Ecological memory and relocation decisions in fungal mycelial networks: responses to quantity and location of new resources

Abstract

Saprotrophic cord-forming basidiomycetes, with their mycelial networks at the soil/litter interface on the forest floor, play a major role in wood decomposition and nutrient cycling/relocation. Many studies have investigated foraging behaviour of their mycelium, but there is little information on their intelligence. Here, we investigate the effects of relative size of inoculum wood and new wood resource (bait) on the decision of a mycelium to remain in, or migrate from, inoculum to bait using Phanerochaete velutina as a model. Experiments allowed mycelium to grow from an inoculum across the surface of a soil microcosm where it encountered a new wood bait. After colonisation of the bait, the original inoculum was moved to a tray of fresh soil to determine whether the fungus was still able to grow out. This also allowed us to test the mycelium's memory of growth direction. When inocula were transferred to new soil, there was regrowth from 67% of the inocula, and a threshold bait size acted as a cue for the mycelium's decision to migrate for a final time, rather than a threshold of relative size of inoculum: bait. There was greater regrowth from the side that originally faced the new bait, implying memory of growth direction.

Effects of wood resource size and decomposition on hyphal outgrowth of a cord-forming basidiomycete, Phanerochaete velutina

“…4 ). This result was apparently inconsistent with previous studies that reported that mycelium growing out from smaller wood blocks showed smaller hyphal coverage or biomass 7 , 16 . The area of soil contact usually becomes larger in wood blocks with larger volumes, which merit hyphal outgrowth.…”

“…Mycelial outgrowths from the inoculum into the soil to search for new resources do correlate with the decay of the wood inoculum 7 . Moreover, the foraging mycelia of a cord-forming fungus, Phanerochaete velutina , can recognize the size of newly found wood resource and determine whether to stay in the original inoculum or move to the new wood resource 16 . Nevertheless, it remains unclear whether the growth of mycelium into the soil depends on the obtained carbon from inoculum through decomposition or whether it grows into the soil because the remaining resource level is depleted.…”

“…In the present study, we compared the relationship between hyphal growth and absolute or percentage wood mass loss in different wood block sizes by preparing 50 soil microcosm replicates for each size. We used P. velutina as a model, because it is a cosmopolitan fungus and a well-studied species in the field of mycelial network behavioral research 2 , 4 , 6 , 16 . Since the geometry of the solid resource is essential for microbial decomposition 17 , we prepared three types of wood blocks with ranges of surface area and soil contact to unit volume (Table 1 ).…”

Plants, climate and humans

“…tissues. Intriguingly, mycelial networks demonstrate goal-directed, memory-based behaviour related to foraging with implications for carbon distribution in forest soils [4]. It seems that this behaviour of mycorrhizal fungi may assist plant roots to explore soils in their search for water and minerals.…”

“…Around 30% of all organic compounds generated via photosynthesis are released from root apices either as exudates or as sugars to feed symbiotic fungi in exchange for water, phosphate, nitrate and critical minerals (Fig ). Exudates released into the rhizosphere also attract or repel microorganism to maintain the root microbiome, and shape the physico‐chemical properties of the soil .…”