Most phytoplankton species have been shown to release CH₄, one of the potent greenhouse gases. However, little has been documented on how changed levels of CO₂ and temperatures affect their CH₄ producing capacity along with photosynthetic C fixation. Here, we examined CH₄ production and photosynthetic performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 ppmv, HC) and low (410 ppmv, LC) CO₂ levels at five temperatures (16, 20, 22, 24 and 27 ℃). The HC treatment did not affect growth but significantly reduced the optimal temperature for CH₄ production, and changes in temperature significantly affected both carbon fixation and CH₄ production. The calculated CH₄ production quotient (MPQ, CH₄ released vs. CO₂ fixed) showed a decreased trend with the increasing temperature under the two pCO₂ levels, implying that the CH₄ production by this microalga will be affected by future global ocean changes, and the CH₄ produced by phytoplankton should be quantified and included in assessing the feedback of marine photosynthetic microorganisms to climate change.

methane, Emiliania huxleyi, ocean acidification, ocean warming