The mechanism of a submerged aquatic plant to various size of micro-nano plastics stress in ecological constructed wetland

Wetlands are the most self-purifying ecosystems in nature and are known as the kidneys of the Earth. The widespread use of plastic products has led to the storage of large amounts of microplastics that can negatively affect wetland plants. This of great concern owing to their refractory degradation and widespread presence in various environmental media. Current research focused on the effects of microplastic concentration gradients and ignored the potential effects of particle size differences. This study investigated the physiological responses of Vallisneria natans (V. natans) to polyethylene microplastics (PE-MPs) of different sizes. Microplastics of different particle sizes exhibit direct and indirect toxicity in V. natans. The uptake of nitrogenous substances by V. natans did not significantly differ among PE-MPs of different sizes. The V. natans had increased chlorophyll content following short-term exposure to 50 nm and 500 nm polyethylene that disappeared after 28 d of continuous exposure. The leaf antioxidant defense system is activated by PE-MP pollution stress, and oxidative stress becomes more pronounced as the particle size decreases. Moreover, the presence of PS-MPs changed the abundance of dominant microbial species in the environment but did not change the composition of the microbial community. PE-MPs caused changes in the dominant microbial communities and increased metabolic activities related to amino acid transport, energy metabolism, and signaling. This study provides a theoretical reference to utilize submerged plants in wetland restoration.