The
15N
and
13C
values
of
earthworms
in
the
6th
month
were
significantly lower than that in the initial period (one-way ANOVA,
P
<
0.001)
(Fig.
4),
probably
attributed
to
the
changes
in
the
organic
food
of earthworms. After the earthworms were introduced to the
vermifiltration system, their food was acclimated to convert from
the cow dung to the sewage sludge. Many researches showed that
the change in the diet with different stable isotopic abundances,
e.g.
15N
and
13C,
cause
the
changes
in
the
stable
isotopic
ratio
of the feeder (e.g. [30,31]). Neilson et al. [28] suggested that an
organism
that
feeds
on
another
near
the
based
of
a
food
chain
is
isotopically less 13C- and 15N-enriched than an organism that feed
on another higher up a food chain. Sampedro and Domínguez [15]
found that there are a different variation in 15N and 13C of earth-
worm in different growth substrates. In the present study, 15N and
13C of the growth substrate for earthworm in the initial samples
(cow dung) were 5.585‰ and −22.714‰, respectively, and signifi-
cantly higher than that in the 6th month samples (sewage sludge)
(one-way ANOVA, P < 0.001) (Fig. 4). Thus, the decrease in 15N and
13C values of the growth substrates were likely an important fac-
tor to cause the drop in 15N and 13C natural abundances of the
earthworms.
The 15N and 13C values of earthworms in the 6th month weresignificantly lower than that in the initial period (one-way ANOVA,P < 0.001) (Fig. 4), probably attributed to the changes in the organicfood of earthworms. After the earthworms were introduced to thevermifiltration system, their food was acclimated to convert fromthe cow dung to the sewage sludge. Many researches showed thatthe change in the diet with different stable isotopic abundances,e.g. 15N and 13C, cause the changes in the stable isotopic ratioof the feeder (e.g. [30,31]). Neilson et al. [28] suggested that anorganism that feeds on another near the based of a food chain isisotopically less 13C- and 15N-enriched than an organism that feedon another higher up a food chain. Sampedro and Domínguez [15]found that there are a different variation in 15N and 13C of earth-worm in different growth substrates. In the present study, 15N and13C of the growth substrate for earthworm in the initial samples(cow dung) were 5.585‰ and −22.714‰, respectively, and signifi-cantly higher than that in the 6th month samples (sewage sludge)(one-way ANOVA, P < 0.001) (Fig. 4). Thus, the decrease in 15N and13C values of the growth substrates were likely an important fac-tor to cause the drop in 15N and 13C natural abundances of theearthworms.
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