Localized metal solubilization in the rhizosphere of Salix smithiana upon sulfur application.

Christoph Hoefer,Jakob Santner,Walter W. Wenzel,Markus Puschenreiter

doi:10.1021/es505758j

Christoph Hoefer, Jakob Santner + Show 2 more

Open Access

https://doi.org/10.1021/es505758j

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Abstract

A metal-accumulating willow was grown under greenhouse conditions on a Zn/Cd-polluted soil to investigate the effects of sulfur (S0) application on metal solubility and plant uptake. Soil porewater samples were analyzed 8 times during 61 days of growth, while DGT-measured metal flux and O2 were chemically mapped at selected times. Sulfur oxidation resulted in soil acidification and related mobilization of Mn, Zn, and Cd, more pronounced in the rooted compared to bulk soil. Chemical imaging revealed increased DGT-measured Zn and Cd flux at the root-soil interface. Our findings indicated sustained microbial S0 oxidation and associated metal mobilization close to root surfaces. The localized depletion of O2 along single roots upon S0 addition indicated the contribution of reductive Mn (oxy)hydoxide dissolution with Mn eventually becoming a terminal electron acceptor after depletion of O2 and NO3–. The S0 treatments increased the foliar metal concentrations (mg kg–1 dwt) up to 10-fold for Mn, (5810 ± 593), 3.3-fold for Zn (3850 ± 87.0), and 1.7-fold for Cd (36.9 ± 3.35), but had no significant influence on biomass production. Lower metal solubilization in the bulk soils should translate into reduced leaching, offering opportunities for using S0 as environmentally favorable amendment for phytoextraction of metal-polluted soils.

Highlights

Metal-contaminated soils are a global problem of environmental quality and land use and pose risks to human health
No visible signs of metal toxicity or other negative effects due to the low pH or excess Mn, Zn, and Cd concentrations in the soil porewater in S1 and S2 could be identified, plant toxicity may occur within the observed concentration range.[37]
Manganese and Zn concentrations in S. smithiana foliar and twig biomass increased with increasing S0 application, with significant (P ≤ 0.05) differences between S2 and control treatments (Supporting Information Table SI-2, Figure SI-4)

Summary

Introduction

Metal-contaminated soils are a global problem of environmental quality and land use and pose risks to human health. Toward the end of the experiment (57 DAP), metal concentrations were significantly (P ≤ 0.05) higher in the rooted S0 treatments, compared to the corresponding bulk soil concentrations.

Results

Conclusion