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This article in JEQ

  1. Vol. 34 No. 6, p. 2157-2166
     
    Received: Nov 9, 2004
    Published: Nov, 2005


    * Corresponding author(s): junw@chem.agr.hokudai.ac.jp
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doi:10.2134/jeq2004.0423

Root Exudation, Phosphorus Acquisition, and Microbial Diversity in the Rhizosphere of White Lupine as Affected by Phosphorus Supply and Atmospheric Carbon Dioxide Concentration

  1. Jun Wasaki *a,
  2. Annett Rotheb,
  3. Angelika Kaniac,
  4. Günter Neumannc,
  5. Volker Römheldc,
  6. Takuro Shinanoa,
  7. Mitsuru Osakid and
  8. Ellen Kandelerb
  1. a Creative Research Initiative ‘Sousei’ (CRIS), Hokkaido University, N21W10, Kita-ku, Sapporo 001-0021, Japan
    b Institute of Soil Science, University of Hohenheim, Emil-Wolff-Strasse 27, 70599 Stuttgart, Germany
    c Institute of Plant Nutrition, University of Hohenheim, Fruwirthstrasse 20, 70599 Stuttgart, Germany
    d Graduate School of Agriculture, Hokkaido University, N9W9, Kita-ku, Sapporo 060-8589, Japan

Abstract

White lupine (Lupinus albus L.) was used as a phosphorus (P)-efficient model plant to study the effects of elevated atmospheric CO2 concentrations on (i) P acquisition, (ii) the related alterations in root development and rhizosphere chemistry, and (iii) the functional and structural diversity of rhizosphere microbial communities, on a P-deficient calcareous subsoil with and without soluble P fertilization. In both +P (80 mg P kg−1) and −P treatments (no added P), elevated CO2 (800 μmol mol−1) increased shoot biomass production by 20 to 35% and accelerated the development of cluster roots, which exhibit important functions in chemical mobilization of sparingly soluble soil P sources. Accordingly, cluster root formation was stimulated in plants without P application by 140 and 60% for ambient and elevated CO2 treatments, respectively. Intense accumulation of citrate and increased activities of acid and alkaline phosphatases, but also of chitinase, in the rhizosphere were mainly confined to later stages of cluster root development in −P treatments. Regardless of atmospheric CO2 concentrations, there was no significant effect on accumulation of citrate or on selected enzyme activities of C, N, and P cycles in the rhizosphere of individual root clusters. Discriminant analysis of selected enzyme activities revealed that mainly phosphatase and chitinase contributed to the experimental variance (81.3%) of the data. Phosphatase and chitinase activities in the rhizosphere might be dominated by the secretion from cluster roots rather than by microbial activity. Alterations in rhizosphere bacterial communities analyzed by denaturing gradient gel electrophoresis (DGGE) were related with the intense changes in root secretory activity observed during cluster root development but not with elevated CO2 concentrations.

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