Role of C4 carbon fixation in Ulva prolifera, the macroalga responsible for the world’s largest green tides
Dongyan Liu, Qian Ma, Iván Valiela, Donald M. Anderson, John K. Keesing, Kunshan Gao, Yu Zhen, Xiyan Sun, Yujue Wang
Abstract
Abstract Most marine algae preferentially assimilate CO 2 via the Calvin-Benson Cycle (C 3 ) and catalyze HCO 3 − dehydration via carbonic anhydrase (CA) as a CO 2 -compensatory mechanism, but certain species utilize the Hatch-Slack Cycle (C 4 ) to enhance photosynthesis. The occurrence and importance of the C 4 pathway remains uncertain, however. Here, we demonstrate that carbon fixation in Ulva prolifera , a species responsible for massive green tides, involves a combination of C 3 and C 4 pathways , and a CA-supported HCO 3 − mechanism. Analysis of CA and key C 3 and C 4 enzymes, and subsequent analysis of δ 13 C photosynthetic products showed that the species assimilates CO 2 predominately via the C 3 pathway, uses HCO 3 − via the CA mechanism at low CO 2 levels, and takes advantage of high irradiance using the C 4 pathway. This active and multi-faceted carbon acquisition strategy is advantageous for the formation of massive blooms, as thick floating mats are subject to intense surface irradiance and CO 2 limitation.