Introduction

Forest soil serves as vast carbon (C) pools in terrestrial ecosystems, depositing about 1500 ± 230 Pg C. It accounted for about 73% of global organic carbon1. Minor fluctuations in forest soil C pools might significantly impact atmospheric CO2 concentration, ultimately affecting global climate dynamics2. Climate warming has become a concern with widespread impacts on global biogeochemical cycles3. Many studies indicate that climate warming accelerates the mineralization and decomposition of organic carbon4,5. However, most field warming experiments have been conducted in high-latitude alpine regions6,7. Little is known about the sensitivity of organic carbon in low-latitude subtropical forests to climate change. Elevation can achieve microclimates and hydrothermal cycling processes by controlling zonal climatic conditions across vertical gradients, making it a suitable natural tool for understanding ecosystem homeostasis under climate change8. Therefore, investigating the stabilization mechanisms of organic carbon in subtropical forests across an elevation gradient is crucial to our understanding of future climate change at global scales.

Soil active C pool comprises various components, each with distinct stability, decomposition rate, and turnover characteristics9. It contains particulate organic carbon (POC), easily oxidizable organic carbon (EOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC)10. They exhibit diverse responses to climate change and soil fertility11. POC is primarily derived from plant residues and plays a crucial role in aggregate binding and stabilization12. EOC is stemmed from the leaching of plant residue, decomposition of organic matter, and root secretion13. It accounts for a relatively large proportion of SOC, and changes in the soil C pools mainly occur in EOC14. DOC and MBC, as key factors in nutrient turnover, are sensitive to short-term ecosystem changes15. A study revealed that warming increased above- and below-ground biomass, resulting in a 2.3% increase in DOC and a 15.5% rise in light fraction organic carbon (LFOC)16. This underscored the significant impact of environmental factors such as temperature and humidity on the soil C pools15. Elevation is a combined effector, inducing spatial variations in temperature and humidity17. However, the results of studies on the distribution of soil C pools across elevations were inconsistent18. For example, Ma et al.19 showed that SOC and labile organic carbon (LOC) contents of the same vegetation type were significantly higher in high-elevation than in low-elevation, with the contents of MBC, LFOC, and SOC being regulated by temperature, humidity, and elevation. In contrast, in the alpine meadow region of Tibet, China, the concentrations of SOC, DOC, and EOC exhibited a unimodal distribution along the elevation gradient, peaking at 4800 and 4950 m, and subsequently declining. This pattern was attributed to the distribution of aboveground biomass (AGB)20. Dai and Huang21 analyzed the SOC data from different regions of China to detect the relationship between soil organic matter and climate as well as elevation, concluding that there exist regional differences in the main factors influencing soil C pools.

Furthermore, SOC, which serves as the cementing substance for aggregates, enhances their formation and stabilization. The higher its content, the more beneficial it is to soil aggregate stability22. Therefore, the SOC contents in aggregate fractions are often employed as a crucial metric in assessing the sequestration and stability of organic carbon23. Based on aggregate size, it can be categorized into three classes: macroaggregates (> 0.25 mm), microaggregates (0.053–0.25 mm), and silty + clay fractions (< 0.053 mm)24. Their distribution affects the transportation and transformation of SOC25. Notably, the mechanisms of organic carbon stabilization and soil quality varied significantly among different-sized aggregates26. According to Six et al.26, most of the organic carbon was retained in microaggregates and silty + clay fractions, and the physical protection of organic carbon by soil aggregates tended to increase as their size decreased. However, there have also been noted that aggregate C increased when aggregate size increased27. Since soil aggregates physically protect organic carbon from microbial degradation, their stability is a key factor influencing carbon sequestration28. Apart from particle size, climate change can significantly affect aggregate C17. Guan et al.29 performed warming experiments on the Tibetan Plateau. They found that short-term climate warming significantly increased macroaggregate C while decreasing microaggregate C. Zhou et al.30 found that long-term warming-dominated climate change positively affected the DOC, free microaggregate C, and nonaggregated silt + clay C, while negatively affected the EOC, MBC, silt + clay inside microaggregates within macroaggregates C and aggregate stability. Given the diverse sensitivities of organic carbon components to environmental change, it is essential to reveal the response mechanisms of soil aggregate C to climate change in forest ecosystems.

