Low-molecular organic acids in the rhizosphere soil solution of beech forest ( Fagus sylvatica L.) cambisols determined by ion chromatography using supported liquid membrane enrichment technique

Abstract

Soil solution from the A-horizon (0–5 cm) beneath six different plant cover types of beech forest Dystric Cambisols, south Sweden, was expelled by high-speed centrifugation using freshly sampled soil at field moisture. Concentrations of low molecular weight organic acids (LOAs) were determined by an application of ion chromatography using a supported liquid membrane enrichment technique. This method facilitates the detection of LOAs at 60–200 nM in complex matrices and (most important in acid soil solutions) minimizes interferences from Al and Fe. To test the capacity of soils to immobilize LOAs from solution, the recovery of added LOAs was also studied. Between 8 and 10 LOAs were detected in measurable concentrations in most soil solutions. Monocarboxylic acids (acetic, lactic and formic acid) were the most abundant, though rather consistent differences were measured in several acids among the vegetation types, partly related to vascular plant species and soil acidity. There were also consistent differences between seasons (late spring and summer). However, recovery tests (20 min) with several of the soils clearly demonstrated that added LOAs were to a great extent rapidly immobilized, with the exception of acetic and lactic acid, probably a main reason for the high share of these monocarboxylic acids in soil solutions. The ecological relevance of determining LOAs in soil solutions is discussed briefly.