evapotranspiration II

Question 1

is water surface evaporation greater when air is moist or dry?

Answer 1

dry

Question 2

as air temperature decreases, the maximum amount of water vapor that can exist in the air..

Answer 2

decreases

Question 3

what is transpiration?

Answer 3

indirect transfer of water from the root-stomatal system to the atmosphere. Basically plant-mediated evaporation

Question 4

what are the necessities before transpiration can occur?

Answer 4

• a flow of energy to the transpiring surfaces
• flow of liquid water to these surfaces
• flow of vapor away from these surfaces

Question 5

how do plants pull water up from the ground?

Answer 5

• polarity, water has adhesive, tension and cohesion properties that allow it to stick together and travel together
• energy differences, water moves from areas with less negative water pressure to areas with more negative water pressure

Question 6

what is the cohesion-tension theory?

Answer 6

water within the whole plant forms a continuous network of liquid columns from the film of water around soil particles to absorbing surfaces of roots to the evaporating surfaces of leaves

Question 7

where does most water uptake occur in the soil profile?

Answer 7

in the upper half of the soil root zone

Question 8

what are stomata?

Answer 8

also known as “ecohydrologic engineers”, they are air openings mostly on leaf under-side
- they allow plants to acquire CO2 from air
- allow plants to expel water
- open and close diurnally and in response to soil water and atmospheric water pressure

Question 9

how do stomata know when to close?

Answer 9

triggered by darkness or the release of ABA (absicisic acid) when soil water supply cannot keep up with transpiration

Question 10

what is the driving force of transpiration?

Answer 10

difference in water vapor concentration between internal spaces in the leaf and the atmosphere around the leaf

Question 11

what are plant factors that affect transpiration?

Answer 11

• plant type
• number of stomata
• number of leaves
• leaf size
• presence of plant cuticles

Question 12

what are 5 environmental factors that affect transpiration?

Answer 12

• air temperature
• relative humidity
• wind: more air movement around a plant -> lower RH -> higher transpiration rate
• soil moisture availability
• light: more rapidly in light than in dark

Question 13

what are the three transpiration steps from the soil-plant-atmosphere continuum?

Answer 13

1. plant-water uptake
2. water travelling upward
3. water reaching leaf, 95% will be lost to transpiration process

Question 14

what is the cohesion-tension theory?

Answer 14

movement as continuous chain of water molecules due to water cohesion -> more tension at root-level, due to increased water pressure difference between roots and leaves so the soil water moves into roots

Question 15

what are 2 methods to estimating transpiration?

Answer 15

• leaf-level gas exchange
• tree-level xylem sapflow

Question 16

what are the disadadvantages of leaf-level gas exchange measurements

Answer 16

measurement interrupts the ambient environment and a lot of measurements are needed to scale up

Question 17

does transpiration or evaporation dominate at the plant level?

Answer 17

transpiration