Turning sunlight into sugar - Hawaiian ʻakoko trees do it differently

By Lena SchnellSeptember 27, 2022

The Hawaiian ʻakoko (Euphorbia olowaluana)
The Hawaiian ʻakoko (Euphorbia olowaluana) at US Army Garrison Pohakuloa Training Area. (Photo Credit: Lena Schnell) VIEW ORIGINAL

US Army Garrison Pōhakuloa Training Area (PTA) is home to many amazing flora and fauna. But one stands out as the only known tree species that use a specialized type of photosynthesis to make sugar known as C4 photosynthesis – the Hawaiian ʻakoko (Euphorbia olowaluana).

The ʻakoko population at PTA is increasing and thousands of trees are protected within conservation fence units maintained by the PTA Natural Resources Program. These conservation fence units were emplaced by PTA at a cost of almost $10 million and span nearly 40 miles to protect 40,000 acres of land from ungulates and other predators. These fences allow flora and fauna, such as the ‘akoko to thrive.

To investigate why so few trees evolved C4 photosynthesis, Sophie Young, a doctoral candidate from the University of Lancaster, UK, traveled to Hawaii to study ʻakoko. She is working in partnership with the PTA Natural Resources Program and the Colorado State University Center for Environmental Management of Military Lands Program (CEMML).

“PTA is proud to host researchers, like Young, to assist in contributing to the scientific body of knowledge of flora and fauna such as the ‘akoko,” said PTA Commander Lt. Col. Kevin Cronin.

ʻAkoko is an important dry forest species and is a food resource for native Hawaiian insects such as yellow-faced bees (Hylaeus species). The thick white latex-sap was used by Hawaiians as medicine and to paint canoes. Young’s research will add to the reasons to conserve this special species, and help scientists understand the complex evolutionary processes of photosynthesis.

“Insights into the ecology and physiology of these unique species will also facilitate decision-making regarding their conservation by revealing the environmental conditions that they are best suited to,” said Young.

All plants use solar energy to turn water and carbon dioxide into sugar during the process of photosynthesis. Similar to other plant species found in hot, dry environments, ʻakoko evolved C4 photosynthesis, which is a more efficient way to make sugar with less water.

Many of our important food crops, such as corn, also use C4 photosynthesis and Young’s research will help shed light on crop security and biodiversity conservation under progressively changing climate conditions.

“Being stewards of the land is part of the PTA mission. We are honored caretakers and take great pride in protecting the precious natural and cultural resources,” said PTA Commander Lt. Col. Kevin Cronin.