中沙大环礁四种大型海藻的光生理特征比较及其对升温的响应*

生活于珊瑚礁区的大型海藻可以与珊瑚一起为礁栖生物提供食物和栖息地, 它们在维护珊瑚礁生态系统生物多样性中起着极为重要的作用。本论文比较研究了生活于我国南海中沙大环礁区4种优势海藻的生化组分、光合特征及其对海水升温的生理响应,其中厚膜藻(Grateloupia ellipitica)和粉枝藻(Liagora samaensis)为红藻, 钙扇藻(Udotea flabellum)和仙掌藻(Halimeda discoidea)为绿藻。结果显示, 与绿藻相比, 红藻藻体叶绿素(Chl a)和类胡萝卜素含量更低且含有藻胆素, 红藻的光补偿点(E_C)和呼吸速率(R_d)均显著低于绿藻。海水升温提高了4种海藻的光能利用效率(α)、E_C、R_d和日净光合固碳量; 同时, 升温还降低红藻的饱和光强(E_K)、提高绿藻的最大光合放氧速率(P_max)。结果还显示, 海水升温在光强较低时提高红藻的光合放氧速率, 光强较高时则降低其放氧速率; 升温也提高绿藻的光合放氧速率, 但光强变化对升温效应的影响不显著。基于4种海藻的光生理特征以及升温效应的种间差异性可见, 短时间升温(~4℃)有利于中沙大环礁区海藻的光合作用; 与绿藻相比, 该升温效应更有利于红藻。

Comparative study on photophysiology of four macroalgae from the Zhongsha Atoll,with special reference to the effects of temperature rise*

Macroalgae, together with corals, provide faunal foods and habitats in clear tropical waters, maintaining the rich biological diversity in coral reefs. In this paper, we compared biochemical compositions and photosynthetic features, as well as photophysiological responses to temperature rise of two red algae (i.e., Grateloupia ellipitica and Liagora samaensis) and two green algae (i.e., Udotea flabellum and Halimeda discoidea), the dominating macroalgae species in the Zhongsha Atoll of the South China Sea. Results showed that the red algae contain less chlorophyll a and carotenoids than the green ones, but contain the unique phycoerythrin and phycocyanin. Both the light compensation point (E_C) and dark respiration (R_d) of the red algae are lower than the green algae. The temperature rise enhances E_C, R_d and light utilization efficiency (α), as well as the daily carbon fixation of both red and green algae; and it lowers the saturation irradiance (E_K) of the former algae species but enhances the maximum photosynthetic oxygen evolution rate (P_max) of the later species. Moreover, the temperature rise enhances the photosynthetic rate of the red algae under lower light, but reduces it under higher light, while such temperature-induced enhancement on the photosynthetic rate of the green algae occurs throughout the measured light range. Considering the inter-specific photophysiological characteristics of the four macroalgae as well as the effects of temperature, the temperature rise would benefit the photosynthesis of macroalgae in the Zhongsha Atoll and benefit the red algae better than the green algae.