Soil, Roots and Water Balance of the Plant

Soil Profile – aka Soil Layers

Soil 101

1. Humus = organics layer on top

2. Topsoil = mix of humus, sand, clay and minerals

3. Subsoil = mix of rocks, inorganic soil with little air or water for plant roots

4. Bedrock = solid rock

Soil Nutrients

1.1. NitrogenNitrogen – critical for leaf, stem development

2.2. PhosphorusPhosphorus – critical for flowering

3.3. PotassiumPotassium – proteins and carbohydrates4. - Roots (stunted if not

enough)

4.4. CalciumCalcium – metabolism, growth, cell wall

5.5. MagnesiumMagnesium – essential for chlorophyll

6.6. Trace Elements:Trace Elements: S, Fe, Zn, Mb, B, Cu, Mn, Cl

Modified Roots and Root AssociationsProp roots develop from branches (or a vertical stem) to offer support to the plant

Mycorrhizae = fungus root; Root Nodules may form from a symbiotic association with soil bacteria

A root graft is a natural union between the roots of two trees, same or different species

The 4 main functions of roots:The 4 main functions of roots: 1)Anchorage, 2) absorption, 3) Conduction 4) storage

Two main types of root systems are:Two main types of root systems are: 1) Taproot (DICOTS)2) Fibrous root systems (MONOCOTS)

Nutrient transport in plants

1. Roots absorb water and minerals from the soil

2. Below ground gaseous exchange - roots

3. Xylem - water and minerals4. Transpiration = water loss

through leaves (evaporation) via stomata

5. Photosynthesis – cells need a lot of water to do this

6. Phloem - Sugar transport to non-photosynthetic tissues

Xylem and Water movement Two types of xylem cells

TracheidsTracheids - gymnosperms VesselsVessels and tracheids - angiosperms

Water is moved through xylem by

1.1. Root pressureRoot pressure – water is pushed by absorption of more water by roots

2.2. Transpiration tensionTranspiration tension - pulled by evaporation from leaves

3.3. CohesionCohesion – water molecules are “stickysticky” or attracted to each other, which help pull water up the plant

Primary tissues of a young Dicot RootPrimary tissues of a young Dicot RootEx. Beans or ButtercupsEx. Beans or Buttercups

Cross-section through a Monocot rootCross-section through a Monocot rootEg. CornEg. Corn

Roots have a root cap and root hairs; they do not usually have nodes, internodes, leaves, or buds

Endodermis- the innermost layer of the cortex; regulates movement of minerals into root xylem (which will eventually be transported up the plant); cells of the endodermis contain the Casparian strip, which blocks movement of water; this prevents loss of water out of roots back to the soil

Waterproof layer between the veins and outside.

Cuts off water loss!

Primary roots possess an epidermis, ground tissues (cortex and pith in certain plants), and vascular tissues

Epidermis- protects the root; root hairs aid in water/nutrient absorption (isn’t permeable)

Cortex- consists of parenchyma cells which store starch

Pericycle- gives rise to lateral roots and lateral meristemXylem conducts water and dissolved minerals

UPWARDS Phloem conducts dissolved sugars up and down the plant

Leaf surfaces are dotted with millions of stomata such as this one. This stomate is lined by two guard cells that control its aperture. Because control requires movement, and movement requires energy, these cells contain numerous mitochondria and chloroplasts (the little green photosynthetic factories that look a bit like brussel sprouts in this shot). Thus they are the only cells in the epidermis that are green.

Guard CellsGuard Cells