Tuesday, 11 July 2006

Localized Sampling of Root Exudates and Rhizosphere Soil Solution by Use of Sorption Media.

Susan Haase1, Ellen Kandeler1, Yakov Kuzyakov1, Angelika Kania2, Iris Edelkott2, Petra Marschner3, Volker Römheld2, and Günter Neumann2. (1) Hohenheim University,, Institute of Soil Science and Land Evaluation, Stuttgart, 70599, Germany, (2) Hohenheim University, Institute of Plant Nutrition, Stuttgart, 70599, Germany, (3) The University of Adelaide, Waite Campus, PMB 1 GLEN OSMOND, Adelaide 5064, Australia

Knowledge about the chemical composition of the soil solution in the rhizosphere is a key factor for the understanding of root-induced modifications in solubility of nutrients and toxic elements in soils and of plant-microbial interactions. Soil solution chemistry in the rhizosphere strongly depends (1) on rhizodeposition and root activity, affected by the plant nutritional status, plant species and genotypes and external stress factors, (2) on sorption characteristics and mechanical impedance of the soil matrix and (3) on rhizosphere-microbial activity. Rhizodeposition is frequently not uniformly distributed along plant roots. Considerable gradients exist in radial and longitudinal direction and intense root exudation can be confined to special root structures. The variability of root exudation along the root needs to be considered for attempts to understand chemical changes in the rhizosphere and therefore, requires localized sampling techniques with a high spatial resolution. This study presents an evaluation of sampling techniques for low-molecular weight organic compounds and inorganic salts based on sorption media (chromatography paper, membrane filters) placed onto the root surface of soil-grown plants, cultivated in rhizoboxes or in the field with root observation windows. Aspects of sampling time, microbial degradation, sorption to the soil matrix and the impact of these factors on recovery are discussed, as well as analytical approaches for the detection of individual substances or classes of compounds. Moreover, approaches for the combination of the sampling techniques with isotope labelling, with visualization of rhizosphere processes and with investigations on root physiology and the activity and diversity of rhizosphere microbial communities are presented in case studies.

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