Beneficial Services of Arbuscular Mycorrhizal Fungi - From Ecology to Application

Abstract

Arbuscular mycorrhiza (AM) is the most common symbiotic association of plants with microbes. AM fungi occur in the majority of natural habitats and they provide a range of important ecological services, in particular by improving plant nutrition, stress resistance and tolerance, soil structure and fertility. AM fungi also interact with most crop plants including cereals, vegetables, and fruit trees, therefore, they receive increasing attention for their potential use in sustainable agriculture. Basic research of the past decade has revealed the existence of a dedicated recognition and signaling pathway that is required for AM. Furthermore, recent evidence provided new insight into the exchange of nutritional benefits between the symbiotic partners. The great potential for application of AM has given rise to a thriving industry for AM-related products for agriculture, horticulture, and landscaping. Here, we discuss new developments in these fields, and we highlight future potential and limits toward the use of AM fungi for plant production.

Keywords: Glomeromycota; abiotic stress; arbuscular mycorrhiza; plant growth; plant nutrition; plant protection; soil structure; symbiosis.

FIGURE 1

Characteristics of AM fungal arbuscules. (A) Arbuscules are highly branched hyphal structures that nearly fill the cortex cells of the host. Green staining of fungal structures with wheat germ agglutinin (WGA) coupled to fluorescein isothiocyanate (FITC), red staining of the cell wall with propidium iodide (from Kretzschmar et al., 2012). (B) Transmission electron micrograph of a colonized host cell with an arbuscular branch (fungus), surrounded by the periarbuscular membrane. (C) A colonized root stained with Neutral Red which accumulates in acidic compartments, in this case the space between the periarbuscular membrane and the fungal cell wall [compare with (B)]. Size bars, 20 μm in (A,C); 1 μm in (B).

FIGURE 2

Mycorrhizal growth response (MGR) depends on the symbiotic partners. Various plants were inoculated with G. etunicatum. After 16 weeks of coculture, the dry weight of the host plants was determined and the percent change relative to the non-mycorrhizal controls (referred to as MGR) was calculated. MGR ranged between –50% and +50% change in dry weight. The 10 most responsive plants (five positive, five negative) are indicated (modified from Klironomos, 2003).

FIGURE 3

Increase in the number of companies in the European AM market. A survey on the number of firms selling AM inocula in Europe was determined by an internet surveyed. Based on the year of foundation, the number of firms was determined for three time points (year 2000, 2010, 2017).

FIGURE 4

Main players in the AM market in the European Union. The number of companies selling AM inocula is expressed in relation of their location of the main house. Main producer countries are Germany (DE), Italy (IT), Spain (SP), the United Kingdom (UK), France (FR), and the Netherlands (NL).

FIGURE 5

Main domains of application of AM products. The number of products of European firms was determined for each domain of application. Main fields of application are gardening and landscaping, horticulture, agriculture, and forestry.