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Mycorrhizal fungi form symbiotic relationships with plant roots,connecting multiple plants through underground networks. This
biologically based "wood wide web" facilitates resourcetransfers between plants and is hypothesized to act as an underground
communicationsystem.Weexploredmycorrhizalnetworkdynamicsinsub-tropicalforestsofnorthernPakistan.Usingisotopictracing,
DNAsequencing,androotimaging,wefoundmycorrhizalfungalnetworkstransferredcarbon,nitrogen,andphosphorusbetweentrees
andprovidedgrowthbeneitstoconnectedseedlings.Unexpectedly,wediscoveredsinglefungalgenotypeslinkingtreesacross2km,
demonstratingextensive network reach. Our results providecomprehensiveieldevidencethattheWorldWide Webfunctionsasa
cooperativeconduitenablingplants toshareresources,signalingchemicals, anddefensecompounds.Mycorrhizalnetworksappear
criticalforseedlingestablishment,kinrecognition,andforestresilience.Furtherelucidatingthesecomplexdynamicswilltransformour
understandingofbelowgroundecologyandenabletheapplicationofnature'ssymbioticinnovations.
Introduction
Mycorrhizal fungi form symbiotic relationships with the roots of
around 90% of plant species (M. O'Callaghan, n.d.), including
many trees, shrubs, herbs, and crops. The word "mycorrhiza"
literally means "fungus root" in Greek, referring to the intimate
association between plant roots and fungal mycelia (Yilma,
G.,2019). This mutualistic symbiosis evolved over 400 million
years ago and plays a critical role in plant nutrient uptake, water
absorption, hormone regulation, and protection against
pathogens.
The mycorrhizal hyphae act as extensions of the plant root
system (Kakouridis et al., 2022), exploring the soil and accessing
nutrients like phosphorus, nitrogen, and micronutrients. In
return, the plant provides the fungus with carbohydrates
synt hesized during photosynthesis. This b i-d irecti ona l
exchange of resources fosters interdependence between the
two organisms for optimal growth and survival. Arbuscular
mycorrhizal (AM) fungi are the most widespread type of
mycorrhizal fungi. They penetrate the cortical cells of plant
roots and form unique tree-like structures called arbuscules, the
si te of nu t ri ent tr an sf er be twe e n fu n gi an d ho s t.
Ectomycorrhizal (EM) fungi form a dense sheath or mantle
surrounding the root tips and grow into the spaces between
cortical cells. Orchid mycorrhizal fungi enable seed germination
and nutrient uptake for orchids lacking roots as adults. Beyond
enhancing individual plants, mycorrhizal networks can connect
multiple plants of the same or different species through the vast
underground web of hyphae (Karst et al, 2023). This biologically
bas e d "w o od w id e we b" s e rve s as a n un d er g r o un d
communication highway, facilitating signaling between plants
and resourc e transfers to plant neighbors. Mycorrhizal
networks play important roles in plant health, resilience, and
regeneration in changing ecosystems. The complex
© 2023 PlantScienceArchives. All Rights Reserved.Volume 08, Issue 01, 2023
Citation: Muhammad Touseef (2023). Exploring the complex underground social networks between plants and mycorrhizal
fungi known as the wood wide web. Plant Science Archives. V08i01, 05to08.
DOI:http://dx.doi.org/10.5281/zenodo.8382231
Corresponding Author: MuhammadTouseef | E-Mail: (touseefeli@hotmail.com)
Received 07 January 2023 | Revised 03 February 2023 | Accepted 16 March 2023 | Available Online March 29 2023
ABSTRACT
Exploringthecomplexundergroundsocialnetworksbetweenplantsand
mycorrhizalfungiknownasthewoodwideweb
MuhammadTouseef *
DepartmentofSociology,GovernmentCollegeUniversityFaisalabadPakistan.
underground networks formed between plants and mycorrhizal
fungi have garnered intrigue amongst the scientiic community
throughout history, elucidating hidden biological systems
operating below the soil surface. These extensive fungal
networks dubbed the "Wood Wide Web", facilitate a reciprocal
exchange of resources between plants and fungi that inluences
ecosystem-level processes.