The Dabie Mountains are one of the major mountain ranges in the East China, rich in plant resources. Comprehensive research on the preservation of organic carbon along the elevation gradient in the Dabie Mountains’ ecosystem is relatively scarce. Thus, studying the spatial distribution characteristics of the active carbon pools in the Dabie Mountains ecosystem can aid in understanding the stabilization mechanisms of SOC. As the global temperature rose, significant changes in environmental and spatial patterns such as temperature and precipitation have occurred. These influence plant physiological and ecological adaptations31, thereby altering soil C pools. Chinese fir (Cunninghamia lanceolata), a fine coniferous timber species in southern China, is widely cultivated, with the upper limit of its vertical distribution varying based on topography and climatic conditions. Our study explored the distribution patterns of active C pools and aggregates along an elevation gradient (750–1150 m) in the Chinese fir plantations at the northern foothills of the Dabie Mountain. We aimed to quantify the response of active C pools, aggregate C, and aggregate stability to the elevation gradient. We hypothesized that: (1) due to the decrease of mean annual temperature (MAT), and the increase of mean annual precipitation (MAP) and organic matter inputs, active C pools, macroaggregate, and aggregate stability were higher in high-elevation sites than in low-elevation sites, and (2) physical protection of microaggregates was the main mechanism for organic carbon preservation because of the long-term protective effect of microaggregates on soil organic matter. Overall, this study emphasized the changes in active C pools and aggregate stability with elevation gradient in subtropical forests. It can provide a reference for assessing the impact of global climate change on forest ecosystems.

Materials and methods

Site description

The experimental area is situated in the Mazongling State-owned Forest Farm in Mt. Dabie, Anhui Province, China (31°10′–31°20′ N, 115°31′–115°50′ E), with a total forest area of 3500 ha and an elevation range of 600–1671 m. The area has a variety of landforms such as mountains and hills, as well as valleys and intermountain basins. This area falls under the northern subtropical humid monsoon climate zone, with a mean annual temperature (MAT) of 14.6 ℃ and mean annual precipitation (MAP) of 1510 mm (at the elevation of 680 m a.s.l.), mostly concentrated in May-September. The soils are developed from gneiss-weathered material and are acidic. The soil types are yellow-brown soil at low elevations and mountain yellow soil at high elevations, which are Ferric Alisols and Haplic Alisols according to the FAO soil classification32. The forest types in the area are rich, mainly the north subtropical evergreen and deciduous broad-leaved mixed forest. The dominant tree species are Quercus glauca, Q. myrsinifolia, Castanopsis sclerophylla, and Q. variabilis. There are also a small number of natural forests of Euptelea pleiosperma, Carya dabeishansis, and Cercidiphyllum japonicum. The plantation forests mainly include timber forests such as Chinese fir, Pinus hwangshanensis, and Phyllostachys edulis. In particular, since Chinese fir is an important timber tree species with high economic benefits, a large number of Chinese fir plantations were cultivated from the 1970s to 1980s in the area. In 2012, the area was designated as a national nature reserve, and the Mazongling Forest Farm stopped logging. At present, there are more than 1500 hectares of Chinese fir plantation existing in this area.

