Kaplan–Meier curves describing the relationships between
cumulative metamorphosis percent and different NO3–N concentrations
are illustrated in Fig. 1A. Interestingly, the first individual
to reach metamorphosis climax (stage G42) occured on the 57th day of exposure in 100 mg/L NO3–N. In comparison, the first larvae
reaching metamorphosis climax initiated on the 65th day in both
control and 10 mg/L NO3–N groups. In addition, we found the first
one reaching metamorphosis climax was on the 67th day of exposure
in 50 mg/L NO3–N, which was 10 days later than that of controls.
At the end of the experiment (on the 78th day), the mean
metamorphosis percent of larvae was 50% in control groups, while
only 23.75% could be observed in 50 mg/L NO3–N. However, the
mean metamorphosis percent of larvae exposed to 10 and
100 mg/L NO3–N were 45.23% and 37.01%, respectively. Exposure
to 50 and 100 mg/L NO3–N a highly significant increase of metamorphosis
percent was detected (one-way ANOVA, p 6 0.01) (Fig. 1B).