Plant Diversity Characteristics and Environmental Interpretation Under the Land–Sea Gradient in the Yellow River Delta

Understanding the characteristics and key driving factors of plant diversity is of great significance for maintaining biodiversity and the ecosystem. Current studies on plant diversity in the Yellow River Delta are limited to local areas; there is a lack of comprehensive discussion on the spatial heterogeneity of plant diversity and the driving factors at a regional scale. Based on field investigations, this study explored the characteristics of plant composition and diversity under the land–sea gradient, with particular emphasis on the differences of plant diversity under different riverbanks and at a distance from the sea. Using the regression, redundancy, and Mantel test analysis, we analyzed soil properties, environmental factors, and human influence to assess their potential impacts on plant diversity. The results demonstrated that Asteraceae, Poaceae, and Amaranthaceae are the dominant plant families in the Yellow River Delta. As the distance from the sea increases, the community transitions from the monospecies dominance of Suaeda salsa to one dominated by various plants. The species similarity was higher in the adjacent environment and coastal areas. The overall level of plant diversity was not high, and the Margalef, Shannon–Wiener, Simpson, and Pielou index showed a fluctuating downward trend from land to sea. Notably, there was a peak value in the region of 3–17 km and >42 km from the sea. The plant diversity of the main stream bank was higher than that of its tributaries, where the former was more susceptible to human interference and the latter to soil electrical conductivity. In terms of the region, soil electrical conductivity had the greatest influence on plant diversity. This study could provide theoretical support for vegetation restoration and ecological protection in the Yellow River Delta.