How Earthworms Affect Plant Growth: Burrowing into the Mechanisms - Earthworm Ecology - page 11

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How Earthworms Affect Plant
Growth: Burrowing into the
Mechanisms

George G. Brown

Embrapa Soja, Londrina, Brazil

Clive A. Edwards

Soil Ecology Laboratory, The Ohio State University, Columbus, OH, U.S.A.

Lijbert Brussaard

Soil Quality Section, Wageningen University, Wageningen, The Netherlands

CONTENTS

Effects of Earthworm on Plants: The History.................................................................................14
Earthworms and Plant Production in the Tropics....................................................................15
The Mechanisms by Which Earthworms Affect Plant Growth:
A Conceptual Background...........................................................................................................17
Types and Modes of Interaction...............................................................................................17
Spatial and Temporal Scales of Earthworm Action.................................................................17
Why Focus on Effects of Earthworms on Plant Roots?..........................................................18
The Seven Main Mechanisms by Which Earthworms Affect Plants..............................................18
1. Dispersal and Changes in Populations and Activities of Beneficial Microorganisms........19
2. Changes in Populations and Impacts of Plant Pests, Parasites, and Pathogens..................23
Potential Role of Earthworms in the Reduction of Plant Disease and
Pest Problems ..............................................................................................................23
Potential Role of Earthworms in Increasing Plant Disease or Pest Problems ..............25
3. Earthworms and Plant Growth-Regulating and Growth-Influencing Substances...............25
4. Root Abrasion and Ingestion of Living Plant Parts by Earthworms...................................26
5. Interactions of Earthworms with Seeds ...............................................................................27
6. Changes in Soil Structure Caused by Earthworms..............................................................27
Earthworm Casts .............................................................................................................28
Earthworm Burrows ........................................................................................................30
7. Changes in Nutrient Spatiotemporal Availability Caused by Earthworms .........................31
Nutrients from Earthworms (Death, Excretion) .............................................................34
Crawling Forward: The Challenge of Identifying and Quantifying the Potential of
Earthworms to Increase Plant Growth .........................................................................................34
ÑAll-Minus-OneÒ Tests and Field Trials...................................................................................35
The Earthworm Threshold Concept .........................................................................................36
Future Needs in Earthworm Research......................................................................................36

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