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Abstract

Summary 1. Carbon (C), nutrients and water (H2O) have been known for five decades to flow between plants through ectomycorrhizal (EM) networks. This flux has the potential to affect plant and fungal performance and resource distribution within communities. 2. We asked two questions: 1) What are the pathways and mechanisms for C, nutrient and H2O fluxes between plants through EM networks? 2) What are the magnitude, fate and importance of C, nutrient and H2O transfer among EM plants? 3. Mycorrhizal networks provide a distinct pathway for resource fluxes among plants and mycorrhizal fungi, partitioning them away from other competing soil microbes and plant roots in the soil matrix, and potentially providing a competitive advantage (or disadvantage) for some individuals involved in the network. Carbon and nutrients flow symplastically and apoplastically through mycorrhizal symbionts, hyphae and rhizomorphs along source-sink gradients across the networking mycelia and plant community. Hydraulic redistribution from wetter to drier soil or plant pools can also be facilitated by mycorrhizal networks following water potential gradients. 4. Carbon fluxes through EM networks have been shown to supply 0-10% of autotrophic, up to 85% of partial myco-heterotrophic (MH), and 100% of fully MH plant C. This C supply has been loosely associated with increased survival and growth of autotrophic plants, but shown to be essential for survival of MH plants. Network-mediated nitrogen (N) fluxes between N2-fixing and non-N2-fixing plants have supplied up to 40% of receiver N, and this has been associated with increased plant productivity. Fluxes between non-N2-fixing plants have supplied <5% of receiver N. Hydraulic redistribution involving EM fungi has supplied up to 50% of plant water, and in some cases this has been shown as essential for plant survival, but how much of this water transfers through EM networks remains uncertain. Phosphorus transfer through EM networks has not been adequately demonstrated. 5. Overall, this review chapter shows that resource fluxes though EM networks are sufficiently large in some cases to facilitate plant establishment and growth. Resource fluxes through EM networks may thus serve as a method for interactions and cross-scale feedbacks for development of communities, consistent with complex adaptive system theory. How this may affect ecosystem stability depends on the environment.

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... verbrauchen Mykorrhizapilze im Rotbuchenwald (Fagus sylvatica) immerhin ein Drittel des produzierten Zuckers. Mykorrhizapilze übernehmen noch weitere Aufgaben: Sie vernetzen sich mit anderen Mykorrhiza-Pilzen sowohl desselben Wirtsbaumes, als auch mit denen anderer Bäume(Lüder 2018;Klein et al. 2016;Simard et al. 2015). Dabei werden nicht nur zwei Individuen derselben Art, sondern auch artenübergreifend Bäume vernetzt(Klein et al. 2016;Gorzelak et al. 2015;Simard et al. 2015). ...
... Mykorrhizapilze übernehmen noch weitere Aufgaben: Sie vernetzen sich mit anderen Mykorrhiza-Pilzen sowohl desselben Wirtsbaumes, als auch mit denen anderer Bäume(Lüder 2018;Klein et al. 2016;Simard et al. 2015). Dabei werden nicht nur zwei Individuen derselben Art, sondern auch artenübergreifend Bäume vernetzt(Klein et al. 2016;Gorzelak et al. 2015;Simard et al. 2015). Dadurch können die Pflanzen Wasser, Zucker, Stickstoff(Gorzelak et al. 2015;Simard et al. 2015), Phosphor(Eason and Newman 1990;Eissenstat 1990), Pflanzenhormone(Song et al. 2010) und sogar genetisches Material(Giovannetti et al. 2006), aber auch Signale, wie zum Beispiel bei einem Schädlingsbefall, untereinander austauschen(Babikova et al. 2013). ...
... Dabei werden nicht nur zwei Individuen derselben Art, sondern auch artenübergreifend Bäume vernetzt(Klein et al. 2016;Gorzelak et al. 2015;Simard et al. 2015). Dadurch können die Pflanzen Wasser, Zucker, Stickstoff(Gorzelak et al. 2015;Simard et al. 2015), Phosphor(Eason and Newman 1990;Eissenstat 1990), Pflanzenhormone(Song et al. 2010) und sogar genetisches Material(Giovannetti et al. 2006), aber auch Signale, wie zum Beispiel bei einem Schädlingsbefall, untereinander austauschen(Babikova et al. 2013). Durch die große Ähnlichkeit mit dem world wide web nennt man dieses Zusammenspiel wood wide web. ...
