Download Crop Roots - Missouri State University

9/15/2011
Roots
Essential for Plant Growth
• Root System & Soil
Environment Have
Great Effect on Plant
Life & Productivity
http://www.biologyreference.com/Re-Se/Roots.html
Radicle
• First Root from a Seed
Is the Radicle
– Develops into the
Primary Root
Fibrous Root System
• Primary Root Does not
Develop much
• Fibrous Systems Are
more thoroughly
Distributed & Absorb
more Water & Nutrients
within the Root Zone
than Tap Root Systems
• Allows Greater Contact
within Rooting Zone
Taproots
• If Primary Root Continues to Grow & Develop,
Plant Has a Taproot System
– Can Grow Deeply into Soil
– Some Harvested for Food
Secondary Roots
• Branch from 1° Roots or
Arise from Plant Stem
Tissue
• May Be Roots from
Underground
– Common in Grass Crops
1
9/15/2011
And More
• Tertiary Roots
– Arise from 2° Roots
• Quaternary Roots
– Arise from Tertiary
Roots
• Quinary Roots
Adventitious Roots
• Arise from Stem or other
non-Root Meristems
• May Be 2° Roots
• Adventitious Stem Roots
usually Originate at a
Node
– Arise from Quaternary
Roots
Photo by Jared Deckard, Natural Resource Specialist, Pomme de Terre Lake
Brace &
Prop Roots
• Types of
Adventitious
Roots
Monocot
vs. Dicot
• Fibrous Root System
• Root System
Develops from
Adventitious Roots
• Scattered Vascular
System around
Perimeter of Stele
• Taproot System
• 1° Root Persists,
Produces Branches &
Continues as main
Root of Plant
• Vascular System in a
Cross in the Center
of the Stele
Root Structure
• Roots Grow from Meristems Near the Tip of
Roots
Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
(www.sinauer.com) & WH Freeman (www.whfreeman.com), used with permission.
http://www.lima.ohio-state.edu/academics/biology/archive/roots.html
2
9/15/2011
• Root Cap Is at Tip
• Being Regenerated by the
Root Tip It Protects
• Above Root Cap Is an
Apical (Tip) Meristem
where Cells Divide fairly
Rapidly
– Cells Deposited to the
Sides, Leaving Thin GelLike Coating on Soil
Particles
– High Energy Process
– Cells Actively Divide to
Produce more Cells
– Dividing Cells Are Protected
by the Root Cap
– Some Cells Are Used in the
Root Cap
– Some Cells Become Root
Tissues
• 20-30% of Photosynthetic
Energy!
http://www.lima.ohio-state.edu/academics/biology/images/onioncap.jpg
http://www.botany.hawaii.edu/faculty/webb/BOT410/Roots/ApicalMeristems.htm
• Above Meristem Is
Zone of Elongation
http://www.lima.ohio-state.edu/academics/biology/images/onioncap.jpg
• Root Hairs Develop from
Epidermal Cells
• Once Epidermal Cells
Cease Elongation, they
Produce Tiny Extensions
into Soil Area
• Up to 200 Root
Hairs/mm2 of Root
– 1 to 10mm Long
– Newly-Formed Cells
Take on Water &
Elongate to Mature Size
– Primary Function Is to
Increase Root Length
• Above Elongation Zone
Is Differentiation Zone
or Zone of Maturation
http://www.lima.ohio-state.edu/academics/biology/images/zeahair.jpg
• Root Hairs Greatly
Increase the Surface Area
of a Root
• 1-Month-Old Rye Plant =
14 Billion Root Hairs with
Surface Area of ~4,300 ft2
• Reach Full Size in a few
Hours
• Essential for Rapid
Absorption of Water &
Nutrients
• In Typical Soil, Water mostly
Is Thin Film Surrounding
every Microscopic Soil Particle
• Root Hairs Absorb this Water
• Water Diffuses Molecule by
Molecule
– Through the Root Hair's Cell Membrane
– Toward the Main Roots
– Then Enters Xylem
http://www.backyardnature.net/roots.htm
http://www.rsbs.anu.edu.au/profiles/Brian_Gunning/Web%20PCB/Ch%2002%20Intr
oduction%20to%20Plant%20Cells/Topic%203%20AS&V%20Cells/02%2003%2001.htm
Bacterial cells, each less than one-thousandth of a millimetre long, are shown stained
green on a soil particle. http://www.grdc.com.au/growers/gc/gc48/soil2.htm
3
9/15/2011
Root Anatomy
• Cross-Section in
Maturation
Zone Shows
Cells Have
Differentiated
• Outermost Cells Called Epidermis
– Single Layer of Cells on the Root Surface
– Absorb Water & Nutrients
• Next Is the Cortex
– Loosely Packed Cells
– Can Be several Layers
Thick
– Conduct Water &
Nutrients to Vascular
Bundle
– Stores Food & Nutrients for
the Root
– Specialized
Functions
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
• Next Is Endodermis
– Single Layer of Cells that Separates the Vascular
Bundle from Cortex
– Regulates Types of Absorbed Nutrients Allowed
to Enter Vascular Cylinder
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
The Pathway of Water in Roots
Symplast—Living Portion of Cells
Apoplast—Spaces between Cells
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
Vascular Cylinder Tissues
• Pericycle
– Separates the Xylem & Phloem
– Layer of Meristematic Cells where
