Root Architecture & Primary Stem Analysis

Lab 2: Root Architecture & Primary Stem Analysis

Objectives

By the end of this laboratory exercise, you will be able to:

• Characterize root system architecture in different plant types using quantitative measurements

• Identify and classify root systems as taproot, fibrous, or modified types

• Analyze primary growth patterns in stems through internode measurements and node counts

• Quantify branching patterns and growth strategies

• Connect root and shoot morphology to ecological strategy and habitat requirements

• Calculate root:shoot ratios as indicators of resource allocation

• Compare monocot and eudicot growth patterns

• Create accurate scale diagrams of plant structures

Background Information

Root System Architecture

Why roots matter: Roots anchor plants, absorb water and nutrients, and sometimes store food. In Mohave County's desert environment, root architecture is crucial for survival in sandy, rocky soils with limited water.

Major Root System Types

1. Taproot Systems (common in desert plants!)

• What they are: One main thick root growing straight down with smaller side branches

• Found in: Most eudicots (broadleaf plants) like dandelions, mesquite, creosote bush

• Advantages: Reach deep water (can go 3+ meters deep); strong anchorage in wind

• Desert adaptation: Critical for accessing deep groundwater in dry climates

2. Fibrous Root Systems (common in grasses)

• What they are: Many thin roots spreading out from the stem base like a mop

• Found in: Monocots (grasses, lilies)

• Advantages: Capture surface water quickly after rain; prevent soil erosion; spread widely but stay shallow

• Desert adaptation: Efficient at capturing brief rainfall events

3. Modified Root Systems (specialized structures)

• Adventitious roots: Roots growing from stems or leaves (not from other roots)

• Prop roots: Support roots that grow from the stem (like corn)

• Storage roots: Enlarged roots storing food (like carrots, sweet potatoes)

• Root nodules: Swellings containing nitrogen-fixing bacteria (on legumes like mesquite)

Root Zones (from tip to base)

Simple explanation: Roots have different zones doing different jobs:

1. Root cap - Protective "helmet" at the very tip

2. Zone of cell division - Where new cells are made (growing region)

3. Zone of elongation - Where cells stretch out and the root gets longer

4. Zone of maturation - Where cells finish developing; root hairs grow here

Root hairs: Tiny fuzzy projections that look white and fuzzy. They dramatically increase surface area for water absorption. Very delicate!

Primary Stem Growth

Simple explanation: Stems grow longer at their tips (primary growth). The stem structure includes:

• Node: The bump where a leaf attaches (like joints on your fingers)

• Internode: The smooth stem section between nodes (like the space between your knuckles)

• Apical meristem: Growing tip making new cells

• Axillary bud: Baby branch waiting to grow in the leaf angle

Leaf Arrangement Patterns (Phyllotaxis)

• Alternate: One leaf per node, zigzagging up the stem (most common)

• Opposite: Two leaves per node, facing each other across the stem

• Whorled: Three or more leaves in a ring around one node (less common)

Resource Allocation & Root:Shoot Ratios

Simple explanation: Plants must "decide" how much energy to invest in roots (underground) vs. shoots (above ground). The root:shoot ratio tells us about this investment strategy.

What the numbers mean:

• High ratio (>1.0): More root than shoot - plant investing in water/nutrient gathering

  • Common in: Desert plants, nutrient-poor soils, drought conditions

  • Example: Mohave County plants like creosote bush

• Low ratio (<0.5): More shoot than root - plant investing in light capture and growth

  • Common in: Moist, fertile areas; shaded locations

  • Less common: In Mohave County's dry environment

• Balanced ratio (0.5-1.0): Equal investment

  • Common in: Moderate environments

Arizona connection: Expect most Mohave County plants to have higher root:shoot ratios due to desert conditions!

Materials

Field Equipment

• Trowel or small shovel

• Pruning shears

• Metric tape measure (5 meter length)

• String (for measuring curved structures)

• Camera or smartphone

• Field notebook and pencil

• Permanent markers

• Soft brush (old toothbrush works!)

• Water bottles for rinsing (bring several gallons)

• Gloves (recommended for desert plants)

Plant Selection for Mohave County, Arizona

Important: Only collect from private property with permission, or public areas where collection is permitted. Avoid protected species.

