From the soil to the sky: Researchers quantify the amount of energy that plants use to lift water on a global scale: Every day, about one quadrillion gallons of water are silently pumped from the ground to the treetops. Earth’s plant life accomplishes this staggering feat using only sunlight. It takes energy to lift all this liquid, but just how much was an open question until this year.
Researchers at UC Santa Barbara have now calculated the tremendous amount of power used by plants to move water through their xylem from the soil to their leaves. They found that on average, it was an additional 14% of the energy the plants harvested through photosynthesis. On a global scale, this is comparable to the production of all of humanity’s hydropower. Their study, published in the Journal of Geophysical Research: Biogeosciences, is the first to estimate how much energy goes into lifting water up to plant canopies, both for individual plants and worldwide. “It takes power to move water up through the xylem of the tree. It takes energy. We’re quantifying how much energy that is,” said first author Gregory Quetin, a postdoctoral researcher in the Department of Geography.
This energy is in addition to what a plant produces via photosynthesis. “It’s energy that’s being harvested passively from the environment, just through the tree’s structure.” The team combined a global database of plant conductance with mathematical models of sap ascent to estimate how much power the world’s plant life devotes to pumping water. They found that the Earth’s forests consume around 9.4 petawatt-hours per year. That’s on par with global hydropower production, they quickly point out.