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Aims Over the past decades, vast croplands have been converted into forestland on the Chinese Loess Plateau (CLP). Although a few studies have investigated the effects of afforestation on soil inorganic carbon (SIC), there has been little information on the changes in the two fractions of SIC, pedogenic inorganic carbon (PIC) and lithogenic inorganic carbon (LIC), along a deep profile following afforestation. Methods We selected forestland ( Robinia pseudoacacia ; 31 years) and adjacent cropland (control), and investigated the stocks of SIC, PIC and LIC, at 0-300 cm under the two lands on the CLP. Results The SIC stock significantly decreased by 60.2 Mg ha −1 at 0-80 cm but increased by 57.8 Mg ha −1 at 80-220 cm, and no significant difference in total SIC stock at 0-300 cm was observed between the two lands. Afforestation significantly reduced the LIC stock in each layer; afforestation decreased the PIC stock at 0-80 cm but elevated it at 80-300 cm. In the 80-220 cm layer of forestland, the LIC stock decreased by 41.1 Mg ha −1 while the PIC stock increased by 98.9 Mg ha −1 . Conclusions Afforestation on cropland induces the loss of SIC in upper layers. However, it promotes the accumulation of PIC in deep layers, which causes an increase of SIC in these layers. Because the net increased PIC in deep layers compensates for the loss of SIC in the upper layers, afforestation on cropland does not alter the total SIC storage but redistributes the SIC along the profile on the CLP.

In arid and semiarid areas, the effects of afforestation on soil organic carbon (SOC) have received considerable attention. In these areas, in fact, soil inorganic carbon (SIC), rather than SOC, is the dominant form of carbon, with a reservoir approximately 2-10 times larger than that of SOC. A subtle fluctuation of SIC pool can strongly alter the regional carbon budget. However, few studies have focused on the variations in SIC, or have used stable soil carbon isotopes to analyze the reason for SIC variations following afforestation in degraded semiarid lands. In the Mu Us Desert, northwest China, we selected a shifting sand land (SL) and three nearby forestlands ( ) with ages of 8 (P-8), 20 (P-20) and 30 (P-30) years, and measured SIC, SOC, soil organic and inorganic δ C values (δ C-SOC and δ C-SIC) and other soil properties. The results showed that SIC stock at 0-100 cm in SL was 34.2 Mg ha , and it increased significantly to 42.5, 49.2, and 68.3 Mg ha in P-8, P-20, and P-30 lands, respectively. Both δ C-SIC and δ C-SOC within the 0-100 cm soil layer in the three forestlands were more negative than those in SL, and gradually decreased with plantation age. Afforestation elevated soil fine particles only at a depth of 0-40 cm. The entire dataset (260 soil samples) exhibited a negative correlation between δ C-SIC and SIC content ( = 0.71, < 0.01), whereas it showed positive correlation between SOC content and SIC content ( = 0.52, < 0.01) and between δ C-SOC and δ C-SIC ( = 0.63, < 0.01). However, no correlation was observed between SIC content and soil fine particles. The results indicated that afforestation on shifting SL has a high potential to sequester SIC in degraded semiarid regions. The contribution of soil fine particle deposition by canopy to SIC sequestration is limited. The SIC sequestration following afforestation is very probably caused by pedogenic carbonate formation, which is closely related to SOC accumulation. Our findings suggest that SIC plays an important role in the carbon cycle in semiarid areas and that overlooking this carbon pool may substantially lead to underestimating carbon sequestration capacity following vegetation rehabilitation.

• The evolutionary and ecological story of coccolithophores poses questions about their heterotrophy, surviving darkness after the end-Cretaceous asteroid impact as well as survival in the deep ocean twilight zone. Uptake of dissolved organic carbon might be an alternative nutritional strategy for supply of energy and carbon molecules. • Using long-term batch culture experiments, we examined coccolithophore growth and maintenance on organic compounds in darkness. Radiolabelled experiments were performed to study the uptake kinetics. Pulse–chase experiments were used to examine the uptake into unassimilated, exchangeable pools vs assimilated, nonexchangeable pools. • We found that coccolithophores were able to survive and maintain their metabolism for up to 30 d in darkness, accomplishing about one cell division. The concentration dependence for uptake was similar to the concentration dependence for growth in Cruciplacolithus neohelis, suggesting that it was taking up carbon compounds and immediately incorporating them into biomass. We recorded net incorporation of radioactivity into the particulate inorganic fraction. • We conclude that osmotrophy provides nutritional flexibility and supports long-term survival in light intensities well below threshold for photosynthesis. The incorporation of dissolved organic matter into particulate inorganic carbon, raises fundamental questions about the role of the alkalinity pump and the alkalinity balance in the sea.

