What will happen if we remove a ring of bark leaving a narrow strip in a plant?

Girdling (Ringing) Experiment: Effects

Removing a ring of bark (including phloem, cortex, and cork) from a tree trunk while leaving the xylem intact demonstrates the unidirectional translocation of organic nutrients in phloem.

What Happens:

Immediate Effects (Hours to Days):

1. Upward Water Transport Unaffected:
   • Xylem remains intact
   • Water and minerals continue moving upward from roots
   • Leaves receive adequate water supply
   • No wilting observed initially
2. Downward Food Transport Blocked:
   • Phloem removed in ringed area
   • Sucrose and other organic solutes cannot move below the ring
   • Upward translocation from roots (if any) also blocked

Short-Term Effects (Days to Weeks):

1. Swelling Above the Ring:
   • Sugars accumulate in phloem above the girdled area
   • Osmotic pressure increases
   • Bark swells and bulges
   • Visible callus formation as plant attempts to reconnect
2. Sugar Depletion Below Ring:
   • Root system receives no photosynthates
   • Stored starch reserves in roots depleted
   • Root growth slows, then stops

Long-Term Effects (Weeks to Months):

1. Root Starvation:
   • Roots cannot perform cellular respiration (no glucose)
   • Active transport of minerals stops (no ATP)
   • Mineral/water absorption ceases
   • Roots begin to die
2. Shoot System Consequences:
   • Although leaves still photosynthesize, water supply diminishes
   • Leaves begin to wilt
   • Photosynthesis declines
   • Eventually, entire plant dies

Timeline:

• Herbaceous plants: Die within 2-4 weeks
• Woody plants: May survive several months using stored reserves
• Complete girdling: Fatal
• Partial girdling: Plant may recover if phloem reconnects

Why Does This Occur?

BEFORE GIRDLING:

↑ Water (Xylem)

Roots ⇄ Leaves

↓ Food (Phloem)

AFTER GIRDLING:

↑ Water (Xylem intact)

Roots ╳ Leaves

╳ Food (Phloem removed)

Diagram:

Bulge (sugar accumulation)

↓

┌────────────────┐

│ │

│ RING OF │ ← Bark, Phloem removed

│ BARK │

│ REMOVED │

│ │

└────────────────┘

↓

Growth below ring stops

Roots eventually starve

Biological Significance:

1. Proves Phloem Function:

• Demonstrates phloem transports organic nutrients
• Shows downward translocation from source (leaves) to sink (roots)

1. Agricultural Applications:

• Girdling: Used to increase fruit size (temporary sugar accumulation)
• Scoring: Partial girdling promotes flowering in some fruit trees
• Caution: Must be temporary or plant dies

1. Ecological Impact:

• Animals (porcupines, deer) can accidentally girdle trees
• Disease/pests that damage bark can cause girdling effect

Recovery Possibility:

• If girdling is narrow (<1 cm) and treated quickly, phloem can reconnect
• Bridge grafting: Technique to bypass girdled area using scions
• Adventitious roots: May form above ring, creating independent root system

Historical Note: This experiment was famously conducted by Marcello Malpighi (1675), providing early evidence for phloem function.