The fractal characteristics of soil particle-size distribution (PSD) constitute an important soil physical property, and fractal models of soil PSD are increasingly used to describe the effects of vegetation on the improvement of soil-related properties. Based on the fractal theory, this paper selected four typical vegetation restoration types (Quercus acutissima, QAC; Robinia pseudoacacia, RPL; Pinus densiflora, PDS; QAC × PDS) in the Taiyi mountainous area as the research object, and the single-fractal dimension (D) and multi-fractal parameters of PSD and its correlation with soil-associated properties were studied. The results show that (1) QAC × PDS reduced the heterogeneity of soil sand distribution, which also increased the range and concentration of soil PSD in the dense area. Soil clay and silt contents showed QAC × PDS > RPL > QAC > PDS. QAC × PDS significantly increased clay and silt content in 0–20 cm soil. (2) D varies among different vegetation restoration types, which was QAC × PDS > RPL > QAC > PDS, and the D of 0–20 cm soil was greater than that of 20–40 cm. For the multi-fractal parameters of PSD, the capacity dimension (D₀), information dimension (D₁), correlation dimension (D₂) and D₁/D₀ in 0–20 cm soil of different vegetation restoration types showed significant differences. (3) D and multi-fractal parameters were significantly positively correlated with clay and silt contents, which were significantly negatively correlated with sand contents. (4) QAC × PDS had the smallest soil bulk density and largest porosity. Fractal dimension was negatively correlated with soil bulk density and positively correlated with soil total porosity and capillary porosity. These results indicate that the soil fractal dimension can well characterize the vegetation improvement on soil structure and properties in the earthy-rocky mountain areas of northern China.

Phosphorus is a crucial nutrient for plant growth, primarily found as insoluble phosphates in soil. The impact of climate change on the phosphorus cycle, particularly through geochemical cycling in forest soils, is underexplored. To address this gap, we investigated soil phosphorus distribution across five elevation gradients in different forest types using the modified Hedley fractionation method and high-throughput sequencing to assess phosphorus-solubilizing microorganisms (PSMs). Our study included evergreen broadleaf forest, coniferous and broadleaf mixed forest, coniferous forest, subalpine dwarf forest, and alpine meadow. We observed that with increasing elevation, organic phosphorus forms such as NaOH-Po and HCl-Po significantly increased, while H ₂ O-Po and NaHCO ₃ -Po varied, peaking in specific forest types. The proportion of labile phosphorus decreased with elevation, whereas stable phosphorus increased. Soil PSM diversity was highest in lower elevations and declined with altitude, with significant shifts in dominant PSM groups across vegetation types. PSMs analysis revealed correlations between specific phosphorus forms and microbial taxa, indicating that elevation and vegetation type influence PSM diversity and phosphorus form distribution. The differences in soil conditions between low and high elevations present distinct characteristics: rapid mineral weathering and organic matter decomposition occur at lower elevations, while higher elevations exhibit higher total phosphorus content but a lower proportion of labile phosphorus. These distinctions open avenues for future research on adaptive strategies for phosphorus management in agriculture and forestry across different altitudes. These findings suggest that rising temperatures may enhance PSM diversity, potentially increasing the proportion of bioavailable phosphorus and accelerating its cycle in forest ecosystems. IMPORTANCE: This study provides critical insights into how climate change influences soil phosphorus cycling in forest ecosystems. By examining the distribution of phosphorus forms and the diversity of phosphorus-solubilizing microorganisms (PSMs) across different elevation gradients, we uncover how varying environmental conditions affect phosphorus availability. Our findings reveal that higher elevations, despite having increased total phosphorus content, exhibit reduced bioavailable phosphorus. This suggests that climate change, particularly rising temperatures, could enhance PSM diversity at lower elevations, potentially increasing phosphorus bioavailability and accelerating its cycle. These insights are crucial for developing adaptive phosphorus management strategies in agriculture and forestry, ensuring sustainable nutrient supply and improving ecosystem resilience in the face of global climate change. Understanding these dynamics helps predict future soil fertility patterns, aiding in the formulation of policies and practices aimed at maintaining healthy forest ecosystems and ensuring long-term ecosystem productivity under changing climatic conditions.

Introduction: Inputs of additional organic matter to the soil will accelerate or inhibit the decomposition of soil organic carbon (SOC), resulting in a priming effect (PE), which is a key mechanism affecting soil carbon (C) cycling. The impact mechanism of changes in soil properties on the PE is still unclear after vegetation restoration; in particular, the contribution of C pools with different turnover rates to the PE has not been distinguished and quantified.Methods: In this study, the secondary shrub (SB) (Vitex negundo var. heterophylla) formed by the enclosure of barren grassland was selected as the research object, and the barren grassland (GL) was taken as the control. Equal amounts of ¹³C-labeled glucose were added to the topsoil for a 45-day incubation experiment to measure the PE. Moreover, soil samples were destructively sampled to explore the fate of new C and changes in POC and MAOC fractions during incubation.Results: After 45 days of incubation, most of the new C formed by glucose flowed to MAOC, with 95.45% in SB soil and 92.29% in GL soil. In the experiment, all soils showed a positive PE. The PE, POC mineralization and MAOC accumulation were higher in SB soil than in GL soil. During incubation, the mineralization of POC was positively correlated with the PE and made a major contribution to the PE. Partial correlation analysis showed that after vegetation restoration, SB further promoted the mineralization of POC by increasing the soil moisture, fungal diversity and necromass C of bacteria, which led to an increase in PE.Conclusion: The SB mainly enhanced PE by increasing soil fungal diversity and mineralization of POC. And increasing PE due to the SB may lead to an increase in soil C emissions. Therefore, we need to adopt forest management and other measures to address the potential risks of increased soil C emissions in the vegetation restoration process.