Branch Roots Develop
• Stele
– The Root Center Tissues
including the Pericycle,
Phloem & Xylem
– Stele Diameter Is Larger
in Monocots than in Dicots
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
Video
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html
• Vascular System
– Very Center of Root
– Made up of Phloem &
Xylem
– Monocots
• Xylem & Phloem Are
Separate
• Form Ring around the
Center of the Root
– Dicots
• Phloem Surrounds &
Eventually Is Outside
the Xylem
• Xylem will Be in the
Very Center of the Root
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
4
9/15/2011
• Pith
– Found in the Center of a
Monocot
• Cambium
– Cells can Divide to Produce
2° Growth in Perennial Plants
– Found only in Dicots
– Not Important in Annual Plant
Plants
Root Functions
• Water & Nutrient Uptake
– Most Uptake Occurs near Root Tip, through Root
Hairs
– 80% Absorption Occurs in Top 18 Inches of Soil
– Plant Management Practices will Affect Uptake
Zones
– Region of Greatest Root Volume not always Area
of Greatest Water/Nutrient Uptake
• Depends on the Plant Species’ Rooting Pattern
– Root Does not ‘Grow toward’ Water & Nutrients
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm
• Water & Nutrient
Transport
– Once Water Enters
Root, Moves through
Cortex to Endodermis,
through Endodermis to Pericycle & then to
Xylem
– From Xylem, Moves Rapidly upward in Plant to
Stems & Leaves, Carrying Nutrients with It
– Injury to Roots can Reduce/Prevent this Flow,
Hurting Above-Ground portions of Plant
• Support & Anchoring
– Roots Provide Support for
Upright Stem Portions of
Plants & Help Hold the
Plant in the Soil against
Wind & Rain
• Storage
– Most of Carbohydrates Transported to Roots Are
Used for Active Root Growth, but some Crops
will Store in their Roots Carbohydrates for later
Growth/Regrowth
– Stored Carbohydrates Allow Plants to Produce
New Shoot Growth
• Symbiotic Relationships
with Microbes
Super roots
with
Frankia
Frankia, nitrogen-fixing bacteria that form
associations with some plants
http://www.laspilitas.com/advanced/advroots.htm
5
9/15/2011
Rhizobium
•
•
•
•
•
•
Azospirillum
Nitrogen-Fixing Species of Bacteria
Symbiotic Relationship with Legumes
N-Fixing Enzyme Nitrogenase
Converts Atmospheric N into Ammonia
Gives N to Plant
Plant Gives Food to Bacteria
• Nitrogen-Fixing Genus
of Bacteria in many
Grasses including Grain
Crops
(Photo: a cross-section of a root
nodule--a tiny lump in which
Rhizobium bacteria would do their
clean-up work. Each nodule is
occupied by about a billion of the
rod-shaped microbes.)
http://www.parksideorchids.com/images/Supplies/phyton.jpg
http://www.ars.usda.gov/is/kids/environment/story3/rhizobium.htm
http://www.patentlens.net/daisy/bioforge_bioindicators/3201/version/default/part/ImageData/data/Rice%20Azospirillum.jpg
Frankia
•
Many secondary pioneer species are associated with Frankia. In California these include; Datisca glomerata,
Frankia
fixes nitrogen from the air & produces
secondary chemicals that feed friendly
associated free living bacteria & fungi. The
plant-mycorrhiza-frankia Tripartite relationship
often becomes a multi-layered community of
associated free living & plant related organisms
that protect & support each other. The relationships are
Ceanothus, Alnus, Cercocarpus, Myrica, Purshia, Cowania, Chamaebatia, & Shepardia species.
• Nitrogen
• Defense
• Increase # Root
Hairs
• Mineral & Water
Uptake
• Transport of
Hormones through
Roots
•
http://www.laspilitas.com/advanced/pictures/ceanothus_frankia.jpg
complex with only the most obvious presently recognized. The different associated organisms are responsible
for root hormones, pathogen control, nematode control, root exploration, plant community resource sharing,
mineral mining, water retention & many more. The plants become increasingly instable as these organisms are
replaced with non-supportive or parasitic pathogens or weedy organisms, including weedy plants. These
problems can be very difficult to diagnose as everything is interrelated, & human intervention can often make
the problem worse.
Ceanothus get branded as short lived because the mychorriza-frankia & associates are not properly allowed to
develop & grow. Ceanothus can live for a hundred or more years in the wild, & commonly for twenty to fifty
years in a garden, if the appropriate Ceanothi are planted & left alone. Watering & fertilizing the plants more
than required fools the plant into thinking that they do not need friends & can do all things themselves. The
plants, if they do not die that day from pathogens, grow fast & robust, then die of pathogens.
