Linking root traits to phytoremediation in trees and shrubs: implications of root economics spectrum.
Abstract
Phytoremediation is a promising technique for removing or stabilizing metal ions from metallic trace elements (MTEs) contaminated soils. Despite the significant role of roots in plant growth and survival, limited information is available on the functional covariation of root traits under MTE stress, and linkages between root resource-use strategies and phytoremediation functioning. Sixteen root traits were measured across 11 trees and shrubs grown in Pb-Zn mine tailings in Southeastern China, to examine whether a hypothesized root economics spectrum (RES) exists under extremely high levels of multiple MTEs stress and evaluate the importance of root functional traits in explaining phytoremediation functioning. Our findings offer evidence supporting the widely accepted resource-use strategy of acquisitive-conservative. Furthermore, we have identified a distinct dimension of RES representing the trade-off between root system size and root tissue density. This new dimension highlights the critical importance of root size, shape and proliferation strategy in the context of metal-contaminated soil. Moreover, a trade-off between root cadmium concentration and root dry matter content was observed, which implies the existence of a presumable biomass cost for MTEs accumulation. We identified specific key root traits and their contributions to MTE translocation and bioconcentration, and established linkages between root resource-use strategy and phytoremediation: roots with more acquisitive traits promote MTE translocation, while conservative roots foster bioconcentration. In addition, acquisitive roots usually exhibit lower biomass costs for accumulating MTEs than do conservative roots. Synthesis and applications. Our results highlight the important role of root size-related traits in the root economics spectrum (RES) framework in metal-contaminated soil. Furthermore, we discovered that woody species exhibit different capacities for accumulating or translocating metallic trace elements (MTEs), depending on their root system shapes and their position on axis of RES. These findings provide valuable support for the accurate selection of suitable plant species for ecological restoration purposes. And they hold significant potential in guiding the development of efficient phytoremediation strategies specifically targeting sites contaminated with MTEs.