Thesis
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Die Arbeit gliedert sich in einen fachwissenschaftlichen und einen fachdidaktischen Teil. Im fachwissenschaftlichen Teil kann sich die Leserin bzw. der Leser einen detaillierten Überblick zu den naturwissenschaftlichen Kenntnissen über Großpilze verschaffen. Besonders hervorzuheben ist hier die Morphologie von Fruchtkörpern in Stiel, Hut und Fruchtschicht, die Fortpflanzung über Sporen und die Ökologie der Pilze, die sich entweder symbiotisch, parasitär oder saprobiontisch ernähren. Außerdem werden sieben Pilzarten vorgestellt, die leicht erkennbar sind und sich für den Grundschulunterricht eignen Der darauf folgende fachdidaktische Teil ordnet Pilze zunächst in die Curricula von Rheinland-Pfalz und Baden-Württemberg ein. Im Gegensatz zu Pflanzen und Tieren werden Pilze in den Lehrplänen nie explizit erwähnt, Den Kern des fachdidaktischen Teils stellt eine siebenstündige Unterrichtsreihe, in der Grundschülerinnen und -schülern verschiedene mykologische Phänomene mit Hilfe von Exkursionen, Kurzvorträgen, Spielen und Versuchen erklärt und erfahrbar gemacht werden. Inhaltlich baut sich die vorgeschlagene Unterrichtsreihe aus einer Pilzexkursion einer damit einhergehenden Orientierung im Thema, einer Unterrichtsstunde über Aufbau und Fortpflanzung 2 der Pilze, einer Stunde zur Ökologie und einer zu Speise-und Giftpilzen auf. Weiterhin wird durch die Konzipierung eines individuellen Pilzbuches die Artenkenntnis ausgebaut und zuletzt eine Unterrichtsstunde über das Färben von Wolle oder Seide mittels Pilzen vorgestellt. Den Ausblick stellt eine engere Vernetzung zwischen Pilzexpertinnen und-experten mit Grundschullehrerinnen und Grundschullehrern und skizziert weiteren Forschungsbedarf zu mykologischer Fachdidaktik. The paper is divided into a mycological and a didactical part about fungi in elementary school. The mycological part introduces the reader into the scientific knowledge about macrofungi. Especially important is the morphology of fruit bodys into stipe, cap and hymenium the reproduction via spores and the ecology of fungi, which can be symbiotic, parasitic or saprobiotic. Furthermore there will be seven species presented, which are easy to recognize and are useful for primary education. The didactical part will be opened with an insight the subject of fungi in the curriculum of Rhineland-Palatinate and Baden-Wuerttemberg. Although animals and plants are a crucial part of the curriculum, mushrooms are never explicit mentioned. The crux of the didactical part is an exemplary teaching unit, which will intodruce pupils into fungi via excursions, short-lectures made by the pupils themselfes, games and experiments. After the excursion and the overview about fungi in the first lesson, the second one gives information about the structure and reproduction of fungi, then follows a lesson about ecology, and one about eatable and poisonous mushrooms. In the next lesson, the pupils create their own individual fungal book, to increases their knowledge of species. The teaching unit will be closed with the dyeing of silk scarfs with fungi. In the prospect the paper demands a closer exchange between fungi experts and elementary school teachers and addictional research in mycological didactics.
... First, two plants connected to the same fungus may asymmetrically contribute to its carbon need, resulting in a benefit for the less providing one (Walder et al., 2012). Second, both nutrients and information exchanges can occur between plants species (Klein et al., 2016;Selosse & Roy, 2009;Simard et al., 1997Simard et al., , 2015 even though their consequences are not always easy to experiment or observe (Booth, 2004;Liang et al., 2020). ...
... From a fungal point of view particularly, rerouting resources among different partners increases sustainability and resilience by creating a diverse host set (Selosse et al., 2006). Thus, isotopic labelling should be performed in the epiphytic habitats to reveal whether the CMNs revealed in this study are truly functional or not (Klein et al., 2016;Selosse & Roy, 2009;Simard et al., 1997Simard et al., , 2015. ...
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1. In soils, plants and fungi can form complex mycorrhizal networks allowing nutrient transfers between plant individuals and species. It is less clear, however, whether such networks exist on the bark of trees where epiphytic plant communities thrive in rainforests. Previous work showed that tropical epiphytic orchids especially, harbor symbiotic fungi in their roots, but the structure and determinants of the resulting networks remain unknown at the tree scale. 2. We tested the hypothesis that epiphytic orchids rooted in the same area on the bark share mycorrhizal fungi, regardless of their species (i.e., spatial determinant). For this purpose, we selected the trunk of six trees of two common species in a rainforest and sampled orchid roots, protocorms and surrounding bark. We identified mycorrhizal fungi including Tulasnellaceae using high‐throughput sequencing of the ITS2 marker, and reconstructed orchid‐fungus bipartite networks for each tree to analyse their structure and the spatial turnover of this symbiosis. 3. We found that epiphytic orchid communities form anti‐nested and highly modular networks with mycorrhizal fungi spread on the bark. As expected, modules of interactions are explained by their spatial structure, with nearby roots sharing fungi, but also by the orchid species involved. These results reveal the presence of shared mycelial networks in epiphytic habitats, whose roles in the resilience and facilitation of epiphytic plant communities need to be assessed. 4. Synthesis. Tropical tree barks are densely colonised by certain mycorrhizal fungi that can form symbioses in nearby adult and young orchids simultaneously. These mycorrhizal networks may allow water and nutrient transfers to alleviate the stressful conditions of the epiphytic habitats.
... This communication, on the other hand, is thought to happen more swiftly and efficiently between plants via speech transmission across networks, or "wired communication" (Gagliano 2013). Although the exact manner of communication is unknown (Simard 2018), these communication signals are sent between fungal synapses and trees and/or plants by diffusion or active transport processes (mass flow) along source-sink gradients (Twieg et al. 2007;Simard et al. 2015). For example, leaf photosynthetic activity in donor plants causes N and C source-sink gradients that allow amino acids to be transported to mycorrhizal roots, which are subsequently transferred by mass flow from the connecting mycelium to the xylem of the connected recipient sink plants. ...
... Glycine is the most frequent inhibitory neurotransmitter in the brain and spinal cord, and it is quite active (Bowery and Smart 2006). Glutamate and glycine are expected to be the primary amino acids that transport N and C across source-sink gradients via mycorrhizal networks if there is mycorrhizal network similarity (Teste et al. 2009;Simard et al. 2015;Deslippe et al. 2016). Furthermore, Darwin (1880) offered the "root-brain" theory, according to which the root tip, which is located between the apical meristem and the elongation region, functions as a brain-like organ that regulates the plant's behavior in the same manner it does in humans. ...
