But these assumptions don't take into consideration human efforts to boost plant productivity through genetic manipulation, plant breeding and land management, DeLucia said. Such efforts have already yielded some extremely productive plants.
For example, in Illinois a hybrid grass, Miscanthus x giganteus, without fertilizer or irrigation produced 10 to 16 tons of above-ground biomass per acre, more than double the productivity of native prairie vegetation or corn. And genetically modified no-till corn is more than five times as productive in terms of total biomass generated per acre as restored prairie in Wisconsin.
Some non-native species also outcompete native species; this is what makes many of them invasive, DeLucia said. In Iceland, for example, an introduced species, the nootka lupine, produces four times as much biomass as the native boreal dwarf birch species it displaces. And in India bamboo plantations produce about 40 percent more biomass than dry, deciduous tropical forests.
Some of these plants would not be desirable additions to native or managed ecosystems, DeLucia said, but they represent the untapped potential productivity of plants in general.
"We're saying this is what's possible," he said.
The team used a model of light-use efficiency and the theoretical maximum efficiency with which plant canopies convert solar radiation to biomass to estimate the theoretical limit of net primary production (NPP) on a global scale. This newly calculated limit was "roughly two orders of magnitude higher than the productivity of most current managed or natural ecosystems," the authors wrote.
"We're not saying that this is even approachable, but the theory tells us that what is possible on the planet is much, much higher than what current estimates are," DeLucia said.
Taking into account global water limitations reduced this theoretical limit by more than 20 percent
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign