Water

1
Water

• Plants are 50-90 water
• More water is absorbed by plants than any other
  compound
• Most crops require about 1 of water/precipitation
  per week

2
Functions

• photosynthesis
• cell enlargement
• seed germination
• transpiration
• transport of nutrients and carbohydrates

3
Physical ChemicalProperties of Water

• 1. high specific heat
• A large energy input is required to raise
  temperature of water.
• Large bodies of water moderate local temperature
  changes.
• 2. polar molecule - universal solvent
• charge distribution
• oxygen negative, H positive

4
Physical ChemicalProperties of Water

• 3. Cation and anions will associate with
  opposite charged portion of water molecule.
• this determines nutrient availability in soil
  solution and uptake transport in plant
• 4. water is necessary for translocation of
  metabolites
• e.g. sugars, hormones

5
Physical ChemicalProperties of Water

• 5. surface tension - hydrogen bonding
• cohesion - water molecules bind to each other
• adhesion - water molecules bind to other
  surfaces
• 6. capillary rise - capillary action
• surface tension greater than gravitational pull,
  water rises
• water evaporation from soil surface

6
Water Uptake Movement in Plants

• Transpiration - loss of water vapor from plant
• drives water and nutrient uptake from soil
• Water moves from a site of high relative humidity
  to lower humidity
• from interior of the leaf to external atmosphere

7
Water Uptake Movement

• Relative humidity
• (amount of water vapor in air/amount air could
  hold at that temperature)
• totally saturated air has 100 relative humidity
• The higher the temperature the more water air can
  hold.
• An increase in temperature can promote increased
  transpiration due to increased gradient.

8
Factors Influencing Water Uptake

• 1. Root system
• water must pass through membranes
• nutrient selection
• resistance to water movement
• xylem - water moves in response to vapor pressure
  gradients

9
Factors Influencing Water Uptake

• 2. Healthy plants can absorb water better
• greater distribution of root system
• greater number of roots

10
Factors Influencing Water Uptake

• 3. Environmental Factors
• wind increases water loss from plant (up to 10
  mph)
• there is increased water uptake if available in
  root environment
• higher light intensity - greater water loss
• photosynthesis
• higher temperature - greater water loss
• vapor pressure gradient

11
Factors Influencing Water Uptake

• 4. Soil Factors
• texture - water holding capacity
• temperature - resistance to water uptake
  influenced by temperature

12
Water Deficits

• reduce photosynthesis
• stomata close - decrease CO2
• reduce yields
• smaller flowers
• lower (older) leaves yellow
• hard growth - lignin development
• decreased winter survival in perennials

13
Excess Water

• Mild
• soft growth
• increased cell size
• long internodes - leggy plants
• Extreme
• no oxygen ---- root death
• root death ---- reduced water uptake
• reduced water uptake ---- water deficit symptoms
  (yellow leaves)

14
Water Management

• p.199-226 examples that will be discussed in
  other classes
• observe irrigation, mist systems in greenhouse
• environmental control - cooling, frost protection
• soil or growing medium