Once cheatgrass invades, fires start earlier, when native plants are more susceptible to injury. Repeated burning eventually kills all the native plants, and cheatgrass competition prevents their re-establishment.
"A cheatgrass landscape is about as ecologically rich as a parking lot," said the L.A. Times.
The mystery of photorespiration
Schaefer wanted to know whether differences at the molecular level gave the plant its competitive edge.
All plants make a living by tapping the energy in sunlight to "fix" the carbon in carbon dioxide by incorporating it in carbon-based molecules such as sugar.
Soybeans and cheatgrass are both C3 plants that use an enzyme to bind carbon dioxide from the air and join it to a five-carbon molecule, producing a six-carbon molecule that quickly splits into two three-carbon molecules (hence the name C3).
But, as Schaefer was aware, C3 plants have a puzzling metabolic quirk. On a hot day, the plants close their stomata, the pores mainly on the undersides of leaves, to cut down on water loss. This in itself is adaptive.
But when the stomata close, the carbon dioxide concentration in the air spaces inside the leaf also falls.
Instead of binding carbon dioxide, the enzyme then binds oxygen and forms a five-carbon rather than a six-carbon molecule, which gets split into a three-carbon and a two-carbon molecule.
The math doesn't work.
The two-carbon molecule can't go through the carbon-fixing process directly. Instead it goes through a cascade of reactions and is then fed back into the carbon fixation cycle.
This process, called photorespiration because it occurs in the light and releases carbon d
|Contact: Diana Lutz|
Washington University in St. Louis