水体N:P比对甲藻藻华响应阳光紫外辐射机制的影响研究

With the global environment deterioration by human activity, it was increased significantly that the solar ultraviolet radiation (UVR) reached to the earth surface because of the damaged ozone layer, and that eutrophication around coastal area tended to be more serious with the water pollution. Solar UVR inhibited the growth of phytoplankton, changed the cellular morphology, and adjusted the metabolism of nutrients, whereas eutrophication increased the biomass of phytoplankton and led to harmful algae bloom (HAB) breakout. The phytoplankton, which is the most important part of the primary producer in the ocean, not only affected by solar UVR, but also by eutrophication. It was, however, ambiguous how these two environmental factors impacted on the HAB until now. So, this project aimed to study the following questions, 1) the co-effect of solar UVR and ratio of N:P on HAB, 2) the response of HAB to solar UVR under different N:P ratio. The typical species around the China coastal water zone, Karenia mikimotoi and Alexandrium taramarens were chose in this project. The quartz incubators and three kinds of cut-off filters were used for the whole experiments to insure the cells can receive the three different solar radiation treatments, 1) photosynthetic activity radiation (PAR, 395-700nm), 2) photosynthetic activity radiation + ultraviolet A (PA, 315-700nm), and 3) photosynthetic activity radiation + ultraviolet radiation (PAB, 295-700nm). The different N:P ratio was achieved by adding nitrate in the artifical sea water. To analyze the response of cells to solar UVR under the different N:P ratio. The acute effects of solar UVR on cells cultured in different N:P ratio were finished in 1 day, whereas the chronic effect and the acclimation of cells were lasted to 1 or two weeks. The co-effect of solar UVR and ratio of N:P on cells were analyzed by growth, pigments, photosynthetic carbon fixation, photosynthetic efficiency, cellular morphology and size, the damaged DNA and protein, etc.

随着全球环境的逐渐恶化，一方面，导致臭氧层变薄，使得达到地球表面的阳光紫外辐射强度增强，从而抑制浮游植物的生长、改变细胞形态和大小，并影响着浮游植物的营养代谢。最新研究发现北极也出现了大规模的臭氧空洞，因此，急需在北半球广泛开展阳光紫外辐射的研究；另一方面，人类活动导致水体出现的富营养化现象，如N、P营养盐浓度的增加及N:P比例改变，提高了河口沿岸水域浮游植物生物量，有害藻华频发。作为受到人类影响最严重的河口沿岸水域，同时也是受到这两个环境因子影响最显著的区域。而有关这两个环境因子的耦合效应如何影响有害藻华，目前尚缺乏认识。为此，本项目选取可产生有害藻华的米氏凯伦藻和塔玛亚历山大藻作为目标藻，探讨不同N:P比例背景下，有害藻华对阳光紫外辐射的响应机制，并分析阳光紫外辐射与水体营养盐比例改变（N:P）对有害藻华的耦合效应。

由于人类活动，导致全球气候变化加剧，探讨有害藻华对气候变化的响应机制日益成为海洋生态学者的研究热点之一。所以，在紫外辐射增强的背景下，探讨水体营养（N:P比）失衡对有害藻华生长和生理参数的影响，对于正确认识有害藻华的演替和合理控制其生长，具有重要意义。经过3年的连续研究，结果表明：1）水体N:P的波动对两种有害藻华种（米氏凯伦藻和塔玛亚历山大藻）存在显著影响，两种藻最适生长的N:P为16:1,而N:P的增加或降低，都会对藻的生长造成显著的抑制。细胞的生长速率与N:P之间符合一元二次方程的规律。2）水体N:P还可以影响藻细胞的色素、SOD活性、光系统IID1蛋白的修复损伤速率。3）阳光紫外辐射对藻细胞的生长和生理参数存在显著抑制作用。但阳光紫外辐射的抑制程度与藻所经历的光背景有关，并且存在种间差异。4）藻对阳光紫外辐射存在较强的适应机制。可通过合成紫外吸收物质来增加藻对阳光紫外辐射的耐受性。5）N:P对藻生长和生理参数的影响，不受阳光紫外辐射的影响。即两者之间不存在明显的耦合效应。因此，本项目探讨的两种有害藻华种，在全球变化的背景下，虽然会受到阳光紫外辐射和水体N:P比的显著影响，但藻细胞存在较强的适应机制，从而降低了阳光紫外辐射增强对藻生长的影响，同时，水体中N:P比的波动存在显著的年周期变化，所以，这两种有害藻华在未来依然可以抵抗逆境，并在合适的N:P情况下继续爆发藻华，对水环境造成破坏。