Chapter 34.2, Problem 2R

Summary Introduction

To review:

To draw out inferences for the given questions on the basis of the table that shows the water potential measurements in a 100-meter tall tree and its surroundings, with the gravity force of –0.01 MPa (megapascal) per meter of height above the ground and states the reasons for:

(a) Sufficient leaf water potential in order to draw the water to the top of the tree,

(b) Continuation of transpiration if the soil potential is decreased to –1.0 MPa, and

(c) Effect on water potential of xylem if all the stomata are closed.

Introduction:

Water potential refers to the relative measurement of the tendency of water to flow along a concentration gradient, that is, from the region of high potential to the lower potential regions. It is caused by osmosis, surface tension, and any physical pressure. It is measured in MPa (megapascals) and represented by the Greek letter “psi” ($\Psi$).

The following table represents the region of the plant and the water potential values in these regions:

Region	Water potential (MPa)
Soil water	–0.3
Xylem of root	–0.6
Xylem of trunk	–1.2
Inside of leaf	–2.0
Outside air	–58.5