４种绿藻对除莠剂西草净（Simetryn）的反应有很大差异，小球藻、羊角月芽藻、衣藻和四鞭藻的ＥＣ_５０（影响浓度）值分别为７００、２５、２７和１１μｇ／Ｌ不同浓度西草净都能影响绿藻的光合作用，浓度为２００ｐｐｍ６时，羊角月牙藻和四鞭藻的光合抑制率分别为９５．３％和９４．０％，但对小球藻几乎无影响，当浓度增至２０００ｐｐｍ时，对小球藻的光合抑制率为８７％。小球藻中活性氧防御物（ＳＯＤ、ＡｓＡ－ＰＯＤ、ＧＲ等）的活性均比衣藻、羊角月牙藻等高几倍到几十倍，显示小球藻对西草净的抗性和忍耐性可能与它细胞内所含的活性氧防御物活性有关，它们的高活性使小球藻在西草净污染后，对体内生成的活性氧（¹Ｏ_２、Ｈ₂Ｏ_２、Ｏ_２^-·等）伤害有解毒作用。

The results from the study indicated that the reactions of four green aglaes to Simetryn were different. The values of EC₅₀ vary with different. The values of EC₅₀ vary with  different kinds of algaes, varying with its kinds. When Selenastrum capricor nutum and Carteria sp. were put in Simetryn with a concentration of 1 hour, their inhibitory rates of photosynthesis were 95.3% and 94.0% respectively; but no influence was observed on Chlorela vulgaris. When concentration being to 2000 ppm, the inhibitory rate of photosynthesis of Chlorela rulgaris was 87%.The estimated results for preventing substances against the toxicity of active oxygen in some green algaes show that the activation of superoxide dismutase (SOD), ascorbate peroxidase (AsA-POD),and glutathine reductase (GR) in Chlorela rulgaris was several to dozens times higher than that in Chamydomonus sp.and Selenastrum, which suggests that the resistance and tolerance of Chlorela vulgaris against Simetryn may be associated with the activation of the detoxicating substances plays a role in getting rid of the harmful effects prduced by active oxygen in Chlorela rulgariscontaminated by Simetryn.