Soil, Plant Nutrition
& Roots Chapters 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
clay
•  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
sand
silt
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
•
A horizon
•
B horizon
•
C horizon
• organic, few cm thick
• humus – organic decay products
• contained within A horizon in some
classifications
• topsoil, 10-30cm thick
• greatest physical, chemical, and
biological activity
• 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
• 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
Soil erosion
20 tons/acre
40,000lbs/acre
Some farms in Iowa have
no topsoil remaining
(Mary Skopec, Iowa DNR)
June 2008 Rainfall
http://www.srh.noaa.gov
Cedar Rapids Iowa
http://www.treehugger.com
Essential Elements for Plants
Required for normal growth & reproduction
No other element can replace
Direct or indirect action in plant metabolism
Macronutrients (9)
• required in greater amounts
• What do these macronutrients do?
C, H, O - basic organic constituents
N, 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
Chlorosis
Magnesium deficiency
Iron deficiency
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 water
Copper: associated with
enzymes involved in
redox reactions
Iron: component of
enzymes involved in the
transfer of electrons
Etc…..
Plant Growth Medium for fern
gametophytes (C-fern)
• Macronutrients
NH4NO3, KH2PO4, MgSO4, CaCl2
• Micronutrients
MnSO4, 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 water
Cortex:
• just interior to epidermis, waxy
protective layer
• parenchyma tissue: most of
cortex, often contains starch
• endodermis: tightly packed
cells with casparian strip
Dicot Root
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
Endodermis change
through aging
Dicot - young stele
Dicot - mid-aged stele
Dicot - old stele
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
Unique Properties of Water
due to molecular structure
a polar molecule - excellent solvent
hydrogen bonding
between water molecules
cohesion
tensile strength
between water and other molecules
adhesion
capillarity - from cohesion
and adhesion
O
H
+
H
+
Leaf
Anatomy
H2 O
•85-95% of plants is water
•95% of H20 taken up by
plant transpired back into
atmosphere
Cohesion-tension theory
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
vessel elements
tracheid
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