Choose 4-5 plants representing different categories:

Category 1: Grasses and Grass-Like Plants (Fibrous Roots)

Available in Mohave County:

• Big galleta grass (Pleuraphis rigida) - native desert grass

• Indian ricegrass (Achnatherum hymenoides) - common native

• Annual grasses (introduced species in disturbed areas)

• Bermuda grass (in irrigated lawns) - easy to find

• Any common lawn or roadside grass

Why these work: Excellent examples of fibrous root systems; easy to excavate in sandy soils

Category 2: Herbaceous Forbs (Non-Woody Broadleaf Plants)

Available in Mohave County:

• Desert dandelion (Malacothrix glabrata) - spring annual

• Russian thistle/Tumbleweed (Salsola tragus) - taproot, common weed

• Desert chia (Salvia columbariae) - native annual

• Puncture vine (Tribulus terrestris) - common weed with taproot

• Desert marigold (Baileya multiradiata) - perennial, yellow flowers

• Any small roadside weeds in disturbed areas

Good for lab: Choose young plants (< 6 months old) with manageable root depth

Category 3: Woody Plants (SEEDLINGS ONLY - 1-2 years old)

Available in Mohave County:

• Creosote bush seedlings (Larrea tridentata) - THE iconic Mohave plant, deep taproot

• Catclaw acacia seedlings (Senegalia greggii) - legume with nodules

• Brittlebush seedlings (Encelia farinosa) - common on rocky slopes

• Desert willow seedlings (Chilopsis linearis) - near washes

• Joshua tree seedlings (if you can find very young ones - they're protected as adults!)

• Landscape seedlings from yards (with permission)

Caution: Only excavate very young woody plants. Mature desert shrubs have massive root systems!

Category 4: Vines or Prostrate Plants

Available in Mohave County:

• Desert vine (Janusia gracilis) - native vine

• Morning glory species (introduced, common in disturbed areas)

• Any trailing annual weeds in gardens or agricultural areas

Note: This category may be limited in natural desert areas; focus on disturbed habitats

Category 5: Modified or Specialized Roots

Available in Mohave County:

• Any legume (mesquite seedlings, acacia, lupines) - look for root nodules

• Garden plants with storage roots if growing vegetables (carrots, radishes)

• Any plant with visible adventitious roots growing from stems

Procedure

Step 1: Plant Selection and Initial Assessment

Before you dig:

• Choose isolated plants (not tangled with neighbors)

• Select young, small plants you can fully excavate

• Get permission if on private property

• Check it's not a protected species

a. Photograph the intact plant Take photos from multiple angles showing:

• Overall plant shape and size

• Height and width

• Leaf arrangement

• Surrounding habitat (sandy wash? rocky slope? disturbed roadside?)

b. Measure above-ground portions:

• Total height: _____ cm

• Maximum lateral spread (widest point across): _____ cm

• Number of main stems: _____

• Basal stem diameter: _____ mm (measure with ruler at soil line)

Step 2: Systematic Excavation

Arizona soil tip: Mohave County soils are often sandy or gravelly, making excavation easier than clay soils. Rocky areas may be challenging.

Excavation steps:

1. Estimate dig area: Dig a circle 1.5-2× wider than the plant's canopy, and about as deep as the plant is tall (30-40 cm minimum)

2. Begin digging a trench around the plant at your marked boundary

   • Work at a 45° angle inward

   • Check for roots extending outward as you dig

   • If you find major roots going further, expand your circle

3. Work from outside inward - NEVER pull on the stem!

   • This tears fine roots and ruins your specimen

4. For sandy soil: Roots should come out relatively easily For rocky soil: Work carefully around rocks; roots may grow through crevices

5. Follow the taproot (if present) as deep as practical

   • 30-50 cm is usually enough to characterize the system

   • Desert taproots can be VERY deep - don't try to get the entire thing

   • Cut cleanly with shears if needed

6. Gently lift the root ball from underneath (don't pull from stem)

7. Fill in your hole to prevent hazards and minimize disturbance

Safety note: Watch for spines, thorns, and sharp rocks. Wear gloves!

Step 3: Cleaning Roots

Arizona challenge: Desert soils are often sandy and clean easily, but caliche (calcium carbonate layer) may be present and difficult to remove.

