Determination of organic acids in soil solution with high spatial -temporal resolution using the rhizotrone methodology

摘要

Organic acids as exudates from living plant roots have been hypothesized to be involved in the solubilization of nutrients for the roots and the detoxification of metals. The composition and amounts of exudates in the rhizosphere soil solution varies with the spatial and temporal dynamics of root exudation. The rhizotrone methodology consisting of micro suction cups in combination with special root chambers ("rhizotrones") is particularly suitable for sampling of soil solution at high spatial resolution. But a serious problem with organic acids is their fast microbial degradation upon sampling. Therefore, a number of different materials for micro suction including borosilicate, aluminium oxide, nylon membrane and polypropylene hollow fibre have been tested for their impermeabilities for microorganisms (MOs) and adsorption affinities for organic acids. Only the polypropylene hollow fibre of overall 5 tested materials passed the test for MO (Pseudomonas fluorescens) impermeability. Adsorption tests revealed that the recoveries of organic acids were slightly lower with plastic materials than with ceramic materials. In first experiments white lupin (Lupinus albus L.) which is known to exude high amounts of organic acids in response to phosphorus deficiency was planted in sand filled rhizotrones. Micro suction cups made of polypropylene hollow fibre were installed through the front plate after sterilization. Organic acid analysis was performed by capillary electrophoresis. The first qualitative results indicated the release of several organic acids.