Experimental design and soil sampling

In October 2021, according to the growth and distribution of Chinese fir plantations in the area, the plantation stands at four elevations (750 m, 850 m, 1000 m, and 1150 m) that were selected for the study (Table 1). Three standard 20 m × 20 m plots were randomly designed for each elevation. We used a stainless steel soil drill (inner diameter 3 cm) to collect soil samples at 0–10 cm, 10–30 cm, 30–50 cm in each plot. Three subsamples for each plot. A total of 108 soil samples were collected. All soil samples were further divided into 2 parts for analysis. One was used for the determination of active organic carbon components, and another was air-dried and used to determine soil aggregate fractions.

Table 1 Stand characteristics of Chinese fir plantation at different elevations in Mazongling area.
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Soil aggregate separation and aggregate stability analysis

Soil aggregate fractions were sieved using the conventional wet-sieving method described33. At first, the soil samples were air-dried at ambient temperature (25 °C), and the other visible materials such as fine roots, plant residues, and gravels, etc. were removed from the soils. It was then sieved using a 5-mm sieve. Finally, 100 g of soil was placed in the 0.053 mm and 0.25 mm sieves in the soil aggregate analyzer for separation. After the separation, each fraction was dried at 60 °C and weighed. The aggregates of > 0.25 mm were classified as macroaggregates, 0.053–0.25 mm aggregates were microaggregates, and < 0.053 mm aggregates were silt + clay fractions.

The mean weight diameter (MWD) and geometric mean diameter (GMD) reflect aggregate stability. The specific calculation formulas are as follows34.

$$\text{MWD} = \sum_{i=1}^{n}{\bar{x}}_{i}{w}_{i}$$
(1)
$$\text{GMD} = exp\left[\frac{{\sum}_{i=1}^{n}{w}_{i}In{x}_{i}}{{\sum}_{i=1}^{n}{w}_{i}}\right]$$
(2)

where \({\bar{x}}\)i is the mean diameter of aggregates at level i (mm); wi is the amount of aggregates at level i (%).

Soil properties

Soil pH and EC were measured according to the soil and distilled water ratio (w:v) of 1: 2.5 and 1: 5, respectively. The contents of SOC and TN were determined by an elemental analyzer (EA 3000, Vector, Italy). Particulate organic carbon (POC) was extracted by the sodium hexametaphosphate method33, easily oxidizable organic carbon (EOC) was extracted by KMnO4 oxidation method35, and then POC, EOC, and the SOC contents in the aggregate fractions were determined by using an elemental analyzer. Dissolved organic carbon (DOC) was extracted by K2SO4 leaching and microbial biomass carbon (MBC) was extracted by chloroform fumigation extraction method36 and then determined using a TOC/TN analyzer (Multi N/C 3100, Analytik Jena, Germany).

Statistical analysis

The significance of the differences in the data was tested by the Least Significant Difference (LSD) method (p < 0.05). Two-way ANOVA was used to test the effects of elevation and soil layer on the distribution and stability of aggregates, aggregate C, and active organic carbon components. Before the ANOVA, the homogeneity test of the difference was performed, and if the hypothesis was not met, the data was converted logarithmically. Spearman correlation analysis, principal component analysis (PCA), and regression analysis were used to investigate the relationship between the distribution of aggregates and organic carbon fractions along the elevation gradient. R Studio 4.3.1 and SPSS 22.0 were used to analyze data, Origin 2021 was used for plotting.

Results

Aggregate fractions distribution and stability along an elevation gradient

The distributions of soil aggregate fractions at different elevations in Mt. Dabie were significantly different (p < 0.05, Table 2). At the different elevations, macroaggregates (> 0.25 mm) had the highest proportion of 80.33–88.42% in all fractions (Fig. 1).

Table 2 Two-way ANOVA of the effects of elevation (E) and soil depth (D) on soil aggregate fractions.
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Fig. 1
figure 1

The distribution of aggregate fractions in Chinese fir plantations at different elevations.