Article
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Plants, animals, and even microbes well communicate with each other if we look at nature in cartoon terms. However, in the real world, there is little evidence on how this communication is established. In this context, we have focused on how plants communicate with mycorrhizal fungi and how they communicate with each other using mycorrhizal networks. We divide this communication in the rhizosphere into three categories: (i) communication of the plant with the fungus (plantish), (ii) communication of the fungus with the plant (fungish), and (iii) communication among plants through mycorrhizal networks (wired communication). We propose that molecules involved in inter-kingdom symbiotic communication, such as strigolactones, chitin-related compoundsand cutin monomers in plant-fungal communication, are initially unrelated to symbiosis, but they play important roles in its development. It’s not, however, known exactly whether the dialogue between plant-fungi is fungish or plantish; Despite this, since it is a language on which they agree, we consider it appropriate to call this language “symbioticish”. Moreover, mycorrhizal networks offer inter-plant communication by transferring nutrients, stress signalsand allelochemicals. We present evidence showing that these mycorrhizal networks impart sophisticated intelligence to plants and that their topology is similar to that of the human’s brain, with some features including scale-free and small-world network topology. The evidence presented in this review can contribute to the study of plant-mycorrhizal fungus communication and mycorrhizal networks in the inter-plant communication by establishing a better human empathy, taking a more holistic approach to examining ecosystems and caring about the health of our plants.
... V tomto pohledu se díváme na les jako na celek a rovněž tak posuzujeme adaptaci jeho recyklace na příslušné podmínky prostředí. Koncept celoekosystémové výživy je pak podpořen objevy provázání stromů skrze mykorhizní houby [14], kořenovými srůsty či schopností stromu do určité míry poměrně rychle reagovat na změny prostředí díky epigenetickým mechanismům [15]. ...
... Stabilizace je tu výsledkem vhodných kombinací specifických vlastností těchto dřevin [29]. [14]. Hydraulický lift se stává především v obdobích sucha stěžejním mechanismem, jelikož mělčeji kořenícím dřevinám přináší až 50 % spotřebované vody [35]. ...
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Skrze bolestné pohledy na rozsáhlé kalamitní holiny a chřadnutí řady druhů dřevin v našich lesích jsme svědky konce jedné epochy v lesnictví. Tato epocha se opírala o dobrou předvídatelnost přírodních podmínek a výnosů a s tím související schopnost managementu „mít věci pod kontrolou“, z čehož pramenila i možnost velkoobjemové produkce několika málo sortimentů. S tím je konec. Proč? Jelikož les sestává ze živých organismů a z toho vyplývá, že není možno pěstovat libovolný les kdekoliv. Zkrátka jednotlivé druhy mají své limity. Není tak možno ignorovat hluboké změny v přírodních podmínkách, jichž jsme svědky v současné době. Klimatická změna mnohde představovala poslední šťouchnutí k pádu do propasti nestability, kam naše hospodářské lesy již dlouho směřovaly v důsledku uniformního složení, degradace půdy a působení široké palety polutantů.
... These mycorrhizal connections are referred to as common mycorrhizal networks (CMNs). It has been shown that sugars (monosaccharides), amino acids, lipids, water, and micronutrients can all be transported via CMNs [33,34,117]. In addition to nutrient exchange, CMNs have been shown to carry infochemicals, including plant hormones, enzymes, allelochemicals, and secondary compounds not involved in growth and development of the plant [118][119][120]. ...
Article
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Purpose of Review Approximately 40 years ago, key papers indicating that volatile chemicals released by damaged plants elicited defense-related changes in their neighbors, brought prominence to the idea of plant communication. These studies were conducted with several tree species and the phenomenon observed was dubbed “talking trees.” Today there is a wealth of evidence supporting the idea that plants can send and receive information both above and belowground. However, while early reports of plant-plant communication concerned trees, the literature is now heavily biased towards herbaceous plants. The purpose of this review is to highlight recent research on tree-tree communication with an emphasis on synthesizing knowledge on the ecological relevance of the process. Recent Findings Aboveground, information is often provided in the form of biogenic volatile organic compounds (VOCs), which are released by both undamaged and damaged plants. The blends of VOCs released by plants provide information on their physiological condition. Belowground, information is conveyed through mycorrhizal networks and via VOCs and chemical exudates released into the rhizosphere. Recent findings have indicated a sophistication to tree communication with more effective VOC-mediated interactions between trees of the same versus a different genotype, kin-group, or chemotype. Moreover, common mycorrhizal networks have been shown to convey stress-related signals in intra- and interspecific associations. Together these two forms of communication represent “wireless” and “wired” channels with significance to facilitating plant resistance to herbivores. Summary In this review, we examine tree-tree communication with a focus on research in natural forest ecosystems. We particularly address the effects of tree-tree communication on interactions with herbivorous insects. Aboveground and belowground interactions are both reviewed and suggested implications for forest management and future research are presented.
... Beiler et al., 2010;Rog et al., 2020). CMNs efficiently convey carbon and nutrients (Simard et al., 1997;Simard et al., 2003;Simard et al., 2015;Klein et al., 2016) and water among conspecific or heterospecific plants, either through extraradical hyphae or through "highways" formed by hyphal cords (Cairney, 2005;Lehto and Zwiazek, 2011). Host plants connected by common fungal symbionts can be said to form functional "guilds of mutual aid" where resources are potentially available to all plants connected by a CMN (Perry et al., 1989). ...
Article
Plant interactions play a key role in forest ecosystem dynamics. The tallest plants, namely the overstorey trees, are obvious major drivers, particularly in competition for light. This process has already been amply described. However, the role played by lower strata has often been underestimated. In this review, we first briefly recall the role of over- and understoreys in structuring forest microclimate, mostly through light sharing. We then focus on belowground interactions between over- and understorey, where knowledge is more piecemeal, partly because of measurement difficulties. Even so, some studies show that competition for water and nutrients by the overstorey controls the development of understorey vegetation much more than competition for light. The reverse (overstorey limitation by the understorey) has also been encountered, but has been much less well researched. We also address the involvement of mycorrhizae, specifically their role in alleviating overstorey drought stress and contributing to nutrient cycling. We go on to show how another example of key ecosystem engineers, large mammalian herbivores, shape above- and belowground resources and intervene in over- and understorey interactions. In conclusion, for a better understanding of forest dynamics and adapted management, particularly in the context of global climate change, we advocate taking account not only of trees but of all forest components. Belowground processes need more research. The roles of mycorrhizal networks, root exudates, microbiota, and chemical cues need to be further explored to gain a finer understanding of the interactions between over- and understorey.
