水华微囊藻对除草剂S-异丙甲草胺胁迫的光合活性响应

随着农业生产的发展，酰胺类除草剂的大量使用造成了一系列环境污染问题.为探究酰胺类除草剂——S-异丙甲草胺对水生生态系统造成的影响，运用浮游植物分类荧光仪(Phyto-PAM)，以蓝藻中的水华微囊藻(Microcystis flos-aquae)为受试生物，测定了水华微囊藻在不同ρ(S-异丙甲草胺)胁迫下7 d内光合色素含量及相关叶绿素荧光参数的变化.结果表明:①培养周期内，随ρ(S-异丙甲草胺)的增加水华微囊藻叶绿素a与类胡萝卜素的含量均受到不同程度的抑制.②各S-异丙甲草胺处理组的实际光能转化效率〔Y(Ⅱ)〕在培养后1~5 d均低于对照组，到第7天时均恢复正常水平.③从第3天起，各S-异丙甲草胺处理组最大光能转化效率(F_v/F_m)、半饱和光照强度点(I_k)均高于对照组，并且10、25和50 mg/L S-异丙甲草胺处理组的最大电子传递速率(P_nmax)也高于对照组.④从第5天起，10、25和50 mg/L S-异丙甲草胺处理组的快速光响应曲线均高于对照组.⑤除50 mg/L S-异丙甲草胺处理组的α(光能利用率)显著低于对照组外，其余各S-异丙甲草胺处理组的α值随培养时间的增加出现波动，到第5天又恢复正常水平.研究显示:当ρ(S-异丙甲草胺)范围为0.1~50 mg/L时，水华微囊藻中光合色素含量降低，而水华微囊藻能通过稳定实际光能转化效率及光能利用率来提高最大光能转化效率、电子传递速率及耐强光能力，从而增强光合活性耐受外来胁迫；当ρ(S-异丙甲草胺)为50 mg/L时，水华微囊藻抗胁迫能力有所降低. 

Effects of S-Metolachlor on Photosynthetic Characteristics of Microcystis flos-aquae

With the development of agriculture, the extensive use of amide herbicides inevitably caused a series of environmental pollution problems. In order to explore the effects of the amide herbicide S-metolachlor on aquatic ecosystems, pulse amplitude modulation chlorophyll fluorimeter (Phyto-PAM) was used to detect the change of photosynthetic pigment content and related chlorophyll fluorescence parameters of Microcystis flos-aquae with different ρ(S-methachlor) in 7 days. The results showed that: (1) As ρ(S-methachlor) increased, the content of chlorophyll a and carotenoid of Microcystis flos-aquae were inhibited in various degrees during the exposure period. (2) The actual photochemical quantum efficiency (Y(Ⅱ)) of different S-methachlor treatment groups was significantly lower than that of the control group from days one to five, and recovered to normal levels on day 7. (3) The maximal photochemistry efficiency (F_v/F_m), the half-saturated light intensity point (I_k) of different ρ(S-methachlor), and the maximum electron transfer rate (P_nmax) in the 10, 25, 50 mg/L groups increased compared with the control group from day 3. (4) The rapid light-response curves of 10, 25, 50 mg/L groups were significantly higher than those of the control group from day 5. (5) The initial slope (α) of different S-methachlor treatment groups fluctuated with the cultivation time and recovered to normal levels on day 5, except that the α of 50 mg/L group was significantly lower than that of the control group. This study demonstrated that the photosynthetic pigment of Microcystis flos-aquae was reduced when ρ(S-methachlor) was in the range of 0.1-50 mg/L, but Microcystis flos-aquae could enhance photosynthetic activity and endure external stress by stabilized Y(Ⅱ), α and enhance F_v/F_m, P_nmax. However, the tolerance of Microcystis flos-aquae to S-metolachlor stress was reduced when the concentration of S-metolachlor was 50 mg/L.