Slurping hundreds of litres of water up to its leaves or needles, where photosynthesis occurs, can be a difficult task for a tall tree. Even in short grasses and shrubs, rising sap must overcome gravity and plant tissue resistance. A first-of-its-kind research has now determined the power required to elevate sap to plants’ leaves worldwide — and it’s enormous, accounting for nearly all hydroelectric power generated globally.
Vegetation harness 9.4 quadrillion watt-hours of sap-pumping electricity over the course of a year, climatologist Gregory Quetin and colleagues write August 17 in the Journal of Geophysical Research: Biogeosciences. That is around 90% of the amount of hydro power produced globally in 2019.
According to Quetin of the University of California, Santa Barbara, evaporation of water from leaves produces the suction that pushes sap upward. The scientists segmented a map of the world’s land area into cells that span 0.5° of latitude by 0.5° of longitude and studied data for the mix of plants in each cell that were actively pumping sap each month to estimate the total evaporative power for all plants on Earth yearly. Naturally, the amount of electricity required was greatest in tree-rich regions, particularly in tropical rainforests.
The scientists found that if plants in forest habitats were to rely on evaporation to pump sap, they would have to squander around 14 percent of the energy provided by photosynthesis. Grasses and other plants in nonforest habitats would need to waste little over 1% of their energy storage, owing to their shorter stature and lower resistance to sap flow inside their tissues than woody plants.
image credits: BAAC3NES/MOMENT/GETTY IMAGES PLUS
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