Uptake and Translocation of Heavy Metals in Maize Leaves Exposed to Atmospheric Fallout

Atmospheric deposition is considered a source of heavy metals in plants. However, research on the uptake pathways of atmospheric particulate matter by leaves and the subsequent translocation of heavy metals within plants remains limited. In this study, the foliar uptake and translocation of heavy metals in two maize cultivars (fresh corn and silage corn cultivars, called Baiyunuo909 and Qingzhu932, respectively) were investigated through foliar exposure using soil from a mining area to simulate dry deposition under controlled chamber conditions. The height and biomass of maize were inhibited after three and five exposures to fallout deposition, and this inhibitory effect became increasingly pronounced with prolonged exposure. Furthermore, the activities of catalase (CAT) and superoxide dismutase (SOD), along with the malondialdehyde (MDA) content, significantly decreased in both cultivars relative to the control. This decrease was more significant in fresh maize, with the reduction ranges being 94.3%, 42.1%, and 40.8%, respectively. Fallout exposure elevated the contents of cadmium, lead, arsenic and zinc in the leaves, stems, and sheaths of both cultivars, despite no significant increase in the roots. The bioconcentration factors of leaves for heavy metals ranged from 0.0002 to 0.0007, representing a 3.5-fold variation; however, the overall low values showed no significant differences. Scanning electron microscopy with energy-dispersive spectroscopy revealed the accumulation of particulate matter on the leaf surface, with a higher density around the cuticle and stomata. Additionally, the fresh corn cultivar demonstrated greater sensitivity to fallout than the silage corn cultivar. In summary, heavy metals present in atmospheric particulate matter can be absorbed by leaves and subsequently translocated to other plant tissues. This study provides a theoretical foundation for understanding the mechanisms of foliar heavy metal uptake in maize.