光、温限制后铜绿微囊藻和斜生栅藻的超补偿生长与竞争效应

研究了铜绿微囊藻(Microcystis aeruginosa)和斜生栅藻(Scenedesmus obliquus)低温和低光照限制后的超补偿效应,以及共培养条件下的竞争效应。结果表明,低温和低光照均显著抑制微藻的生长发育,但低温对铜绿微囊藻的抑制效应更强,而斜生栅藻则对低光胁迫更敏感。经过低光和低温培养后,铜绿微囊藻和斜生栅藻在恢复正常培养时藻细胞密度短期内都表现出超补偿增长效应,但不同藻类超补偿模式不同,斜生栅藻补偿生长时间不超过1周,而铜绿微囊藻的补偿效应可以持续10天;此外,统计结果表明铜绿微囊藻细胞密度对低温限制解除表现出更显著的补偿生长,斜生栅藻则在低光解除后表现出更强的超补偿效应。微藻叶绿素a指标在光恢复条件下都表现出显著的补偿效应,但温度恢复过程中叶绿素a含量与藻密度增长不同步,低温胁迫对恢复正常培养后微藻叶绿素a的形成产生了一定的负效应;铜绿微囊藻产毒株(912)在两种恢复模式下脱氢酶活性显著高于对照,产毒株(912)脱氢酶活性的补偿响应明显高于其它两种材料。共培养实验结果表明斜生栅藻同铜绿微囊藻产毒株(912)相比处于竞争劣势,而在同无毒株(469)的共培实验中,尽管连续正常培养情况下两者竞争能力差异不显著,但在恢复培养条件下斜生栅藻竞争能力显著高于后者。因此产毒型铜绿微囊藻低温和低光后的补偿生长效应以及对斜生栅藻的竞争优势可能是蓝藻爆发的内源性机制之一。

Overcompensation and competitive effects of Microcystis aeruginosa and Scenedesmus obliquus after low temperature and light stresses

Changes of temperature and light significantly influence the growth and activity of phytoplankton. To explore the effects of these two variables on the cyanobacterial blooms, we analyzed the growth of Microcystis aeruginosa and Scenedesmus obliquus, as well as the competition between the two species, under conditions of low temperature and low light, and under conditions of release from these two stress factors. The results showed that low temperature and low light significantly inhibited the growth of microalgae. Low temperature led to a stronger inhibitory effect on M. aeruginosa than low light did; however, the growth inhibition of S. obliquus was more sensitive to low light than to low temperature. After release from low temperature or limiting light, all of the experimental taxa exhibited the overcompensation growth within a limited time and this response varied by species. Two M. aeruginosa strains showed a greater response to increased temperature than increased light. However, overcompensation of S. obliquus was greater in response to increased light than increased temperature. When the species were grown together, results showed that under all culture conditions, the toxic Microcystis strains (912) had a competitive advantage over S. obliquus. Although there was no significant difference between the competitive ability of the nontoxic Microcystis strain (469) and S. obliquus under the normal, the former (469) showed a competitive disvantage to S. obliquus under conditions of release from low light and low temperature. Chlorophyll-a content of all experimental algae overcompensated when released from light limitation. In the temperature experiments, the increase of chlorophyll-a content and algal density were asynchronism for all species, and cryogenic pre-treatment had a negative after-effect on microalgae chlorophyll-a content under release from low temperature. The response of dehydrogenase activity of algae when released from low temperature or low light stress varied with algae species, and the compensating increase of dehydrogenase activity of toxic strains (912) was significantly higher than that of the other two taxa. The results suggested that higher the compensatory growth of toxic Microcystis as well as its competitive advantage over S. obliquus while released from low temperature and light stresses, might be the important mechanisms that result in blue-green algae bloom.