All earthworms survived by the end of the experiment except
those that were exposed to the highest Cd (1000 mg kg1). The
mortalities of earthworms in soils spiked with 1000 mg kg1 of Cd
were 15.0 13.8% and 73.3 5.4% (mean SD, n ¼ 4), respectively,
with and without maize plants, indicating that maize plants could
reduce the toxicity of Cd to earthworms survival. Similarly, the
presence of maize plants mitigated the toxicity of Cd to earthworm
reproduction (F ¼ 187.461, p < 0.01). At lower range of Cd exposure
levels (<220 mg Cd kg1), earthworms cohabited with maize plants
produced more cocoons than those that were exposed to the same
corresponding levels of Cd but tested with no maize plants (Fig.1a).
When Cd concentrations added were larger than 460 mg kg1, no
cocoon was produced by earthworms regardless of the presence or
not of maize plants (Fig. 1a). The EC10, EC20, and EC50 for cocoon
output were 80.7, 101.2, and 152.8 mg kg1, and 58.1, 76.9, and
129.4 mg kg1, respectively, with and without maize plants
(Table 1). The earthworm biomass change was expressed as the
percentage of the initial weight. A reduction of 30e50% of body
mass was observed after 28 d inoculation of earthworms in the
fluvo-aquic soils (Fig. 1b). Generally, earthworms in soils without
maize plants had a sharper change in body mass reduction than
those worms that inhabited in the corresponding Cd-contaminated
soils with maize plants, indicating again that the presence of maize
plants could effectively reduce the toxicity of Cd to earthworms
(F ¼ 15.616, p < 0.01). However, comparing to the earthworm
reproduction endpoint (i.e., the cocoon output in the present
study), the biomass change of the earthworms seemed not to be a
sensitive endpoint to Cd and, therefore, the effective concentrations
for earthworm body mass were not determined.
การแปล กรุณารอสักครู่..