Cleaning procedure:

1. Rinse with water using gentle spray (shower setting on hose or spray bottle)

2. Start with large roots, work toward fine roots

3. Use soft brush (old toothbrush) to remove clinging soil

4. Be VERY gentle with root hairs (white, fuzzy areas)

5. Don't worry about getting 100% of soil off - 95% is fine

6. Caliche note: White crusty deposits are natural; don't over-scrub

Step 4: Root System Layout and Photography

a. Prepare background:

• Dark poster board for light-colored roots (most desert roots are light tan/cream)

• Large enough surface (cardboard works)

• Outdoor location with good natural light (avoid harsh midday sun)

b. Spread root system naturally:

• Main root in center

• Lateral roots spread outward radially

• Don't overlap major roots

• Try to show natural 3D structure in 2D layout

• Pin or tape roots in position if needed

c. Add scale and labels:

• Place ruler at edge of frame

• Label card showing: species name, date, your name, location

d. Photograph from directly overhead:

• Camera parallel to surface (not angled)

• Even lighting, no harsh shadows

• Take multiple photos

• Close-up photos of:

  • Root crown (where roots meet stem)

  • Fine root branches

  • Root hairs (if visible)

  • Any specialized structures (nodules, storage regions)

e. Quick sketch: Draw simplified diagram in field notebook while fresh

Step 5: Dimensional Measurements

Measure and record for each root system:

a. Depth measurements:

• Longest root from crown to tip: _____ cm

• If taproot was cut, note: "Taproot extends deeper than _____ cm"

b. Lateral spread:

• Measure in 4 directions (N, S, E, W)

  • North: _____ cm

  • South: _____ cm

  • East: _____ cm

  • West: _____ cm

• Average lateral spread: _____ cm (add all 4, divide by 4)

• Maximum lateral spread: _____ cm

c. Root system shape ratio:

• Calculate: Depth ÷ Lateral spread = _____

• If > 1.0: Deep, narrow system (typical taproot)

• If < 1.0: Shallow, wide system (typical fibrous)

• If ≈ 1.0: Balanced system

d. Root spread profile (create depth zones):

• At 5 cm depth: _____ cm diameter

• At 10 cm depth: _____ cm diameter

• At 15 cm depth: _____ cm diameter

• At 20 cm depth: _____ cm diameter

• Continue in 5 cm intervals to maximum depth

This shows how roots spread at different depths

Step 6: Architectural Characterization

a. Root system classification

Primary type: Taproot, Fibrous, Modified

If TAPROOT system:

• Primary root diameter at base: _____ mm

• Primary root diameter at 10 cm depth: _____ mm (is it tapering?)

• Number of first-order lateral roots (main branches off taproot): _____

• Spacing between laterals: _____ cm

• Maximum lateral length: _____ cm

If FIBROUS system:

• Number of primary roots from stem base: _____

• Average diameter of primary roots: _____ mm

• Root density: count roots crossing a 5 cm line: _____

b. Root hair assessment:

• Visible root hairs present?  Yes / No

• If yes:

  • Location:  Tips only / Throughout / On laterals

  • Appearance:  Dense-fuzzy / Sparse

  • Zone length: _____ cm

  • Color: White / Cream / Brown / Other: _____

c. Specialized structures (check all that apply):

• Root nodules (count: _____, diameter: _____ mm)

  • Expected in: Mesquite, acacia, other legumes

• Storage/swollen roots (describe: _____________)

• Adventitious roots from stem

• Mycorrhizal associations (swollen root tips)

• Other features: _____________

Step 7: Root:Shoot Ratio Determination

This important measurement shows resource allocation strategy

a. Total root length:

For simple systems:

• Measure each root, add together: _____ cm

For complex systems:

• Measure 5 representative roots: _____, _____, _____, _____, _____ cm

• Average length: _____ cm

• Count total number of roots: _____

• Estimated total root length (average × count): _____ cm

b. Total shoot length:

• Main stem length: _____ cm

• Number of branches: _____

• Average branch length: _____ cm

• Total shoot length (main stem + all branches): _____ cm

c. Calculate ratio:

Root:Shoot Ratio = Root length ÷ Shoot length = _____

Interpretation:

• > 1.0: More root than shoot (common in Mohave County!)