Macroalgal ecosystems remain underrepresented in blue carbon frameworks, largely due to uncertainties surrounding the fate of macroalgal carbon during decomposition. Laboratory experiments on Sargassum horneri, Codium fragile, and Ulva australis revealed concurrent increases in total alkalinity and dissolved inorganic carbon, indicating substantial bicarbonate (HCO3−) production via previously unrecognized mechanisms in oxygenated environments. This pattern was corroborated by field data from Korean coastal macroalgal habitats and Yellow Sea macroalgal blooms. Contrary to the conventional view that macroalgal decomposition primarily releases CO2, over half of the inorganic carbon is released as HCO3− in oxygenated waters. This bicarbonate surge—potentially driven by sulfate reduction in anoxic macroalgal aggregates or intracellular HCO3− release—not only raises seawater alkalinity but also enhances carbon sequestration potential and mitigates ocean acidification. These findings highlight the critical role of macroalgal habitats in the global carbon cycle and call for their inclusion in blue carbon strategies.

Soil organic carbon (SOC) pool has been extensively studied in the carbon (C) cycling of terrestrial ecosystems. In dryland regions, however, soil inorganic carbon (SIC) has received increasing attention due to the high accumulation of SIC in arid soils contributed by its high temperature, low soil moisture, less vegetation, high salinity, and poor microbial activities. SIC storage in dryland soils is a complex process comprising multiple interactions of several factors such as climate, land use types, farm management practices, irrigation, inherent soil properties, soil biotic factors, etc. In addition, soil C studies in deeper layers of drylands have opened-up several study aspects on SIC storage. This review explains the mechanisms of SIC formation in dryland soils and critically discusses the SIC content in arid and semi-arid soils as compared to SOC. It also addresses the complex relationship between SIC and SOC in dryland soils. This review gives an overview of how climate change and anthropogenic management of soil might affect the SIC storage in dryland soils. Dryland soils could be an efficient sink in C sequestration through the formation of secondary carbonates. The review highlights the importance of an in-depth understanding of the C cycle in arid soils and emphasizes that SIC dynamics must be looked into broader perspective vis-à-vis C sequestration and climate change mitigation.

Purpose Basalt weathering has the potential to absorb and sequester CO 2 as inorganic carbon, while its weathering byproducts, montmorillonite and kaolinite, have the capacity to stabilize organic carbon. Nonetheless, the practical viability of basalt weathering in achieving the stabilization of inorganic carbon and its impact on organic carbon dynamics in the soil priming effect (PE) remains unclear. Methods An incubation experiment was conducted by adding 13 C-glucose with or without basalt, montmorillonite, or kaolinite to a Luvisol soil planted with peach ( Prunus persica (L.) Batsch) for more than 20 years. CO 2 emission and its 13 C value were continuously measured to calculate the PE and soil net carbon balance. Results After a 28-day incubation, basalt resulted in an increase in soil pH from 5.32 to 7.17 and showed a 143.7% and 168.6% increase in dissolved organic carbon (DOC) and soil inorganic carbon (SIC), respectively. Subsequently, basalt induced the highest cumulative PE among all treatments, with the activities of soil β-glucosidase (S-β-GC), soil leucine amino peptidase (S-LAP), and soil catalase (S-CAT) being the highest. Furthermore, kaolinite significantly decreased emissions of CO 2 -C, glucose mineralization, and cumulative PE ( P  < 0.05). It is worth noting that all treatments significantly enhanced the net soil net carbon balance, with the most significant improvement observed in the kaolinite treatment. Conclusions The weathering process of basalt can significantly promote the stabilization of SIC in PE, whereas kaolinite exhibits the most pronounced impact on the stabilization of soil organic carbon (SOC), resulting in the greatest increase in soil net carbon balance.

During 2016–2017, the Indian Ocean experienced a pronounced increase in dissolved inorganic carbon (∼0.39 PgC/yr), approximately four times greater than the annual mean air–sea CO2 flux. Using a reconstructed data product and a state‐of‐the‐art ocean biogeochemical model, we attribute this anomaly to an enhanced Southern Ocean inflow and a weakened Indonesian Throughflow associated with an El Niño event accompanied by a positive Indian Ocean Dipole (IOD), and followed by a negative IOD during the El Niño‐to‐La Niña transition. The resulting carbon accumulation leads to a decline in aragonite saturation and a shoaling of the aragonite saturation horizon in the southeastern Indian Ocean. This subsurface acidification may pose risks to deep‐water calcifying organisms. Our findings demonstrate that ocean carbon storage and acidification are strongly modulated by circulation‐driven transport processes, highlighting the need for improved subsurface observations and model capabilities to better capture the interior carbon response to climate variability.

