Salt-driven mechanisms of selenium behavior in coastal saline-alkali soils: A multi-model intelligent analysis from...

Coastal saline-alkali lands are key ecological zones in the global selenium (Se) cycle, yet the mechanisms by which salinity regulates Se behavior remain unclear. This study, conducted in China's Yellow River Delta, employed a multi-model approach-integrating Geodetector, CatBoost-SHAP, and PLS-PM-to investigate salinity-driven Se dynamics from soil to plant response. The results showed that: (1) Soil Se exhibited strong spatial heterogeneity, with increased Se bioconcentration factor (Se-BCF) in Phragmites australis observed in high-salinity areas. (2) Soil organic carbon (SOC) and salinity-related factors-particularly the K/Na ratio, Na, and available potassium (aK) -played key regulatory roles in determining the occurrence forms and contents of Se in soils. (3) SOC contents above 3.03 g/kg promoted the accumulation of soil available Se (aSe); when available sodium (aNa) exceeded 0.81 mg/kg or aK surpassed 0.19 mg/kg, their increases promoted Se enrichment in the aboveground parts of Phragmites australis. (4) High SOC modulated salinity ion behavior, enhancing the positive effects of aNa and Ca/Mg on Se uptake, while intensifying the negative effects of aK and pH. This study provides a theoretical foundation for understanding the environmental drivers of Se behavior and its bioavailability regulation in coastal saline-alkali ecosystems.