Lecture L/M: Transpiration and Water Stress

What general techniques are there for measuring water potential?

Pressure bomb

Dewpoint psychrometer

Osmometer

Pressure probe

What is the purpose of transpiration?

Supplies water for photosynthesis (minor)

Transports minerals from soil to entire plant

Cools leaf surface through evaporative cooling

Keeps cells turgid; maintain plant shape/structure

Reference evapotranspiration equation (important)

ETc = Kc* ETo

ETc: crop or landscape ET

Kc: crop or landscape coefficient

ETo: reference evapotranspiration

What enviromental factors affect rate of transpiration? (important)

Vapor pressure gradient

Soil water availability

Water stress effect on plant growth and cell wall synthesis (important)

Plants cells need high water potential (not very negative) to grow and synthesize cell walls

In order to grow, the cell needs to have as much turgor pressure as possible. So as turgor pressure decreases, the growth rate of the leaf also decreases

Cavitation

Event of water vapor-filled bubble filling a vessel

Embolism

Result of cavitation, a gas bubble that fills the vessel

What causes cavitation?

When water potential is very negative