不同藻密度下Zn^2＋浓度对萼花臂尾轮虫实验种群增长参数的影响

Effects of Zn^(2+) concentration on population growth parameters of Brachionus calyciflorus under different Scenedesmus obliquus densities

为了比较不同食物密度下污染物浓度对受试生物的慢性毒性,筛选出以轮虫为受试生物对水环境中Zn2+污染进行监测的敏感指标,在不同斜生栅藻(Scenedesmus obliquus)密度(1.0×106、2.0×106和4.0×106个/m L)下不同浓度(0、0.1、0.3、0.5、0.7、0.9 mg/L)的Zn2+对萼花臂尾轮虫(Brachionus calyciflorus)实验种群增长参数的影响。结果表明,25℃以及1.0×106、2.0×106和4.0×106个/m L藻密度下Zn2+对萼花臂尾轮虫的24 h LC50值分别是6.647、8.102和5.873 mg/L。与各食物密度下的对照组相比,当食物密度为1.0×106个/m L时,各浓度的Zn2+对萼花臂尾轮虫的各种群增长参数均无显著性影响(P>0.05)。当食物密度为2.0×106个/m L时,各浓度的Zn2+均显著延长了轮虫的生命期望、世代时间和平均寿命,提高了轮虫的净生殖率;除0.3 mg/L外,其他浓度的Zn2+显著提高了轮虫的种群内禀增长率。当食物密度为4.0×106个/m L时,0.1、0.3和0.7mg/L的Zn2+显著提高了轮虫的种群内禀增长率,0.7和0.9 mg/L的Zn2+显著提高了轮虫的后代混交率。藻密度对轮虫的生命期望、世代时间、净生殖率、种群内禀增长率、平均寿命和后代混交率均有极显著性影响(P<0.01),Zn2+浓度对轮虫的生命期望、世代时间、净生殖率、种群内禀增长率和后代混交率均有极显著性影响(P<0.01),藻密度和Zn2+浓度之间的交互作用对轮虫的生命期望、种群内禀增长率和后代混交率均有显著性影响(P<0.05)。2.0×106个/m L食物密度下,Zn2+浓度与轮虫的生命期望、世代时间、净生殖率和平均寿命之间具有显著的剂量-效应关系;4.0×106个/m L食物密度下,Zn2+浓度与轮虫的后代混交率间也具有显著的剂量-效应关系。

As a result of industrial activities, aquatic ecosystems have been contaminated increasingly by metals. Such occurrences pose a threat to aquatic organisms in particular and to the whole ecosystem in general. Because of their importance as a part of the food chains in the freshwater ecosystems, as well as their high vulnerability to metal contaminants, rotifers have attracted attention by toxicologists. Zinc is essential for life at trace level, but it involved in the endocrine processes and reproduction of mammals. As one of the major metal contaminants in freshwater ecosystems, zinc is of ecotoxicological interest. In order to investigate the chronic toxicity of Zn^2＋ to organisms in an aquatic environment under different food densities, and to screen out sensitive endpoints for monitoring Zn^2＋ pollution with rotifers as test animals, this paper studied the effects of Zn^2＋ concentrations （0.1, 0.3, 0.5, 0.7 and 0.9 mg/L） on the population growth parameters of Bracionus calyciflorus under different Scenedesmus obliquus densities （1.0×10^6, 2.0×10^6 and 4.0×10^6 cells/mL）. The results showed that at 25℃, the 24 h LC50 of Zn^2＋ to B. calyciflorus under 1.0×10^6, 2.0×10^6 and 4.0×10^6 cells/mL of Scenedesmus obliquus was 6.647, 8.102 and 5.873 mg/L, respectively. Compared with the controls under the same food density, when S. obliquus density was 1.0×10^6 cells/mL, all the concentrations of Zn^2＋ had no significant effects on all the population growth parameters of B. calyciflorus （P 〉 0.05）. When S. obliquus density was 2.0×10^6 cells/mL, Zn^2＋ at all the test concentrations significantly prolonged the life expectancy at hatching, the generation time and the average lifespan, and increased the net reproductive rate, but Zn^2＋ at all the test concentrations except 0.3 mg/L decreased the intrinsic rate of population increase of B. calyciflorus. When S. obliquus density was 4.0×10^6 cells/mL, Zn^2＋ at 0.1, 0.3 and 0.7 mg/L increased the intrinsic rate of population increase, Zn^2＋ at 0.7 and 0.9 mg/L increased the proportion of sexual offspring of B. calyciflorus. S.obliquus density had significant effects on the life expectancy at hatching, the generation time, the net reproduction rate, the intrinsic rate of population increase, the average lifespan and the proportion of sexual offspring （P 〈 0.01）, Zn^2＋ concentration had significant effects on the life expectancy at hatching, the generation time, the net reproduction rate, the intrinsic rate of increase and the proportion of sexual offspring （P 〈 0.01）, and the interaction between S. obliquus density and Zn^2＋ concentration had significant effects on the life expectancy at hatching, the intrinsic rate of increase and the proportion of sexual offspring of B. calyciflorus （P 〈 0.05）. When S. obliquus density was 2.0×10^6 cells/mL, there were significant dose-effect relationships between Zn^2＋ concentration and the life expectancy at hatching, the generation time, the net reproductive rate as well as the average lifespan, and the relationships could be described as y=-73.949x^2＋110.190x＋109.573, y=-37.568x^2＋47.452x＋78.233, y=-18.799x^2＋23.226x＋14.908 and y=-45.602x^2＋54.730x＋66.303, respectively. When S. obliquus density was 4.0×10^6 cells/mL, there was a significant dose-effect relationship between Zn^2＋ concentration and the proportion of sexual offspring, and the relationship could be described as y= -9.648x^2-1.978x＋22.222.