FLOODING EFFECTS: ROOTS

I. INTRODUCTION

Roots experience flooding first, then shoots respond to root changes

II. DYNAMIC COMPONENT OF FLOODING EFFECTS

A. Physiologically active gases accumulate

B. Waterlogged environment becomes increasingly reduced

C. Plants continually adjust

Stomatal closure

Leaf senescence

Root growth

III. EARLY ROOT RESPONSES TO INUNDATION

A. Hypoxia as opposed to anoxia

B. Ethylene buildup

C. Inhibited root elongation

D. Root directional growth

E. Aerenchyma

IV. MECHANISMS OF FLOODING INJURY

A. Anoxia

B. Toxins (Mn ²⁺, Fe²⁺,S^-)

C. Metabolism by-products

D. Diminished soil nitrogen

V. ROOT GROWTH, STRUCTURE AND FUNCTION

A. Relative sensitivities among species to soil anoxia

growth stops but plant OK til mitochondria degenerate

growth slows at 1/2 atmospheric O₂ concentration

B. Root performance in field

Flooding drives roots up

Phenology affects growth

Moving water less anoxic

C. Affects on nodulation and mycorrhizae

Nodules swell, decrease N-fixing

Mycorrhizal plants more sensitive

D. Oxygen and root meristems

DNA replication energy-demanding

Mitosis/celldivision cease

E. Structural changes

1. Root anatomy

Aerenchyma in cortex (slide)

Target cells/ethylene

Roots suberize

2. Mitochondrial structure

Key to cell integrity

General degeneration, 24-48 hrs.

3.. Membrane properties

O₂ important in synthesis of fatty acids

O₂ depression alters permeability, membrane transport

4. Ion transport

NPK decrease

Flooding inhibits uptake from solution

Allows leakage out

F. Respiratory metabolism