Potential spread of forest soil-borne fungi through earthworm consumption and casting

Abstract

© iForest -Biogeosciences and Forestry IntroductionSince the late 1940s, there has been a growing interest in soil mycology and soilborne fungal diseases of plants, motivating studies on soil fungi and their ecology (Subramanian 1982, 1986, Carroll & Wicklow 1992. Such fungi are involved in many plant-soil relationships, including water and nutrient uptake and cycling, plant disease expression or suppression. From a functional standpoint, such fungi can be grouped according to energy derivation: (i) decomposers (saprotrophic), utilizing dead organic material, sometimes acting antagonistically with others; (ii) mutualists (mycorrhizal), colonizing plant roots, supplying soil nutrients and protection against root parasites in exchange for sugars and possibly other components; (iii) parasites, reducing the growth of plant structures or causing diseases by acting as pathogens.Relationships among soil-borne fungal species involved in forest plant fitness are complex, in that expansion and spread of one population versus another linked and associated with other variables (e.g., plant susceptibility, soil pH, temperature, humidity) may lead to changes in plant health. In line with well-known biocontrol strategies (Butt et al. 2001), a parasitic species can seldom express its full pathogenicity against a plant when sufficient mutualistic and/or antagonistic species are present outside of, or within, the rhizosphere (Tousson et al. 1970, Laflamme 2010. The rhizosphere represents a peculiar ecological niche: a common physiological stress on a healthy plant (e.g., an unusual drought period) can easily be reflected in different root exudates, such as sugars and other components, which are important signals of the plant vigor to rhizosphere inhabitants. In this way, a multifaceted dynamic of microbiological interactions, which may awaken their resting stages or chemotactically attract their mobile propagating organs, could lead to establishment of root diseases (e.g., by Phytophthora, Armillaria, Fusarium, Nectria, Verticillium species), the most dangerous in forestry (Manion 1981). In an established forest soil, decomposer fungi (sometimes with an antagonistic behavior against other microorganisms, including parasites, such as Trichoderma) are commonly present both within and outside of the rhizosphere. By contrast, mutualistic fungi, usually in the rhizosphere (e.g., Laccaria, Pisolithus, Suillus, Xerocomus), can produce toxic metabolites, inhibiting infection by parasitic fungi or physically masking root tips (Smith & Read 2008). Therefore, the higher is fungal abundance, dispersal rate and positive synergistic effects useful to plants (by decomposers and mutualists), the lower the probability of root disease is likely to be.Soil fungi represent a large biomass in the soil (Ingham et al. 1989), providing a rich and abundant resource for fungivorous soil invertebrates (Hågvar & Kjøndal 1981, Takeda & Ichimura 1983, Visser 1985. Among the latter, earthworms have an active role in soil ecology, altering soil structure, water...

Impact of different earthworm ecotypes on water stable aggregates and soil water holding capacity

“…2). This could be because the contribution of earthworm mucus to organic binding agents (Knowles et al 2016;Schomburg et al 2018) or the stimulation of fungal activity via the increased supply of soluble organic compounds (Montecchio et al 2015;Parle 1963;Rashid et al 2016) is more significant in low-organic matter soils. Alternatively, or additionally, the earthworm activity may have a bigger impact on aggregate formation where there are more clay-sized particles available for aggregation.…”

Effects of different earthworm ecotypes on soil nutrients distribution under straw return management in a maize agroecosystem

“…Epi‐anecic earthworms have more access to food supplies than epigeic earthworms; thus, they affect the content of soil bacteria, actinomycetes, and fungi more than epigeic earthworms. Moreover, epi‐anecic earthworms can form vertical burrows in the soil; the content of bacteria, actinomycetes, and fungi is significantly higher in the burrows than in the general soil (Montecchio et al, 2015). Earthworm casts are also high in soil microbes, and earthworm casts produced by epi‐anecic earthworms can increase the content of soil microorganisms (Sun et al, 2020).…”

Responses of non‐native earthworms to experimental eradication of garlic mustard and implications for native vegetation

“…Some earthworms are negatively influenced by consumption of ectomycorrhizal fungi, but others are positively influenced by consuming pathogenic fungi (Montecchio et al. ). Garlic mustard invasions can reduce ectomycorrhizal fungal abundance (Wolfe et al.…”

“…However, the emergence of garlic mustard seedlings in the eradication plots indicates that seeds may still arrive from surrounding plots and/or were present in a persistent seed bank within the timeframe of our experiment. Some earthworms are negatively influenced by consumption of ectomycorrhizal fungi, but others are positively influenced by consuming pathogenic fungi (Montecchio et al 2015). Garlic mustard invasions can reduce ectomycorrhizal fungal abundance and increase pathogenic and pathotrophic fungal abundance (Anthony et al 2017), which may confer a benefit to earthworm nutrition.…”