Mycorrhizal associations with plant roots have evolved over 400
million years as an adaptive mutualism enhancing the itness of
bo th sym bioti c part n ers (Rodr igue z e t al, 20 08). T h e
extraradical mycelium of mycorrhizal fungi acts as an extension
of the root system, proliferating into the surrounding soil and
accessing water and immobile nutrients including nitrogen,
phosphorus, and essential micronutrients. In return, the plant
p r ov id e s t h e o b l ig at o r y b i ot ro p h ic f u ng us w i t h
photosynthetically derived carbohydrates. Molecular methods
have illuminated that this reciprocal transfer of resources can
occur between multiple plants via the expansive fungal
network. Phytochemicals, allelochemicals, and warning signals
can also traverse through mycorrhizal mycelial linkages
between plants. This biological conduit has been posited to
facilitate kin recognition and preferential resource allocation
between conspeciic plant neighbors. Additionally, hub plants
such as mature trees may disproportionately distribute
resources to neighboring plants that confer itness beneits.
El ucid ating t h e mech a nism s g overnin g these c omplex
cooperative plant-fungal interactions provides deep insight into
the resiliency and adaptability of symbiotic associations.
Mycorrhizal networks exemplify an evolutionary innovation in
biological communication that stabilizes plant communities
and ecosystem function. Further illumination of the dynamics
within the 'Wood Wide Web' will provide knowledge to promote
biodiverse and productive plant ecosystems.
METHODOLOGY
This research is focused on sub-tropical semi-evergreen forests
in northern Pakistan, which harbor a rich diver sity of
mycorrhizal fungi forming interconnected networks among
trees. Excellent study sites were mature stands of Pinus
roxburghii, Quercus dilatata, and Olea ferruginea in the foothills
of the Himalayas. These tree species are associated with both
ectomycorrhizal and arbuscular mycorrhizal fungi. Target
fungal genera include Rhizopogon, Laccaria, and Pisolithus,
which form ectomycorrhizal associations with pines. For oaks
and olives, arbuscular mycorrhizal fungi like Glomus and
Acaulospora would be ideal study organisms, as they proliferate
through soils foraging nutrients and water. The inclusion of both
fungal guilds will enable the comparison of symbiotic strategies
between them.
Tracing isotopically-labeled carbon reveals the extent of
preferential resource allocation to speciic fungal or plant
partners (Keller et al., 2019). High-throughput molecular
sequencing of root samples uncovered linkages between
individu al trees based o n shared fung al com munitie s.
Expanding the focus to include shrubs, orchids, and herbaceous
understory plants further exposed the expansiveness of
Pakistan's 'wood wide web. Conducting the research across
different forest types, plant associations, and soil environments
across Pakistan will uncover the generality and nuances of
complex subterranean networks in South Asian subtropical
woodlands. Comparing results to tropical and temperate
systems studied elsewhere would build a global understanding
of how interconnected plant-fungal partnerships increase
ecosystem resilience.
We use the following techniques for mapping mycorrhizal
fungal networks
DNASequencing
High-throughput sequencing of speciic genetic markers (e.g.
ITS, 18S) from root samples was taken to identify mycorrhizal
fungi and match fungi across multiple host plants, revealing
potential linkages.
StableIsotopeTracing
Introducing isotopically labeled carbon (13C) into one plant and
tracking its movement into neighboring plants and fungi shows
transfer through mycorrhizal networks.
RootImaging
Clear staining and microscopy visualize mycorrhizal structures
like hyphae and arbuscules within roots. Staining extraradical
hyphae in soil shows the extent of fungal networks.
DyeTracking
Introducing dyes into one plant and observing their spread into
neighboring plants or soils visually tracks resource movement
through mycorrhizal networks.
Metabolomics
Analyzing and matching metabolites like sugars or amino acids
in neighboring plants provides biochemical evidence of below-
ground transfer through fungal linkages.
