When it comes to lifting water, plants are true energy lifters.
For a tall tree, sucking hundreds of liters of water each day down to its leaves or needles, where photosynthesis takes place, can be a huge boon. Even for short grasses and shrubs, the rising sap must somehow overcome gravity and the resistance of the plant tissues. Now, a first-of-its-kind study has estimated the energy needed to pump sap into the foliage of plants around the world, and it’s a prodigious amount, almost as much as all the hydroelectric power generated globally.
Over the course of a year, plants harness 9.4 quadrillion watt-hours of sap-pumping powerclimatologist Gregory Quetin and colleagues report August 17 in the Journal of Geophysical Research: Biogeosciences. That’s about 90 percent of the amount of hydropower produced worldwide in 2019.
Evaporation of water from foliage. drives the suction that pulls the sap up, says Quetin of the University of California, Santa Barbara (Serial number: 03/24/22). To estimate the total evaporative power of all plants on Earth annually, the team divided a map of the world’s land surface into cells spanning 0.5° latitude by 0.5° longitude and analyzed the data from the mix of plants in each cell that are actively pumping out sap each month. As expected, the required power was higher in areas rich in trees, especially in the rain forests of the tropics.
If plants in forest ecosystems were to tap into their own energy reserves instead of relying on evaporation to pump sap, they would need to expend about 14 percent of the energy they generated through photosynthesis, the researchers found.. Grasses and other plants in non-forest ecosystems would need to expend a little more than 1 percent of their energy reserves, largely because such plants are much shorter and have less resistance to sap flow within their tissues than woody plants. .