... Mycorrhizal fungi enable a host plant to expand its N prospection area and help it compete for N with decomposer microbes (Fellbaum et al., 2012;Hodge & Fitter, 2010;Simard et al., 2015). ...
Article
The nitrogen (N) economics of plants are generally described in terms of functional traits and how these affect N availability in a given environment. However, recent studies have shown that plant symbionts play a crucial role in plant N economics. A plant together with its symbiont can be considered as a meta‐organism, the holobiont. Plant‐associated symbionts are shaped by the plant, thereby extending the plant’s phenotype. Decomposers also play an important role in plant N economics yet are usually not included in the plant holobiont. ▪In this review, we show the important roles that both symbionts and decomposers play in plant N economics. We focus on how plants respond to fluctuating N availability in a complex interaction network, which includes the plant’s strategies and its interactions and feedback loops with the soil biota and with neighbouring plants, through competition for N by exploitation and interference. ▪Synthesis: Plant N economics and the outcome of plant‐plant interactions in a community cannot be fully described solely through the functional traits of plant individuals. Properties emerging from the interaction network bring new insights into plant N economics. Further research is now needed to gain a deeper understanding of plant N economics and resource economics in plant communities by integrating a broader extended plant phenotype.
... Decomposition of organic matter by soil fungi provides nutrients for plant growth (Frąc et al., 2018). Networks of mycorrhizal fungi also facilitate the flow of water and nutrients (e.g., carbon, nitrogen) among plants, contributing to the growth, establishment, and survival of some species (Simard et al., 2015). Plants contribute to soil formation through root growth (which can help to stabilize materials as well as help weather and break apart rocks), chemical reactions (e.g., releasing organic acids and carbon dioxide), microclimate creation (e.g., by reducing wind speeds), and by providing a source of carbon through organic matter (CSSS, 2020). ...
Technical Report
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Plants sustain life on Earth, providing humans and other organisms with food, shelter, and clean air. They are foundational to the economic, cultural, physical, and spiritual well-being of people in Canada. Although plants are a constant ― often unnoticed ― presence in our lives, they are increasingly at risk and under pressure. Plants face many threats, such as rising temperatures, changing precipitation patterns, extreme weather events, disease, and new predators, all of which have been exacerbated by climate change, the global movement of people and goods, and evolutionary processes. There is still a great deal to learn about how stressors affect plants and their relationships with pests and the environment. It’s clear, however, that the risks to plant health also threaten the health of broader ecosystems, affecting climate, human and animal health, biodiversity, and food security. Addressing current and emerging risks to plant health is vital to the survival of life on Earth. Cultivating Diversity examines the existing and emerging risks to plant health in Canada and offers insights into promising practices that may help to mitigate them. The report focuses on key areas of risk, rather than specific risks, as well as strategies to reduce vulnerability and increase resilience.
... Thus, a better understanding of the forces driving such interactions is required, since it has profound implications for our understanding of plant communities and competition. Depending on the species involved in the CMN and the possible effects for its fitness, it will drive forest community composition and dynamics (Beiler et al., 2010;Simard et al., 2015). ...
Article
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Most terrestrial plants establish symbiotic associations with mycorrhizal fungi for accessing essential plant nutrients. Mycorrhizal fungi have been frequently reported to interconnect plants via a common mycelial network (CMN), in which nutrients and signaling compounds can be exchanged between the connected plants. Several studies have been performed to demonstrate the potential effects of the CMN mediating resource transfer and its importance for plant fitness. Due to several contrasting results, different theories have been developed to predict benefits or disadvantages for host plants involved in the network and how it might affect plant communities. However, the importance of the mycelium connections for resources translocation compared to other indirect pathways, such as leakage of fungi hyphae and subsequent uptake by neighboring plant roots, is hard to distinguish and quantify. If resources can be translocated via mycelial connections in significant amounts that could affect plant fitness, it would represent an important tactic for plants coexistence and it could shape community composition and dynamics. Here, we report and critically discuss the most recent findings on studies aiming to evaluate and quantify resources translocation between plants sharing a CMN and predict the pattern that drives the movement of such resources into the CMN. We aim to point gaps and define open questions to guide upcoming studies in the area for a prospect better understanding of possible plant-to-plant interactions via CMN and its effect in shaping plants communities. We also propose new experiment setups and technologies that could be used to improve previous experiments. For example, the use of mutant lines plants with manipulation of genes involved in the symbiotic associations, coupled with labeling techniques to track resources translocation between connected plants, could provide a more accurate idea about resource allocation and plant physiological responses that are truly accountable to CMN.
... We thus posit that fertilizer-mediated changes in microbiota could foster relative increases in fungal biomass or, alternatively, could stimulate the growth of ectomycorrhizal and rhizosphere fungi associated with B. glandulosa, which in turn could increase the fitness of this plant species, making it more competitive. Previously, mycorrhizal networks, which promote the sharing of resources among plants and fungi, have been associated with an increased competitive advantage for a number of plants (Simard et al. 2015). Furthermore, B. glandulosa is the only ectomycorrhizal host plant species in most low Arctic tundra ecosystems and certainly in the mesic birch hummock tundra at our site. ...
