They say: “Fungal networks support much of life on earth. SPUN is a science-based initiative founded to map fungal networks and advocate for their protection. In collaboration with researchers and local communities, we aim to accelerate efforts to protect underground ecosystems largely absent from conservation and climate agendas.”
Episode 75 of the Big Biology podcast, Hidden network: The evolutionary relationship between arbuscular mycorrhizal fungi and plants, discusses the ecology of fungi.
Show description: “On this episode, we talk to Toby Kiers, an evolutionary biologist at VU University Amsterdam, about the massive networks of arbuscular mycorrhizal fungi (AMF) that inhabit the soil beneath our feet. Toby studies the symbiotic relationship between AMF and 80-90% of plant species, through which the tube-shaped fungi cells trade nutrients with plant roots in exchange for carbon. We draw connections between these networks and human networks, and discuss whether economists should be taking notes from these systems. We also talk about SPUN, a non-profit initiative Toby’s group recently launched with the goal of mapping these fungal networks and advocating for their protection worldwide.”
Some related scientific articles.
A. “Topology of tree–mycorrhizal fungus interaction networks in xeric and mesic Douglas-fir forests” (Journal of Ecology, 17 February 2015, https://doi.org/10.1111/1365-2745.12387) by Kevin J. Beiler, Suzanne W. Simard, Daniel M. Durall.
Summary
Summary.
1. From the phytocentric perspective, a mycorrhizal network (MN) is formed when the roots of two or more plants are colonized by the same fungal genet. MNs can be modelled as interaction networks with plants as nodes and fungal genets as links. The potential effects of MNs on facilitation or competition between plants are increasingly recognized, but their network topologies remain largely unknown. This information is needed to understand the ecological significance of MN functional traits.
2. The objectives of this study were to describe the interaction network topologies of MNs formed between two ectomycorrhizal fungal species, Rhizopogon vesiculosusand R. vinicolor, and interior Douglas-fir trees at the forest stand scale, identify factors leading to this structure and to contrast MN structures between forest plots with xeric versus mesic soil moisture regimes.
3. Tuberculate mycorrhizas were sampled in six 10 × 10 m plots with either xeric or mesic soil moisture regimes. Microsatellite DNA markers were used to identify tree and fungal genotypes isolated from mycorrhizas and for comparison with reference tree boles above-ground.
4. In all six plots, trees and fungal genets were highly interconnected. Size asymmetries between different tree cohorts led to non-random MN topologies, while differences in size and connectivity between Rhizopogon species-specific subnetwork components contributed towards MN nestedness. Large mature trees acted as network hubs with a significantly higher node degree compared to smaller trees. MNs representing trees linked by R. vinicolor genets were mostly nested within larger, more highly connected R. vesiculosus-linked MNs.
5. Attributes of network nodes showed that hub trees were more important to MN topology on xeric than mesic sites, but the emergent structures of MNs were similar in the two soil moisture regimes.
6. Synthesis. This study suggests MNs formed between interior Douglas-fir trees and R. vesiculosus and R. vinicolor genets are resilient to the random loss of participants, and to soil water stress, but may be susceptible to the loss of large trees or fungal genets. Our results regarding the topology of MNs contribute to the understanding of forest stand dynamics and the resilience of forests to stress or disturbance.
B. “Mycorrhizal Networks Facilitate Tree Communication, Learning, and Memory” by Suzanne W. Simard.
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Abstract. Mycorrhizal fungal networks linking the roots of trees in forests are increasingly recognized to facilitate inter-tree communication via resource, defense, and kin recognition signaling and thereby influence the sophisticated behavior of neighbors. These tree behaviors have cognitive qualities, including capabilities in perception, learning, and memory, and they influence plant traits indicative of fitness. Here, I present evidence that the topology of mycorrhizal networks is similar to neural networks, with scale-free patterns and small-world properties that are correlated with local and global efficiencies important in intelligence. Moreover, the multiple exploration strategies of interconnecting fungal species have parallels with crystallized and fluid intelligence that are important in memory-based learning. The biochemical signals that transmit between trees through the fungal linkages are thought to provide resource subsidies to receivers, particularly among regenerating seedlings, and some of these signals appear to have similarities with neurotransmit- ters. I provide examples of neighboring tree behavioral, learning, and memory responses facilitated by communication through mycorrhizal networks, including, respectively, (1) enhanced understory seedling survival, growth, nutrition, and mycorrhization, (2) increased defense chemistry and kin selection, and (3) collective memory-based interactions among trees, fungi, salmon, bears, and people that enhance the health of the whole forest ecosystem. Viewing this evidence through the lens of tree cognition, microbiome collaborations, and forest intelligence may contribute to a more holistic approach to studying ecosystems and a greater human empathy and caring for the health of our forests.
C. “Below-ground plant–fungus network topology is not congruent with above-ground plant–animal network topology” (Science Advances, 23 Oct 2015, Vol 1, Issue 9,n DOI: 10.1126/sciadv.1500291) by Hirokazu Toju, Paulo R. Guimaraes, Jr., Jens Olesen, and John N. Thompson.
Abstract. In nature, plants and their pollinating and/or seed-dispersing animals form complex interaction networks. The commonly observed pattern of links between specialists and generalists in these networks has been predicted to promote species coexistence. Plants also build highly species-rich mutualistic networks below ground with root-associated fungi, and the structure of these plant–fungus networks may also affect terrestrial community processes. By compiling high-throughput DNA sequencing data sets of the symbiosis of plants and their root-associated fungi from three localities along a latitudinal gradient, we uncovered the entire network architecture of these interactions under contrasting environmental conditions. Each network included more than 30 plant species and hundreds of mycorrhizal and endophytic fungi belonging to diverse phylogenetic groups. The results were consistent with the notion that processes shaping host-plant specialization of fungal species generate a unique linkage pattern that strongly contrasts with the pattern of above-ground plant–partner networks. Specifically, plant–fungus networks lacked a “nested” architecture, which has been considered to promote species coexistence in plant–partner networks. Rather, the below-ground networks had a conspicuous “antinested” topology. Our findings lead to the working hypothesis that terrestrial plant community dynamics are likely determined by the balance between above-ground and below-ground webs of interspecific interactions.