Researchers Determine Photosynthesis Rate Of Ocean Microorganisms Nearly In Real Time

Phytoplankton play an important role in the ocean, and even global, ecosystem. The tiny photosynthesizing organisms are a major nutrient source in the marine food web, and because they sequester in their shells billions of tons of carbon dioxide from the atmosphere, they’re an important factor in climate models.

But researchers haven’t had a good way to measure in real time the organisms’ contributions to the marine ecosystem. This week in Honolulu, at the 7th International Chemical Congress of Pacific Basin Societies, or Pacifichem, Australian researchers presented a model they developed that predicts phytoplankton composition and photosynthesis productivity from infrared spectroscopy measurements.

Philip Heraud of Monash University and coworkers tested their model by taking shipboard IR measurements of phytoplankton during the maiden voyage of the Australian research vessel Investigator in March. To Heraud’s knowledge, that voyage—which traversed the Southern Ocean encircling Antarctica—marks the first time such measurements have been made on a ship.

Heraud’s team developed its model from earlier lab studies of phytoplankton with fast, easy IR measurements (ISME J. 2015, DOI: 10.1038/ismej.2015.123). The IR spectra provide a comprehensive picture of the phytoplankton’s biochemical makeup and, thus, its photosynthetic productivity.

To make the shipboard measurements, Heraud’s team pumped water onto the ship and passed it through sequential filters to divide the phytoplankton into different size fractions, which the researchers analyzed by attenuated total reflectance Fourier transform IR spectroscopy. Their model predicted the organisms’ photosynthetic rate within 5% of the measured value.

“The new work gives data virtually in real time, which represents a technological innovation and a significant step forward for marine biology,” Leanne Armand, a diatom expert at Macquarie University and chief scientist on the Investigator,told C&EN. Armand has previously collaborated with Heraud but was not directly involved with the shipboard measurements. “In the past, the best we could do was preserve samples and send them back to the lab for some bulk, generalized analysis months later.”

“We envisage that we can get real-time information about the state of phytoplankton communities within minutes, rather than having data that are months old,” Heraud said.