Article
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Recent climate warming in the Arctic is enhancing microbial decomposition of soil organic matter, which may result in globally significant greenhouse gas releases to the atmosphere. To better predict future impacts, bacterial and fungal community structures in both the bulk soil and the rhizosphere of Arctic birch, Betula glandulosa, were determined in control, greenhouse summer warming, and annual factorial nitrogen (N) and phosphate (P) addition treatments twelve years after their establishment. DNA sequence analyses at multiple taxonomic levels consistently indicated substantial bulk soil and rhizosphere microbial community differences among the fertilization treatments but no significant greenhouse effects. These results suggest that climate warming will likely increase the activity rates of soil microbial decomposers but without substantially altering the structure of either the bacterial or fungal communities. Differential abundance testing revealed changes in ectomycorrhizal fungal species of the genus Thelephora in both bulk soil and rhizosphere, with increases in their relative abundance in P and N + P amended plots compared with warming and controls. Because birch is the principal low Arctic ectomycorrhizal host, our results suggest that these fungi may promote this shrub’s competitiveness where tundra soil nutrient availability is enhanced by warming or other means, ultimately contributing to arctic vegetation “greening.”
... Consequently, soil resource acquisition by EcM could enhance overall resource availability for roots as a result of complementary resource acquisition (Baxter & Dighton, 2001;Köhler et al., 2018). It may also point to the role of mycorrhizal networks facilitating nutrient transfer among different species in mixtures (Simard et al., 2015). Hence, these observations may provide evidence of below-ground abiotic facilitation and positive biotic feedback from mycorrhizae (Barry et al., 2019). ...
Thesis
Mixed-species forests have often been shown to enhance above-ground ecosystem properties and functions compared to their mono-specific counterparts. For example, they are often more productive than pure stands. However, the underlying mechanisms of positive diversity-ecosystem functioning relationships have been analysed mainly for above-ground processes, with less attention paid to the role of below-ground interactions. Consequently, our understanding of the functioning of mixed forests is still largely incomplete. To promote diverse, productive, and resilient forests capable of adapting to the impacts of climate change, a comprehensive understanding of the functioning of mixed-species forest is indispensable. Fine roots generally play a fundamental role for plant growth and fitness, but also in carbon and nutrient cycling. Nevertheless, as to how species diversity affects below-ground functions driven by fine roots, including soil resource exploitation, remains largely unknown. Methodological constraints related to root research and inconsistent root classification bear major challenges for analysing the role of the below-ground ecosystem component. Consequently, contradictory results of previous studies do not allow broad conclusions to be drawn about the role of fine roots for positive biodiversity-ecosystem functioning relationships. The overarching goal of this thesis was to assess the effect of tree diversity on fine-root soil exploitation and decomposition in four wide-spread European forest types. The main research objectives were: (1) To assess the soil space occupation by tree fine roots in response to tree species mixing (2) To examine soil exploitation strategies by tree fine roots and mycorrhizal partners in response to tree species mixing (3) To investigate tree fine-root litter decomposition rates in response to tree species mixing In total, 63 mostly mature forest plots distributed across four sites across Europe were selected from an existing exploratory plot network (FunDivEUROPE) in semi-natural forests. The sites were located in four countries and representative of boreal (Finland), hemiboreal (Poland), mountainous beech (Romania), and thermophilous deciduous forests (Italy). The plots either represented tree species mixtures with three target species or mono-specific stands. Within each plot, five tree neighbourhoods (triplets) were selected for soil sampling and subsequent incubation of root litter samples. In the centre of each of these neighbourhoods, soil cores at three depth increments (0-10, 10-20, 20-30 cm) were taken in spring 2017. The following year, in spring 2018, 1,330 litter bags with fine-root material were incubated near the soil sampling spots for one year. In total, 928 soil samples were processed in the laboratory, and morphological, chemical, and microbial fine-root traits were measured. The vertical distribution of fine roots across soil depths was examined. Roots were sorted by species, and the functional classification approach was applied to distinguish absorptive, i.e., the first three most distal root orders, from transport fine roots, i.e., fourth or fifth-order roots with a diameter ≤2 mm. Moreover, ectomycorrhizal diversity and abundance data from nearby soil samples were integrated into subsequent analyses. Fine-root decomposition rates were determined via mass loss after one year of incubation. Initial fine-root traits of tree species that were incubated were measured to determine initial litter quality. Across all sites, tree species mixing significantly affected tree fine-root traits and decomposition rates. Tree species mixtures supported on average less biomass of absorptive fine roots than corresponding mono-specific stands. This underyielding was mainly reflected in negative complementarity effects, and to a lesser extent, in negative selection effects. The species-specific and overall rooting patterns across the three soil depth layers did not provide evidence for vertical root stratification in mixtures. Nevertheless, as total length density of absorptive fine roots (i.e., across the entire soil profile) did not significantly differ between mixtures and mono-specific stands, overall soil space occupation by tree fine roots and thereby the trees’ resource uptake capacity did not change in response to mixing. Instead, an increased root length density in mixtures in the most nutrient-rich soil depth (0-10 cm) indicates an enhanced soil resource uptake capacity compared to pure stands. The second analysis suggested that the observed underyielding of biomass of absorptive roots in response to tree species mixing was related to changes in fine-root traits. Fine roots in mixtures were characterised by higher specific root lengths, lower diameters, lower root tissue densities, and higher root nitrogen concentrations than trees in pure stands. Overall, these changes at the community level suggest a shift in soil resource acquisition strategies by trees in mixtures compared to mono-specific stands towards a faster resource foraging. A higher ectomycorrhizal colonisation intensity of roots and, at the same time, higher diversity and abundance of ectomycorrhizae in soil samples in mixtures compared to mono-specific stands suggest positive biotic feedbacks from mycorrhizae likely enhancing soil resource capture by trees in mixtures. An important finding was that thin-rooted broadleaved tree species showed stronger responses to mixing than thick-rooted conifer tree species, particularly in terms of root morphology and ectomycorrhizal colonisation. The decomposition study suggested that decomposition rates of mixed-species fine-root litter in mixed tree neighbourhoods can differ from component single-species litter in mono-specific neighbourhoods. As such, mixed-species litter decomposed faster than single-species litter across the four study sites. Differences in micro-environmental conditions between mixed and mono-specific tree neighbourhoods rather than interactions among litter species in mixed-species litter likely caused these non-additive effects. Nevertheless, the analyses further showed that initial chemical traits explained a greater proportion of the variability in the data than tree diversity. The additional incubation of standard root litter species across the plot network further suggests that macro-climate and regional-scale differences, as well as litter species identity, may be more important predictors of fine-root litter decomposition than tree diversity. This thesis enhances our understanding of overall tree diversity effects on ecosystem functioning by shedding more light on the role of the hidden half, i.e., the below-ground component of forest ecosystems. The obtained results provide evidence for positive below-ground species interactions in mixtures, possibly enhancing soil resource acquisition by trees. Hence, these findings contribute to a better mechanistic understanding of positive diversity-productivity relationships in forest ecosystems. Overall relatively consistent tree species mixing effects on fine-root soil exploitation and decomposition across a broad range of environmental conditions and different species compositions in four wide-spread European forest types demonstrate the generality of the results.
