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: –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 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: –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