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In the 0–10 cm soil layer, the content of macroaggregates showed a “U” distribution with elevation, and the highest proportion was found at 1150 m. However, the microaggregates and silt + clay fractions were in the opposite trend. In the soil layer of 10–50 cm, the macroaggregates showed a gradual increase, while a gradual decrease in the microaggregates and silt + clay fractions with elevation. The results of two-way ANOVA (Table 2) showed that the distribution of soil aggregates was significantly affected by elevation (p < 0.05), and not significantly affected by soil depth and the interaction between elevation and soil depth.

The MWD and GMD of aggregates changed with elevation in a consistent trend, showing a down then up trend in the 0–10 cm soil layer, and a gradual increase in the 10–50 cm soil layer, both of which reached their highest at 1150 m (Fig. 2). Overall, MWD and GMD were significantly higher in high-elevation stands than in low-elevation stands.

Fig. 2
figure 2

The mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregate in Chinese fir plantations at different elevations. Different letters on the bars (Means ± S.E., n = 9) indicate significant differences between elevations in the same soil layers (A and B), and between the different soil layers in the same elevations (a and b) (LSD test, p < 0.05).

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Distribution of SOC in different aggregate fractions

The SOC contents were significantly affected by elevation and soil depth (p < 0.01, Fig. 3d). SOC content variated from 21.85 to 67.39 g kg−1. In the 0–10 cm soil layer, SOC decreased first and then increased with the increase of elevation. The soil layer of 10–50 cm showed a gradually increasing trend.

Fig. 3
figure 3

The contents of soil organic carbon in Chinese fir plantations at different elevations. Different letters on the bars (Means ± S.E., n = 9) indicate significant differences between elevations in the same soil depth (A and B), and between the different soil depths in the same elevations (a and b) (LSD test, p < 0.05).

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The SOC contents in the different aggregate fractions were significantly affected by elevation and soil depth (p < 0.05, Fig. 3a–c). The contents of macroaggregate C ranged from 21.79 to 56.67 g·kg−1, microaggregate C and silt + clay C were 19.76 –51.96 g kg−1 and 29.72–77.19 g kg−1, respectively. The change pattern of C in the macro- and micro-aggregates with elevation was not obvious, and C in the silt + clay showed a unimodal distribution. In general, the SOC contents of aggregate fractions showed a gradual increase with decreasing size, with the highest in silt + clay fractions. In addition, the SOC contents of aggregate fractions decreased gradually (p < 0.05) with soil depth.

Distribution of soil active organic carbon components along an elevation gradient

The elevation gradient significantly affected the soil active organic carbon components (p < 0.05, Figs. 4 and 5). POC was the dominant active organic carbon component at the different elevations with the highest contents varied from 5.46 to 23.42 g kg−1, followed by EOC, MBC, and DOC. The contents of EOC and POC were significantly higher in high-elevation stands than in low-elevation stands (Fig. 8). The contents of MBC showed a unimodal distribution pattern with increasing elevation, while DOC showed a “U”-shaped distribution pattern. In addition, soil depth also significantly affected soil active organic carbon components. EOC, POC, and MBC contents all decreased with deepening soil layers, while DOC appeared no significant change.

Fig. 4
figure 4

The contents of soil active organic carbon components in Chinese fir plantations at different elevations. EOC easily oxidizable organic carbon, POC particulate organic carbon, DOC dissolved organic carbon, MBC microbial biomass carbon. Different letters on the bars (Means ± S.E., n = 9) indicate significant differences between elevations in the same soil layers (A and B), and between the different soil layers in the same elevations (a and b). (LSD test, p < 0.05).

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Fig. 5
figure 5

Principal component analysis (PCA) of soil active organic carbon components at different elevations. EOC easily oxidizable organic carbon, POC particulate organic carbon, DOC dissolved organic carbon, MBC microbial biomass carbon.

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Relationship between soil aggregates and active organic carbon components and environmental factors

Linear mixed effect model (Fig. 6) showed that MWD was significantly positively correlated with macroaggregates, DOC, macro- and micro-aggregates C, while significantly negatively correlated with microaggregates and silt + clay fractions. In addition, DOC was significantly positively correlated with macro- and micro-aggregates C. MBC was positively correlated with macroaggregate C and silt + clay C (Fig. 7).

