Mycorrhizas and soil structure

Contents

•  Summary 41

• I. 
  Introduction 42
• II. 
  How mycorrhizal fungi can influence soil aggregation at various scales 42
• III. 
  Effects of fungal mycelium: a mechanistic discussion 44
• IV. 
  Role of fungal diversity 48
• V. 
  Emerging foci, new directions and tools 49
• VI. 
  Conclusions 50

•  Acknowledgements 50

•  References 50

Summary

In addition to their well-recognized roles in plant nutrition and communities, mycorrhizas can influence the key ecosystem process of soil aggregation. Here we review the contribution of mycorrhizas, mostly focused on arbuscular mycorrhizal fungi (AMF), to soil structure at various hierarchical levels: plant community; individual root; and the soil mycelium. There are a suite of mechanisms by which mycorrhizal fungi can influence soil aggregation at each of these various scales. By extension of these mechanisms to the question of fungal diversity, it is recognized that different species or communities of fungi can promote soil aggregation to different degrees. We argue that soil aggregation should be included in a more complete ‘multifunctional’ perspective of mycorrhizal ecology, and that in-depth understanding of mycorrhizas/soil process relationships will require analyses emphasizing feedbacks between soil structure and mycorrhizas, rather than a uni-directional approach simply addressing mycorrhizal effects on soils. We finish the discussion by highlighting new tools, developments and foci that will probably be crucial in further understanding mycorrhizal contributions to soil structure.