RESPONSE CHARACTERISTICS OF VALLISNERIA NATANS AND RHIZOSPHERE MICROBIAL COMMUNITY UNDER SEDIMENT-CADMIUM POLLUTION

In this study, the typical submerged macrophyte Vallisneria natans was selscted, and the fresh weight, plant height, chlorophyll, malondialdehyde (MDA), superoxide dismutase (SOD) and peroxidase (POD) activities of Vallisneria natans were measured at 0, 1, 5, 10, 20 and 50 mg/kg of sediment cadmium contamination to analyze the cadmium tolerance effect of Vallisneria natans, and the enrichment capacities were indicated by the values of Biota-sediment accumulation factor (BSAF) and translocation factor (TF), while the 16S rRNA gene amplicon sequencing technique was used to study the community structure of Vallisneria natans rhizosphere bacteria response to the sediment cadmium contamination. The results showed that: (1) When Cd≥20 mg/kg treatment, the fresh weight, plant height, chlorophyll content and the stress resistance decreased of Vallisneria natans. The activities of SOD and POD increased firstly and then reduced, MDA content increased with increasing concentration; (2) in all the treatments, BSAF exceeded 1, indicating that Vallisneria natans could effectively enrich cadmium in the contaminated sediment, and TF was less than 1, indicating that Vallisneria natans relied on root filtration mechanism to enrich cadmium, and needed to be harvested regularly; (3) the sequencing results showed that the rhizosphere bacteria of Vallisneria natans were mainly composed of 37 phylum, such as Actinobacteria, Firmicutes and Proteobacteria, including plant growth-promoting bacteria such as Sphingomonas, Flavisobacter, Massilia, Bacillus, and Arthrobacter, which may play important roles in promoting the growth, tolerance, and enrichment of cadmium in Vallisneria natans. In this study, we preliminarily analyzed the changes of morphological, physiological and biochemical indicators of Vallisneria natans under varied cadmium stress environments, and the composition of Vallisneria natans rhizosphere bacterial community and its response characteristics to cadmium stress, which provide guidance for the subsequent improvement of Vallisneria natans restoration efficiency.