CHAMPAIGN, Ill. -- Arundo donax, a giant reed that grows in the Mediterranean climate zones of the world, isn't like other prolific warm-weather grasses, researchers report. This grass, which can grow annually to 6 meters (nearly 20 feet) in height, uses a type of photosynthesis that is more common to crop plants like soybeans, rice and peanuts. The new findings are published in Scientific Reports, a Nature publishing group journal.

"Most highly productive grasses, like sugarcane, miscanthus and switchgrass, use these types of photosynthesis called C4, which we know to be very efficient," said study leader , a professor of crop sciences and of plant biology at the University of Illinois. "We confirmed that giant reed uses C3, a less efficient type of photosynthesis, and yet it's really productive. We just had to find out how."

The new findings could help scientists improve C3 photosynthesis in other plants.

Only a few detailed studies have evaluated the productivity of Arundo donax, "but some studies suggest it could produce as much as 60 tons of dry matter per hectare," Long said. "That's about the maximum you'd ever see from Miscanthus x giganteus, also known as giant elephant grass, a C4 grass that, as its name suggests, is considered very productive." 

For this reason, Arundo donax has attracted attention as a potential bioenergy crop despite questions about its invasive tendencies.

In the new study, the researchers focused on a naturally growing stand of Arundo donax in a mixed, five-acre site in southern Portugal. They measured how quickly the grass took in carbon dioxide and lost water through the pores in its leaves, the amount of chlorophyll in the leaves, how much light upper and lower leaves received or reflected, and how efficiently they photosynthesized in high- and low-light conditions.

These measurements offered insight into some of the factors that make the plant so productive.

"We found first of all that it is a classical C3 plant. It has all the properties of C3 photosynthesis and none of those of C4," Long said.