Fungal-driven carbon sequestration within soil aggregates under paddy multicropping

Saline‐alkaline soils are wide‐spread and approximately 6.5% of the world's land area is reported as being saline and sodic. Increasing soil organic carbon (SOC) concentration and aggregate stability in saline‐alkaline soils has been challenging due to the deleterious effects of soil salinity and sodicity. To address this issue, a 2‐year filed experiment was conducted to evaluate the effects of biochar (BC), farmyard manure (FM), corn straw (CS), and sheep manure (SM) in combination of chemical fertilizer (CK) on soil aggregation and C sequestration in mildly and moderately alkaline soils in Hetao Irrigation District, China. For mildly alkaline soil, the proportion of macroaggregates (>0.25 mm) was significantly higher under FM, CS, and SM (34.6%–51.2%) compared with CK (13.2%). The mean weight diameter (MWD) and geometric mean diameter (GMD) of water‐stable aggregates significantly increased under FM, CS, and SM by an average of 172.7% and 58.7% over CK. In addition, FM, CS, and SM enhanced the distribution of organic carbon (OC) in macroaggregates (>0.25 mm) and accelerated the accumulation of particulate organic matter within macroaggregates. Treatment BC enhanced OC distribution in microaggregates (0.053–0.25 mm) and exhibited a 7.40 g kg−1 SOC content, followed by SM and FM which exhibited SOC contents of 7.10 and 6.76 g kg−1. For moderately alkaline soil, data obtained in this study showed a slight influence from organic amendments on soil aggregates and C sequestration, suggesting that the moderately alkaline soil was not as sensitive to organic amendments as the mildly alkaline soil. Overall, the results of this study demonstrated that FM and SM combined with chemical fertilizer were the top organic amendments to improve soil aggregation and C sequestration in the mildly alkaline soil but not the moderately alkaline soil over the short term.

Straw returning has an effective strategy for improving soil carbon sequestration and aggregate stability, as well as promoting sustainable agricultural development. Although in recent years, predecessors have conducted in-depth studies on the impact of tillage patterns and straw returning levels on soil organic carbon (SOC) and aggregate stability, we remain unclear on which tillage modes and straw return levels were the most suitable combinations in the study area. In view of this, we examined the influence of two tillage modes (tillage with straw returning, TS; no-tillage with straw mulching, NTS) and four straw addition levels (one-time treatment, 3500 kg/ha; two-time treatment, 7000 kg/ha; three-time treatment, 10,500 kg/ha; four-time treatment, 14,000 kg/ha) to soil aggregate size distribution, stability, SOC content, and carbon fractions content by split-plot experiment. The results showed that NTS3 enhanced the proportion of middle macro-aggregates fraction (MM) and unstable macro-aggregates fraction (UM), as well as SOC and hot-water extraction C (HWC) content with NTS mode. TS3 enhanced the proportion of MM, small macro-aggregates fraction (SM) with TS mode. Pearson correlation analysis suggested that the effect of straw input level on SOC and soil aggregates is greater for NTS than TS. In conclusion, considering the aspects of not affecting soil aggregate stability and improving SOC content, we think that NTS plays a significant role in promoting and enhancing the capacity of farmland soil to retain organic carbon in the research area; particularly, NTS3, HWC, and dissolved organic carbon (DOC) serve as indicative indices for SOC changes.

<p>Soil degradation is a major concern worldwide and tropical agriculture is a major contributor to CO<sub>2</sub> release from soils. There is growing interest in stabilizing atmospheric CO<sub>2</sub> abundance to reduce its direct effect on global warming, by focusing on the potential of soil to sequester carbon. Soil structure directly influences soil stability and carbon sequestration. Arbuscular mycorrhizal fungi (AMF) are one of the most important microbial soil components for soil aggregate formation and stabilization through physical and biochemical processes allowing the encapsulation of organic carbon. However, the contribution of AMF to soil aggregation remains to be demonstrated under field and farming conditions and has only been shown in pot experiments with sterilized non-mycorrhizal controls. Large differences in cassava (Manihot esculenta Cranz), yield when inoculated under field conditions with diverse isolates of the AMF species Rhizophagus irregularis, suggests that carbon directed belowground and more importantly carbon sequestered within soil aggregates after harvesting might be driven by differences among AMF inocula. Thus, we evaluated the effect of 11 different isolates of Rhizophagus irregularis on CO<sub>2</sub> emissions to the atmosphere (soil respiration), soil aggregation and the amount of soil organic carbon stored in aggregates in soils under commercial cassava cropping. Soil respiration was measured in situ by infrared gas analyser (IRGA, Li-COR 8100A) means. Soil samples were taken in surface (10 cm) and subsoil (30 cm) were taken to determine water stable aggregates size distribution (6.3, 4, 2, 1 and 0.5 mm), total stable aggregates (TSA) and total organic carbon (TOC) per aggregate size. After just one-year, our results showed that carbon decomposition (as measured by soil respiration), soil aggregation and carbon storage (in soil aggregates) were significantly affected by inoculation with AMF. Soil respiration was strongly and differentially affected by R. irregularisisolates with a difference of up to 78% in CO<sub>2</sub> release from the soil. In surface, we found differences in TSA of up to 20% among inoculation treatments driven principally by an increase up to 6.3% in macroaggregate sizes. In subsoil, the TSA differences were up to 40% between AMF lines and at 2 mm aggregate size differences were up to 9,22% compare with non-inoculated treatment. Interestingly in this experiment, TOC and soil aggregation were not correlated. Although TOC in macroaggregates was significatively different up 44% among AMF treatments. Soil aggregation is a soil property often thought as static. Moreover, changes in soil aggregation as the ones we have shown here had only been reported after long-term experiments (up to 30 years) with low intrusive tillage practices (non- or reduced-tillage). Our results clearly show the enormous potential of using AMF in field conditions as a primary tool to improve ecosystem services and soil health in short periods of time.</p><p><strong>Keywords: </strong>Soil aggregation, AMF, Cassava, carbon storage, soil respiration</p>

