Predicting Al, Cu, and Zn concentrations in the fine roots of trembling aspen (Populus tremuloides) using bulk and rhizosphere soil properties

We compared the predictions of Al, Cu, and Zn concentrations in fine roots of trees using properties of the bulk and rhizosphere soils to find the best approach to assess the ecological risks of metals to trees. Predictions were made from 18 trembling aspens ( Populus tremuloides Michx.) equally distributed on six sampling sites using multiple linear regressions with soil Al, Cu, and Zn speciation data and chemical and microbial properties as explanatory variables. Fine root Al, Cu, and Zn concentrations ranged, respectively, from 2137 to 7480, from 7.03 to 206, and from 41.2 to 360 µg·g dry root mass^–1. No significant prediction was obtained for Al. The soil total water-soluble Cu and Zn concentrations better predicted the metal concentrations in fine roots than the concentration of labile metal species. The concentrations of reactive Zn, water-soluble organic C, and NH₄ ⁺ together with microbial biomass of N were the other significant explanatory variables. The best regression models for Cu and Zn were obtained in the rhizosphere and explained, respectively, 79.2% and 95.7% of the variation of metal concentrations in fine roots. This work pointed out that the rhizosphere properties and processes need to be considered to correctly assess the ecological risks of metals to tree.