Lecture 4: Water Relations
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Unique Properties of Water
- High specific heat
- High heat of vaporization
- Greatest density at 4C
- Solvent
- Cohesion, surface tension
Water Moves Down Concentration Gradients
Water in Air
Different ways to say the same thing...
- Relative Humidity
- Vapor Pressure Deficit
- Atmospheric Water Potential
Water Regulation
Use water budget to understand gains and losses
Plants: Wip = Wr + Wa – Wt – Ws
Animals: Wia = Wd + Wf + Wa – We - Ws
Evaporative Water Loss - Animals
Evapo-transpiration from soils & plants
- Cohesion-Tension Theory of Water Transport
- Cohesion=
- Tension=
- Potential energy =
- Water potential: Measured in Mpascals. Represented as Ψ.
- Ψ of pure water = 0
Evapotranspiration
Water moves down gradient of high to low potential
Ψplant = Ψsolutes + Ψmatric + Ψpressure
Less potential than pure water
Matric forces (cohesion) decrease water potential
Evaporation – negative pressure (tension)
Water Regulation on Land Animals
Wia = Wd + Wf + Wa – We - Ws
What strategies can animals use?
Water Acquisition by Animals
Most terrestrial animals satisfy their water needs via eating and drinking.
Metabolic water refers to the water released during cellular respiration.
Example: Kangaroo Rat, Tenebrinonid Beetles, Scorpions
Water Regulation by Plants
Wip = Wr + Wa – Wt – Ws
What strategies are available to plants?
Plant Strategies
Change biomass allocation
Increase root mass under dry conditions
Plant Strategies
Decrease leaf area
Ocotillo lose leaves under dry conditions
Wilting effectively reduces leaf area
Water relations are often coupled to temperature regulation
Water in Water
Osmoregulation
Isosmotic Organisms
Hypoosmotic organisms
Hyperosmotic Organisms
Water Budgets for Aquatic Organisms
Wi = Wd – Ws + Wo
What are their strategies?
Example: Sharks, Marine Fishes, Freshwater fish
