Basic study on effects of environmental stresses on algal communities

研究了两株绿色栅藻（Scenedesmus gutwinskii var. heterospina分离的除草剂处理和未处理的实验池塘。当除草剂浓度低于10-15 μ g/L时，耐除草剂品系的生长速率和最大产量低于敏感品系。这一事实表明，在没有除草剂污染的情况下，敏感品系是上级竞争者。浓度10-15 μ g/L相当于抑制栅藻敏感品系种群增长50%的值（EC 50）。使用EC 50值，我推测，最敏感的群体，如衣原体。将受到除草剂胁迫的影响，在河流中，因为在河水中的除草剂浓度低至10微克/升。除草剂施用中期和后期，来自流经农业区的河流。西草净和丙草胺的EC 50值增加时，在水中的除草剂浓度的增加，属衣原体和小环藻属菌株，虽然西草净和丙草胺的最大浓度分别低至2和4.5微克/升。西草净耐受性的增加似乎与丙草胺耐受性的增加相关。因此，丙草胺似乎对河流附着生物群落施加了选择性压力。从这些结果中，我得出结论，除草剂胁迫只给河流附着生物群落的影响很弱。

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.