Effects of Enhanced UV-B on Pigment-based Phytoplankton Biomass and Composition of Mesocosm-enclosed Natural Marine Communities from Three Latitudes
Effects of Enhanced UV-B on Pigment-based Phytoplankton Biomass and Composition of Mesocosm-enclosed Natural Marine Communities from Three Latitudes
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DOI：
10.1562/2005-09-03-ra-674
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发表时间：
2006-07
期刊：
影响因子：
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通讯作者：
Suzanne Roy;Bruna Mohovic;S. Gianesella;I. Schloss;M. Ferrario;S. Demers
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作者：
Suzanne Roy;Bruna Mohovic;S. Gianesella;I. Schloss;M. Ferrario;S. Demers
摘要 在里穆斯基（加拿大）、乌巴图巴（巴西）和乌斯怀亚（阿根廷南部）进行了一系列三个户外中生态实验，以研究灯增强 UV-B（280-320 nm）对每个地点从海水中分离出的浮游植物群落的影响。详细的色素成分被用来识别这些群落。每个实验比较了三种重复的 UV-B 处理，包括自然阳光条件 (NUVB)、对应于局部 30% 臭氧消耗的低水平 UV-B 增强 (LUVB) 和对应于 60% 臭氧消耗的高水平增强 (HUVB)。将每个中层（约 2 m 深）连续混合（周转时间约 1.3 小时），并在 7-10 天内每天采集样品。在里穆斯基，第一周就发生了大规模的硅藻华。以时间作为重复因子的重复测量方差分析 (RM-ANOVA) 显示，HUVB 处理后叶绿素 (Chl) a 水平略有增加，但具有统计学显着性，这在实验的最后 3 天尤其明显。与这种处理同时观察到的食草动物（纤毛虫）的大量减少是叶绿素 a 水平增加的最可能的解释。增强的 UV-B 不会对藻类生物量产生负面影响，这归因于中生态系统内部的混合以及相对较低的 UV-B 穿透力。在乌巴图巴，大多数色素的水平随着时间的推移而下降，特别是岩藻黄质、叶绿素 c3 和四黄质。 RM-ANOVA 显示 UV-B 处理没有影响，但 Chl c3 除外，其在自然 UVB 条件下的浓度显着较低，表明增强的 UV-B 直接或间接有利于 Chl c3 藻类（可能是绿藻植物）。尽管 HUVB 处理期间颗粒有机碳浓度显着高于其他处理期间，但 Chl a 未受影响，表明增强的 UV-B 有利于异养生物。该实验期间藻类生长不足的原因是营养物浓度低（这是三个地点中最低的）、高辐照度（这是三个地点中午入射的光合可用辐射和紫外线最高的）以及 UV-B 渗透到中生态系统的底部。在乌斯怀亚，前 5 天出现了小规模的开花。 RM-ANOVA 显示 UV-B 处理对所检查的任何颜料均没有总体影响，但在实验的最后 3 天，几种绿藻类颜料（例如 Chl b 和 siphonein）在 HUVB 处理下显示出浓度增加。因此，UV-B 的增强有利于绿藻，从与 HUVB 处理相关的叶绿素 b 与叶绿素 a 的比率随着时间的推移更强的增加可以看出。 UV-B 增强似乎也导致生理状况略有下降，因为在乌巴图巴，特别是乌斯怀亚（乌巴图巴，尤其是乌斯怀亚，UV-B 也渗透到中生态系统底部）的 HUVB 处理过程中，叶绿素 a 和一些可能是垂死藻类产物的脱镁叶绿酸的相对浓度有所增加。对于所有三个地点，由于 UV-B 处理造成的浮游植物生物量变化很小，尽管 UV-B 增强很重要。这项研究表明，增强的 UV-B 对浮游植物及其食草动物群落结构的影响可能比对总体藻类生物量的影响更重要。
Abstract A series of three outdoor mesocosm experiments was undertaken in Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (southern Argentina) to examine the effects of lamp-enhanced UV-B (280–320 nm) on phytoplankton communities isolated from seawater at each site. Detailed pigment composition was used to identify these communities. Each experiment compared three replicated UV-B treatments, consisting of natural sunlight conditions (NUVB), low-level UV-B enhancement corresponding to local 30% ozone depletion (LUVB) and high-level enhancement corresponding to 60% ozone depletion (HUVB). Each mesocosm (ca 2 m deep) was mixed continuously (turnover time, ca 1.3 h) and samples were obtained daily over 7–10 days. In Rimouski a large diatom bloom occurred during the first week. Repeated-measures analysis of variance (RM-ANOVA), with time as the repeated factor, showed slight but statistically significant increases in the chlorophyll (Chl) a level with the HUVB treatment, which were especially obvious over the last 3 days of the experiment. A large decrease in grazers (ciliates) that was observed concurrently with this treatment is the most likely explanation for the increase in Chl a level. The lack of negative effect on algal biomass by enhanced UV-B is attributed to the mixing inside the mesocosms and to the relatively low UV-B penetration. In Ubatuba levels of most pigments decreased over time, particularly fucoxanthin, Chl c3 and alloxanthin. The RM-ANOVA showed no effect of the UV-B treatments, except for Chl c3, which had significantly lower concentrations under natural UVB conditions, indicating that enhanced UV-B directly or indirectly favored Chl c3 algae (likely prymnesiophytes). Although particulate organic carbon concentration was significantly larger during HUVB treatment than during the other treatments, Chl a was unaffected, suggesting that enhanced UV-B favored heterotrophs. Lack of algal growth during this experiment was attributed to low nutrient concentrations (which were the lowest of the three sites), high irradiances (which were the highest noon incident photosynthetically available radiation and UV of the three sites) and UV-B penetration down to the bottom of the mesocosms. In Ushuaia a small bloom took place over the first 5 days. The RM-ANOVA showed no overall effect of the UV-B treatments for any of the pigments examined but on the last 3 days of the experiment several green algae-type pigments, such as Chl b and siphonein, showed increased concentrations under the HUVB treatment. UV-B enhancement hence favored green algae, as seen from the stronger increase over time in the ratio of Chl b to Chl a associated with the HUVB treatment. UV-B enhancement also seemed to cause a slight decrease in physiological condition, because the relative concentration of chlorophyllide a and some pheophorbides that may be the product of dying algae increased during the HUVB treatments in Ubatuba and particularly in Ushuaia (where UV-B also penetrated to the bottom of mesocosms). For all three sites changes in phytoplankton biomass due to the UV-B treatments were minor, even though UV-B enhancement was important. This study indicates that effects of enhanced UV-B on the community structure of both phytoplankton and their grazers are potentially more important than effects on overall algal biomass.