Abstract: A semi-static toxicity test was conducted to determine the 96h median lethal concentration (96h LC₅₀ value) of nonylphenol (NP) to Paphia undulata. In the meantime, the variations of superoxide dismutase (SOD), glutathione (GSH), and peroxidase (POD) activities and malondialdehyde (MDA) content in the visceral mass of P. undulata were studied when exposed to different concentrations NP (low: 1 μg·L^-1; medium: 10 μg·L^-1; and high: 25 μg·L^-1) and during the recovery stage in clear sea water. The 96h LC₅₀ value was 260 μg·L^-1. At the early stage of stress, the SOD activity in the visceral mass of P. undulata exposed to low and medium NP concentration was inhibited (P<0.01) while the POD activity was induced (P<0.01), showing the typical “excitotoxicity effect”. During the stress period, the SOD activity and GSH content in the visceral mass at low and medium NP concentrations  increased after an initial decrease, while the POD activity and MDA content were in adverse. When exposed to high NP concentration, the SOD activity was inhibited first and induced then, the POD activity and MDA content increased after an initial decrease, while the GSH content was significantly higher than that of the control level in whole exposure time. The GSH and MDA contents in whole exposure time appeared sharp fluctuation, and the variation increased with increasing NP concentration. During recovery period, all the test indices in the visceral mass of P. undulata exposed to low and medium NP concentration recovered gradually to the normal level, but, for the P. undulata exposed to high NP concentration, these indices remained significant difference, as compared to the control group. The above results indicated that NP had obvious impact on the antioxidant system in the visceral mass of P. undulata, while P. undulata had self-repairing ability for the oxidative damage caused by certain degree of NP stress, but, at high NP concentration, the lipid peroxidation damage could not recover to the level of the control group in a short time.

Key words: Baotianman warm temperate forest, soil bacterial community, 16S rRNA, Illumina Miseq.