plants and water
DESCRIPTION
Plants and Water. Plant Cells and Water Whole Plant Water Relations. Physical and chemical properties of water. Water Compared with other liquids. Water is the universal solvent. Capillary action. Hydrophobic Hydrophilic. What is cohesion? What is adhesion? How high in the tube?. - PowerPoint PPT PresentationTRANSCRIPT
Plants and Water
Plant Cells and Water
Whole Plant Water Relations
Physical and chemical properties of water
MoleculeMass
(Da)
Specific Heat (J/g/C)
Heat of vaporization (J/g)
Melting Point (C)
Boiling Point (C)
Water 18 4.2 2452 0 100
Ammonia 17 5.0 1234 -77 -33
Methanol 32 2.6 1226 -94 65
Ethanol 46 2.4 878 -117 78
Water Compared with other liquids
Water is the universal solvent
• Hydrophobic• Hydrophilic
Capillary action
What is cohesion?What is adhesion?How high in the tube?
Water Movement
• Bulk Flow• Diffusion
Diffusion
Fick’s Law of Diffusion:
Driving force behind diffusion is the difference in concentration
Osmosis – a special case of diffusion
•Why does water move?•Why is the energy of pure water (or with lesser solute concentration) greater than water with a higher concentration of dissolved solutes?•Chemical potential = free energy/mole: as solutes ↑ chemical potential ↓
•Chemical potential of water = solute potential (ψs)
Solute gradients are needed to move water in and out of plant roots
NO-3-----------------------------------
H2O ---------------------------------
Ion pumps bring in nitrate against concentration gradient
Chemical potential of water is also affected by pressure
Water will rise in tube as a result of solute differences: the forcenecessary to prevent this rise is called osmotic pressure: thegreater the difference, the greater the osmotic pressureneeded Osmotic pressure of an isolated solution is called osmotic orpressure potential (ψp)
Osmotic pressure helps to explain why only a certain amount of water moves into a plant cell
Water ------------------------
<----------------Water
Why does water flow into these yeast cells?Why does this influx eventually stop?
Water Potential
Water potential = solute potential + pressure potential
Ψ water = ψs + ψp
Units = mPa (megaPascals) = pressure
Ψs = 0 or – (pure water = 0)
Ψp = 0 or +
Net difference determines direction of water movement
Measurement of water potential and water status
-Thermocouple psychrometer - water potential (Ψwater) of leaves, soil orsolute potential (Ψs) of leaves
-Scholander Pressure Bomb – pressure potential (Ψp) in xylem (stems)
-Relative Water Content (RWC) = water status of all plant tissues
RWC = (FW – DW)/(TW – DW)
FW = fresh weightDW = dry weightTW = turgid weight
-Tissue-volume measurements – water potential of tubers, roots
Movement of water into, through and out of plants is governed by a water potential
gradient
Soil ------------------ Roots
Atmosphere ←---------Leaf
↑↑
↑
↑
↑
Where will the water potential be the highest (closest to Ψ=0)?
Transpiration: Facts & Figures
1 corn plant: 200 liters/growing season
Maple tree: 225 liters/hour
Appalachian Forest: 1/3 annual precipitation absorbed by plants and returned as rainfall
Transpiration is driven by a water potential gradient
Mesophyll Cells (moist cell walls)--------
Substomatal Cavity-----------
AtmosphereStoma
Transpiration is about water vaporization
Vapor pressure = “e”
As solutes ↑ e ↓
As temperature ↑ e ↑
Transpiration ≈ eleaf-eair
Transpiration ≈ eleaf-eair/rair +rleaf
Relationship between Ψ and relative humidity
RH = actual water content of air/maximum amount of water that can be held at that temperature
As RH ↑ Ψ ↑
% Ψ100 095 -6.990 -14.250 -93.520 -217.1
As the air dries out, the water potential gradient between the leaf (in the substomatal cavity) and air increases increasing transpiration rate
Transpiration can also continue at 100% RH if the leaf temperature is higher than the air temperature (see previous slide)
Water Transport in the Plant
Xylem – “plumbing” consisting of trachieds and vessel elements
Cross sectionLongitudinal section
Evidence for Tension in Stems
Pressure “bomb” demonstrates tension in cut stems
Where would the tension in the water column be the highest?
Root Systems are Extensive
Prairie grasses – 1.5 m depth
Corn plant – 6 m depth
Single rye plant – 623 km length 639 m2 total area
Most water uptake occurs 0.5 cmFrom tip of root through root hairs
Water Uptake From Soil
Well-watered soil:Ψ ≈ 0
If Ψ drops to -1.5 MPaplants will wilt
Clay soils high waterretention, low O2
Sandy soils low waterretention, high O2