Root trait values of 11 trees and shrubs grown on mine tailings

<ol> <li>Root traits play significant roles in plant resource-use strategies, and are good predictors of plant growth and survival. However, their predicting role in phytoremediation remains poorly understood and we know much less about the functional covariation of root traits with soil heavy metal (HM) contamination.</li> <li>The objective of this study was to assess the importance of root traits to predict phytoremediation services and to quantify biomass cost (BC) for HM accumulation in eleven woody species grown on a Pb-Zn mine tailing of Southeastern China. Sixteen traits associated with root morphological and chemical features, as well as HM accumulation characteristics, were measured to examine whether there is a RES under HM stressors and whether the covariation among root traits was related to individual or multiple heavy metal translocation and bioconcentration.</li> <li>Our findings provide evidence for a multidimensional RES including one main trend of 'slow-fast' strategy, and a trend representing a trade-off between root system size and root tissue density, indicating root proliferation strategy in a metal-contaminated soil. Another trade-off between root cadmium concentration and root dry matter content implied the existence of a presumable biomass cost for HM accumulation, which was proved to be constrained by RES.</li> <li>Root traits were good predictors of individual or multiple HM translocation and bioconcentration, and linked with phytoremediation services: roots with more acquisitive traits promote HM translocation, whilst conservative roots fostered bioconcentration.</li> <li>This study demonstrates that woody species grown on HM-contaminated soils exhibit different capacities for accumulating or translocating HMs depending on their root system shapes, and their position on the RES. Our results highlighted the importance of root size-related traits in the framework of RES when plants face unfavorable soil conditions and narrow the gap in trait-based ecology. We, for the first time, define and quantify the biomass cost for HM accumulation, providing a better understanding of the resource-allocation theory.</li> </ol>