Ramet-specific responses of intact Vallisneria natans clones to localized sediment amendment with polystyrene nanoplastics and cadmium.

Localized sediment amendment with nanoplastics and cadmium produces spatially heterogeneous effects on stolon-connected clonal plants. In a 49-day factorial experiment, parent ramets of Vallisneria natans were exposed to sediment amended with polystyrene nanoplastics (PSNPs; 100 nm; 0, 5, or 10 mg kg-1) and cadmium (Cd; 0, 0.5, or 1 mg kg-1), while connected offspring colonized surrounding unamended sediment. Under low Cd co-exposure (0.5 mg kg-1), 10 mg kg-1 PSNPs reduced parent height and fresh mass. Without Cd, 5 mg kg-1 PSNPs increased offspring number and total offspring fresh mass; however, under high Cd co-exposure (1 mg kg-1), 10 mg kg-1 PSNPs decreased total offspring and stolon fresh mass. Physiologically, the highest combined amendments resulted in divergent responses: parent chlorophyll concentrations and antioxidant activities were lower, whereas connected offspring maintained or exhibited higher pigment and antioxidant levels. These results demonstrate that localized sediment amendment induces concentration-dependent and ramet-specific responses within intact clonal networks, indicating that conventional single-plant bioassays may not fully capture the spatially complex responses of clonal macrophytes in heterogeneous environments.