Enhancing soil organic carbon (SOC) and aggregate stability is pivotal for maintaining soil health and ensuring agricultural sustainability. However, conventional organic amendments often exhibit suboptimal efficiency in achieving these goals. Hydrochar, synthesized via hydrothermal carbonization (HTC), offers a promising solution by integrating labile and recalcitrant carbon fractions to synergistically address these challenges. However, its mechanisms of action remain not fully understood. In the present study, a microcosmic incubation experiment was conducted to evaluate the short-term impacts of hydrochar on SOC sequestration and soil aggregation in comparison with biochar and straw in a purple soil ( Entisol ). Hydrochars derived from maize straw (SH), pig manure (PH), and Zanthoxylum stalks (HH) were also compared to assess feedstock-driven variability. The results demonstrated the superior performance of hydrochars, particularly those derived from Zanthoxylum stalks, which significantly increased the mean weight diameter (MWD) by 70–100% and SOC content by 143–149%, outperforming biochar and straw. Specifically, hydrochar-originated carbon persisted primarily as particulate organic matter (POM) and accumulated in macro-aggregate, while shifts in microbial communities contributed to SOC stabilization. In comparison, soil aggregation was driven by labile carbon fractions (e.g., dissolved organic carbon, DOC) and soil microorganisms, specifically Actinobacteria and Ascomycota . Feedstock properties, such as the C/N ratio and lignin content, modulated the effectiveness of hydrochar as a soil amendment. Notably, stalk-derived hydrochar exhibited superior carbon retention (12% total carbon loss vs. 30–44% for other amendments) and aggregate stability due to its recalcitrant lignin structure. Nutrient content and ratio further influenced these outcomes, with manure-derived hydrochar promoting microbial biomass carbon (845 mg kg −1 vs. 350 mg kg −1 in control), while stalk-derived hydrochar was more effective at optimizing carbon sequestration. These findings highlighted the dual role of hydrochar in enhancing soil structure and SOC sequestration, with feedstock selection critically determining functional priorities. Such insights could provide valuable guidance for tailoring hydrochar production and application to improve agricultural sustainability through soil quality improvement. Graphic Abstract

Organic materials input promotes the soil aggregate sequestration through changing soil aggregates structure and stability.

Soil carbon and nutrient sequestration linking to soil aggregate in a temperate fen in Northeast China

ABSTRACTBackgroundLong‐term continuous cropping alters soil physicochemical properties, causing nutrient imbalances and disruptions in microbial communities. However, the priming effect (PE) in long‐term continuous cropping systems remains poorly understood.AimsThe objective of this study is to investigate the direction and magnitude of soil PE under varying organic amendments (quality and quantity) and mineral nitrogen (N) co‐inputs.MethodsThe soil of a long‐term continuous cropping tobacco field was collected and incubated for 32 days. Six treatments were designed: CK (no additions), mineral N, low 13C glucose + mineral N, high 13C glucose + mineral N, low 13C straw + mineral N, and high 13C straw + mineral N. This study investigated how organic amendments regulate soil PEs by mediating microbial nutrient limitation, community structure, and soil aggregation, based on measurements of carbon dioxide release, microbial biomass carbon (C) and N, extracellular enzyme activities, phospholipid fatty acid analysis, and aggregate stability.ResultsMineral N addition reduced microbial N immobilization and soil aggregate stability, while stimulating soil organic matter (SOM) mineralization (positive PE). The addition of glucose or straw provides C sources and energy for microorganisms, stimulating soil microbial activity and enhancing community stability, whereas increased extracellular enzyme activities alleviate nitrogen limitation and improve soil nitrogen availability. The direction of PEs was determined by the carbon‐to‐nitrogen (C/N) ratio of external organic inputs and mineral nitrogen, with low C/N ratios inducing negative PEs and high C/N ratios producing positive PEs. Straw addition induced weaker PEs (both directions) than labile glucose, while enhancing fungal biomass (K‐strategists) to promote soil aggregation and aggregate stability, thereby facilitating soil organic carbon (SOC) sequestration (negative PE).ConclusionsExcessive mineral‐N addition and deficient organic material inputs are key drivers of SOC loss in continuous cropping fields. The quality and quantity of the organic substrates regulate the magnitude and direction of the PEs, underscoring the importance of organic substrate inputs in the long‐term continuous cropping field.

