Mycorrhizal Mediation of Soil

Fertility, Structure, and Carbon Storage

Nancy Collins Johnson, Catherine Gehring, Jan Jansa

• Publisher: Elsevier
• Year: 2016
• ISBN:
  9780128043837
• Topic: Naturwissenschaften
• Subtopic: Mineralogie

Mycorrhizal Mediation of Soil: Fertility, Structure, and Carbon Storage offers a better understanding of mycorrhizal mediation that will help inform earth system models and subsequently improve the accuracy of global carbon model predictions. Mycorrhizas transport tremendous quantities of plant-derived carbon below ground and are increasingly recognized for their importance in the creation, structure, and function of soils. Different global carbon models vary widely in their predictions of the dynamics of the terrestrial carbon pool, ranging from a large sink to a large source.

This edited book presents a unique synthesis of the influence of environmental change on mycorrhizas across a wide range of ecosystems, as well as a clear examination of new discoveries and challenges for the future, to inform land management practices that preserve or increase below ground carbon storage.

• Synthesizes the abundance of research on the influence of environmental change on mycorrhizas across a wide range of ecosystems from a variety of leading international researchers
• Focuses on the specific role of mycorrhizal fungi in soil processes, with an emphasis on soil development and carbon storage, including coverage of cutting-edge methods and perspectives
• Includes a chapter in each section on future avenues for further study

Chapter 1

Mycorrhizas

At the Interface of Biological, Soil, and Earth Sciences

N.C. Johnson¹, and J. Jansa^{2 1}Northern Arizona University, Flagstaff, AZ, United States ²Academy of Sciences of the Czech Republic, Prague, Czech Republic

Abstract

Mycorrhizas are among the most widespread and ancient symbioses on Earth. These plant–fungus associations improve nutrition and water relations of most plants. This chapter introduces key features of four main types of mycorrhizas: arbuscular, ericoid, and orchid mycorrhizas, and ectomycorrhizas. The published literature on mycorrhizas has evolved over time. During the past 130 years, the study of mycorrhizas has progressed from descriptions of their nutritional benefits to recognition of their: (1) importance as components of soil fertility, (2) role in structuring and stabilizing soils, and (3) importance for below-ground carbon storage. This book provides a unique perspective of mycorrhizal research advances at the interface of biological, soil, and earth sciences. Its 26 chapters review and synthesize the burgeoning literature about mycorrhizas by bringing together the perspectives and expertise of more than 50 mycorrhizal experts, including some of the pioneers in the field.

Keywords

History of mycorrhizal research; Interdisciplinary sciences; Types of mycorrhizal symbioses; Web of Science

1.1. Successful Coexistence of Plants and Fungi

Mycorrhizas are symbioses between plants and fungi. These nutritional partnerships have evolved independently hundreds of times in multiple lineages in the plant and fungal kingdoms (Bidartondo et al., 2011; Tedersoo and Smith, 2013). Estimates suggest that approximately 50,000 species of fungi form mycorrhizal associations with approximately 250,000 species of plants (van der Heijden et al., 2015). Photosynthetic plants require minerals and water to synthesize organic compounds, but these essential resources are often in limited supply. Mycorrhizas greatly expand the capacity of plants to acquire nutrients and water because fungi have several traits that make them particularly well suited for mining minerals from organic and inorganic substrates and improving the hydraulic properties of soil. Fungal mycelium is composed of fine, threadlike hyphae that can access pores too small for roots to enter; consequently by associating with mycorrhizal fungi, plants substantially increase their contact with mineral particles and organic residues in the soil. Also, fungi have the capacity to synthesize organic acids and other compounds that may depolymerize organic compounds and solubilize mineral nutrients (Smith and Read, 2008). From the perspective of biological markets, plants can often increase their fitness by investing photosynthate in fungal partnerships (Werner et al., 2014). The prevalence of mycorrhizas in all types of vegetation throughout the Earth’s history suggests that this symbiosis is a mechanism for innovation in a constantly changing environment.

