Roots and Mineral Nutrition:
Chapter 34
Root Function
1. Anchor plant in ground
2. Absorb water and dissolved nutrients
3. Storage of surplus sugars
Root Systems
• Taproot:
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One main root
Lateral roots branch out of taproot
Characteristic of dicots and gymnosperms
Adapted to absorb water deep underground
• Fibrous root system:
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Many roots of similar size
Main roots branch off of stem
Characteristic of monocots
Adapted to absorb water over a large area of shallow
soil
General Structure
• Root cap
– Covers and protects the apical meristem
– Cells are worn off by the soil and replaced by the
meristem
– Secretes ‘slime’ to allow root to move through soil
easier
– Helps to orient the root to grow downward
• Root hairs
– Extensions of epidermal cells
– Increase the absorptive surface area of the cells
Herbaceous dicot
roots
• Epidermis – no cuticle to allow for water
absorption
• Cortex – primarily functions as storage
– Lots of intercellular spaces to allow for gas exchange
needed for cellular respiration
• Endodermis – regulates the movement of
nutrients
– Casparian strip – the endodermis cells have a
specialized waterproofing that makes the water move
into the cells
Herbaceous dicot
roots…
• Vascular cylinder – in the center of the root
– Contains an X shaped area of xylem
– Phloem cells are in between this
• Dissolved nutrients are brought into the
root from the soil by active transport
– Root cells require sugars for the energy to do
this
Monocot roots
• Lots of variation
• Xylem does NOT form a solid cylinder
Woody plant roots
• Secondary growth at lateral meristems
– Vascular cambium
– Cork cambium
• Roots can have both wood and bark
• Roots can also have annual rings, just like
stems
Some specialized
roots
• Prop roots – adventitious roots that
develop from stems and help hold up the
plant; more common in monocots
• Buttress roots – swollen trunks bases
found in tropical trees with shallow roots
• Pneumatophores – ‘knees’ in flooded
areas to allow roots to obtain air
• Aerial roots – on epiphytes to anchor the
plant to another plant
Soil
• Parent material is usually rock
• Rock is broken down by weathering
– Mechanical weathering
• Plant roots, water action
– Chemical weathering
• Acid rain
• Components:
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Inorganic material
Organic matter
Water
Air
Soil…
• Texture is important
– Size of particles – sand, silt, clay
• Organic matter
– Humus – partially decay organic material
• Pore spaces
– Allow room for water and air
• pH
– Different plants prefer different pH levels
• Nutrients
– Micronutrients (needed in small amounts)
– Macronutrients (needed in larger amounts)
Soil can be damaged
• Acid precipitation
– Leaches away certain mineral nutrients
• Soil erosion
– Water, wind, ice wear away or remove soil
– More likely when plant roots are not in place
• Salinization
– Accumulation of salts in the soil