According to the Ministry of Land and Resources Report on the national soil contamination survey, 16.1% of the soil surveyed was classified as polluted, the main pollutants were heavy metals and metalloids, particular cadmium (Cd). Therefore, it is exigent for remediation Cd contaminated soil in China. As a landscape, energy plant, and the characteristics of fast growing, productive, easy to manage, as well tolerace to stresses and heavy metals accumulated, willow is a alternative species for[]{#_Hlk535935356 .anchor} phytomanagement.
The pollutants tolerace and phytoremediation efficiency of willows varies with genotypes. Thus, three willow genotyes (1011, 172, 2345) were seleceted based on the capacity of Cd accumulation from 160 cultivars to optimize phytoremediation. The three willows genotypes showed considerable Cd tolerance and bioaccumulation in both slight and serious polluted soils. The bioconcentration factors (BCFs) of aerial parts were 6.73, 6.43, 8.81 at slight polluted site and 4.30, 4.48, 7.44 at serious polluted site for 1011, 172, 2345, respectively. However, the biomass of 1011 were about 10.8 t/ha (DW) in the first growing season, significantly higer than 172, 2345. The overall results showed that the phytoremediation efficiency of 1011 was higher than other two genotypes because of the larger biomass. Furthermore, the risk of brownfield sites can be reduced by willows planting as vegetation buffers. The heavy metals (Cd, Pb, Cu, et al) in runoff from polluted site were decreased by more than 80% by willows buffers.
Besides the own traits of willows, rhizosphere microbiome and their interactions also determined the efficiency of phytoremediation. Rhizosphere microbiomes composition and interactions were assessed to explore the mechanism of phytoremediation efficiency variation with willow genotypes. The results showed that microbial communities in rhizosphere were highly influenced by willow genotypes. Different taxa of plant growth promoting bacteria were accumulated in willows rhizosphere, and the relative abundance of AMF in rhizosphere of 1011 was richer than other two genotypes at serious polluted sites. Molecular ecological networks analyses indicated more symbiotic relationships among microbes in the rhizosphere of 1011, as evidenced by higher ratio of positive links and negative links between microbes than other two genotypes. Furthermore, two keystone taxa were identified in the rhizosphere of 1011 which involved to nitrogen cycling and nitrogen absorption. This results well supported that microbial community and interactions in rhizosphere associated with larger biomass of 1011 at Cd contaminated soil, which contributed to higher phytoremediation efficiency.
The current study provide a cost-effective technology for phytomanagement of heavy metals polluted soils, and enhanced the understanding of influence of microbial communities and interactions on phytoremediation efficiency among willow genotypes.