<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Define water potential and explain how it is influenced by solutes, pressure, gravity, and the matric potential
  • Describe how water potential, evapotranspiration, and stomatal regulation influence how water is transported in plants
  • Explain how photosynthates are transported in plants

The structure of plant roots, stems, and leaves facilitates the transport of water, nutrients, and photosynthates throughout the plant. The phloem and xylem are the main tissues responsible for this movement. Water potential, evapotranspiration, and stomatal regulation influence how water and nutrients are transported in plants. To understand how these processes work, we must first understand the energetics of water potential.

Water potential

Plants are phenomenal hydraulic engineers. Using only the basic laws of physics and the simple manipulation of potential energy, plants can move water to the top of a 116-meter-tall tree ( [link] a ). Plants can also use hydraulics to generate enough force to split rocks and buckle sidewalks ( [link] b ). Plants achieve this because of water potential.

 Photo (a) shows the brown trunk of a tall sequoia tree in a forest. Photo (b) shows a grey tree trunk growing between a road and a sidewalk. The roots have started to lift up and crack the concrete slabs of the sidewalk.
With heights nearing 116 meters, (a) coastal redwoods ( Sequoia sempervirens ) are the tallest trees in the world. Plant roots can easily generate enough force to (b) buckle and break concrete sidewalks, much to the dismay of homeowners and city maintenance departments. (credit a: modification of work by Bernt Rostad; credit b: modification of work by Pedestrians Educating Drivers on Safety, Inc.)

Water potential is a measure of the potential energy in water. Plant physiologists are not interested in the energy in any one particular aqueous system, but are very interested in water movement between two systems. In practical terms, therefore, water potential is the difference in potential energy between a given water sample and pure water (at atmospheric pressure and ambient temperature). Water potential is denoted by the Greek letter ψ ( psi ) and is expressed in units of pressure (pressure is a form of energy) called megapascals (MPa). The potential of pure water (Ψ w pure H2O ) is, by convenience of definition, designated a value of zero (even though pure water contains plenty of potential energy, that energy is ignored). Water potential values for the water in a plant root, stem, or leaf are therefore expressed relative to Ψ w pure H2O .

The water potential in plant solutions is influenced by solute concentration, pressure, gravity, and factors called matrix effects. Water potential can be broken down into its individual components using the following equation:

Ψ system = Ψ total = Ψ s + Ψ p + Ψ g + Ψ m

where Ψ s , Ψ p , Ψ g , and Ψ m refer to the solute, pressure, gravity, and matric potentials, respectively. “System” can refer to the water potential of the soil water (Ψ soil ), root water (Ψ root ), stem water (Ψ stem ), leaf water (Ψ leaf ) or the water in the atmosphere (Ψ atmosphere ): whichever aqueous system is under consideration. As the individual components change, they raise or lower the total water potential of a system. When this happens, water moves to equilibrate, moving from the system or compartment with a higher water potential to the system or compartment with a lower water potential. This brings the difference in water potential between the two systems (ΔΨ) back to zero (ΔΨ = 0). Therefore, for water to move through the plant from the soil to the air (a process called transpiration), Ψ soil must be>Ψ root stem leaf atmosphere .

Questions & Answers

Is the "growth and maintenance phase" in a cell's life cycle when cell division is about to occur
Somto Reply
what is the common name of Basidiomycetes
Ogechukwu Reply
الاجزاء النباتية لابد من تعقيمها قبل زراعتها في القوارير
whats this?
do you speak arabic?!
what are bio elements
Shahzad Reply
which are present In Body And such elements Have Great role in our Body there are 16 bio elements that maintains human Body but on The basis of amount There are 6 bio elements present in Concen. of 99% and More Valuable And Highly Concen. element is Oxygent with 65 %
how je pollution brought about
Lamina Reply
how je pollution brouhgt about
non is pollution brouhgt about
describe the anatomy of cell division
Ivanovic Reply
Complex traits such as height result from 
Ruben Reply
what is the difference between chloroplasts and mitochondria
Nkalubo Reply
chloroplast in plants and bacterial cell ; mitochondria in animal cells
Diagram of a living cell
Eliza Reply
what is cell
A cell is the smallest basic unit of life.
what's biology
Ogochukwu Reply
this is da study of living and non-living thing in an eco-system
it is the study of living and non living organism in the ecology
I agree with you dat biology is d study of living nd nonliving features
why do plants store carbohydrates in form of starch and not glucose?
Nutty Reply
Describe the structure of starch?
wat is diffusion
water is life!.. Discuss?
Nutty Reply
why do plants store carbohydrates in form if starch not glucose!
study of living thing
Dennis Reply
what is beyond a liveing cell
what is biology
Gabriel Reply
d study of living nd non living thing
what is vasectomy
Evelyn Reply
The surgical removal of d spermduct

Get the best Biology course in your pocket!

Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?