Combined Soil and Atmospheric Cadmium Stresses: Cadmium Accumulation and Physiological Responses in Nicotiana tabacum L.

Cadmium (Cd) pollution threatens agricultural ecosystems and human health, yet the combined impacts of atmospheric and soil Cd exposure on plant accumulation dynamics remain underexplored. The investigation focuses on the two main Cd uptake routes, soil-root and atmosphere-leaf, in Nicotiana tabacum L., a commercial crop with a notable ability to hyperaccumulate Cd. Controlled experiments were conducted to simulate realistic exposure conditions, providing insights into how these pathways interact and influence Cd accumulation in plants. The key findings revealed that soil was the dominant Cd source (88.29%-92.63%), while atmospheric deposition contributed 3.54%-7.36%, with leaves acting as the primary sink (> 70% of total Cd). Subcellular distribution identified the cell walls (48%-75%) and vacuoles (21%-50%) as critical sequestration sites, mediated by pectin binding and phytochelatin-Cd complexes. Low atmospheric Cd enhanced biomass (10%) and antioxidant activity, whereas combined high stress (AHSH group) suppressed growth (plant height (PH) 18%, root length (RL) 26%) and chlorophyll synthesis (29%), alongside oxidative stress escalation (H₂O₂ 53%, MDA 147%). Antioxidant enzymes (SOD, CAT, APX) exhibited threshold-dependent responses, being stimulated at low Cd levels but suppressed at high doses, which indicates limits to the detoxification capacity. These results underscore atmospheric Cd as a non-negligible risk factor in tobacco-growing regions, advocating for integrated soil-air monitoring frameworks to safeguard crop safety and ecosystem health.