产毒与不产毒铜绿微囊藻对模拟酸雨及紫外辐射的生理响应

为了比较研究酸雨与紫外辐射对淡水水体常见藻华蓝藻的生理学影响,选取铜绿微囊藻(Microcystis aeruginosa)产毒(FACHB-905)与不产毒(FACHB-469)株系作为实验材料,通过人工模拟酸雨,研究了不同p H处理后2藻株的光合生理变化以及对紫外辐射的敏感性的异同。实验设置3个p H梯度,p H7.10为对照组(正常培养基培养的藻体),两模拟酸雨处理组(p H5.65和p H4.50);两种辐射处理,可见光处理(PAR)以及全波长辐射处理(PAB)。研究结果表明,905藻株细胞粒径在各p H处理下都要显著高于469藻株,模拟酸雨处理显著降低了两藻株细胞的平均粒径及体积,但叶绿素含量显著提高;酸雨处理同时也引起细胞死亡率的增加,表现为藻体有效光化学效率显著降低,生长速率显著受到抑制,低p H下呈负增长,且这种抑制程度在469下更为显著。高的可见光以及紫外辐射处理,使两株系有效光化学效率随p H的降低而呈降低趋势,其中469藻株降低至更低的水平,且高光辐射以及紫外诱导的抑制率要显著高于905藻体,这可能与469藻株较低的光保护色素有关(较低的类胡萝卜素以及紫外吸收物质)。在未来全球变化背景下,不同种类的浮游植物对环境变化的响应及适应能力不同,可改变水体的群落结构和种群丰度,铜绿微囊藻905较469较强的耐受酸雨以及紫外辐射的能力,可能会使该株系在竞争力上占据优势。

Physiological responses of toxigenic and non-toxigenic strains of Microcystis aeruginosa to simulated acid rain and UV radiation

Acid precipitation from natural and human activities can lead to different extents of acidification in different freshwater ecosystems, with noticeable changes in the carbonate system and aquatic chemistry. For example, acidification is known to decrease the ionic concentrations of magnesium and calcium, but enhance aluminum concentrations. The changes to chemicals associated with freshwater acidification could induce physiological disturbance to most aquatic organisms, which would then need to spend additional energy to cope with acidic stress. Phytoplankton species with different sensitivities to acid stress may have differential physiological responses;thus, acid stress may lead to altered community structure and species richness. Alternatively, UV-B (280-320 nm) irradiance has been increasing due to stratospheric ozone depletion, which would also impact freshwater phytoplankton. Meanwhile, significantly decreased dissolved organic matter as a result of acid rain may further enhance the penetration of solar UV radiation (UVR, 280-400 nm) in the water column due to decreased light attenuation. Therefore, freshwater acidification and solar UVR may interact to influence phytoplankton physiology. This study examined the physiological responses of a freshwater bloom forming cyanobacterium, Microcystis aeruginosa, to acidification and UVR. Two strains were used for the experiments;a toxigenic strain (FACHB-905) and a non-toxigenic strain (FACHB-469). Microcystis aeruginosa cells were grown under simulated acid rain (with a mole ratio of H₂SO₄ : HNO₃ = 8 : 1) under a solar simulator with and without UVR, to observe whether photosynthetic performance and sensitivity to UV irradiance differed between the two strains. Three pH levels were used, pH 7.10 (regular BG11+N medium), 5.65, and 4.50, with the latter two pH levels reflecting acidification conditions. Two solar radiation treatments were carried out, including: photosynthetically active radiation alone (PAR, 400-700 nm) and PAR+ UV-A+UV-B (PAB, 295-700 nm). Our results indicate that the mean cell size and cell volume of the 905 strain was significantly higher than those of the 469 strain in all pH treatments. Acidification treatment significantly lowered mean cell size and volume, but enhanced the chlorophyll a content in both strains. Under the lowest pH (4.50), higher mortality rates were observed for both strains, with decreased effective quantum yield. The inhibition of the growth rate was more pronounced in the non-toxigenic strain. The effective quantum yield declined with decreasing pH level when cells were exposed to high levels of PAR and PAR+UVR. UV-induced inhibition of effective quantum yield was much higher in the non-toxigenic strain compared to the toxigenic strain. This differential response may be attributed to different contents to UV absorbing compounds and carotenoids. Under the global climate change scenario, increasing aquatic acidification and UV irradiance might decrease the competence of the non-toxigenic strain over the toxigenic one.