关键词: 刺槐人工林, 落叶灌木, 退耕草地, 沙蒿群落, 细根生物量, 生产量

Abstract: In order to evaluate the acute toxicity of chromium (Cr) on amphibian larvae, the Rana chensiensis tadpoles at the stages 28-29 were exposed to the water contaminated by 30-35 mg·L^-1 of Cr(III) and 10-45 mg·L^-1 of Cr(VI), with the death rate of the tadpoles and the sublethal concentration (LC₅₀) of Cr(III) and Cr(VI) for 24, 48, 72, and 96 h determined, respectively. Both the Cr(III) and the Cr(VI) had obviously acute toxicity on the tadpoles. The LC₅₀ of Cr(III) for 24, 48, 72, and 96 h was 34.09±1.06, 33.47±0.65, 32.58±0.11, and 32.05±0.20 mg·L^-1, and the LC₅₀ of Cr(VI) was 91.97±5.32, 51.19±4.62, 35.79±1.40, and 28.81±1.87 mg·L^-1, respectively. The safe concentration (SC) of Cr(III) and Cr(VI) was 3.21±0.02 and 2.88±0.19 mg·L^-1, respectively. The acute toxicity of Cr(III) was from its combination with the skin secretion of the tadpoles, forming a complex compound sticking on the gill chamber, and then, causing the tadpoles dead from breath obstacle; whereas the acute toxicity of the Cr(VI) was due to its strong oxidizing property, causing the tadpoles skin fester, gill atrophy, and ultimately, the mortality of the tadpoles. The assessment of the sublethal concentrations of Cr(III) and Cr(VI) on the growth and development of R. chensiensis tadpoles showed that Cr was a teratogenic substance which could restrain the growth and development of the tadpoles. This effect also had a doseeffect relationship with the Cr concentrations, but the time cumulative effect was irregular.

Key words: Robinia pseudoacacia plantation, deciduous shrubs, abandoned grassland, Artemisia desertorum community, fine root biomass,   production.