Root-induced soil acidification and cadmium mobilization in the rhizosphere of Sedum plumbizincicola: evidence from a high-resolution imaging study

  • Xi Sun
  • Zhu LiEmail author
  • Longhua WuEmail author
  • Peter Christie
  • Yongming Luo
  • Dario A. Fornara
Regular Article



Plant roots can significantly alter soil pH and the chemical concentration and distribution of different elements in the rhizosphere environment. Here we ask whether cadmium (Cd) bioavailability in the rhizosphere of Cd-hyperaccumulator Sedum plumbizincicola can be influenced by root-induced effects on soil pH.


The Cd-hyperaccumulator S. plumbizincicola and the Cd non-hyperaccumulator ecotype Sedum alfredii were both grown in four different Cd-contaminated soils. We used the planar optode imaging technique to produce two-dimensional and high-resolution measurements of soil pH. Shoot excess cation concentration, root architecture and Cd concentrations ([Cd]) in soil pore water were also measured. Spatial analyses based on kernel density estimate of roots (KDE) and a Moran’s I correlogram were performed to assess spatial patterns and potential relationships among root distribution, soil pH and [Cd].


Both Sedum species showed root-induced increases in soil acidification (i.e. soil pH decreases of 0.1 to 0.62 units), which were clearly associated with greater root density of these plants. Remarkable excess cation uptakes by both Sedum species were detected and likely a driving factor for the root-induced acidification. The presence of the roots of S. plumbizincicola were then related to higher [Cd] in the rhizosphere than in bulk soil in Orthic Acrisol (+342%) and in Hydragric Antrosol soils (+296%). The hyperaccumulator S. plumbizincicola had larger root systems, higher acidification ability, and was associated with greater soil [Cd] than S. alfredii. Spatial patterns of root distribution and soil pH were similar between Sedum plants, however, spatial patterns of [Cd] differed across polluted soils.


Rhizosphere acidification induced by S. plumbizincicola plants can play an important role on soil Cd mobilization, but overall effects on soil Cd bioavailability will depend on intrinsic soil biogeochemical properties.


Acidification Rhizosphere Sedum plumbizincicola Planar optode Spatial analysis 



Kernel density estimation


Non-hyperaccumulating ecotype


Water holding capacity


Soil organic carbon



We thank Dr. Guillaume Lobet for his advice and inspiration on the root density calculation. We thank Prof. Weiming Shi for his advice on the driving factor of rhizosphere acidification. We also thank the two anonymous reviewers for their helpful comments. This research was financially supported by the National Natural Science Foundation of China (41325003, 41501348).

Supplementary material

11104_2018_3930_MOESM1_ESM.docx (4.7 mb)
ESM 1 (DOCX 4809 kb)


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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil ScienceChinese Academy of SciencesNanjingChina
  2. 2.University of the Chinese Academy of SciencesBeijingChina
  3. 3.Agri-Food & Biosciences Institute (AFBI)BelfastUK

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