Rhizosphere pH gradient controls copper availability in a strongly acidic soil

Environ Sci Technol. 2009 Aug 1;43(15):5686-91. doi: 10.1021/es900055k.

Abstract

Using a root mat approach, we quantified how root-induced alkalization controlled the establishment of copper (Cu) gradients in the rhizosphere of durum wheat (Triticum turgidum durum L.) cropped in a strongly acidic, Cu-contaminated soil. Rhizosphere pH increased over 6 mm in soil, reaching up to +2.8 units close to root mat surface. Conversely, free Cu2+ activity decreased by 3 orders of magnitude and total Cu concentration by 3-fold in the rhizosphere solution, while labile Cu assessed by DGT (diffusive gradients in thin films) was halved. The DIFS (DGT-induced flux in soils and sediments) model failed to adequately simulate Cu depletion in the rhizosphere solution, showing that root-induced alkalization almost entirely explained Cu depletion while plant uptake had little impact. We modeled the observed pH gradient to recalculate its radial extension around a single root. The gradient of free Cu2+ activity in solution, deduced from pH modeling, extended over 1-4 mm in the rhizosphere depending on root radius and OH- efflux from root. Rhizosphere alkalization dramatically decreased root exposure to Cu, substantiating that root-induced chemical changes in the rhizosphere should be better accounted for to assess metal bioavailability to plants.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Buffers
  • Copper / chemistry*
  • Copper / metabolism*
  • Environment
  • Environmental Monitoring / methods
  • Hydrogen-Ion Concentration
  • Models, Statistical
  • Plant Roots / metabolism
  • Regression Analysis
  • Soil
  • Soil Pollutants / chemistry*
  • Time Factors
  • Triticum / metabolism*

Substances

  • Buffers
  • Soil
  • Soil Pollutants
  • Copper