Internal Sodium-Potassium Translocation Drives the Growth Adaptation of Suaeda salsa in a Coastal Wetland Ecosystem

Understanding the internal translocation of sodium (Na) and potassium (K) within the soil–plant continuum is crucial for elucidating their mechanistic roles in plant growth adaptation. We investigated these processes in the Suaeda salsa across a natural salinity gradient in the Yellow River Delta coastal wetlands. Using field surveys, we quantified Na and K enrichment and translocation coefficients among soil, roots, stems, and leaves. The correlation analysis and Random Forest modeling were then employed to identify the key drivers linking these ion dynamics to plant morphological traits (height, density, biomass). Results revealed a pronounced Na compartmentalization, with leaves acting as the primary sink (enrichment coefficient = 5.62), exhibiting values 4.68- and 3.81-fold higher than roots and stems, respectively. In contrast, K enrichment levels remained relatively stable across plant organs (roots: 0.50; stems: 0.57; and leaves: 0.62). Internal Na+ loading in stems and leaves positively correlated with leaf Na enrichment. Conversely, high soil Na suppressed both leaf Na enrichment and stem-to-leaf K translocation, while elevated soil K reduced K enrichment in all organs and soil-to-root Na translocation. Critically, plant height was negatively correlated with Na-K enrichment coefficients in all organs. Population density and biomass were specifically linked to stem-related Na dynamics (stem-leaf Na translocation and stem Na enrichment), with K translocation showing no significant relationship. The Random Forest model identified the stem K enrichment coefficient, leaf K content and its enrichment coefficient, and stem Na content as the most influential coefficients governing plant growth (relative importance: 6.37~12.82%). We conclude that the growth adaptation of S. salsa in this coastal ecosystem is driven by a synergistic yet organ-specific regulation of Na and K translocation and homeostasis. These findings provide a mechanistic physiological basis for informing ecological restoration strategies of S. salsa wetlands and support the sustainable management of estuarine ecosystems.