Distribution of cadmium accumulated in the wood cells of poplar

Abstract Poplar is an important tree species in the phytoremediation of Cadmium (Cd) in the soil. However, the research on its transport and accumulation mechanism in wood cells has not been conducted. In this paper, Poplar 69 [ Populus deltoides Bartr. cv. ‘Lux’ (I-69/55)] was selected to study the distribution of Cd accumulated in the wood, both macroscopically, by Cd analysis along the trunk heights, and microscopically, by scanning electron microscope with energy dispersion spectrum (SEM-EDS) observation, through a pot experiment, where four treatments with different Cd application in the soil and one control without Cd addition were set. The results demonstrated that the Cd concentration in the wood of all heights increased significantly with the increase of Cd addition in the soil and it also increased, though not significantly, from the basal to the top along the trunk heights at all treatments. Through SEM-EDS Cd was found to be accumulated in the inner wall and pits of the vessels, the wood fibers, and the wood rays, indicating that Cd could enter all three types of wood cells. The distribution of Cd in the three types of wood cells followed the order as wood fiber > vessel > wood ray, based on the calculation of the proportion of Cd enrichment spots in different types of cells. About half of the Cd in the wood was stored permanently in the wood fibers with the rest being in the vessels and wood rays probably temporally.