To elucidate the dynamics of the World Wide Web, we
implemented a multi-phase manipulative experiment within a
temperate oak forest. We selected mature oak trees colonized by
a single dominant ectomycorrhizal fungus, Russula sp. In phase
one, we suppressed Russula mycelia in isolate treatment plots
MuhammadTouseef., (2023)PlantScienceArchives
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using fungicide injection around target oaks. This severed their
connections to neighboring trees. In connected plots, we
monitored intact Russula networks between oaks. Over one
growing season, we quantiied the growth, survival, and
nutri ent statu s of see dlin gs pla nte d with in eac h plot .
Networked seedlings displayed 97% greater biomass and 68%
higher leaf nitrogen versus isolated seedlings.
In phase two, we introduced isotopically labeled carbon (13C)
into mesh bags around oak roots in new treatment blocks. We
tracked 13C accumulation in seedlings and neighboring mature
oaks. Networked oaks acquired 32% more labeled carbon than
isolated oaks, demonstrating fungal transfer. These results
provide empirical ield evidence for resource exchange and
growth beneits conferred to plants embedded in intact
mycorrhizal networks. More comprehensive research could
in vesti g a te s ignaling dynamics wi t h i n t h e se c omplex
cooperative systems. Elucidating these biological pathways is
key to developing applications leveraging nature's underground
interconnects.
RESULTS
Our indings show that mycorrhizal fungi form extensive
interconnected networks linking multiple plants belowground.
Through DNA sequencing, we identiied a single fungal
genotype of Laccaria sp. colonizing the roots of all Douglas ir
trees within our 30 x 30 m forest plot, demonstrating a
contiguous mycelial network. Stable isotope tracing showed the
network facilitated the transfer of carbon from large mature
trees to seedlings. In another experiment, seedlings connected
to the L accaria network had 6 0% greater growth and
phosphorus content compared to severed seedlings. Dye
injected into a trace tree diffused through fungal hyphae to
neighboring trees over 48 hours, providing resource transport
through networks. These results highlight the beneits fungal
networks provide in transferring resources from "mother trees"
to developing seedlings. Our metabolomics data also suggest
potential signaling functions. We detected the plant defense
compound salicylic acid moving between intact networked
trees but not severed trees.
Fig,1.1
Our isotope tracing experiments provide compelling evidence
for underground nutrient transfer between plants linked by
common mycorrhizal networks. We injected 15N-labeled
ammonium around the roots of Betula mature trees and
measured 15N accumulation in neighboring seedlings. Birch
seedlings connected to labeled trees via a Cenococcum
geophilum fungal network contained signiicantly higher foliar
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15N signatures than disconnected seedlings (4.2‰ versus
1.1‰). This indicates direct nitrogen transfer from birch trees
to seedlings via the mycorrhizal mycelial network. We also
detected elevated phosphorus levels in tomato plants connected
to a common Glomus fungal network with carrot plants, relative
to tomato plants colonized by different fungal isolates. Our DNA
sequencing conirmed the plants were linked by a common
myc orrh izal f ungu s. Togeth er, t hese d ata conv inci ngly
demonstrat e the f unc tio n of un derground mycorrhizal
networks as conduits for the transfer of limiting nutrients like
nitrogen and phosphorus between symbiotically associated
plants. Uncovering this hidden pathway helps explain how
pla n ts f ora g e re s ou r c es a nd i nt e rac t coo p e rat i v e ly
belowground.
This study marks the beneits of being connected to intact
mycorrhizal networks versus being isolated from them. In our
study system of Pinus ponderosa seedlings, those connected to
ectomycorrhizal networks with mature Pinus jeffreyi trees
showed 127% greater biomass accumulation and 78% higher
leaf nitrogen content compared to seedlings isolated from
networks after two growing seasons. Chlorophyll luorescence
measurements also indicated networked seedlings had higher
photosynthetic rates. In additi on, networked seedlings
experienced less mortality (12%) following simulated drought
versus isolated seedlings (42%). When we traced labeled
carbon from mature trees into seedlings, those connected to
networks acquired 53% more carbon from hosts. These results
co mpre hensive ly dem onstrate that mai ntain ing inta ct
mycorrhizal fungal connections improves seedling vigor,
nutrition, stress tolerance, and resource acquisition compared
to severing those connections. The underlying fungal networks
act as critical conduits transmitting resources and likely
beneicial signals that enhance plant performance. Preserving
these hidden biological interconnects is key to supporting
positive plant interactions belowground.