Although mycorrhizas have evolved independently many times, four general types are often recognized based upon the identities of the plant and fungal partners (Table 1.1). Arbuscular mycorrhizas, the most ancient and widespread type of mycorrhiza, form between fungi in the phylum Glomeromycota and the majority of plant species, ranging from nonvascular plants to angiosperms (Parniske, 2008; Brundrett, 2009). Ectomycorrhizas form between thousands of Basidiomycota or Ascomycota and many important trees and woody species that are often stand dominants in temperate and boreal forests (Tedersoo et al., 2010; Tedersoo and Smith, 2013). Ericoid mycorrhizas are associations between highly specialized Ascomycota (and a few Basidomycota) and several large families within the order Ericales and also bryophytes that occur in vast areas of tundra, boreal forests, and heathlands (Straker, 1996; van der Heijden et al., 2015). Orchid mycorrhizas are associations between Basidiomycota and all members of the Orchidaceae, a remarkably diverse family encompassing 9% of all angiosperm species (Brundrett, 2009). Orchid mycorrhizas are particularly interesting because orchids have a prolonged seedling stage, during which they are unable to photosynthesize and are entirely dependent upon mycorrhizal symbioses to provide an exogenous supply of carbohydrate (Smith and Read, 2008). In this regard, orchid mycorrhizas represent an unconventional carbon dynamic in which a heterotrophic fungus provides carbohydrate to its plant host. Although orchid mycorrhizas are fascinating, only Chapter 21 will consider orchid mycorrhizas. The other chapters will mainly focus on the arbuscular mycorrhizal (AM), ectomycorrhizal (EcM), and ericoid mycorrhizal (ErM) symbioses because of their key roles as mediators of soil fertility, structure, and carbon storage.

Table 1.1

Four Major Types of Mycorrhizas Distinguished by the Taxa of Host Plants, Fungal Symbionts, and the Biomes Where the Mycorrhizas Are Most Common

Mycorrhizal Type	Host Plants	Main Fungal Symbionts	Predominant Biomes
Arbuscular mycorrhizal (AM)	∼200,000 Species of angiosperms, gymnosperms, bryophytes, and pteridophytes	∼300–1600 species of Glomeromycota	Tropical and temperate forests, grasslands, savannas, shrublands, deserts, and most agricultural crops including fruit trees
Ectomycorrhizal (EcM)	∼6000 Species of angiosperms and gymnosperms	∼20,000 species of Basidiomycota and Ascomycota	Boreal (taiga), temperate, and tropical forests; tundra; and agroforestry
Ericoid mycorrhizal (ErM)	Members of the Ericaceae, Epacridaceae, and Empetraceae families, and some bryophytes	>150 species of Ascomycota (primarily) and some Basidiomycota	Tundra, boreal, and temperate forests
Orchid mycorrhizal	All Orchidaceae	∼25,000 species of Basidiomycota	Tropical and temperate biomes

Information derived from Smith, S.E., Read, D.J., 2008. Mycorrhizal Symbiosis. Academic Press, New York and van der Heijden, M.G.A., Martin, F.M., Selosse, M.-A., Sanders, I.R., 2015. Mycorrhizal ecology and evolution: the past, the present, and the future. New Phytologist 205, 1406–1423.

1.2. Mycorrhizal Research: Past, Present, and Future

It has long been recognized that fungi inhabit plant roots. Frank coined the term mycorrhiza in 1885; but, many published descriptions of fungal associations with plant roots predate this classic paper (Frank, 1885; Trappe and Berch, 1985). In a subsequent paper, Frank suggested that EcM fungi aided nitrogen uptake from humus and thus increased the growth of host plants (Frank, 1894). This insight initiated a period of experimentation on the nutritional role of EcM symbioses (Harley, 1985). Although AM fungi were described inside plant roots several decades before Frank’s publication, the identity of the fungal partner remained elusive because Glomeromycota are obligate biotrophs that cannot be cultured using traditional mycological methods (Koide and Mosse, 20...