomass carbon was two to three times greater in forest patches (106.39 ± 88.40 Mg C ha −1 ), with significantly higher carbon accumulation (2.62 ± 2.18 Mg C ha −1 yr −1 ) and CO 2 fixation rates (9.60 ± 7.98 Mg CO 2 -eq ha −1 yr −1 ) than banana plantations. Although SOC levels were statistically comparable between the two land uses, further research is needed to confirm whether the apparent stability of SOC in banana plantations is sustainable or whether it represents a transient stage before eventual depletion. Nonethless, we recommend to prioritize the conservation and restoration of forest patches as permanent features within agricultural landscapes to optimize carbon storage and mitigate ecological degradation.

Carbon dioxide (CO₂) is an important carbon feedstock for a future green economy. This requires the development of efficient strategies for its conversion into multicarbon compounds. We describe a synthetic cycle for the continuous fixation of CO₂ in vitro. The crotonyl-coenzyme A (CoA)/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) cycle is a reaction network of 17 enzymes that converts CO₂ into organic molecules at a rate of 5 nanomoles of CO₂ per minute per milligram of protein. The CETCH cycle was drafted by metabolic retrosynthesis, established with enzymes originating from nine different organisms of all three domains of life, and optimized in several rounds by enzyme engineering and metabolic proofreading. The CETCH cycle adds a seventh, synthetic alternative to the six naturally evolved CO₂ fixation pathways, thereby opening the way for in vitro and in vivo applications.

Carbon dioxide (CO 2 ) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO 2 concentrations. Using a global compilation of high-frequency CO 2 measurements, we demonstrate that nocturnal CO 2 emissions are on average 27% (0.9 gC m −2  d −1 ) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO 2 by photosynthesis. Because current global estimates of CO 2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr −1 ) rely primarily on discrete measurements of dissolved CO 2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO 2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr −1 . Failing to account for emission differences between day and night will lead to an underestimate of global CO 2 emissions from rivers by up to 0.55 PgC yr –1 , according to analyses of high-frequency CO 2 measurements.

The increase in atmospheric CO₂ in the future is one of the most certain projections in environmental sciences. Understanding whether vegetation carbon assimilation, growth, and changes in vegetation carbon stocks are affected by higher atmospheric CO₂ and translating this understanding in mechanistic vegetation models is of utmost importance. This is highlighted by inconsistencies between global-scale studies that attribute terrestrial carbon sinks to CO₂ stimulation of gross and net primary production on the one hand, and forest inventories, tree-scale studies, and plant physiological evidence showing amuch less pronounced CO₂ fertilization effect on the other hand. Here, we review how plant carbon sources and sinks are currently described in terrestrial biosphere models. We highlight an uneven representation of complexity between the modelling of photosynthesis and other processes, such as plant respiration, direct carbon sinks, and carbon allocation, largely driven by available observations. Despite a general lack of data on carbon sink dynamics to drive model improvements, ways forward toward a mechanistic representation of plant carbon sinks are discussed, leveraging on results obtained from plant-scale models and on observations geared toward model developments.

Carbon capture and utilization for concrete production (CCU concrete) is estimated to sequester 0.1 to 1.4 gigatons of carbon dioxide (CO 2 ) by 2050. However, existing estimates do not account for the CO 2 impact from the capture, transport and utilization of CO 2 , change in compressive strength in CCU concrete and uncertainty and variability in CCU concrete production processes. By accounting for these factors, we determine the net CO 2 benefit when CCU concrete produced from CO 2 curing and mixing substitutes for conventional concrete. The results demonstrate a higher likelihood of the net CO 2 benefit of CCU concrete being negative i.e. there is a net increase in CO 2 in 56 to 68 of 99 published experimental datasets depending on the CO 2 source. Ensuring an increase in compressive strength from CO 2 curing and mixing and decreasing the electricity used in CO 2 curing are promising strategies to increase the net CO 2 benefit from CCU concrete. Carbon curing or mixing in concrete is promising for carbon dioxide sequestration. Here, the authors show that the increased use of binder material to compensate the loss in compressive strength and electricity for carbon dioxide curing is more likely to increase carbon dioxide emissions on a life cycle basis for carbon cured or mixed concrete.

The CO 2 concentration at ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is crucial to improve photosynthetic efficiency for biomass yield. However, how to concentrate and transport atmospheric CO 2 towards the Rubisco carboxylation is a big challenge. Herein, we report the self-assembly of metal-organic frameworks (MOFs) on the surface of the green alga Chlorella pyrenoidosa that can greatly enhance the photosynthetic carbon fixation. The chemical CO 2 concentrating approach improves the apparent photo conversion efficiency to about 1.9 folds, which is up to 9.8% in ambient air from an intrinsic 5.1%. We find that the efficient carbon fixation lies in the conversion of the captured CO 2 to the transportable HCO 3 − species at bio-organic interface. This work demonstrates a chemical approach of concentrating atmospheric CO 2 for enhancing biomass yield of photosynthesis. Concentrating CO 2 around Rubisco is critical to improve photosynthetic efficiency for biomass yield. Here, the authors report the self-assembly of metal-organic frameworks (MOFs) on the surface of green alga Chlorella pyrenoidosa to enhance the photosynthetic carbon fixation.