Smooth vetch covering alters soil aggregate microbial metabolic limitations in citrus orchards

Effects of long-term cropping regimes on soil carbon sequestration and aggregate composition in rainfed farmland of Northeast China

The use of biochar as a soil amendment has substantial potential to enhance soil quality and carbon sequestration. However, the responses to the addition of biochar based on soil microbial residues are not well understood, particularly at the aggregate level. Herein, a two-year field experiment investigated the characteristics of distribution of microbial residues in calcareous fluvo-aquic soil aggregates (SA) in Henan Province, China. Four treatments were established as follows: no fertilizer (CK), chemical fertilizer (NPK), biochar (BC), and biochar combined with chemical fertilizer (NPK + BC). The results showed that the effects of particle size substantially impacted the microbial residues with 2–0.25 mm SA having the largest contents of amino sugars and microbial residual carbon (MRC), followed by >2 mm SA. Compared with the CK, the NPK treatment markedly enhanced the levels of glucosamine (GluN), galactosamine (GalN), muramic acid (MurA), total amino sugar (TAS), and MRC in the 2–0.25 mm SA by 26.69%, 24.0%, 23.62%, 25.11%, and 24.82%, respectively. The NPK + BC treatment significantly increased the contents of GluN, GalN, TAS, and MRC in the bulk soil and 0.25–0.053 mm SA compared with the NPK treatment. Bacterial biomass and the activity of N-acetyl-glucosaminidase in the bulk soil and SA markedly and positively affected the content of carbon in the amino sugars and microbial residues. Overall, the 2–0.25 mm SA were microenvironments with the largest accumulation of soil microbial residues, and the combined application of NPK + BC was more effective at increasing the accumulation of microbial residues in the SA, which provides an ideal fertilization strategy to improve the soil microenvironment and enhance soil quality.

Application of various methodological approaches for assessment of soil micromorphology due to VESTA program applicable to prediction of the soil structures formation

Soil aggregation and intra-aggregate carbon fractions in relation to vegetation succession on the Loess Plateau, China

The contribution of microbial necromass carbon to soil organic carbon in soil aggregates

Soil aggregates, as the basic component of soil, make great contributions to the stability of soil structure and soil carbon (C) sequestration. Recently, grasslands have been experiencing continuous grazing, which has had a significant impact on soil aggregation and soil C storage. However, how soil aggregates and soil C in different grasslands respond to grazing remains unclear. Therefore, three national fenced grassland-monitoring sites that represented mountain meadow (MM), temperate steppe (TS), and temperate steppe desert (TSD) were selected to investigate the differences in the responses of soil aggregates and soil C among grazing of different types of grasslands. Soil samples of 0–10 cm was collected from both inside and outside the fence of each site to analyze soil properties and soil aggregate characteristics. The results showed that soil nutrients varied greatly among the three grassland types, with the highest values in MM. At each site, grazing increased the content of sand and decreased the contents of silt and clay compared to fenced plots. Soil aggregate composition showed significant responses to both grassland type and grazing, especially the proportions of soil aggregates >2 mm, which significantly decreased by 51.7% on average in grazing plots compared with fenced plots. A significant decrease (on average, 25.1%) in the mean weight diameter (MWD) of soil aggregates under grazing was detected across all grassland types. The effect of grazing on nutrients in macroaggregates (>0.25 mm) was greater than that in microaggregates (<0.25 mm). Aggregate-associated SOC concentration decreased under grazing in MM and TS. However, grazing had no significant influence on the SOC density of MM, while it led to a significant decrease in TS and an increase in TSD. The magnitude of grazing effect size on aggregate-associated SOC varied with different soil particle sizes, with greater responses in aggregates >2 mm and the biggest value in TDS. In addition, the results of the correlation analysis and redundancy analysis (PDA) indicated that soil bulk density and nutrients made the main contribution to soil composition and stability of soil aggregates. Overall, grazing had a significant influence on soil aggregation, stability, and SOC, playing a crucial role in grassland soil stability and the accumulation of SOC.

Intense wet-dry cycles weakened the carbon sequestration of soil aggregates in the riparian zone