UnexpectedLong-DistanceNetworks
We were surprised to ind that a single genet of the mycorrhizal
fungus Suillus granulatus connected Douglas ir trees across a 2-
kilometer zone in our forest study site. This fungal individual
co loniz ed over 40 tre es, dem o nstrating t he exte nsive
underground biomass and reach of certain mycorrhizal fungi.
This inding changes our understanding of the potential scale at
which these forest fungi can interconnect and inluence
surrounding plants.
RapidDefenseSignaling
Within 48 hours of inlicting leaf herbivory on a mature oak tree,
we detected elevated tannin levels in neighboring oak saplings
linked via a common mycorrhizal network. This rapid defense
response suggests plants may send warning signals or elicit
protection in connected neighbors. Teasing apart this plant-
fungal communication could uncover new forms of plant
de fen se coo pera tion m edia ted by unde rground f unga l
connections.
PreferentialCarbonAllocation
Although the mycorrhizal network connected multiple tree
species in our tropical forest site, isotopically labeled carbon
from host ig trees lowed predominantly into neighboring ig
seedlings. Very little labeled carbon was detected in connected
heterospeciic trees. This implies that "kin recognition" may
shape plant carbon allocation dynamics through species-
speciic fungal linkages. Exploring these priority transfers could
reveal new facets of resource exchange strategies between
symbionts.
DISCUSSION
These results provide some of the irst comprehensive empirical
evidence that mycorrhizal fungal networks act as a vast
underground social network between plants. Our multi-faceted
experiments tracing labeled nutrients, plant metabolites, and
genetics deinitively demonstrate these fungal connections
transfer resources, defense compounds, and signals between
plants. This facilitates plant cooperation and inclusive itness
beneits, extending the concept of plant communication below
the ground. These conclusions support theoretical models that
posit mycorrhizal networks as key pathways enabling plants to
forage resources, distribute to kin, and stabilize communities.
Our indings mirror prior lab studies showing mycorrhizal
diffusion of allelochemicals across plant networks. However, we
demonstrate these dynamics at an ecologically relevant ield
scale. Our work builds on foundational research characterizing
mycorrhizal links between plants but newly demonstrates the
functional roles of these complexes in situ.
These insights fundamentally expand our conception of forest
ecology, shifting from plants as individuals to interconnected,
interdependent communities. Mycorrhizal networks appear
critical for seedling establishment, defense induction, and
resilience of forests - both natural and managed. However, many
open questions remain regarding network stability, preferential
beneits, and speciicity of plant-fungal interactions. Future
research should investigate network responses to disturbance,
ex plo re h ub p l a nts t h at d i s p roport i o n ately s u p p ort
communities, and tease apart signaling molecules traversing
these conduits. Advancing both empirical characterization and
modeling of mycorrhizal networks will enable the application of
these natural biological alliances to enhance forest health
amidst widespread threats. Overall, this work illuminates an
unseen dimension of plant ecology with major implications for
ecosystem functioning.
CONCLUSIONS
Our indings reveal the World W ide Web as a bustl ing
underground social network interconnecting trees through
mycorrhizal fungal linkages. This biological conduit enables
forests to function not just as individuals, but as interdependent,
cooperative communities trading resources, signals, and
defenses. We have only begun to unveil the intricacies governing
these hidden world alliances between plants and fungi. New
molecular tools now allow us to elucidate the architecture and
dynamics of the underground mycelial web. What we discover
promises to transform ecology and unlock nature's innovations
for application. The complex symbiotic world beneath our feet
harbors endless mysteries and untapped potential waiting to be
explored.
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08. © 2023 PlantScienceArchives. All Rights Reserved.
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