Foliar exposure to microplastics disrupts lettuce metabolism and negatively interferes with symbiotic microbial communities

Abstract

Plant leaves are considered an important sink for atmospheric microplastics (MPs) because they serve as a vital interface between the atmosphere and terrestrial ecosystems. However, there is still a dearth of information regarding how plant-symbiotic microbe-soil systems are affected by foliar exposure to MPs. In this study, MPs (polystyrene (PS), polyethylene (PE), and polypropylene (PP)) were sprayed over soil-cultivated lettuce (Lactuca sativa L.) four occasions, with final sprays containing 0.4 and 4 μg of MPs per plant. MPs had no discernible impact on lettuce growth as compared to the control group. However, MPs led to reductions in relative chlorophyll content from 16.91 to 30.64 % and net photosynthetic rate from 6.64 to 81.41 %. These results validate the phytotoxicity linked to MP exposure through foliar application. The presence of MPs triggered interspecific competition among phyllosphere microbial species and reduced microbial network complexity by forming ecological niches and regulating carbon- and nitrogen-related metabolic pathways. Furthermore, MPs inhibited the growth of beneficial bacteria in the rhizosphere soil, including a variety of plant growth-promoting bacteria (PGPR) such as Rhizobiales, Pseudomonadales, and Bacillales. This study identifies the ecological health risks associated with atmospheric MPs, which may have a detrimental impact on crop production and further compromise soil ecosystem security.