Translocation of ³²P between interacting mycelia of a wood‐decomposing fungus and ectomycorrhizal fungi in microcosm systems

Abstract

Interactions between saprotrophic and ectomycorrhizal fungi have been largely ignored, although their mycelia often share the same microsites. The mycelial systems show general similarity to each other and, although the enzymatic potential of the saprotrophic fungi is generally considered to be higher, the importance of organic nutrient sources to ectomycorrhizal fungi is now widely accepted. In the experiments described here, nutritional interactions involving transfer of elements from one mycelium to the other have been monitored dynamically using radioactive tracers and a non-destructive electronic autoradiography system. Microcosms were used in which mycelial systems of the ectomycorrhizal fungi Suillus variegatus and Paxillus involutus, extending from Pinus sylvestris host plants, were confronted with mycelia of the saprotroph Hypholoma fasciculare extending from wood blocks. The fungi showed a clear morphological confrontation response. The mycorrhizal mycelium often formed dense patches over the Hypholoma mycelia. Up to 25 % of the $#P present in the Hypholoma mycelium was captured by the mycorrhizal fungi and translocated to the plant host within 30 d. The transfer of $#P to the saprotroph from labelled mycorrhizal mycelium was one to two orders of magnitude lower. The significance of this transfer as a ' short cut ' in nutrient cycling is discussed.

Disruption of root carbon transport into forest humus stimulates fungal opportunists at the expense of mycorrhizal fungi

“…In addition, root disruption may have relaxed mycorrhizal interference competition, allowing free-living saprotrophs to increase in abundance. This field-based finding is in accordance with previous observations of mycorrhizal interference competition in laboratory microcosms (Lindahl et al, 1999(Lindahl et al, , 2001(Lindahl et al, , 2002Werner et al, 2002). The relative importance of reduced mycorrhizal interference and substrate enrichment is, however, difficult to establish.…”

“…In the organic humus layers of coniferous forests, ectomycorrhizal species have been found to dominate fungal communities (O'Brien et al, 2005;Lindahl et al, 2007), and in laboratory microcosms, ectomycorrhizal fungi have been found to compete successfully with saprotrophs for soil space and nutrients (Lindahl et al, 1999(Lindahl et al, , 2001(Lindahl et al, , 2002Werner et al, 2002). Being supported by carbohydrates from their host plants rather than depending on energy from organic matter, mycorrhizal fungi may exclude saprotrophs from energy-depleted substrates, to monopolise nutrients for themselves and their hosts (Lindahl et al, 2007).…”

Stratégie saprophyte ou symbiotique durant le développement d’ascocarpes de truffes dans une truffière à chêne vert. Une réponse basée sur l’abondance naturelle du 13C et du 15N

“…From these different results or observations, it seems obvious that during Tuber sporophore differentiation, a direct transfer of hexose exists between the host and the fungus via ectomycorrhizal structures, and an indirect transfer of carbon from dead host cells or dead mycorrhizae or dead roots or exfoliating root bark via free hyphae displaying saprotrophic abilities. Nevertheless, according to Lindahl et al (1999) and Leake (2001), ectomycorrhizal fungi do not need to produce costly ligninases to acquire nutrients from dead organic matter. Rather than direct nutrient capture, ectomycorrhizal fungi may obtain nutrients via absorption of small organic molecules exogenously decomposed by saprotrophic fungi.…”

Ecosystem Fertility: A new paradigm for nutrient availability to plants in the humid tropics

“…In addition, the digestion (predation) of bacteria by protozoa (predators) may release nutrients (N), and mycorrhizal symbiosis increases the transfer of the mobilized N (amino acids and ammonium) and P (orthophosphate) to the host plant through the microbial loop (Koller et al 2013). Mycorrhizal fungi may transfer nutrients; that is, N from dead nematodes (Perez-Moreno and Read 2001) and P from saprotrophic fungi (Lindahl et al 1999). Thus, high species diversity may decrease the limitations of residue decomposition and increase the rates of nutrient release under both favorable and unfavorable conditions (Loeau et al 2001).…”