Question

What is a typical water potential in soil? In xylem? In leaves? In air? Your answers should be in MPa units. (Hint: See figure in your textbook or research online.)

Answer 1

Typical water potential in soil: Total soil water potential is defined as the amount of work per unit quantity of pure water that must be done by external forces to transfer reversibly and isothermally an infinitesimal amount of water from the standard state to the soil at the point under consideration.

Typical water potential in xylem:In plasmolysed cells, pressure potential is almost zero. Negative pressure potentials occur when water is pulled through an open system such as a plant xylem vessel. Withstanding negative pressure potentials (frequently called tension) is an important adaptation of xylem

Typical water potential in leaves:A plant's leaves wilt when the turgor pressure decreases and revive when the plant has been watered. Pressure potentials are typically around 0.6–0.8 MPa, but can reach as high as 1.5 MPa in a well-watered plant.

Typical water potential in air:At a potential of −33 kPa, or −1/3 bar, (−10 kPa for sand), soil is at field capacity. ... In contrast, atmospheric water potentials are much more negative—a typical value for dry air is −100 MPa, though this value depends on the temperature and the humidity.