Artificial humic acid facilitates biological carbon sequestration under freezing-thawing conditions

Microbial community assemblage altered by coprecipitation of artificial humic substances and ferrihydrite: Implications for carbon fixation pathway transformation

The suppression of soil carbon mineralization has been demonstrated to be effectively facilitated by carbon‑iron interactions, yet the specific mechanisms by which artificial humic substances (A-HS) coupled with ferrihydrite influence this process remain insufficiently explored. This study is to investigate how the A-HS, specifically artificial fulvic acid (A-FA) and artificial humic acid (A-HA), coupled with ferrihydrite, affect carbon mineralization under anaerobic system that simulates paddy flooding conditions. The object is to investigate trends in carbon emissions and to delineate microbial community structure and functional pathways. The findings indicate that A-HA and A-FA substantially reduce CO2 and CH4 emissions, with A-FA having a particularly pronounced effect on carbon fixation, halving CO2 concentrations. The low concentration of Fe(II) observed suggest that A-FA and A-HA impede the dissimilatory iron reduction (DIR) process. Detailed 16S rDNA sequencing and gene prediction analyses reveal changes in microbial community structures and functions, highlighting Methanobacterium as the dominant hydrogenotrophic methanogens. The reductive citric acid cycle, predominantly utilized by Clostridium carboxidivorans, was identified as the principal carbon fixation pathway. This work provides a novel insight into the microbial mechanisms of carbon sequestration and highlights the potential of A-HS in improving soil fertility and contributing to climate change mitigation through enhancing soil carbon storage.

Synergistic enhancement of cadmium immobilization and soil fertility through biochar and artificial humic acid-assisted microbial-induced calcium carbonate precipitation

Microbially induced carbonate precipitation (MICP) is emerging as a favorable alternative to traditional soil remediation techniques for heavy metals, primarily due to its environmental friendliness. However, a significant challenge in using MICP for farmland is not only to immobilize heavy metals but also to concurrently enhance soil fertility. This study explores the innovative combination of artificial humic acid (A-HA), biochar (BC), and Sporosarcina pasteurii (S. pasteurii) to mitigate the bioavailability of cadmium (Cd) in contaminated agricultural soils through MICP. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses revealed that the integration of BC and A-HA significantly enhances Cd immobilization efficiency by co-precipitating with CaCO3. Moreover, this treatment also improved soil fertility and ecological functions, as evidenced by increases in total nitrogen (TN, 9.0-78.2 %), alkaline hydrolysis nitrogen (AN, 259.7-635.5 %), soil organic matter (SOM, 18.1-27.9 %), total organic carbon (TOC, 43.8-48.8 %), dissolved organic carbon (DOC, 36.0-88.4 %) and available potassium (AK, 176.2-193.3 %). Additionally, the relative abundance of dominant phyla such as Proteobacteria and Firmicutes significantly increased with the introduction of BC and A-HA in MICP. Consequently, the integration of BC and A-HA with MICP offers a promising solution for remediating Cd-contaminated agricultural soil and synergistically enhancing soil fertility.

Successive Years of Rice Straw Return Increased the Rice Yield and Soil Nutrients While Decreasing the Greenhouse Gas Intensity

Straw return has important impacts on black soil protection, food security, and environmental protection. One year of straw return (S1) reduces rice yield and increases greenhouse gas (GHG) emissions. However, the effects of successive years of straw return on rice yield, soil nutrients, and GHG emissions in the northeast rice region are still unclear. Therefore, we conducted four successive years of straw return (S4) in a positional experiment to investigate the effects of different years of straw return on rice yield, soil nutrients, and GHG emissions in the northeast rice region. The experimental treatments included the following: no straw return (S0), a year of straw return (S1), two successive years of straw return (S2), three successive years of straw return (S3), and four successive years of straw return (S4). Compared with S1, the rice yields of S2, S3, and S4 increased by 10.89%, 15.46%, and 16.98%, respectively. But only S4 increased by 4.64% compared to S0, while other treatments were lower than S0. S4 increased panicles per m2 and spikelets per panicle by 9.34% and 8.93%, respectively, compared to S1. Panicles per m2 decreased by 8.06% at S4 compared to S0, while spikelets per panicle increased by 13.23%. Compared with S0, the soil organic carbon, total nitrogen, NH4+-N, NO3--N, available phosphorus, and available potassium of S4 increased by 11.68%, 10.15%, 24.62%, 21.38%, 12.33%, and 13.35%, respectively. Successive years of rice straw return decreased GHG intensity (GHGI). Compared with S1, the GHGI of S4, S3, and S2 decreased by 16.2%, 11.84%, and 9.36%, respectively. Thus, S4 increased rice yield and soil nutrients, reducing GHGI.

