title: Quantitative imaging of rhizosphere pH and CO2 dynamics with planar optodes.
abstract: OBJECTIVE
  Live imaging methods have become extremely important for the exploration of biological processes. In particular, non-invasive measurement techniques are key to unravelling organism-environment interactions in close-to-natural set-ups, e.g. in the highly heterogeneous and difficult-to-probe environment of plant roots: the rhizosphere. pH and CO2 concentration are the main drivers of rhizosphere processes. Being able to monitor these parameters at high spatio-temporal resolution is of utmost importance for relevant interpretation of the underlying processes, especially in the complex environment of non-sterile plant-soil systems. This study introduces the application of easy-to-use planar optode systems in different set-ups to quantify plant root-soil interactions.
  
  
  METHODS
  pH- and recently developed CO2-sensors were applied to rhizobox systems to investigate roots with different functional traits, highlighting the potential of these tools. Continuous and highly resolved real-time measurements were made of the pH dynamics around Triticum turgidum durum (durum wheat) roots, Cicer arietinum (chickpea) roots and nodules, and CO2 dynamics in the rhizosphere of Viminaria juncea.
  
  
  RESULTS
  Wheat root tips acidified slightly, while their root hair zone alkalized their rhizosphere by more than 1 pH unit and the effect of irrigation on soil pH could be visualized as well. Chickpea roots and nodules acidified the surrounding soil during N2 fixation and showed diurnal changes in acidification activity. A growing root of V. juncea exhibited a large zone of influence (mm) on soil CO2 content and therefore on its biogeochemical surrounding, all contributing to the extreme complexity of the root-soil interactions.
  
  
  CONCLUSIONS
  This technique provides a unique tool for future root research applications and overcomes limitations of previous systems by creating quantitative maps without, for example, interpolation and time delays between single data points.
authors.affiliation: Forschungszentrum Jülich GmbH, Institute of Bio- and Geosciences, IBG-2: Plant sciences, Jülich, Germany. s.blossfeld@fz-juelich.de
authors.forename: Stephan
authors.initials: S
authors.lastname: Blossfeld
authors.forename: Christina Maria
authors.initials: CM
authors.lastname: Schreiber
authors.forename: Gregor
authors.initials: G
authors.lastname: Liebsch
authors.forename: Arnd Jürgen
authors.initials: AJ
authors.lastname: Kuhn
authors.forename: Philippe
authors.initials: P
authors.lastname: Hinsinger
mesh_terms: D002138:Calibration; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D029863:Cicer / Q000378:metabolism*; D007887:Fabaceae / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D055096:Optical Devices; D061848:Optical Imaging / Q000295:instrumentation / Q000379:methods*; D018517:Plant Roots / Q000378:metabolism; D058441:Rhizosphere; D053204:Root Nodules, Plant / Q000378:metabolism; D012815:Signal Processing, Computer-Assisted; D012984:Software; D014908:Triticum / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide
keywords: CO2 dynamics; Cicer arietinum; Triticum turgidum durum; Viminaria juncea; pH dynamics; planar optodes; quantitative imaging; rhizosphere