Microalgae-augmented cadmium accumulation in Perilla frutescens: an integrated plant-microbe strategy for enhanced...

Cadmium (Cd) contamination severely threatens agricultural productivity and ecosystem health. Phytoremediation offers a sustainable solution for Cd-contaminated soils, but its efficiency may decline as plant growth and detoxification capacity are inhibited. To address this, the present study developed a microalgae-Perilla frutescens remediation system and assessed its performance under low (50 mg/kg) and high (150 mg/kg) Cd conditions. Microalgae co-treatment increased Cd accumulation in roots, stems and leaves by 82.01 %, 14.83 % and 8.04 % under low Cd stress, and by 40.26 %, 86.40 % and 28.90 % under high Cd stress, while reducing soil Cd by 20.65 % and 31.00 %. Cd-induced growth inhibition and photosynthetic impairment were also alleviated. Mechanistic analysis revealed distinct regulatory strategies under stress intensities. Under low Cd stress, microalgae elevated superoxide dismutase (88.49 %) and catalase activities (283.30 %), upregulating genes associated with ROS (RBOH), jasmonic acid signaling (LOX, MYC2), and metal transport (CAX3, ABC transporters) to enhance stress perception, defense responses, and Cd detoxification. At higher Cd intensity, plants showed increases in SOD and POD activities by 122.86 % and 62.60 %, while ROS- and jasmonic acid-related genes were downregulated and metal transport-related genes remained upregulated. Changes in transcript profile revealed a shift toward cellular homeostasis maintenance and metabolic reprogramming for secondary metabolite biosynthesis, supporting detoxification and stress mitigation. Microalgae additionally improved soil nitrogen (8.69-9.34 %) and phosphorus (2.26-31.65 %), and enriched nitrifying taxa such as Candidatus Nitrososphaera and Nitrospira. Collectively, these findings demonstrate that microalgae integration strengthened phytoremediation performance of Perilla frutescens, offering a scalable and sustainable strategy for remediation of Cd-contaminated farmland.