Increase of apatite dissolution rate by Scots pine roots associated or not with Burkholderia glathei PML1(12)Rp in open-system flow microcosms

• Published in: Geochimica et cosmochimica acta 2013-04, Vol.106, p.287-306
• Main Authors: Calvaruso, Christophe, Turpault, Marie-Pierre, Frey-Klett, Pascale, Uroz, Stéphane, Pierret, Marie-Claire, Tosheva, Zornitza, Kies, Antoine
• Format: Article
• Language: English
• Subjects: acetates; acidity; apatite; arsenic; Burkholderia glathei; calcium; calcium oxalate; citric acid; copper; crystals; forest ecosystems; gluconic acid; Life Sciences; nitric acid; nutrient solutions; oxalic acid; phosphorus; Pinus sylvestris; protons; rare earth elements; roots; scanning electron microscopy; soil bacteria; strontium; trees; weathering; zinc
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2012.12.014

The release of nutritive elements through apatite dissolution represents the main source of phosphorus, calcium, and several micronutrients (e.g., Zn, Cu) for organisms in non-fertilized forest ecosystems. The aim of this study was to quantify, for the first time, the dissolution rate of apatite grains by tree roots that were or were not associated with a mineral weathering bacterial strain, and by various acids known to be produced by tree roots and soil bacterial strains in open-system flow microcosms. In addition, we explored whether the mobilization of trace elements (including rare earth elements) upon apatite dissolution was affected by the presence of trees and associated microorganisms. The dissolution rate of apatite by Scots pine plants that were or were not inoculated with the strain Burkholderia glathei PML1(12)Rp, and by inorganic (nitric) and organic (citric, oxalic and gluconic) acids at pH 5.5, 4.8, 3.8, 3.5, 3.0, and 2.0 was monitored in two controlled experiments: “plant–bacteria interaction” and “inorganic and organic acids”. Analyses of the outlet solutions in the “plant–bacteria interaction” experiment showed that Scots pine roots and B. glathei PML1(12)Rp produced protons and organic acids such as gluconate, oxalate, acetate, and lactate. The weathering budget calculation revealed that Scots pines (with or without PML1(12)Rp) significantly increased (factor>10) the release of Ca, P, As, Sr, Zn, U, Y, and rare earth elements such as Ce, La, Nd from apatite, compared to control abiotic treatment. Scanning electron microscopy observation confirmed traces of apatite dissolution in contact of roots. Most dissolved elements were taken up by Scots pine roots, i.e., approximately 50% of Ca, 70% of P, 30% of As, 70% of Sr, 90% of Zn, and 100% of U, Y, and rare earth elements. Interestingly, no significant additional effect due to the bacterial strain PML1(12)Rp on apatite dissolution and Scots pine nutrition and growth was observed. The “inorganic and organic acids” experiment demonstrated that the apatite dissolution efficacy of organic acids was higher than for the inorganic acid and varied in function of the acids: oxalic acid>citric acid>gluconic acid>nitric acid for pH ⩽3.5. In addition, apatite dissolution increased with increasing acidity for each acid. Only oxalic acid generated non-stoichiometric release of calcium and phosphorus from apatite in the solution at pH ⩽3.5, due to the precipitation of Ca-oxalate crystals at apatite surfac