The content and stoichiometric ratios of plant biogenic elements are key indicators for understanding plants’ ecological traits and their responses to environmental changes. However, it remains unclear how wetland herbaceous plants allocate these biogenic elements and how they relate to soil conditions. This study examines the variations in carbon (C), nitrogen (N), and phosphorus (P) stoichiometry across different organs and life forms, and their response to soil factors in Yellow River Delta wetlands. We analyzed the stoichiometric characteristics of 44 herbaceous species (17 annuals and 27 perennials) and their organs (leaves and stems). The results showed that annual plants show higher N and P but lower C content compared to perennials, indicating distinct life history strategies. In plant organs, leaves exhibited higher C, N, and P concentrations than stems, reflecting functional adaptation. Notably, random forest analysis identified stem C content as a key indicator for life history strategy differentiation. Furthermore, soil factors directly influenced organ-level stoichiometry but showed limited effects across life forms. The plants demonstrated P limitation with high sensitivity to soil P availability. This study provides new insights into organ-specific nutrient allocation strategies in wetland plants and offers valuable guidance for coastal wetland conservation.

Shrub encroachment in coastal wetlands alters vegetation–soil interactions, yet its impacts on north temperate coastal wetland ecosystems remain poorly quantified. This study investigated the effects of Tamarix chinensis-dominated shrub encroachment in the abandoned Yellow River course wetlands. Encroachment stages (Isolated Tamarix shrub, ITS → Tamarix shrub island, TSI → Tamarix woodland, TWL) were assessed via vegetation surveys and soil sampling (0–60 cm). Encroachment progression significantly increased shrub cover, shrub crown width, and branches per shrub while reducing soil electrical conductivity and soil salt content. Surface soils (0–5 cm) exhibited higher levels of organic carbon (SOC) and elevated total nitrogen (TN) and available nitrogen (AN), while deeper layers (40–60 cm) at the TWL stage exhibited reduced available phosphorus (AP) and total phosphorus (TP). Redundancy analysis (RDA) identified soil bulk density, soil water content, total carbon (TC), and AP as primary drivers of vegetation community restructuring (RDA: 68.68% variance). The average ranges of TC:TN (R_CN), TC:TP (R_CP), and TN:TP (R_NP) were 23.04–92.54, 52.14–92.88, and 0.46–4.29, respectively. T. chinensis encroachment induced nitrogen-limited conditions and reduced deep soil layer phosphorus availability, fundamentally restructuring coastal wetland ecosystems. These findings inform blue carbon ecosystem management in the north temperate zone.