Hyperaccumulation of Zn by Thlaspi caerulescens can ameliorate Zn toxicityin the rhizosphere of cocropped Thlaspi arvense

The metal hyperaccumulating plant Thlaspi caerulescens is effective in depl eting plant-available metals from the soil. We hypothesized that this reduc tion of toxic metals in the rhizosphere of T caerulescens would increase th e growth of less metal-tolerant plants with their roots permitted to interm ingle and develop coincident rhizospheres. The extent of rhizosphere intera ction between T caerulescens and a coplanted nonaccumulator species, Thlasp i arvense, was controlled using barriers. Two media with elevated concentra tions of water-extractable Zn were prepared by enriching one soil with zinc oxide (ZnO) or zinc sulfide (ZnS). The shoot mass of T arvense was increas ed by 30% when its roots were permitted to intermingle with those of T. cae rulescensin the ZnO treatment. The concomitant 2-3-fold reduction in shoot Zn concentration in T arvense confirmed that its improved growth was associ ated with reduced uptake and phytotoxicity of Zn. Thlaspi arvense also show ed increased growth and reduced metal uptake when cocropped with T caerules cens in the ZnS treatment. We conclude that the strong Zn accumulation by T caerulescens might enhance the establishment and development of surroundin g less-tolerant species on soils that are naturally- or anthropogenically-e nriched with metals.