... An example for such a biotic feedback is the nutrient and water transfer between tree species in mixtures through a common mycorrhizal network (Simard et al., 2015). Not only the abundance (e.g. ...
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1. Mixed-species forests have often been shown to enhance above-ground ecosystem properties and processes. Despite the significance of fine roots for tree and ecosystem functioning, the role of tree species diversity for below-ground processes driven by fine roots remains largely unknown. Previously, an underyielding of fine-root biomass (FRB) in tree mixtures across four major European forest types has been reported. To explain this phenomenon, we tested here the effect of tree species mixing on fine-root traits related to soil exploitation efficiency, including biotic feedbacks from ectomycorrhizal fungi (EcM), and assessed the role of root trait dissimilarity. 2. We analysed morphological and chemical traits as well as ectomycorrhizal colonisation intensity of absorptive fine roots (i.e. first three most distal orders) in soil samples from 315 mixed and mono-specific tree neighbourhoods in mainly mature, semi-natural forest stands across Europe. Additionally, we quantified mycorrhizal abundance and diversity in soil samples from the same stands. 3. At the community level, fine roots in tree mixtures were characterised by higher specific root lengths and root nitrogen concentrations, lower diameters and root tissue densities indicating a faster resource acquisition strategy compared to mono-specific stands. The higher root EcM colonisation intensity and soil EcM diversity in mixtures compared to mono-specific stands may further provide evidence for positive biotic feedbacks. Moreover, the diversity of fine-root traits influenced FRB, as mixtures characterised by a higher trait dissimilarity were linked to a lower reduction in FRB. At the level of phylogenetic groups, thin-rooted angiosperm species showed stronger responses to mixing than thick-rooted gymnosperms, especially in terms of root morphology and EcM colonisation, indicating different strategies of response to tree mixing. 4. Our results indicate that a lower FRB can reflect a shift in soil resource acquisition strategies, rather than a lower performance of trees in mixtures. They show that several non-exclusive mechanisms can simultaneously explain negative net effects of mixing on FRB. This study sheds new light on the importance of using integrative approaches including both above- and below-ground biomass and traits to study diversity effects on plant productivity.
... Fungal colonization from established EMF communities can have additional benefits for seedlings and mature trees through the formation of ectomycorrhizal networks. An ectomycorrhizal network can transport nutrients such as carbon, water, or nitrogen between trees along a concentration gradient from 'source' to 'sink' trees (Egerton-Warburton et al., 2007;Teste et al., 2009b;Philip et al., 2010;Simard et al., 2015). The network-derived resources can improve seedling drought resistance and survival (Teste and Simard, 2008;Booth and Hoeksema, 2010). ...
Article
The long-lived five-needle pines, Pinus flexilis (limber pine) and Pinus longaeva (Great Basin bristlecone pine) can co-occur and may form symbiotic partnerships with the same species of ectomycorrhizal fungi. These shared symbiotic relationships may facilitate the persistence of these pine species. Throughout their lives, P. flexilis and P. longaeva may also assemble unique belowground fungal communities, adding to the conservation value of ancient trees. We used MiSeq sequencing of fungal rDNA to compare fungal community similarity for co-occurring P. flexilis and P. longaeva roots and soils in an old-growth forest at the Utah Forest Dynamics Plot, Utah, USA. We cored trees to measure their age and determine whether fungal communities change with advanced tree age. We found 720 amplicon sequence variants associated with P. flexilis roots, 736 with P. longaeva roots, and 199 that were shared between the two pines. Root-associated fungal communities were significantly different between P. flexilis and P. longaeva despite similar soil communities. The fungal community composition on P. flexilis roots and around P. longaeva soil was associated with advanced tree age up to 1340 years. The root-associated fungal community of P. flexilis and the soil community of P. longaeva increased in dissimilarity with tree age, indicating that age heterogeneity within old-growth stands promotes fungal diversity. The significant differences in root-associated fungal communities between the two pine species highlights that they are likely engaged in different bi-directional selection with fungal communities.
... Moreover, due to the fast development of molecular techniques in recently years, the diversity of soil microbes in the rhizosphere have been well revealed, and their functions on plant-plant root interactions are receiving increasing attention (Mommer, Kirkegaard, & van Ruijven, 2016). For instance, compared to solitary plants, those grown with intraspecific neighbours on the one hand may suffer more stress from higher accumulation of species-specific soil pathogens (Hendriks et al., 2015); on the other hand they may also receive photosynthates and soil resources transferred from neighbours via a common mycorrhizal network (Simard et al., 2015). Rather than mutually exclusive, these various effects elicited by the presence of a neighbour are more likely to function simultaneously. ...
