Salt-resistant plants for bioenergy

Ocean flooding, rising sea levels, and even long-term irrigation have left some cropland too salty to farm. But salt-tolerate plants like seashore mallow may offer new hope for reclaiming them.

Growing to about 6 feet tall and almost as wide, Seashore Mallow (Kosteletzkya pentacarpos) grows wild along sea cliffs and the marshy coastline from New England to the Gulf of Mexico. The pink, hibiscus-like blooms make it attractive for landscaping, but biofuel experts are far more interested in another part of the plant. The seeds, which are up to 20 percent oil, are a potential source of biodiesel. "It has roughly the same oil content as soybeans, maybe a little more," says Jack Gallagher, Ph.D., professor of marine biosciences and co-director of the Halophyte Biotechnology Center at the University of Delaware.

Seashore Mallow has few known pests or diseases. Its real promise, however, lies in its amazing ability to tolerate salt. In one dramatic example, plants growing in Gallagher's test plots in Delaware were essentially unfazed by flooding and surges of seawater from Superstorm Sandy. As Gallagher explains, the plant has cellular pumps that excrete sodium before it has a chance to interfere with the enzymes inside the cell. The plant can typically grow in water with a sodium content of up to ten parts per thousands, or about 1/3 the salinity of seawater. He and his team have found that some specimens from North Carolina and Texas could withstand water containing twice as much sodium -- 2/3 the salinity level of seawater.

Gallagher argues that Seashore Mallow could help reclaim cropland now useless after being tainted by ocean flooding in Delaware, Maryland, the Carolinas, and elsewhere. He also believes that the plant could be potentially be grown on land in California river valleys that have become slightly saline after decades of irrigation.

If sea levels keep rising -- or if hurricanes become stronger and more frequent -- Seashore Mallow could prove to be an important safety net. "I see Seashore Mallow as a way for these lands to retain their agricultural value," Gallagher says.

At one time, there was also hope that Seashore Mallow's fibrous steams -- or the lignocellulosic material, as it's called in biofuel circles -- could be refined into ethanol, but Gallagher says that it might actually be better used for another purpose: kitty litter. The material is incredibly absorbent -- up to nine times more absorbent than clay litter. "It could out that kitty litter ends up subsidizing the [Sea Mallow] biodiesel," Gallagher says. "Maybe it won't need as many subsidies as other forms of biofuel."

And it's not just farmers close to seashores who could benefit from salt-resistant energy crops. One to 2 percent of irrigated lands are also lost to salinization each year, according to Drs. Heather Youngs and Chris Somerville of the Energy Biosciences Institute. They report that research on salt-tolerant species such as prairie cordgrass "could be useful in bringing these lands back into production, as well as improving salt tolerance in other crops." They also noted that a recent estimate predicted planting salt-tolerant trees on nearly a billion hectares of saline land could produce 5 to 11 percent of global primary energy consumption annually.

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