Roots and Mineral Nutrition:

Chapter 34

Root Function

1. Anchor plant in ground2. Absorb water and dissolved nutrients3. Storage of surplus sugars

Root Systems• Taproot:

– One main root– Lateral roots branch out of taproot– Characteristic of dicots and gymnosperms– Adapted to absorb water deep underground

• Fibrous root system:– 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 dicotroots• 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 dicotroots…• 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 specializedroots• 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:– 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