Cu binding to root exudates of two cultivated plants, wheat (Triticum aesti
vum) and rape (Brassica napus), and two weeds associated with wheat, dog da
isy (Matricaria inodora) and cornflower (Centaurea cyanus), was studied in
vitro under hydroponic and sterile conditions. Nutrient solutions were prep
ared with or without P. A MetPLATE microbiological test was used to assess
the metal complexing capacity of root exudates. In the P-deficient solution
s, no exudation was observed for any of the four plants; consequently, no C
u binding occurred. When P was present in the nutrient solutions. the plant
exudates displayed differing abilities to complex Cu. No difference was de
tected in the binding capacity of the dog daisy or cornflower, and the blan
k [heavy metal binding capacity (HMBC)=1.07, 1.40 and 1.00, respectively];
however, the rape and wheat exudates were found to complex Cu in rhizospher
ic solutions (HMBC=1.73 and 3.00, respectively). The concentrations of exud
ed organic C were 1.2, 10.8, 15.3 and 15.7 mg l(-1) for the dog daisy, corn
flower, wheat and rape, respectively. These results suggest that the nature
, as well as the amount, of the organic compounds exuded by plant root, is
important in determining the extent of Cu complexation.