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How does transpiration return water from plants to the atmosphere?

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Diagram illustrating Earth's environmental spheres, with labeled sections showing the geosphere (land and crust), biosphere (living things), atmosphere (air), and hydrosphere (water), each extending vertically from the Earth's surface. — hydrosphere Earth's environment includes the atmosphere, the hydrosphere, the lithosphere, and the biosphere.

In the context of the hydrosphere, transpiration is the process by which plants release water into the atmosphere as water vapour.12

This process occurs primarily through stomata, which are small pores located on the surface of leaves. While these openings are essential for gas exchange—admitting carbon dioxide for photosynthesis and allowing oxygen to escape—they also inevitably permit the exit of water vapour.13

As water evaporates from the leaf interior into the surrounding air, it creates a "transpiration pull" that helps draw water and dissolved nutrients upward from the roots through the plant's xylem tissue. Research indicates that as much as 99 percent of the water absorbed by a plant's roots is eventually released into the atmosphere through this mechanism. By returning water to the air, transpiration serves as a key component of the hydrologic cycle, which is vital for sustaining life on Earth.142