Electrophysiological Responses of Seleniferous Tea Seedlings to Cadmium Stress in Astragalus sinicus-Modified Substrates

Seleniferous tea seedlings from Enshi, China, face cadmium (Cd) contamination risks due to the co-occurrence of selenium and cadmium in local soils, posing food safety concerns. While Astragalus sinicus-modified substrates are commonly applied for cadmium remediation, the performance of different monitoring techniques remains inadequately evaluated. This study compared four monitoring methods—growth traits, photosynthesis, chemical Cd removal rate, and plant electrophysiological parameters—in a pot experiment under cadmium stress (10 mg/kg Cd2+). Two tea varieties, Longjing 43 (Camellia sinensis ‘Longjing 43’. LJ 43) and Yulu 1 (Camellia sinensis ‘Yulu 43’. YL 1), were treated with four modified substrates (M1–M4). Specifically, compared to the control (M1), LM3 increased metabolic activity (MA), electrical impedance (EGC), and electrochemical response (ECR) by 140.27%, 122.5%, and 124.41%, respectively. These increases were significantly greater than those observed for the conventional metrics: 52.70% in total biomass (TB), 109.31% in photosynthetic rate (Pn), and 64.15% in chemical Cd removal (RCd). Similarly, in the YM4 treatment, MA and EGC increased by 214.91% and 178.66%, respectively, which also significantly exceeded the increments in TB (48.74%), Pn (116.19%), and RCd (75.26%). Among the electrophysiological parameters, MA proved to be the most sensitive indicator, showing a strong correlation with Cd removal capacity. In conclusion, plant electrophysiology enabled real-time, in situ monitoring of cadmium remediation efficiency, offering a novel technological pathway to ensure the safety of seleniferous tea seedlings and advance precision agriculture.