Functional and ecological consequences of saprotrophic fungus–grazer interactions

Abstract

Saprotrophic fungi are key regulators of nutrient cycling in terrestrial ecosystems. They are the primary agents of plant litter decomposition and their hyphal networks, which grow throughout the soil-litter interface, represent highly dynamic channels through which nutrients are readily distributed. By ingesting hyphae and dispersing spores, soil invertebrates, including Arthropoda, Oligochaetae and Nematoda, influence fungal-mediated nutrient distribution within soil. Fungal physiological responses to grazing include changes to hydrolytic enzyme production and respiration rates. These directly affect nutrient mineralisation and the flux of CO 2 between terrestrial and atmospheric pools. Preferential grazing may also exert selective pressures on saprotrophic communities, driving shifts in fungal succession and community composition. These functional and ecological consequences of grazing are intrinsically linked, and influenced by invertebrate grazing intensity. High-intensity grazing often reduces fungal growth and activity, whereas low-intensity grazing can have stimulatory effects. Grazing intensity is directly related to invertebrate abundance, and varies dramatically between species and functional groups. Invertebrate diversity and community composition, therefore, represent key factors determining the functioning of saprotrophic fungal communities and the services they provide.

Biotic interactions mediate soil microbial feedbacks to climate change

“…Given the regulatory effects of isopods observed under simplified laboratory conditions (20,27), we expected the top-down process to limit fungal biomass across all abiotic scenarios. However, the present study highlights that regulatory effects of grazers are apparent only above the ambient range of soil inorganic nitrogen concentrations (0-20 μg/g soil).…”

“…Increasing availability of fungi, with relatively low carbon:nitrogen ratios, is likely to drive a switch in isopod feeding, from leaf litter to fungal cords. A switch in feeding is likely to have direct functional consequences for the turnover rates of organic material in soil: The grazing and shredding of leaf litter increases microbial activity and decomposition rates (28,31,32), whereas the direct grazing of fungal cords generally limits enzyme activity and decomposition in forest soil (7,20,27). Such a functional switch would reinforce the capacity of soil invertebrates to limit microbial responses to global change as nitrogen enrichment converts their feeding habits from litter consumption (stimulating decomposition) into fungal grazing (limiting decomposition).…”

Ecological succession reveals potential signatures of marine–terrestrial transition in salt marsh fungal communities

“…As succession proceeds to the more mature terrestrial stages, the fungal communities apparently evolved towards a dominance of filamentous and, to a larger extent, saprotrophic fungi, as their mode of exploration for nutrients is fine tuned to the utilization of complex substrates such as the organic matter derived from plant biomass (Richards et al, 2012;Treseder and Lennon, 2015). As primary agents of plant litter decomposition, saprotrophic fungi produce hyphal networks throughout the soil matrix that promote organic matter-derived nutrient distribution through dynamic channels (Crowther et al, 2012). Interestingly, we found the types of putative saprotrophic fungi to shift significantly along the chronosequence (Figure 3b).…”

A systemic approach for modeling soil functions

“…This is especially true for interactions at the interface between different soil science disciplines and the interactions between physical, chemical and biological properties. For example, soil physics typically ignores chemical heterogeneities and biologically induced structure dynamics, while in biology and chemistry soil analyses are often performed in homogenized or standardized samples and the natural structure/habitat is lost (Heemsbergen et al, 2004;Crowther et al, 2012).…”