• 0.5-1.0: Balanced allocation

• < 0.5: More shoot than root (unusual in desert)

What does YOUR ratio suggest about your plant's strategy?

Step 8: Create Scale Architectural Diagram

Choose appropriate scale:

• Small plants (< 30 cm): 1:1 (actual size)

• Medium plants (30-100 cm): 1:2 or 1:5

• Large plants (> 100 cm): 1:10

Draw on graph paper for accuracy

a. Root profile (side view):

• Vertical axis = depth (show soil surface at top)

• Horizontal axis = lateral spread

• Draw major roots to scale

• Show branching patterns

• Shade or mark root hair zones

• Show any specialized structures

b. Root plan view (top-down view):

• Show radial spread from stem

• Use different line weights for shallow vs. deep roots

• Show branching patterns

c. Add detailed annotations:

• Label all major roots

• Add measurement lines with dimensions

• Include soil depth markers

• Create legend for symbols

• Title: "Root Architecture of [Species Name]"

• Include: scale, date, your name

Step 9: Node and Internode Analysis

Choose a stem section for detailed measurement

• Select a 10-15 cm section of main stem

• Include the tip (apical meristem) if possible

• Must include at least 5-10 nodes

a. Count and mark nodes:

• Total number of nodes: _____

• Mark each node with pencil

• Number sequentially from apex: #1 (youngest/tip) to #N (oldest/base)

b. Measure internodes (distance between consecutive nodes)

Calculate:

• Average internode length: _____ mm

• Maximum internode length: _____ mm (which one? #_____)

• Minimum internode length: _____ mm (which one? #_____)

c. Analyze the pattern:

Create a simple graph on graph paper:

• X-axis: Position from apex (1, 2, 3...)

• Y-axis: Internode length (mm)

• Plot your data points

Questions to answer:

• Are internodes longer near the tip or base? _____

• Is there a trend (getting longer/shorter/staying same)? _____

• Any unusual internodes? Why might this be? _____

Step 10: Leaf Arrangement Documentation

a. Determine phyllotaxis pattern:

Alternate (most common)  Opposite / Whorled / Spiral

If alternate or spiral:

• Count leaves in one complete spiral: _____ leaves

• Number of stem rotations: _____ turns

• Phyllotactic fraction (leaves/turns): _____

b. Measure leaf spacing: (distance from one leaf base to next leaf base along stem)

• Leaves 1→2: _____ cm

• Leaves 2→3: _____ cm

• Leaves 3→4: _____ cm

• Leaves 4→5: _____ cm

• Average spacing: _____ cm

Step 11: Branching Analysis

a. Examine axillary buds:

• Count nodes with visible buds: _____

• Count nodes where buds grew into branches: _____

• Percentage that became branches: _____ %

b. Assess apical dominance: (Does the main stem dominate, or do branches compete?)

• Main stem length: _____ cm

• Average lateral branch length: _____ cm

• Apical dominance ratio = Main stem ÷ Average lateral: _____

Interpretation:

• Ratio > 3:1 = Strong apical dominance (tall, upright growth)

• Ratio < 2:1 = Weak apical dominance (bushy, spreading growth)

c. Predict growth form:  Upright-columnar / Bushy-spreading / Intermediate

Does this match the actual plant you observed?

Data Analysis Questions

After completing all measurements, answer these questions:

1. Root System Comparisons

Compare your taproot and fibrous root systems:

• Which had greater depth? _____

• Which had greater lateral spread? _____

• Which would be better for:

  • Accessing deep water? _____

  • Capturing brief rainfall? _____

  • Preventing erosion? _____

2. Desert Adaptations

How do your Mohave County plants show desert adaptations?

• Root:shoot ratios: _____

• Root depths compared to plant height: _____

• Any specialized structures (nodules, storage, etc.)? _____

3. Growth Patterns

What does your internode analysis reveal about:

• Where growth is most active? _____

• How the plant responds to environmental factors? _____

Common Mohave County Plants for This Lab

Excellent Choices (Easy to Find & Excavate):

1. Tumbleweed - perfect taproot example, everywhere in disturbed areas

2. Bermuda grass - perfect fibrous example, in any lawn

3. Puncture vine - taproot with interesting modifications

4. Annual grasses - fibrous systems, roadsides and disturbed areas

5. Young creosote seedlings - classic desert taproot (get permission!)