Frankia on the roots of Shepherdia argetea. http://www.laspilitas.com/classes/Frankia.html
• Propagation (Creeping)
•Mycorrhizae
•
CREEPING OR HORIZONTAL ROOTS - Are lateral branch
roots. These are true roots, arising from a vertical root,
usually an elongated taproot, & lack nodes & leaves.
Adventitious buds may form at any
point along these roots & produce new
plants by sending up leafy shoots.
Creeping roots can penetrate to a much greater depth than creeping
below
cultivating depths, & produce new deeper,
horizontal branches when the upper ones
are destroyed. Also, the horizontal roots can grow
straight downward at any point, thus establishing
very deep, extensive root systems, which are virtually
impossible to eradicate.
stems. Most of the taproot may extend
http://www-mykopat.slu.se/
Newwebsite/mycorrhiza/kantarellfiler
/bilder/C.GIF
•
http://ic.ucsc.edu/~wxcheng/envs161/Lecture8/
http://www.uapress.ari
zona.edu/onlinebks/we
eds/general.htm
Some of the worst prohibited noxious weeds reproduce by creeping
roots, as Russian knapweed (Centaurea repens), hoary cress (Cardaria
draba), field bindweed (Convolvulus arvensis), Canada thistle
(Cirsium arvense), silverleaf nightshade (Solanum elaeagnifolium), &
http://www.ca.uky.edu/agc/pubs/pat/pat1-6/10.jpg
blueweed (Helianthus ciliaris).
6
9/15/2011
Extent of Root Growth
• Root Dry Weight Is usually 1/3 to ¼ of Total
Plant Dry Weight (may be more)
• Root Surface Area Is at Least 20 to 30 Times
Greater than Leaf & Stem Surface Area
• Knowing Extent of Root System Aids in
Water & Fertilizer Placement
• Geotropism
Factors Affecting Root Growth
• Tropism
– When Growth
Responds to
Environmental
Stimuli
• Thermotropism
– Roots Grow Downward, with
Gravity (Positive Geotropism)
– Due to Different Amounts of
Plant Hormones Called Auxins
in different Parts of a Cell
– Upper Side of Horizontal Root
Grows more, Causing Root Tip
to Turn Downward
• Phototropism
– Roots Grow Better in
certain
Temperatures
• Hydrotropism
– Roots Grow more
Rapidly in Favorable
Moisture
Environment
http://www.kalamazoomi.com/photo/Okinawa/banyantree-a-roots.JPG
– Roots Grow away from Light
(Negative Phototropism)
http://www.bioschool.co.uk/bioschool.co.uk/images/pages/geotropism_JPG.htm
http://jp.encarta.msn.com/media_461516459_761568511_-1_1/content.html
• Genetics
http://www.4am.org/photos/kools/Tree%20Roots.jpg
• Soil Fertility & pH
– Determines Basic Structure
of Root Systems
– Can Be Enhanced by Plant
Breeding & Selection & by
Genetic Engineering
– Roots Grow Better,
more Branching &
Spread, in a Fertile Soil
Compared to less
Fertile Soil
– Roots Do not Grow
toward Nutrients
– Excess Nutrients in Soil
– pH beyond Optimum
Ranges Result in
Reduced Root Growth
• Soil Moisture Level
• Soil Physical Condition
– Roots can Grow only where
Root Pressure Is Greater
than the Physical Pressures
Exerted against the Roots
Tillage pans. http://ianrpubs.unl.edu/soil/g831.htm
www.abc.net.au/landline/ stories/s132488.htm
groups.ucanr.org/ kernag/Salinity/
7
9/15/2011
• Soil Aeration
• Soil Temperatures in
Root Zone
– Optimum usually Cooler than
for above-Ground Plant Portions
– Less Temp Fluctuation than
Above Ground
– Temperatures above Optimum?
– Temperatures below the Optimum?
– Temp Affects Root Thickness & Branching
– Effects of Moisture?
– Effects of Soil Color?
– Effects of Plant Canopy or Other Covering?
– 20-25% of Soil Pore Space should Be Air
– Oxygen Needed for Respiration
– Reduced Growth if Soil Aeration < 10%
• Except Hydrophytes
– Anaerobic Microorganisms may Produce Toxins
– CO2 in Soil Air often Higher than in AboveGround Air
www.martiansoil.com/ archives/week_2004_03_14.php
Specialized Roots &
Vegetative Propagation
• Creeping Roots
– Dicots
– Roots Initiate
Adventitious Shoots
– May Grow Deeply
– New Shoots Independent
of Parent Plant
– Killing Shoots Encourages
Formation of New Shoots
ipcm.wisc.edu/uw_weeds/
infosys.ars.usda.gov/
images/CanadaThistle03.jpg
Weeds/Bindweed/sld006.htm
http://www.btny.purdue.edu/Pubs/WS/CanadaThistle/roots.jpg
http://ianrpubs.unl.edu/weeds/graphics/spurge6a.jpg
• Tuberous Roots
– Abruptly Thickened Roots
– Appear to Be Tap Roots, but often Are Types of
2° or Adventitious Roots
8