Understanding the factors governing Cd accumulation in leafy vegetables is critical for Cd remediation and risk control. In theory, root driven Cd accumulation is determined by the product of the soil phytoavailable Cd concentration and plant transpiration; however, this integrated model—particularly in leafy vegetables characterized by large leaf areas and high transpiration potential—remains understudied and may represent a key unaddressed mechanism for understanding the comprehensive effects of different treatments. In this study, gradients of soil water-soluble Cd and transpiration rates were established in water spinach, white amaranth, and red amaranth through open-field, greenhouse, quicklime, biochar, and foliar silicon fertilizer treatments to test this hypothesis. The results revealed a weak relationship between Cd accumulation in leafy vegetables and soil water-soluble Cd, but significant correlations with transpiration rate and leaf area. Moreover, the transpiration-driven Cd accumulation rate (soil water-soluble Cd × transpiration rate) explained 71% of the variance in total plant Cd accumulation under greenhouse conditions, indicating that soil water-soluble Cd and transpiration jointly govern Cd accumulation in leafy vegetables. Additionally, multiple regression analyses showed that total leaf area and the transpiration-driven Cd accumulation rate explained 88% of the variance in Cd mass in leafy vegetables under open-field conditions, indicating that foliar uptake also plays an important role in Cd accumulation. The findings of this study are expected to shed new light on the mechanisms underlying Cd accumulation in leafy vegetables.
