Multifractal characteristics of soil particle distribution under different vegetation types in the Yellow River Delta chenier of China

Vegetation restoration on degenerated cheniers in the Yellow River Delta of China is important to maintain the ecosystem stability in the muddy coastal zone. This study mainly investigates the multifractal characteristics of the soil particle distributions under different vegetation types on a Yellow River Delta chenier, reveals the fractal mechanism of soil improvement by vegetation, and identifies the types of vegetation that provide the best remediation effects on the texture of degenerated chenier soils. Three vegetation types, including two shrub-grass communities, Ziziphus jujuba var. spinosa-Artemisia mongolica (ZA) and Periploca sepium Bunge-Messerschmidia sibirica (PM), and one mixed herbaceous community, Artemisia mongolica-Phragmites australis (AP) at the beach ridge of the Yellow River Delta were used as the study subjects, and bare land was used as the control (CK). The results showed that (1) the shell sand under the different vegetation types had the highest sand contents, with low silt and clay contents, and exhibited a nonuniform soil particle distribution with obvious heterogeneity. Restoration of shrub-grass communities can reduce the heterogeneity of the particle size distribution (PSD) of shell sand by increasing the range of the PSD and its degree of concentration in dense areas. (2) The shrub-grass communities can increase the clay and silt contents and decrease the sand content of shell sand. The shrub-grass communities were more effective than the mixed herbaceous community in refining the soil texture, and the ZA exhibited the strongest shell sand particle refinement capability. (3) The shell sand in the different soil layers under the different vegetation types had significantly different capacity dimensions (D0), information dimensions (D1), correlation dimensions (D2), and D1/D0 and D0-D1 ratios (P < 0.05). The multifractal parameters of the shell sand were correlated to the soil depth. With increasing soil depth, the correlations of D1, D2, and D1/D0 with the clay, silt, and sand contents weaken. (4) The coarseness and nonuniformity of the texture of the shell sand under the shrub-grass communities were significantly lower than those on bare land. Shrub-grass communities can control wind erosion of the soil surface, preventing the coarsening of topsoil and promoting the accumulation of fine particles. The shrub-grass communities were more effective than the mixed herbaceous community in improving the soil structure; furthermore, the ZA was better than the other communities in improving the soil structure. Additionally, the degree of soil improvement in the 10–30 cm layer was better than that in the 0–10 cm layer.