Photosynthetic fuel factories.

Photosynthetic fuel factories

Love may make the world go round, but it's photosynthetic plants that keep the machines running. All fossil fuels are are remains of ancient organic matter, and therefore of ancient photosynthetic processes. The past decade has seen a growing awareness that those remnants are running out.

According to Melvin Calvin, research may be able to sidestep the need for the eons-long geological processes that turn organic matter into oil and gas. With the development of new crops, the Nobel Prize-winning chemist says, modern plants could provide at least half of the fuel energy needs of the United States within the next 40 years.

The idea isn't new. Nearly half of Brazil's fuel comes from sugarcane, for example. But sugar juice from cane must be fermented, to concentrate the carbohydrates into higher-energy hydrocarbons. "We would much prefer . . . plants which would do the whole thing in one step--reduce all the way down to hydrocarbons,' Calvin told an international symposium on grasses last week at the Smithsonian Institution in Washington, D.C.

Calvin reported in 1979 that the Amazonian copa-iba tree (Copaifera langsdorfii) produces diesel fuel that can go directly from the tree into a car's gas tank (SN:9/15/79, p.182). Since then, Brazilian researchers have grown an experimental plantation of the trees, which they hope to begin tapping soon. Copa-ibas grow only in the tropics, but Calvin says researchers may be able to adapt them to temperate climates or to transfer the oil-producing genes into a temperate-adapted tree.

Calvin, at the University of California at Berkeley, also works with hydrocarbon-producing temperate plants. The Euphorbia lathyris, or gopher plant, produces an oil-based latex as well as fermentable sugars and cellulose. After growing small crops of the plants on soil-and water-poor experimental plantations in California, Calvin and his colleagues estimate that an acre of gopher plants would produce the equivalent of 12 barrels of oil from the three components. At that level of productivity, the crop would become economically enticing if oil prices rose above $30/barrel again, Calvin says.

But the gopher plant is an annual, and while that means it can be harvested almost immediately, it also means the crop is relatively expensive and hard on the land. The Pittosporaceae family offers a few candidates for a temperate perennial oil-producer. Growing throughout the U.S. West Coast, P. undulatum's grape-sized fruits are sticky with oil. And in the Philippines (at high altitudes, which bodes well for temperate adaptation), the fruits of P. resiniferum are so oily they are used as torches. Calvin estimates that such trees might keep producing for 10 to 15 years.

Some biologists at the meeting had misgivings about using wild lands for large-scale planting of fuel crops--and, ultimately, still coming up short on fuel. Asked Hugh Iltis of the University of Wisconsin in Madison, "After you provide fuel for the next 5 billion [people], what next?'