Accumulation of Cd by earthworms initially increased with
increasing soil Cd concentration and leveled up with soil Cd concentrations
larger than 220 mg kg1 (Fig. 4a). Maize seedlings
generally could significantly (F ¼ 797.678, p < 0.01) reduce the
accumulation of Cd by earthworms in Cd contaminated soils with
only one exception of 1000 mg kg1 Cd contaminated soil (Fig. 4a).
This result was in line with the observation of the reduced adverse
effects of Cd to earthworms in the presence of maize plants (Fig. 1).
The maize seedlings retained much higher concentration of Cd in
there was no significant difference of the total soil Cd among the
three series of experiments. An increase of total Cd in soils resulted
in an increase of water and CaCl2 extractable Cd. The 0.01 M CaCl2
could generally extract more Cd thanwater from the same soil, and
with respect to each of the two extractants the extractable Cd for
soils treated with only earthworms and soils treated with only
maize plants at the same Cd level was similar. The co-presence of
both earthworms and maize plants in soils could significantly
enhance the extraction of soluble Cd compared to that in corresponding
soils with only earthworms or with only maize plants.
This indicated that the co-presence of earthworms and maize
plants had great impacts on the mobility and availability of Cd in
soil.