The intracellular accumulation of inorganic carbon (Ci) by microalgae and cyanobacteria under ambient atmospheric CO2 levels was first documented in the 80s of the 20th Century. Hence, a third variety of the CO2-concentrating mechanism (CCM), acting in aquatic photoautotrophs with the C3 photosynthetic pathway, was revealed in addition to the then-known schemes of CCM, functioning in CAM and C4 higher plants. Despite the low affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of microalgae and cyanobacteria for the CO2 substrate and low CO2/O2 specificity, CCM allows them to perform efficient CO2 fixation in the reductive pentose phosphate (RPP) cycle. CCM is based on the coordinated operation of strategically located carbonic anhydrases and CO2/HCO3− uptake systems. This cooperation enables the intracellular accumulation of HCO3−, which is then employed to generate a high concentration of CO2 molecules in the vicinity of Rubisco’s active centers compensating up for the shortcomings of enzyme features. CCM functions as an add-on to the RPP cycle while also acting as an important regulatory link in the interaction of dark and light reactions of photosynthesis. This review summarizes recent advances in the study of CCM molecular and cellular organization in microalgae and cyanobacteria, as well as the fundamental principles of its functioning and regulation.

Background and aims Enhanced silicate rock weathering (ERW) on cropland soils can increase crop yield and promote carbon dioxide (CO 2 ) sequestration. Applying silicate rock powder to flooded rice paddies can promote weathering, but the effects of ERW on rice production and CO 2 removal rates in the field remain unclear. Methods We investigated the effects of adding wollastonite (CaSiO 3 ) powder (5 t ha −1 ) to rice paddy plots on soil properties, rice yield, rice grain quality, grain arsenic, grain cadmium, and soil CO 2 sequestration in Liaoning Province, Northeast China. Results Wollastonite application increased soil pH, soil available silicon (Si) content, and Si uptake by rice. Wollastonite application increased grain number by 10% per panicle (15 ± 2), total grain number by 15%, and rice yield by 12% (1.4 ± 0.1 t ha −1 ). After five months of rice growth, soil inorganic carbon (SIC) content in the surface soil increased by 1.20 ± 0.03 t CO 2 ha −1 in wollastonite treatments. We estimated a net profit of $300 (U.S.) ha −1 from yield increase and carbon trade with wollastonite application to this paddy field. Conclusions Wollastonite application to paddy fields in Northeast China promoted rice yield and CO 2 sequestration in the surface soil. This soil CO 2 sequestration triples that from the control soil and is comparable to prior pot trials. Although field trials are needed on the limits to CO 2 sequestration and rice yield increases with wollastonite application, such applications promise to increase soil CO 2 sequestration and profits for a key crop.

Widespread shrub encroachment in global drylands may increase plant biomass and change soil organic carbon stocks of grassland ecosystems. However, the response of soil inorganic carbon (SIC), which is a major component of dryland carbon pools, to this vegetation shift remains unknown. We conducted a systematic field survey in 75 pairs of shrub‐encroached grassland (SEG) and control plots at 25 sites in the grasslands of the Inner Mongolia Plateau to evaluate how shrub encroachment affects SIC density (SICD) in these ecosystems. We found that shrub encroachment significantly reduced SICD in the upper 100 cm (3.85 vs. 4.74 kg C m−2, p < .05), especially in the subsurface soil (20–50 cm layer). The magnitude of SICD changes was related to the change in soil pH, shrub patch size and initial SICD, reflecting that the reduction in SICD might be attributed to the shrub encroachment‐related soil acidification. Our results also revealed that the lost SIC was mainly released into the atmosphere rather than redistributed into deeper soil layers. Synthesis. We provide the first evidence for the soil acidification‐induced SIC loss caused by shrub encroachment. Our findings highlight the non‐negligible role of SIC dynamics in the C budget of SEG ecosystems and the need to consider these dynamics in terrestrial C cycle research. We provide the first evidence for the soil acidification‐induced soil inorganic carbon (SIC) loss caused by shrub encroachment. Our findings highlight the non‐negligible role of SIC dynamics in the C budget of shrub‐encroached grassland ecosystems and the need to consider these dynamics in terrestrial C cycle research.