Article
1. To investigate the responses of plants to their below-ground neighbours independently of nutrient availability, experiments generally require a solitary treatment with one plant grown alone with one unit of nutrients, and a neighbour treatment with two plants grown together with two units of nutrients. This can either be done by doubling nutrient concentration (C) or by doubling soil volume (V) in the neighbour treatment as compared to the solitary treatment. 2. Statistically analysing the same dataset from an experiment that grew plants in solitary or neighbour treatment with a series of V given a fixed amount of nutrients per plant (e.g. 1 g), Chen et al. (2015a) found significant neighbour effects when they controlled for V, while McNickle (2020) found the effects to be insignificant when he controlled for C. 3. The discrepancy in the results of the two studies is caused by a difference in their analytical approaches. This includes (a) different choices of data transformation for the controlling factor, and (b) a mathematical deviation of model structures between V-based and C-based analyses, due to the different inversely proportional V-C relationships between solitary (C = 1/V) and neighbour (C = 2/V) treatments. 4. Choices for either V or C as a controlling factor in the analyses for 'neighbour effect' are based on two different perspectives, focussing either on neighbour-induced nutrient depletion (like McNickle, 2020) or on identity recognition (like Chen et al., 2015a). 5. We also raise concerns about the use of mesh-divided root interaction design and replacement series design in the studies of plant-plant root interactions. We propose to adjust the experimental designs and analytical methods based on the focal perspectives of neighbour effect.
... Mycorrhizal association of fungi with host plant increase drought tolerance by involving in several, physiological and molecular processes. External hyphae increase their size in soil and build extremely branched mycelia that can connect plants together in a network called mycorrhizal network (Simard et al. 2015). The mycelium can absorbed water from deeper soil, which is then transport to cortical tissues, here it is then join to water transport through apoplastic pathways. ...
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Anthropogenic activities in the past and present eras have created global warming and consequently a storm of drought stress, affecting both plants and animals. Being sessile, plants are more vulnerable to drought stress and consequently reduce plant growth and yield. To mitigate the effects of drought stress on plants, it is very crucial to determine the plant response mechanisms against drought stress. Drought response mechanism includes morph-physiological, biochemical, cellular and molecular processes takes place in plants underlying drought stress. These processes include improvement in root system, leaf structure, osmotic adjustment, relative water content and stomata regulation. In addition, calcium and phytohormone (Abscisic acid, Jasmonic acid, Salicylic acid, Auxins, Gibberellins, Ethylene etc.) signaling pathways and scavenging of reactive oxygen species are the key mechanisms to cope with drought stress. Moreover, microorganisms such as bacteria and fungi also have an important role in drought tolerance enhancement. To further elucidate and improve drought tolerance in plants, quantitative trait loci, transgenic approach and application of exogenous substances (nitric oxide, 24-epibrassinoide, glycine betaine and proline) are very crucial. Hereby, the present study integrates various mechanisms of drought tolerance in plants.
... If terrestrial fungi have similar values, this would restrict evaporation, even at low external relative humidity, depending on the radius of the pores and wettability of the walls (79). While the role of matric potentials is well understood for the soil-plant-atmosphere continuum (79), we are only at the beginning of understanding water fluxes through the more complex soil-mycorrhiza-plant-atmosphere or soil-saprotroph-atmosphere systems (76,94). ...
... The seed decay, seedling diseases, foliage diseases, systemic infections, cankers, wilts, and diebacks, root and butt rots, and floral diseases are classified by the fungal pathogens of non-crop plants. The plant populations affected by the fungal pathogens are assumed to be subsidized by the genetic and species diversity of plants and succession in natural systems (Simard et al. 2015). ...
Chapter
In interactions between plants and soil, microorganisms have significant roles. Ecological stability is contributed by the biogeochemical cycling of elements. An emerging body of research is distinguishing the impacts that root-associated microbial communities can have on plant fitness and growth. Rocks and minerals are weathered by the activities of plants, which exude various types of hormones, with a crucial role in the supply of organic matter and formation of soils. Various types of plant species have distinctive biological characteristics that show constraint to precise soil types. Plant–microbe interactions in soil are contributing to a new, microbially based perspective on plant community and ecology. These microorganisms are soil dwellers, diverse, and their interactions with plants vary with respect to specificity, environmental heterogeneity, and fitness impact. The key influences on plant community structure and dynamics are effected by two microbial procedures: microbial intervention of niche diversity in resource use and response dynamics among the soil community and plants. The hypothesis of niche diversity is based on various interpretations that the nutrients of soil are found in different chemical forms: the plant requires accessing these enzymes and nutrients, and the microorganisms of the soil are a major source of these enzymes. Plant–microbe interactions are a significant establishing force for extensive spatial gradients in species abundance. The positive response (a homogenizing force) and negative response (a diversifying force) of virtual balance may contribute to detected latitudinal (and altitudinal) diversity patterns. The microbially based perception for the ecology of plants promises to contribute to our understanding of long-standing issues in ecology and to disclose new areas of future investigation.
... Within a multi-species environment, species can compete for resources such as light, nutrients or water. At the same time, survival of one species can be facilitated by another species providing protection against predators or extreme climate events (Stachowicz, 2001), or by the presence of their mycorrhizal symbionts which could result in mycorrhizal networks (Simard et al., 2015;Pickles and Simard, 2017), or exchanges of resources (Brooker et al., 2008;Teste et al., 2009). Among the consequences of climate change, changes in species distribution are already observed and could result in new or modified species interactions. ...
