Microbial Community Restructuring and Functional Response in Giant Duckweed (Spirodela polyrhiza) Fronds Driven by Cadmium Stress

As a typical heavy metal pollutant, cadmium (Cd) poses significant threats to ecosystems and human health. Giant duckweed (<i>Spirodela polyrhiza</i>), a small aquatic plant characterized by rapid growth and efficient heavy metal accumulation, holds great promise for phytoremediation. However, the mechanisms by which <i>S. polyrhiza</i> enriches Cd-particularly the contributions of its surface-associated microbiota-remain poorly understood. In this study, <i>S. polyrhiza</i> fronds were exposed to 0, 1, and 10 μM Cd, and we observed a concentration-dependent increase in the abundance of epiphytic microorganisms on the frond surfaces. High-throughput 16S rRNA gene sequencing revealed that Cd stress significantly altered the diversity of the frond-epiphytic bacterial community. Notably, the relative abundances of the genera <i>Herbaspirillum</i>, <i>Enterobacter</i>, and <i>Pantoea</i> increased significantly with rising Cd concentrations. Functional prediction using PICRUSt2 indicated enrichment under Cd stress of specific traits-such as the nitrate/nitrite transporter NarK, signal transduction mechanisms, and ion channel proteins-suggesting these taxa may actively participate in Cd uptake and tolerance. Together, our results reveal a synergistic <i>S. polyrhiza</i>-microbiome response to Cd and identify taxa/functions as targets and biomarkers for microbe-augmented remediation.