The dosage- and size-dependent effects of micro- and nanoplastics in lettuce roots and leaves at the growth, photosynthetic, and metabolomics levels
Description
The occurrence of microplastics (MPs) and nanoplastics (NPs) in soil may trigger morphological, physiological, and biochemical changes in plants. The impact of MPs/NPs has been investigated in lettuce (Lactuca sativa L. var Canasta) plants using four different particle sizes of polyethylene micro- and nanoplastics and four concentrations. In this study, photosynthetic activity, plant morphological changes, and roots and leaves metabolome modulations were considered. Our findings indicate that particle size has a hierarchically more significant impact on lettuce morphological (biomass, color segmentation, greening index, leaf area, and photosynthetic activity) and physiological (maximum quantum yield - Fv/Fmmax, or quantum yield in the steady-state Fv/FmLss, NPQLss, RfdLss, FtLss, FqLss) parameters, as well as in terms of metabolome modulation. Small plastic sizes exhibited a stronger impact on plant aerial parts in a dose-response manner, leading to a general enhancement of biosynthetic processes. Conversely, increasing plastic size had a major impact on root metabolome, resulting in negative modulation of biosynthetic processes. Generally, secondary metabolites biosynthesis, phytohormone regulation, and lipids and fatty acids were the most impacted. Moreover, nitrogen-containing compounds were accumulated following treatments. The qPCR of genes related to the soil nitrogen cycle (such as NifH, NirK, and NosZ), the analysis of nitrogen forms in soil (including NO3- and NH4), and metabolites involved in nitrogen pathways are strictly correlated with the morpho-physiological parameters of lettuce plants driven by MPs/NPs contamination.