LOW-MOLECULAR-WEIGHT DICARBOXYLIC-ACIDS IN RHIZOSPHERE SOIL OF DURUM-WHEAT

A gas chromatographic (GC) method was developed for the determination of water extractable and HCl/MeOH extractable low molecular weight dic arboxylic acids in rhizosphere soils of durum wheat (Triticum turgidum var. Durum L.). Rhizosphere soils were collected after 2 weeks of pla nt growth by first removing the bulk soil from the root system and the n by washing off the rhizosphere soil that adhered to the root surface with water. After shaking of the rhizosphere/water mixtures, dicarbox ylic acids were concentrated on anion exchange membranes. Rhizosphere soils were then freeze-dried and the samples shaken with 0.5 M HCl in MeOH to remove any remaining dicarboxylic acids adsorbed to the soil p articles after the water extraction. The efficiency of HCl/MeOH extrac tion from three different soils ranged from 85.9 to 106.3% for most ac ids; however, the recovery of oxalic acid varied with soil type. Oxali c, fumaric, and succinic acids were found in both the water and HCl/Me OH extracts of rhizosphere soils of durum wheat, while malonic acid wa s present only in the HCl/MeOH extracts. Dicarboxylic acids detected b y GC in the water extracts were further identified by ion exclusion an d ion exchange liquid chromatography. Washing soil from roots of durum wheat provided an efficient method for the collection of rhizosphere soil. Extraction of these soils with water and HCl/MeOH provided estim ates of soluble and non-water-soluble low molecular weight dicarboxyli c acids, respectively, using GC. Determination of these acids will aid in further understanding of their role in rhizosphere processes.