Earth can sustain more terrestrial plant growth

Earth can produce much more land-plant biomass - the total material in leaves, stems, roots, fruits, grains and other terrestrial plant parts - than previously thought, according to a new study.
The study recalculates the theoretical limit of terrestrial plant productivity, and finds that it is much higher than many current estimates allow.
"When you try to estimate something over the whole planet, you have to make some simplifying assumptions," said University of Illinois plant biology professor Evan DeLucia, who led the new analysis.
"And most previous research assumes that the maximum productivity you could get out of a landscape is what the natural ecosystem would have produced. But it turns out that in nature very few plants have evolved to maximise their growth rates," said DeLucia.

Estimates derived from satellite images of vegetation and modelling suggest that about 54 gigatons of carbon is converted into terrestrial plant biomass each year, the researchers report.
"This value has remained stable for the past several decades, leading to the conclusion that it represents a planetary boundary - an upper limit on global biomass production," the researchers said.

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 fertiliser or irrigation produced 10 to 16 tonnes 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.
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 said.

"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.
The study was published in the journal Environmental Science and Technology.