Fig. 6
figure 6

Relationships between the MWD and aggregate fractions (a–f) and soil active organic carbon components (g–j). MWD mean weight diameter, LMA macroaggregates, MIA microaggregates, SCA silt + clay fractions, LMA-C macroaggregate C, MIA-C microaggregate C, SCA-C silt + clay C, POC particulate organic carbon, EOC easily oxidizable organic carbon, DOC dissolved organic carbon, MBC microbial biomass carbon. Significant correlations are denoted by *p < 0.05; **p < 0.01; ***p < 0.001.

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Fig. 7
figure 7

Relationships between the SOC in different aggregate fractions and soil active organic carbon components (a–l). LMA macroaggregates, MIA microaggregates, SCA silt + clay fractions, LMA-C macroaggregate C, MIA-C microaggregate C, SCA-C silt + clay C, POC particulate organic carbon, EOC easily oxidizable organic carbon, DOC dissolved organic carbon, MBC microbial biomass carbon. Significant correlations are denoted by *p < 0.05; **p < 0.01.

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The distribution and stability of aggregates and active C pools along the elevation gradient were closely related to environmental factors (Table 3). The results of Spearman correlation analysis showed that MWD, GMD, macroaggregates, macro- and micro-aggregate C, POC, and EOC were significantly positively correlated with elevation and MAP, and negatively correlated with MAT. However, the opposite was true for the microaggregates and their SOC. Moreover, the SOC in aggregate fractions and active organic C components were significantly positively correlated with SOC and TN. In addition, POC, EOC and MBC were positively correlated with C/N. DOC was significantly negatively correlated with pH. The results indicated environmental factors greatly influenced the aggregate stability.

Table 3 Spearman correlation coefficients between soil aggregates, the organic carbon components, environmental factors, and other soil properties along the elevational gradient.
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Discussion

The distribution and stability of soil aggregate are vital indicators for assessing soil structural stability37. It has been shown that the widespread use of indicators such as MWD and GMD in gauging soil aggregate stability, where higher corresponds to a more stable soil aggregate structure38. Our findings reveal a “U”-shaped pattern in the distribution of macroaggregates, MWD, and GMD in the 0–10 cm layer and gradually increased in the 10–50 cm layer as the elevation increased. And all of them reached the peak at 1150 m a.s.l. This suggests that the elevation and soil depth significantly affect aggregate distribution and stability (Figs. 1 and 2). The increase in elevation is often accompanied by changes in environmental factors such as vegetation, temperature, and precipitation. As elevation rises, the MAT gradually decreases, while the MAP increases, which results in low turnover of SOC in the high-elevation. Consequently, aggregate stability was higher in these areas7. Moreover, the canopy cover was higher in high-elevation than in low- and middle-elevation forest stands (Table 1), which favored overall stability. The vegetation cover provided benefits through canopy shading and a surface litter layer, mitigating soil erosion, drastic microclimate changes, and soil water loss. These favorable microclimate conditions and soil moisture supported fine-root growth, turnover, and soil fungal mycelium development. Those changes promoted the development of aggregates29. Some studies have been conducted to show that macroaggregate content at high elevations was associated with higher fungal content and metabolic activity39,40. Our previous study provided evidence that microbial diversity increased with the elevation in the Chinese fir plantations in Mt. Dabie41. The microorganisms regulated the decomposition of organic matter and the production of secondary metabolites, facilitating the transformation of microaggregates into macroaggregates, ultimately enhancing soil aggregate stability19. Bai et al.42 demonstrated that the increased soil moisture significantly promoted the biological process of aggregate formation, strengthening the coupling of aggregates to fungal biomass and exchangeable Mg2+. Furthermore, the input of organic matter is closely related to aggregate stability. In this study, MWD were positively correlated with DOC, macro- and micro-aggregate C (Fig. 6). This underscores the sensitivity of soil aggregate stability to environmental changes and its significant dependence on aggregates C and active C pools. The increased biomass, litterfall, and root exudates along the elevation gradient contribute to increased organic matter inputs, thus promoting aggregate stabilization43.

