Soil, Plant Nutrition & RootsChapters 29, 30,

24

Exam 1 Avg = 86.4%

Soils and Plant Nutrition• Plants require nutrients from soil• In eastern US, 200 yr to form 2 cm

topsoil (even slower in western where arid)

• What is soil? • A mixture of:

• Mineral particles (sand, silt, clay)• Decomposing organic matter (humus)• Air• Water• Living Organisms humus

Mineral Particles• Sand 0.05-2.0 mm• Silt 0.002-0.05 mm• Clay < 0.002 mm• Clay soils

• soil water holding capacity, but all water not available for plants

• infiltration rates so runoff• Loamy soils

• even mixture of particle sizes

• best for agricultural

siltsand

clay

Many soils in southeastern Nebraska were formed in parent materials deposited by the glaciers, usually referred to as glacial drift, glacial till or glacial outwash.

Much of the parent material deposited in ancient times has been covered by windblown material. The windblown silty material is called loess. It covers most of Nebraska to varying depths, except in the Sandhills and western portions of the Panhandle.

Where does soil come from?

• Weathering of parent material (bedrock)

• Soil horizons• O horizon

• organic, few cm thick• humus – organic decay products• contained within A horizon in

some classifications• A horizon

• topsoil, 10-30cm thick• greatest physical, chemical, and

biological activity• B horizon

• subsoil, larger particles, 30-60cm

• leaching from A horizon by water percolation

• iron oxide, clay particles, little organic material

• mixed with A horizon when plowed

• C horizon• soil base• partially weathered parent

material, 90-120 cm

Soil Forming Factors• Parent material• Climate• Living organisms• Topography• Time

Extent of North American glaciation

2008 Iowa Floods

June 2008 Rainfallhttp://www.srh.noaa.gov

Cedar Rapids Iowahttp://www.treehugger.com

Soil erosion20 tons/acre40,000lbs/acreSome farms in Iowa have no topsoil remaining(Mary Skopec, Iowa DNR)

Essential Elements for Plants

Macronutrients (9)• required in greater amounts• What do these macronutrients do?

C, H, O - basic organic constituentsN, K, Ca, P - oh my gosh, some very essential

organics: amino acids, nucleotides, ATP, NADPH, cell wall, regulatory, osmoregulation

Mg, S - chlorophyll, electron transport chain, amino acids

chlorophyll

Required for normal growth & reproductionNo other element can replaceDirect or indirect action in plant metabolism

Magnesium deficiency Iron deficiency

Chlorosis

amine group

Essential Elements (continued)

Micronutrients (8)• required in lesser quantities

Fe, Mn, Cu, Zn, B, Mo, Cl, Ni• What do these micronutrients do?

essential for enzyme function, organ and organelle function, photosynthesis

Manganese: involved in photosynthetic reaction in which oxygen is produced from waterCopper: associated with enzymes involved in redox reactionsIron: component of enzymes involved in the transfer of electronsEtc…..

Plant Growth Medium for fern gametophytes (C-fern)

• MacronutrientsNH4NO3, KH2PO4, MgSO4, CaCl2

• MicronutrientsMnSO4, CuSO4, ZnSO4, H3BO3, (NH4)6Mo7O24, FeSO4

Nickel

Roots

• Roots are 50-80% of plant biomass in prairie

• Plants “forage” for dilute nutrients in environment

Root functions

• Anchor plant into ground• Storage of energy reserves• Absorption of water and dissolved

minerals from soil• Conduction of water and dissolved

nutrients to shoot

Taproot System

• First root formed is the radicle

• In dicots, radicle grows into taproot

• Branch roots grow from taproot

Fibrous Root System

• Mostly in monocots• Extensive mass of

similarly sized roots• Radicle short-lived,

replaced by adventitious root system• adventitious means

not belonging to• roots growing from

stem

Root Structure• Root cap

• protection from desiccation, lubrication, water and nutrient absorption

• Zone of Cellular Division • densely packed cells

undergoing mitosis• Zone of Elongation

• growing cells• Zone of Maturation

• differentiating cells

Epidermis: • one cell thick, usually no

cuticle; absorbs waterCortex:

• just interior to epidermis, waxy protective layer

• parenchyma tissue: most of cortex, often contains starch

• endodermis: tightly packed cells with casparian strip

Stele: • tissue inside cortex• pericycle: interior to

endodermis - a meristem for branch roots

• vascular bundle: xylem as a cross with phloem in armpits

Monocot Root

Dicot Root

Dicot - young stele

Dicot - mid-aged stele

Dicot - old stele

Endodermis change through aging

Casparian Strip

• integral band-like portion of primary wall and middle lamella in endodermal cells

• lignin and suberin “valve”

• regulates water because water • must move

symplastically through the endodermal cells

• through plasmdesmata between cells

• rather than apoplastically

• through intercellular spaces

Casparian Strip

Root hairs

due to molecular structure

OH H

-

++

a polar molecule - excellent solvent

adhesion

hydrogen bondingbetween water molecules

between water and other molecules

cohesion

O

HH

-

++

OH

H

-

++

OH

H

-

++

tensile strength

capillarity - from cohesion and adhesion

Unique Properties of Water

Leaf Anatomy

H2O

• 85-95% of plants is water

• 95% of H20 taken up by plant transpired back into atmosphere

cohesion and adhesion cause water to rise in plants

as water evaporates from the leaf surface,

a column of water

is pulled upward from the soil water

Cohesion-tension theory

vessel elementstracheid

Size comparison of xylem elements

Note distribution of pits in walls of all xylem elements (tracheids and vessels)

pits

perforation plate (end walls)

Problems with water movement

• air bubbles• cavitation

• water column rupture

• embolism• filling with air or

water vapor• solution

• move water around embolism

Is there a limit to water column?

• How tall are the tallest trees?

• What are the tallest trees?

Tallest Tree• Coast Redwood

• Sequoia sempervirens

• Redwood National Park California

• Height = 116m (379.1 feet) named Hyperion; Steve Sillett, Humboldt State U.

• Estimated Age = 2,000+ yrs

Save the Redwoods League

Giant Redwood -Sequoiadendron giganteum

• Top: lithograph showing a party of 32 people dancing on the stump of the Discovery Tree, North Calaveras Grove

• Bottom: 30-foot section of the General Noble Tree, which was displayed at the Columbian Exposition in Chicago in 1893 and later at the Mall in Washington, DC; it was subsequently taken to the US government's Arlington Experiment Farm, where it was "misplaced"

http://en.wikipedia.org/wiki/Image:Giant_sequoia_exhibitionism.jpg

Transpiration and Productivity

• Leaves adapted for photosynthesis• abundant stomata• large number vein endings

• Tradeoff • CO2 in - photosynthesis • H2O out - transpiration

• H2O limits biomass production in most areas

• Evapotranspiration• transpiration & soil

evaporation• problematic in arid areas