LOW-MOLECULAR-WEIGHT ORGANIC-ACIDS IN RHIZOSPHERE SOILS OF DURUM-WHEAT AND THEIR EFFECT ON CADMIUM BIOACCUMULATION

Cadmium (Cd) accumulation has been found to vary between cultivars of durum wheat (Triticum turgidum var. durum), and it is hypothesized tha t low-molecular-weight organic acids (LMWOAs) produced at the soil-roo t interface (rhizosphere) may play an important role in the availabili ty and uptake of Cd by these plants. The objective of this study, ther efore, was Co (1) investigate the nature and quantity of LMWOAs presen t in the rhizosphere of durum wheat cultivars Areola (low Cd accumulat or) and Kyle (high Cd accumulator) grown in three different soils: Yor kton, Sutherland and Waitville, and (2) determine the relationship bet ween Cd accumulation in these plants and LMWOAs present in the rhizosp here. Plants were grown for two weeks in pot-cultures under growth cha mber conditions. Oxalic, fumaric, succinic, L-malic, tartaric, citric, acetic, propionic and butyric acids were found and quantified in the water extracts of rhizosphere soil, with acetic and succinic acids bei ng predominant. No water extractable LMWOAs were identified in the bul k soil. Total amount of LMWOAs in the rhizosphere soil of the high Cd accumulator (Kyle) was significantly higher than that for the low Cd a ccumulator (Arcola) in all three soils. Furthermore, large differences in amounts of LMWOAs were found in the rhizosphere soil for the same cultivars grown in different soils and followed the pattern: Sutherlan d > Waitville > Yorkton. Extractable sail Cd (M NH4Cl) and Cd accumula tion in the plants also followed the same soil sequence as LMWOA produ ction. Cadmium accumulation by the high and low Cd accumulating cultiv ars was proportional to the levels of LMWOAs found in the rhizosphere soil of each cultivar. These results suggest that the differing levels of LMWOAs present in the rhizosphere soil played an important role in the solubilization of particulate-bound Cd into soil solution and its subsequent phytoaccumulation by the high and low Cd accumulating cult ivars.