Basic study on effects of environmental stresses on algal communities

我研究了两个品系的绿藻Scenedesmus gutwinskii var.从除草剂处理和未处理的实验池塘中分离到异尖晶藻。当除草剂浓度低于10~(-15)µg/L时，耐药菌株的生长速度和最高产量均低于敏感菌株，说明在没有除草剂污染的情况下，敏感菌株比耐药菌株具有更好的竞争优势。浓度为10~(-15)µg/L相当于对栅藻敏感品系种群增长抑制50%(EC_(50))。利用EC50值，我推测最敏感的群体，如衣藻属，将受到河流中除草剂胁迫的影响，因为河水中的除草剂浓度低至10µg/L。对从流经农业区的河流中分离的除草剂前、中和后施药期间分离的单个菌株进行了西美特林和丙草胺敏感性检测。对衣藻属和环藻属菌株的EC50值随着水体中除草剂浓度的增加而增大，但西草净和扑草胺的最高浓度分别为2和4.5ug/L。西咪替林耐受性的增加似乎与丙替草胺耐受性的增加有关。因此，丙草胺似乎对河流附生植物群落施加了选择性压力。根据这些结果，我得出结论，除草剂胁迫对河流附生植物群落的影响很小。

I examined growth characteristics of two strains of the green alga Scenedesmus gutwinskii var. heterospina isolated from the herbicide-treated and untreated experimental ponds. Growth rate and maximum yield were lower in the herbicide tolerant strain than the susceptible strain, when the concentration of the herbicide was lower than 10-15 mug/L.This fact indicates that the susceptible strains are superior competitor to tolerant ones in the absence of herbicide contamination. The concentration 10-15 mug/L is equivalent to the value which suppresses population growth of the susceptible strain of the Scenedesmus by 50% (EC50). Using the EC50 values, I presumed that the most susceptible groups examined, e.g.Chlamydomonas.would be affected by the herbicide stress in a river, because the herbicide concentrations in the river water were as low as 10 mug/L.Susceptibility to the herbicide simetryn and pretilachlor were examined for individual strains isolated in the pre-, mid- and post-herbicide application period from a river running through an agricultural region. The EC50 values of simetryn and pretilachlor for strains of the genera chlamydomonas and Cyclotella increased when the herbicide concentrations in the water increased, although the maximum concentrations of simetryn and pretilachlor were as low as 2 and 4.5 mug/L,respectively. The increase in simetryn tolerance seemed to be correlated with the increase in pretilachlor tolerance. Thus, pretilachlor seems to exert a selective pressure on river periphyton communities. From these results, I conclude that the herbicide stress gives only a weak impact on river periphyton communities.