1. Roots and Mineral Nutrition
Chapter 34
Roots and Mineral Nutrition

2. Taproot system has One main root formed from the radicle
Multiple lateral roots extending from the main root

3. Fibrous root system has
Multiple adventitious roots of the same size (developing from the end of the stem)
Multiple lateral roots branching off from the adventitious roots

4. Taproot system
Fibrous root system

5. LM of a lateral root
Lateral roots originate at the pericycle

6. Primary roots have An epidermis Ground tissues Vascular tissues
Cortex and sometimes pith
Vascular tissues
Xylem and phloem

7. Ranunculus root
Cortex comprises the bulk of herbaceous dicot roots; note X-shaped xylem

8. Closeup of the root’s stele

9. Primary roots, cont.
Each root tip is covered by a root cap whose function is to
Protect the delicate root apical meristem
Orient the root so that it grows downward

10. LM of a Quercus sp. root tip showing its root cap
LM of a Quercus sp. root tip showing its root cap. The root apical meristem is protected by the root cap

11. Primary roots, cont. Epidermis protects the root
Root hairs are short-lived extensions of epidermal cells
Increase surface area of root in contact with soil
Aid in absorption of water and dissolved nutrient minerals

12. Root hairs on a radish seedling (length approx. 5 cm)

13. Cortex consists of parenchyma cells that often store starch
Endodermis
Is innermost layer of cortex
Regulates movement of nutrient minerals into root xylem

14. Endodermal cells
Have a Casparian strip around their radial and transverse walls
Strip is impermeable to water and dissolved nutrient minerals.
Have carrier proteins in their plasma membranes
Proteins actively transport nutrient minerals

15. Endodermis and nutrient mineral uptake

16. Root’s stele, or vascular cylinder, consists of
Pericycle
Xylem
Phloem

17. Pericycle gives rise to
Lateral roots
Lateral meristems
Xylem conducts
Water
Dissolved nutrient minerals
Phloem conducts
Dissolved sugar

18. Monocot roots
Often consist of pith surrounded by a ring of alternating bundles of
Xylem
Phloem
Lack a vascular cambium and therefore do not have secondary growth

19. LM of a cross section of a monocot root (Smilax)

20. Herbaceous dicot roots
Xylem forms a solid core in the centre of the root

21. Pathway of water and nutrient mineral ions
Root hair/epidermis
Cortex
Endodermis
Pericycle
Root xylem

22. Water and dissolved nutrient minerals move through epidermis and cortex along
Either the apoplast (along interconnected porous cell walls)
Or the symplast (from one cell’s cytoplasm to the next through plasmodesmata)

23. Pathways of water and dissolved nutrient minerals in the root

24. Roots of gymnosperms and woody dicots develop secondary tissues
Production of these is result of
Activity of two lateral meristems
Vascular cambium
Cork cambium

25. Vascular cambium produces
Secondary xylem (wood)
Secondary phloem (inner bark)
Cork cambium produces
Periderm (outer bark)

26. The tissues in a primary root
At onset of secondary growth, vascular cambium extends out to pericycle, forming continuous, non-circular loop

27. Vascular cambium produces secondary xylem to its inside and secondary phloem to its outside
Ring of vascular cambium gradually becomes circular

28. Prop roots Develop either from branches or from a vertical stem
Grow downwards into the soil to help support certain plants in an upright position

29. Buttress roots Have swollen bases or braces
Support certain tropical rainforest trees that have shallow root systems

30. Pneumatophores Aerial “breathing” roots
May assist in getting oxygen to submerged roots

31. Some epiphytes Have roots modified to photosynthesize Absorb moisture
Or, if parasitic, penetrate host tissues

32. Corms and bulbs Often have contractile roots
These grow into the soil and then contract
Corm or bulb is thereby pulled deeper into the soil

33. Mutualistic relationships between roots and other organisms
Mycorrhizae
Root nodules
Root grafts

34. Mycorrhizae
Mutually beneficial associations between
Roots
Soil fungi

35. LM of ecto- mycorrhizae

36. LM of endo- mycorrhizae

37. Root nodules Swellings that develop on roots of leguminous plants
Swellings house millions of rhizobia (nitrogen-fixing bacteria)

38. Root graft
Natural connection between roots of trees belonging to the same or different species

39. Factors influencing soil formation include
Parent material
Climate
Organisms
Passage of time
Topography

40. Most soils are formed from parent material that is broken into smaller and smaller particles by weathering processes
Climate and organisms work together in weathering rock

41. Important in forming soil and in cycling nutrient materials are organisms such as
Plants
Algae
Fungi
Worms
Insects
Spiders
Bacteria

42. Topography affects soil formation
Steep slopes have little or no soil on them
Moderate slopes often have deep soils

43. Soil is composed of
Inorganic minerals
Organic matter
Air
Water

44. Inorganic minerals provide plants with
Anchorage
Essential nutrient minerals
Organic matter
Increases soil’s water-holding capacity
Releases essential nutrient minerals into the soil as it decomposes

45. Soil air provides oxygen for soil organisms to use during aerobic respiration
Soil water provides water and dissolved nutrient minerals to plants and other organisms

46. Cation exchange
Cations are attracted and reversibly bound to clay particles
Clay particles have predominantly negative charges on their outer surfaces
Roots secrete protons (H+)

47. Cation exchange, cont.
Protons are exchanged for other positively charged mineral ions
Mineral ions are freed into the soil water to be absorbed by roots

48. Cation exchange

49. How acid alters soil chemistry

50. Ten of the nineteen essential elements plants require are macronutrients (required in quantity)
Carbon
Oxygen
Potassium
Magnesium
Sulfur
Hydrogen
Nitrogen
Calcium
Phosphorus
Silicon

51. Nine of the elements are micronutrients (required in trace amounts)
Chlorine
Iron
Boron
Manganese
Sodium
Zinc
Copper
Nickel
Molybdenum

52. Diversity of life in fertile soil

53. Mineral depletion May occur in farmed soils
Because natural pattern of nutrient cycling is disrupted when crops are not allowed to decompose into soil

54. Soil erosion Removal of soil from land by agents such as
Water
Wind
Causes decrease in soil fertility
Because essential nutrient minerals and organic matter are removed