Selective Modifier-Assisted Humic Acid Extraction: Implications for Soil Quality Enhancement

Efficient use of humic acid (HA) for eco-friendly farming and environmental remediation requires further understanding of how targeted modification of HA affects the chemical structure of HA and thereby its effectiveness in enhancing soil quality. We developed novel selective modifiers (SMs) for extracting HA by codoping sodium and copper elements into the birnessite lattice. The structure of SMs was thoroughly examined, and the HAs extracted using SMs, referred to as SMHs, were subjected to a detailed evaluation of their functional groups, molecular weight, carbon composition, flocculation limits, and effectiveness in saline soil remediation. The results showed that replacing manganese with sodium and copper in SMs alters the valence state and reactive oxygen species. In contrast, SMHs exhibited increased acidic functional groups, a lower molecular weight, and transformed aliphatic carbon. Furthermore, the saline soil was improved through increased salt leaching and an optimized soil aggregate structure by SMHs. This research highlights the importance of targeted modification of HA and demonstrates the potential of these modifiers in improving soil quality for eco-friendly farming and environmental remediation.

Effects of Fe3+ on Hydrothermal Humification of Agricultural Biomass

Hydrothermal humification technology for the preparation of artificial humic matters provides a new strategy, greatly promoting the natural maturation process. Iron, as a common metal, is widely used in the conversion of waste biomass; however, the influence of Fe3+ on hydrothermal humification remains unknown. In this study, FeCl3 is used to catalyze the hydrothermal humification of corn straw, and the influence of Fe3+ on the hydrothermal humification is explored by a series of characterization techniques. Results show that Fe3+ as the catalyst can promote the decomposition of corn straw, shorten the reaction time from 24 h to 6 h, and increase the yield from 6.77 % to 14.08 %. However, artificial humic acid (A-HA) obtained from Fe3+ -catalysis hydrothermal humification contains more unstable carbon and low amount of aromatics, resulting in a significantly decreased stability of the artificial humic acid. These results provide theoretical guidance for regulating the structure and properties of artificial humic acid to meet various maintenance needs.

Effect of salinity on carbon sequestration in constructed wetlands and its functional mechanisms

Currently, many constructed wetlands (CWs) are facing the threat of salinization, but its effect on the carbon sequestration function of CWs is still unclear. In this study, three CWs with different salinities (i.e., control: C-CW; low salinity: LS-CW; high salinity: HS-CW) were conducted. Increased salinity significantly reduced the carbon sequestration in CWs. The highest carbon sequestration was observed in C-CW (5.1 ± 0.2 kg C·m-2·y-1), and the carbon sequestration capacity of plants was identified as the major influencing factor. The substrate carbon pool decreased with salinity since it altered plant carbon inputs, enzyme activities, and microbial community structure. However, the decrement in the carbon pool management index with salinity indicated that salinity could enhance carbon pool stability and subsequently reduce carbon emissions of CWs. These findings improve the understanding in relationships between salinity and carbon sequestration in CWs and provide theoretical support for the proper management of CWs.

Synergistic effect of pollution reduction and carbon emission mitigation in the digital economy

Synergetic control of environmental pollution and carbon emissions (SCEPCE) is essential to green development. The emergence of the digital economy has become a significant component in regional economic growth. Investigating the digital driving mode for SCEPCE in developing countries is crucial. This paper empirically analyzes the effect of establishing big data comprehensive experimental areas (BDCEAs) on air pollutants and carbon emissions using panel data of prefecture-level cities from 2009 to 2020 and the time-varying difference-in-differences method. The research found that (1) BDCEA inhibits pollution and carbon emissions, and the policy effect is sustainable. (2) The synergistic effect is significant, particularly in small and medium-sized cities and old industrial-base cities. The benefit of reducing pollution is only significant in the east. The effect of reducing CO₂ emissions is only significant in the west. (3) The pollution reduction effect of digital economic development has the characteristics of an increasing marginal effect, and the marginal effect of its carbon reduction effect is not apparent. (4) The technological innovation and energy efficiency improvement effects are effective mechanisms. This paper enriches the studies on the factors influencing SCEPCE, which will help to realize SCEPCE and the harmonious coexistence of humans and nature in developing countries. However, policy incentives and green development strategies must be fine-tuned to achieve global SCEPCE.

Artificial humic acid regulates the impact of fungal community on soil macroaggregates formation

Artificial humic acid (A-HA), which is synthesized from agricultural wastes and has high similarity to a natural humic substance (HS) extracted from soil, has been proven by our group to have potential for biological carbon sequestration in black soils. However, the mechanism involves in the application of A-HA on soil aggregation processes resulting from microbial activity stimulation and modifications to microbial communities remains unclear. This study investigates the correlation between the formation and stability of soil aggregates and fungal communities with various amounts of A-HA added to the rhizosphere and non-rhizosphere soil. A-HA can increase the total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations in soil, promoting macroaggregate formation and increasing the mean weight diameter (MWD). In addition, soil aggregate binding agents such as polysaccharides, protein, extracellular polymeric substances (EPS), and glomalin-related soil protein (GRSP) are significantly increased by the addition of A-HA. A-HA can drive microaggregate to assemble into macroaggregate by increasing the abundance of beneficial fungi (e.g., Trichoderma and Mortierella). The co-occurrence network supports that A-HA shifted the key species and increased interactions of fungal taxa. This study will lay a solid foundation for sustainable agricultural development of A-HA application for soil fertility restoration in the future.