In forest ecosystems, soils containing a high proportion of macroaggregates are typically regarded as possessing superior soil structure and stability26. Our findings indicate that macroaggregates (> 0.25 mm) accounted for the highest proportion (over 80%) across different elevations (Fig. 1), indicating that the soil aggregates were better structured and stabilized at the study sites. This observation was rationalized with the soil aggregation theory, which posited that macroaggregates are primarily formed by organic matter-derived soil microaggregates and silt + clay fractions, while providing physical protection for microaggregates23. Consequently, the higher the proportion of macroaggregates, the more stable the soil structure becomes. However, the microaggregates and silt + clay fractions decreased with elevation (Fig. 1). Our results showed that MWD were significantly positively correlated with macroaggregates and significantly negatively correlated with microaggregates and silt + clay fractions (Fig. 6). It is consistent with the study conducted by Feyissa et al.44 in the alpine forests and grasslands of the Yulong Snow Mountain in Southwest China. Their study revealed that the proportion of soil macroaggregates was the largest at elevations of 2600 and 3900 m, with 50.54% and 49.11%, respectively, contributing significantly to the total soil C content. Kong et al.45 found that the proportion of 0.25–1.00 mm and 0.053–0.25 mm aggregates decreased significantly with elevation. Notably, the response of macroaggregates is susceptible to external environmental factors46, especially in the topsoil layer.

SOC primarily originated from plant litterfall, roots, animal and microbial residues23. The SOC contents in the different aggregate fractions represented a microscopic characterization of soil organic matter formation and decomposition. Our study found that the SOC content of silt + clay fraction appeared a unimodal pattern along the elevation gradient, peaking at 850 m. In the low- and middle-elevation Chinese fir plantations, the higher soil C/N ratio in the silt + clay fraction compared to the macro- and micro-aggregates indicated an increased accumulation of refractory organic matter within aggregate fractions (Table 1), slower SOC turnover, and differences in microbial community habitats7. It may also be due to differences in microbial biomass and microbial residue accumulation (Figs. 4 and 6)47. In addition, we observed that the SOC content was significantly higher in silt + clay fraction than in macro- and micro-aggregates across different elevations (Fig. 3). This finding highlights the crucial role of silt + clay fraction in organic carbon preservation in soil ecosystems. According to previous studies, it is known that macroaggregates are mainly formed by litterfall residues, microaggregates are formed inside the macroaggregates, and the silt + clay fractions are associated with mineral-associated organic carbon (MAOC)48,49. The input of plant C leads to the decomposition of organic matter. Roots, hyphae, and polysaccharides then preferently bind to mineral particles to form silt-clay-organic composites50. This suggests that physical protection in the silt + clay fractions was the main mechanism for organic carbon preservation26. The contribution of SOC in the silt + clay fractions to organic carbon preservation was relatively greater, which was confirmed by the findings of Virto et al.51. In contrast, many studies showed that the macroaggregate C was significantly higher than that of microaggregates and silt + clay fractions27,52. It may be more in line with the hierarchy theory of aggregates53. However, the macroaggregate C was mainly derived from humus, making it more easily mineralized and less stable than microaggregates24. This implies a high risk of organic carbon loss from soil macroaggregates under a warming climate, especially in subtropical forested areas54. Therefore, understanding the dynamics and stability of different soil aggregate fractions is crucial for effective carbon sequestration strategies in vulnerable ecosystems.

Soil active organic C is not only related to land use practices and vegetation types, but also to the combined effects of climatic factors such as temperature and moisture30,46. In general, elevation indirectly modulates temperature and moisture, thereby affecting the rate of OC mineralization to some extent. Some studies demonstrated that the contents of EOC, POC, and DOC respond significantly to increasing elevation, exhibiting an upward trend19,55. Our study revealed that the contents of EOC and POC were significantly higher at high-elevation than at low-elevation stands (Fig. 4). The results support this by showing that the decrease in soil temperature and increase in humidity with the rising elevation, resulted in slow mineralization and decomposition of soil organic matter and an increase of SOC accumulation. Conversely, SOC accumulation was lower at the lower elevations. Previous studies have shown that elevation can affect soil LOC by regulating soil hydrothermal8,30. Fang et al.16 similarly demonstrated that warming treatments led to substantial decreases in the contents of POC and MBC in low-elevation forests, highlighting the effect of temperature change on soil organic carbon in mountain forests. It can be inferred that the organic carbon turnover occurred more rapidly at the low elevation than at the high elevation. On the other hand, Kong et al.45 demonstrated that changes in organic carbon fractions at high-elevation may be closely related to macroaggregate C. These results are similar to our findings. MBC, the C contained in the microbial biomass, depends on the abundance of soil microorganisms15. DOC primarily originates from the soil microbial-driven decomposition of organic matter, and its content depends on the degree of microbial degradation of organic matter56. Our results showed that MBC appeared a unimodal pattern and DOC was a “U” shape distribution (Fig. 8) that could associated with higher pH and C/N ratio at mid-elevations (850 m and 1000 m)57. In this study, pH increased first and then decreased with increasing elevation (Table 1). As elevation rises, temperature decreases, leading to a slowdown in organic carbon mineralization and a gradual increase in pH, which enhances microbial activity. The highest soil C/N ratio at mid-elevations are largely attributed to the slowed decomposition of organic matter, directly influencing the accumulation of DOC and MBC. Furthermore, our study found a decrease in the SOC contents of active carbon components and aggregate fractions as soil depth increased (Figs. 3 and 4). This trend can be explained by the decreasing inputs of litterfall, reduced root exudates, and diminished microbial activities within the soil profile44,58.

Fig. 8
figure 8

Linear regressions of the EOC (a) and POC (b), and quadratic regressions of the DOC (c) and MBC (d) versus Elevations. R values are shown for all regressions; the significance of regressions is reported.

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Conclusions

In summary, our study revealed the significant influence of different soil depth and elevation on soil properties across the vertical soil profile. Specifically, in the 0–10 cm soil layer, MWD, GMD, and macroaggregates content all exhibit a U-shaped distribution trend with the increase of elevation. Conversely, in the 10–50 cm soil layer, these indicators demonstrate a consistent trend across the elevation gradient. Furthermore, the contents of EOC and POC steadily increase with the rise in elevation, indicating more pronounced accumulation of soil organic matter in high-elevation sites. Notably, MBC and silt + clay C in 0–50 cm soil layers display a unimodal distribution pattern along the elevation gradient, peaking at 850 m a.s.l. The silt + clay C contents were significantly higher than macroaggregate C and microaggregate C along the elevation gradient. Our finding offers a novel perspective on understanding C sequestration mechanisms under elevational gradients. The contents of EOC, POC, MBC, and aggregate organic carbon all decreased gradually with soil depth. Interestingly, the MWD and GMD were significantly positively correlated with DOC, macroaggregates, and macroaggregate- and microaggregate-C, while negatively correlated with microaggregates and silt + clay fractions. This suggests that SOC content has a strong influence on aggregate stability. The results indicated a close relationship among aggregate, active organic C components, and environmental factors. Physical protection of aggregates and organic carbon accumulation may be the main mechanisms for SOC preservation along an elevation gradient in the Dabie Mountain. It is essential to further study organic carbon sequestration under climate change and thus accurately predict the response of organic carbon stability to climate warming.