近日，我院高坤山教授等應邀在Frontiers in Marine Science上發表題為“Effects of Ocean Acidification on Marine Photosynthetic Organisms Under the Concurrent Influences of Warming, UV Radiation, and Deoxygenation”的文章，綜述了海洋酸化對光合生物效應方面的研究進展，分析了多重環境壓力下酸化的影響機制。

在不同海域、不同物種或不同的實驗設計中，酸化、營養鹽、UV與升溫等因子相互作用，可協同、抵消、或拮抗性地影響初級生產過程。對鈣化藻類而言，酸化降低其鈣含量，并與UV或升溫產生協同效應，進一步降低其鈣化作用；對硅藻而言，酸化的正、負效應，依賴于光強與營養鹽濃度；營養鹽限制或高光下，抑制其生長；對固氮光合生物而言，酸化或增加或降低其固氮能力，就多重環境壓力下的復合效應而言，尚存在較大不確定性。而大型海藻，耐受酸化能力較強，其生長受CO₂濃度升高的促進。低氧化對初級生產者的影響，鮮有報道；理論預測，低氧化與酸化，會影響細胞內CO₂與O₂的比率，進而影響核酮糖-1,5-二磷酸羧化酶催化的羧化與氧化作用，左右浮游植物凈固碳量。

該綜述還展望了未來研究趨勢，提出了兩種科學假說：1）海洋全球變化影響下棲息地退化假說；2）酸化與UV輻射協同影響光合固碳，由近岸向大洋，協同抑制光合固碳的同時，加劇浮游植物呼吸丟碳。

Hypothesis 1:  ocean climate changes-induced habitat degradation. Ocean warming, acidification, and deoxygenation associated with increasing atmospheric CO₂ rise. A shoaled upper mixed layer due to warming exposes organisms dwelling there to higher levels of solar radiation. The habitable niche degradation hypothesis: phytoplankton abundance and community structure can be altered within the UML under multiple stressors associated with ocean climate changes; and motile organisms dwelling within the UML are stressed due to increased exposure to solar UV radiation and high levels of PAR, which traps more heat; however, the low O₂ and pH waters below the UML hamper downward migration.

Hypothesis 2:  Ocean acidification (OA) and UV synergistically enhance carbon loss in surface primary producers. This hypothesis is based on the observational data on UV impacts and results that smaller diatoms decrease their growth rate under OA and nutrient-limitation conditions. Diel pH changes in highly productive coastal waters are shown with a sun and a moon symbol to indicate pH rise with increasing photosynthetic C removal during daytime and pH decline with respiratory CO₂ release during night. Note that benthic macroalgae contribute greatly to the diel pH fluctuations, and that their growth and photosynthesis are usually stimulated by rising CO₂ associated with OA. The symbols “+” and “–” indicate more positive effects due to OA and UV in coastal non-nutrient-limited waters and negative effects due to OA and UV in oligotrophic offshore waters, where shoaling of upper mixed layer owing to warming reduces upward transport of nutrients from deeper layers.

Reference：

Gao KS*, Beardall J, Hader DP, Hall-Spencer JM, Gao G, Hutchins DA. 2019. Effects of ocean acidification on marine photosynthetic organisms under the concurrent influences of warming, UV radiation and deoxygenation. Frontiers in Marine Science 6: 322.

原文鏈接：https://www.frontiersin.org/articles/10.3389/fmars.2019.00322/full