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Roots
• Anchorage
• Storage
• Absorption
• Conduction
Root Systems: Definitions
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Taproot system: A central, downward-growing, dominant root (the
“taproot”), with numerous, highly branched lateral roots permeating the
surrounding soil. The tap root itself develops from the radicle (embryonic
root).
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Fibrous root system: Numerous, slender, roots of roughly equal size.to
form a mass of fine roots. No dominant, central root; radicle ceases
development . Develops initially from adventitious roots that emerge
•
Adventitious = originating from an “unusual” source/location .
– Adventitious roots are roots that originate from stems or leaves instead of
developing from the radicle or preexisting root.
– Adventitious buds = buds that form on the roots or stem internodes of some
plants, instead of the “usual” axillary or terminal locations on the stem.
Taproot Systems
• Taproot and downward-growing laterals can
penetrate deep into soil (~4 m, up to ~68 m)
• Tap into deep water sources.
• Deep=penetrating taproots tend occur in
arid/desert habitats.
• Majority of actively absorbing and growing
roots are within 2 feet of soil surface.
• “Feeder roots”
• Absorb nutrients from decomposing organic
matter, surface and rain water.
Taproot Systems
Fibrous Root Systems
Adventitious roots in corn
Develop from the lower nodes of the stem.
Epidemal Root Hairs
• The epidermis of roots is specialized for
absorption of water and minerals.
• Root hairs
– outgrowths from epidermal cells
– as a root grows, the root hairs penetrate the
surrounding volume of soil (
Corn Root Tip
Dicot root
Monocot Root
Casparian Strip
Specialized Roots
• Storage roots: Food reserves
• Aerial roots: adventitious roots, originate and function (at least
partly) aboveground.
– Pneumatophores: aid gas exchange
– Prop and Buttress roots: structural support of trunks, stems, branches
– Photosynthetic & water storing roots: epiphytic orchids
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Contractile roots:
Climbing roots:
Clonal reproduction:
Haustoria: parasitic feeding structures
Mycorrhizae: mutualism with fungi in the soil
Nitrogen-Fixing nodules: mutualism with Nitrogen-fixing bacteria
Symbioses (Symbiotic relationships)
Interaction between 2 organisms (plant-plant, plant-microbe, plant-fungus, etc.)
Commensalism: one benefits, the other unaffected
Parasitism: One (the parasite) benefits, the other
(the host) is “harmed” in some way.
Mutualism: Mutually beneficial interaction
•These interactions typically involve
modified/specialized root structures.
Epiphytes: Commensal Plants
• Most common in relatively moist/humid environments, with
dense vegetation/tree canopy that limits light penetration.
• By living on trees, epiphytes can receive more sunlight.
• Tree surface is actually an arid environment.
• Epiphyte roots often have “drought adaptive”
modifications: e.g. velamen in orchids (water storage)
• Some epiphytes lack leaves (=pathways for water loss!)
• Instead: aerial roots adapted for photosynthesis
Mycorrhizae: plant-fungus mutualism
Endomyccorhizae
Ectomyccorhizae
Haustoria