Photosynthetic adaptation to low iron, light, and temperature in Southern Ocean phytoplankton

Significance Controls on phytoplankton productivity in the extreme environment of the Southern Ocean has received widespread attention. This polar region presents three challenges to primary producers: how to subsist under the joint constraints of low temperatures, low light, and growth-limiting concentrations of the essential trace element iron. The resident phytoplankton have overcome these extreme environmental conditions with a unique combination of physiological adaptations. They have modified parts of their photosynthetic machinery to harvest low levels of light without substantially increasing their iron requirements, and in a way that may exploit the low temperature in their environment. Together, these adaptations enable them to use iron and light more efficiently and grow faster than environmental conditions should otherwise permit.