water movement from plant to air

Question 1

water vapor pressure?

Answer 1

Water vapor pressure – atmospheric pressure exerted by water molecules in the air, moving from
high to low concentrations

Question 2

what does WVP effect? when is it high?

Answer 2

changes the amount of water due to the number of water molecules
-hotter temperature has higher water vapour pressure (warmer air holds more water)
-greater water deficit, the more transpiration

Question 3

what is WVP measured against?

Answer 3

Measured against saturation water vapour pressure:
Vapour pressure deficit (VPD) = saturation water vapour pressure – water vapour pressure\

Question 4

RH?

Answer 4

Relative humidity (RH) = water vapour density / saturation water vapour density x 100
Decreased RH = Increased VPD
B/c the amount of water at 10 degrees it can hold 10g but at 30 degrees it can hold
3x more water = saturated water density

Question 5

how does water move? high VPD vs low?

Answer 5

Water moves from high to low water vapour pressure
Increased VPD = Drier = Increased evapotranspiration
Decreased VPD = Humid = Decreased evapotranspiration (b/c of deficit)

Question 6

transpiration?

Answer 6

ranspiration – evaporation on the surface of leaves
- The leaf is site of photosynthesis and CO2 exchange thus the plant
needs stomata on the surface. The stomata is also the site of gas
exchange for water vapour. Inside the stomata is saturated thus the
plant has a tendency to lose water.

Question 7

transpiration moist vs dry?

Answer 7

Moist soil àno problem losing water
- Dry soil à can’t lose water b/c they need to save it (store) to survive

Question 8

stoma controlled by?

Answer 8

Stoma (water moving from leaves to atm) controlled by:
1. Vapour pressure deficit
2. Soil water supply
3. Stomatal conductance

Question 9

threshold effect?

Answer 9

hreshold effect – soil moisture on transpiration
- Decline in transpiration when about 80% of available water is removed from soil
rooting zone
- After field capacity, rate of transpiration hardly changes
- Threshold is around 25%

Question 10

photosynth - day vs night

Answer 10

Daytime – photosynthesis, high transpiration
Nighttime – no photosynthesis, low transpiration b/c stomata is closed, hydraulic lift – water
moved from deep soil to higher parts of soil through roots where water is absorbed by roots at
shallow profile b/c gradient is weaker (moisture microclimate)