Ch. 3 Water Relations & Energy Dynamics

Water Potential Water in plants/soil has solutes: NEGATIVE What tissue in plant carries water?

Water transport Xylem: water conducting tissue What % water remains in plant?

Water transport Xylem: water conducting tissue Water in plant? <5%! How water move? ?

Water transport Transpiration: evaporation from lvs. Moves by pull (under tension)

Water transport Ex:

Water potential tour..... Soil to air pathway Fig. 3.2a

Soil water g = + total m p s What determines psi soil?

Soil water What determines psi soil? Gravitational: unimportant = + total m p s What determines psi soil? Gravitational: unimportant Pressure: unimportant

Soil water solute potential: important _______ g = + total m p s Dauphin Island: salt marsh

Soil water g = + total m p s matric potential: #1

Soil water Matric potential determined by texture Soil pore space: air spaces Clay most Sand least

Soil water Water added, pores fill 1 ft soil ea. type Water added, pores fill Soil saturated: Saturation water content Note sand<clay loam

Soil water 1.7 Gravity removes water: Gravitational water Most sand 3

Soil water 1.7 Allow gravity drain water: 3 Most sand Gravitational water Most sand Now soil @ field capacity: fully charged 3

Soil water Plant use: becomes stressed Soil @ permanent wilting point (PWP): plant psi = ____ Mesophytes (“normal” plants), PWP @ -1.5 MPa

Soil water 2 1 Field Capacity - PWP: available water capacity Greatest loam, less clay, least sandy 1.8 2 1

Soil water Unavailable water: hold too tight Greatest clay, least sand

Soil water Recap. Coarse: little water held, delivers little. Hold loose! Fine: lots held, delivers good amt. but retains lots @ PWP. Hold tight! Loam (& silt loam): hold Fig. 4.9b

Soil water Texture impacts infiltration: ability penetrate

Soil water Texture impacts infiltration: ability penetrate Coarse soil: hi infiltration. Structure important Texture effect Structure effect

Soil water Vertical movement : not always “a downer!” Hydraulic lift: movement water by roots from deep to shallow Soil dry: Lo psi water Soil moist: Hi psi

Soil water Ex, Acer saccharum (sugar maple) NY Understory herbs: larger < 2 m from tree

Dew in soil Soil distillation: movement up Deserts hot cold med. Day Nite Water vapor cold warm Relative temperatures in day and nite

Water potential tour..... Examine soil to air pathway of water Fig. 3.2a

Water in the plant: roots Root: little cuticle (wax layer) on epidermis

Water in the plant: roots Root must be near water. Why? Hydraulic conductivity: ability water move _____ Conductivity decreases as soil _____ How root contact more? Wet Dry

Water in the plant: roots How root contact more? 1) Root hairs

Water in the plant: roots How root contact more? 2) Grow! Root biomass/productivity hi! Shortgrass prairie root biomass = ______ total biomass! CO prairie

Water in the plant: roots How get to xylem?

Water in the plant: roots 2 ways: apoplastic pathway: along walls (most water: 90%) symplastic pathway: thru plasmodesmata (cell membrane connections) Problem: Apoplastic pathway

Water in the plant: roots Casparian strips (wax) in endodermis stop apoplastic pathway Force

Water in the plant: stem xylem