Gao Kunshan, Li Gang, Helbling E Walter, Villafañe Virginia E
Marine Biology Institute, Shantou University, Shantou, Guangdong, China.
Photochem Photobiol. 2007 Jul-Aug;83(4):802-9. doi: 10.1111/j.1751-1097.2007.00154.x.
From June to September 2005, we carried out experiments to determine the ultraviolet radiation (UVR) -induced photoinhibition of summer phytoplankton assemblages from a coastal site of the South China Sea. Variability in taxonomic composition was determined throughout the summer, with a peak chlorophyll a (chl a approximately 20 microg chl a L(-1)) dominated by the diatom Skeletonema costatum that was detected early in the study period; the rest of the time samples were characterized by monads and flagellates, with low chl a values (1-5 chl a microg L(-1)). Surface water samples were placed in quartz tubes, inoculated with radiocarbon and exposed to solar radiation for 2-3 h to determine photosynthetic rates under three quality radiation treatments (i.e. PAB, 280-700 nm; PA, 320-700 nm and P, 400-700 nm) using different filters and under seven levels of ambient irradiance using neutral density screens (P vs E curves). UVR inhibition of samples exposed to maximum irradiance (i.e. at the surface) varied from -12.2% to 50%, while the daytime-integrated UVR-related photoinhibition in surface seawater varied from -62% to 7%. The effects of UVR on the photosynthetic parameters P(B)(max) and E(k) were also variable, but UV-B accounted for most of the observed variability. During sunny days, photosynthesis of microplankton (>20 microm) and piconanoplankton (<20 microm) were significantly inhibited by UVR (mostly by UV-B). However, during cloudy days, while piconanoplankton cells were still inhibited by UVR, microplankton cells used UVR (mostly UV-A) as the source of energy for photosynthesis, resulting in higher carbon fixation in samples exposed to UVR than the ones exposed only to photosynthetically active radiation (PAR). Our results indicate that size structure and cloudiness clearly condition the overall impact of UVR on phytoplankton photosynthesis in this tropical site of South China. In addition, model predictions for this area considering only PAR for primary production might have underestimated carbon fixation due to UVR contribution.
2005年6月至9月，我们开展了实验，以确定紫外线辐射（UVR）对南海一个沿海站点夏季浮游植物群落的光抑制作用。整个夏季都对分类组成的变化进行了测定，叶绿素a出现峰值（约20微克叶绿素a/升）时，在研究初期检测到以硅藻中肋骨条藻为主；其余时间样本以单细胞生物和鞭毛虫为特征，叶绿素a值较低（1-5微克叶绿素a/升）。将表层水样置于石英管中，接种放射性碳并暴露于太阳辐射下2-3小时，以使用不同滤光片在三种辐射质量处理（即PAB，280-700纳米；PA，320-700纳米和P，400-700纳米）下以及使用中性密度滤光片在七种环境辐照度水平下（P对E曲线）测定光合速率。暴露于最大辐照度（即表层）的样本的UVR抑制率在-12.2%至50%之间变化，而表层海水中与UVR相关的日间综合光抑制率在-62%至7%之间变化。UVR对光合参数P(B)(max)和E(k)的影响也各不相同，但UV-B占观察到的大部分变化。在晴天，超微型浮游生物（>20微米）和微微型浮游生物（<20微米）的光合作用受到UVR（主要是UV-B）的显著抑制。然而，在阴天，虽然微微型浮游生物细胞仍受到UVR抑制，但超微型浮游生物细胞利用UVR（主要是UV-A）作为光合作用的能量来源，导致暴露于UVR的样本中的碳固定量高于仅暴露于光合有效辐射（PAR）的样本。我们的结果表明，大小结构和云量明显影响了UVR对中国南方这个热带站点浮游植物光合作用的总体影响。此外，仅考虑PAR进行初级生产力的该区域模型预测可能因UVR的贡献而低估了碳固定量。
