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TECHNICAL REPORTS

Plant and Environment Interactions

Competitive Mobilization of Phosphate and Arsenate Associated with Goethite by Root Activity

^a UFZ Helmholtz Centre for Environmental Research, Dep. of Soil Ecology, Theodor-Lieser-Str. 4, 06120 Halle, Germany
^b Soil Science and Soil Protection Group, Inst. of Agriculture and Nutritional Sciences, Martin Luther Univ. Halle-Wittenberg, Weidenplan 14, 06108 Halle/Saale, Germany
^c UFZ Helmholtz Centre for Environmental Research, Dep. of Analytical Chemistry, Permoserstr. 15, 04318 Leipzig, Germany
^d UFZ Helmholtz Centre for Environmental Research, Department of Soil Chemistry, Theodor-Lieser-Str. 4, 06120 Halle, Germany

^* Corresponding author (doris.vetterlein{at}ufz.de).

Received for publication September 14, 2006. Arsenate (As^V) is the predominant form of arsenic in soils under aerobic conditions and competes with the major plant nutrient phosphorus (P) in the form of phosphate (P^V) not only for sorption sites on mineral surfaces in soil but also for root membrane transporters. Plants have evolved several mechanisms for the mobilization of P^V in soils in response to P deficiency, such as the release of organic anions and protons. The aim of the present study was to test whether these mechanisms result in a simultaneous mobilization of arsenate and what would be the consequences for As transfer from soil to plant. The compartment system approach with Zea mays as model crop was chosen as an experimental setup. The system is equipped with micro suction cups and allowed us to investigate processes occurring in the vicinity of roots. As a case study, an artificial quartz substrate with well defined soil physical properties was fertilized, spiked with As^V, and amended with increasing amounts of goethite (0, 1, and 4 g kg^–1 in treatments G-0, G-1, and G-4, respectively). The addition of goethite alleviated the As^V-induced growth reduction and reduced As^V transfer from the substrate to the plant but induced P deficiency at the same time. When low amounts of goethite (1 g kg^–1) were added, plants mobilized P^V but not As^V, which might be related to differences in surface complexation reported for P^V and As^V. No mobilization of P^V or As^V was observed with the addition of higher amounts of goethite, probably because of decreasing competition between organic anions, P^V, and As^V for binding sites.

Abbreviations: As^III, arsenite • As^V, arsenate • DAP, days after planting • P^V, phosphate

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