High-latitude and high-altitude regions contain vast stores of permafrost carbon. Climate warming may result in the release of CO₂ from both the thawing of permafrost and accelerated autotrophic respiration, but it may also increase the fixation of CO₂ by plants, which could relieve or even offset the CO₂ losses. The Tibetan Plateau contains the largest area of alpine permafrost on Earth. However, the current status of the net CO₂ balance and feedbacks to warming remain unclear, given that the region has recently experienced an atmospheric warming rate of over 0.3 °C decade−1. We examined 32 eddy covariance sites and found an unexpected net CO₂ sink during 2002 to 2020 (26 of the sites yielded a net CO₂ sink) that was four times the amount previously estimated. The CO₂ sink peaked at an altitude of roughly 4,000 m, with the sink at lower and higher altitudes limited by a low carbon use efficiency and a cold, dry climate, respectively. The fixation of CO₂ in summer is more dependent on temperature than the loss of CO₂ than it is in the winter months, especially at higher altitudes. Consistently, 16 manipulative experiments and 18 model simulations showed that the fixation of CO₂ by plants will outpace the loss of CO₂ under a wetting–warming climate until the 2090s (178 to 318 Tg C y−1). We therefore suggest that there is a plant-dominated negative feedback to climate warming on the Tibetan Plateau.

Considering the rapid increase of CO 2 emission, especially from power plants, there is a constant need for materials which can effectively eliminate post-combustion CO 2 (the main component: CO 2 /N 2  = 15/85). Here, we show the design and synthesis of a Cu(II) metal-organic framework ( FJI-H14 ) with a high density of active sites, which displays unusual acid and base stability and high volumetric uptake (171 cm 3  cm −3 ) of CO 2 under ambient conditions (298 K, 1 atm), making it a potential adsorbing agent for post-combustion CO 2 . Moreover, CO 2 from simulated post-combustion flue gas can be smoothly converted into corresponding cyclic carbonates by the FJI-H14 catalyst. Such high CO 2 adsorption capacity and moderate catalytic activity may result from the synergistic effect of multiple active sites. Increasing CO 2 emissions pose serious environmental issues. Here, the authors report the synthesis of a robust metal-organic framework which displays high volumetric uptake of post-combustion CO 2 under ambient conditions and can catalyze CO 2 fixation into cyclic carbonates.

Global climate is thought to be modulated by the supply of minerals to Earth’s surface. Whereas silicate weathering removes carbon dioxide (CO 2 ) from the atmosphere, weathering of accessory carbonate and sulfide minerals is a geologically relevant source of CO 2 . Although these weathering pathways commonly operate side by side, we lack quantitative constraints on their co-variation across erosion rate gradients. Here we use stream-water chemistry across an erosion rate gradient of three orders of magnitude in shales and sandstones of southern Taiwan, and find that sulfide and carbonate weathering rates rise with increasing erosion, while silicate weathering rates remain steady. As a result, on timescales shorter than marine sulfide compensation (approximately 10 6 –10 7 years), weathering in rapidly eroding terrain leads to net CO 2 emission rates that are about twice as fast as CO 2 sequestration rates in slow-eroding terrain. We propose that these weathering reactions are linked and that sulfuric acid generated from sulfide oxidation boosts carbonate solubility, whereas silicate weathering kinetics remain unaffected, possibly due to efficient buffering of the pH. We expect that these patterns are broadly applicable to many Cenozoic mountain ranges that expose marine metasediments. Unlike sulfide and carbonate, silicate weathering does not increase with physical erosion, which could result in a net release of carbon dioxide associated with uplift, according to stream-water chemistry of southern Taiwan.

Carbon capture and storage (CCS) is a key technology to mitigate the environmental impact of carbon dioxide (CO 2 ) emissions. An understanding of the potential trapping and storage mechanisms is required to provide confidence in safe and secure CO 2 geological sequestration 1 , 2 . Depleted hydrocarbon reservoirs have substantial CO 2 storage potential 1 , 3 , and numerous hydrocarbon reservoirs have undergone CO 2 injection as a means of enhanced oil recovery (CO 2 -EOR), providing an opportunity to evaluate the (bio)geochemical behaviour of injected carbon. Here we present noble gas, stable isotope, clumped isotope and gene-sequencing analyses from a CO 2 -EOR project in the Olla Field (Louisiana, USA). We show that microbial methanogenesis converted as much as 13–19% of the injected CO 2 to methane (CH 4 ) and up to an additional 74% of CO 2 was dissolved in the groundwater. We calculate an in situ microbial methanogenesis rate from within a natural system of 73–109 millimoles of CH 4 per cubic metre (standard temperature and pressure) per year for the Olla Field. Similar geochemical trends in both injected and natural CO 2 fields suggest that microbial methanogenesis may be an important subsurface sink of CO 2 globally. For CO 2 sequestration sites within the environmental window for microbial methanogenesis, conversion to CH 4 should be considered in site selection. Microbial methanogenesis converts up to 19% of the carbon dioxide injected into an oil field to methane, suggesting that microbial methanogenesis may be a globally important subsurface process.