Sipping hundreds of liters of water from the xylem to its leaves, where photosynthesis occurs, can be a difficult task for a tall tree. Even in bushes, the rising sap must overcome gravity and the resistance of the plant tissue. Now, pioneering research in his field has determined the energy required for sap to rise to the leaves of plants around the world.
The amount of energy they need is huge, accounting for almost all of the hydropower generated globally.
Every day, about a billion trillion gallons of water are silently pumped from the ground up into the treetops. The researchers tallied that, over the course of a year, plants harness 9.4 trillion watt-hours of sap-pumping power, that’s about 90 percent of the amount of hydropower produced worldwide in 2019. It is impressive, since plant life achieves this amazing task using only sunlight.
lots and lots of energy
Scientists at the University of California, Santa Barbara found that, on average, it was an additional 14% of energy that plants harvested through photosynthesis. The study, published in the Journal of Geophysical Research: Biogeosciences , is the first to estimate how much energy is used to lift water up to the tops of plants, both for individual plants and globally.
“It takes power to move water through the xylem of the tree. It takes energy. We’re quantifying how much energy that is,” said Gregory Quetin, a postdoctoral researcher in the Department of Geography. “It’s energy that is collected passively from the environment, just through the structure of the tree.”
Lower plants, such as shrubs and other non-forest ecosystems, would need to expend a little more than 1% of their energy reserves, largely because such plants are much shorter and have less resistance to sap flow within their tissues. than woody plants.
Reference: Gregory R. Quetin et al, Quantifying the Global Power Needed for Sap Ascent in Plants, Journal of Geophysical Research: Biogeosciences (2022). DOI: 10.1029/2022JG006922