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Succession is generally well described above-ground in the boreal forest, and several studies have demonstrated the role of interspecific facilitation in tree species establishment. However, the role of mycorrhizal communities for tree establishment and interspecific facilitation, has been little explored. At the ecotone between the mixed boreal forest, dominated by balsam fir and hardwood species, and the boreal forest, dominated by black spruce, several stands of trembling aspen can be found, surrounded by black spruce forest. Regeneration of balsam fir seems to have increased in the recent decades within the boreal forest, and it seems better adapted to grow in trembling aspen stands than in black spruce stands, even when located in similar abiotic conditions. As black spruce stands are also covered by ericaceous shrubs, we investigated if differences in soil fungal communities and ericaceous shrubs abundance could explain the differences observed in balsam fir growth and nutrition. We conducted a study centered on individual saplings to link growth and foliar nutrient concentrations to local vegetation cover, mycorrhization rate, and mycorrhizal communities associated with balsam fir roots. We found that foliar nutrient concentrations and ramification indices (colonization by mycorrhiza per length of root) were greater in trembling aspen stands and were positively correlated to apical and lateral growth of balsam fir saplings. In black spruce stands, the presence of ericaceous shrubs near balsam fir saplings affected ectomycorrhizal communities associated with tree roots which in turn negatively correlated with N foliar concentrations. Our results reveal that fungal communities observed under aspen are drivers of balsam fir early growth and nutrition in boreal forest stands and may facilitate ecotone migration in a context of climate change.
... Additional services of EMF to the host tree include physical and chemical protection from antagonistic/pathogenic fungi (Smith and Read, 2010), and connection and transfer of C among other host trees through common mycorrhizal networks (i.e. shared mycelial connections among trees) (Molina and Trappe, 1982;Molina et al., 1992;Simard et al., 2015). ...
... One reason for this could be that Cortinarius spp., which can be sensitive to fertilization ( Brandrud, 1995) and disturbance ( Sun et al., 2015), benefit from the absence of trampling and fertilization through droppings and urine. It is also conceivable that a greater competition for resources caused by a release from grazing would favor nutrient uptake efficient yet C-demanding mycorrhizal species such as Cortinarius spp., which have high-biomass growth forms, medium-distance exploration types, and the capacity to access limiting N by breaking down complex organic matter ( Simard et al., 2015). However, further studies, with larger sample sizes, are evidently needed to delve deeper into the effects of grazing on fungal community dynamics. ...
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Mycorrhizal associations are widespread in high-latitude ecosystems and are potentially of great importance for global carbon dynamics. Although large herbivores play a key part in shaping subarctic plant communities, their impact on mycorrhizal dynamics is largely unknown. We measured extramatrical mycelial (EMM) biomass during one growing season in 16-year-old herbivore exclosures and unenclosed control plots (ambient), at three mountain birch forests and two shrub heath sites, in the Scandes forest-tundra ecotone. We also used high-throughput amplicon sequencing for taxonomic identification to investigate differences in fungal species composition. At the birch forest sites, EMM biomass was significantly higher in exclosures (1.36 ± 0.43 g C/m2) than in ambient conditions (0.66 ± 0.17 g C/m2) and was positively influenced by soil thawing degree-days. At the shrub heath sites, there was no significant effect on EMM biomass (exclosures: 0.72 ± 0.09 g C/m2; ambient plots: 1.43 ± 0.94). However, EMM biomass was negatively related to Betula nana abundance, which was greater in exclosures, suggesting that grazing affected EMM biomass positively. We found no significant treatment effects on fungal diversity but the most abundant ectomycorrhizal lineage/cortinarius, showed a near-significant positive effect of herbivore exclusion (p = .08), indicating that herbivory also affects fungal community composition. These results suggest that herbivory can influence fungal biomass in highly context-dependent ways in subarctic ecosystems. Considering the importance of root-associated fungi for ecosystem carbon balance, these findings could have far-reaching implications.
... Dies bedeutet zunächst, dass es sich um ein symbiotisches Verhältnis zwischen einem Wirt und einer Ektomykorrhiza-Gesellschaft handelt.Aber die wechselseitigen Beziehungen machen hier nicht halt. Die Hyphen der Ektomykorrhizen verbinden sich untereinander, so dass ein Austausch von Nähr-, Abwehr-und Signalstoffen sogar zwischen den Pilzen und den Wirten stattfinden kann(Simard et al. 2015), es entsteht ein "wood wide web", das plastisch auf Umwelteinflüsse reagieren kann. Hierbei agieren Wirtstaxa, die generalistisch aufgestellt sind, als ein Hotspot für ein breites Ektomykorrhiza-Artenspektrum. ...
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Halbwachs H (2017): Host relations – ectomycorrhizal fungi and their symbiotic partners. Zeit-schrift für Mykologie 83/2:349-356. Abstract: The ectomycorrhizal symbiosis is one of the most fascinationg phenomena in forest ecosystems, especially because only few host taxa face an overwhelming ectomycorrhizal diversity , at least in temperate latitudes. The assumption that both partners automatically benefit by exchanging nutrients and secondary metabolites is certainly too simplistic. Both partners need to constantly balance their " interests " to prevent onesided exploitation. Among both partners exist generalists and specialists. It seems that by forming a hyphal network a mutualistic consortium among these is formed, which enables to plastically react to permanently changing environmental challenges. This explain why our forest ecosystems are relatively stable and able to recover, despite partly harsh climatic conditions. We are still far from a detailed mechanistic understanding of such phenomena. Thus, the hypotheses presented here need further confirmation by future research. Zusammenfassung: Die Ektomykorrhiza-Symbiose ist einer der faszinierendsten Phänome in Wald-Ökosystemen. Faszinierend schon deshalb, weil nur wenige Wirtsgehölze einer überwältigenden Vielfalt von Ektomykorrhizapilzen gegenüberstehen, zumindest in unseren temperaten Breiten. Die Annahme, dass beide Partner durch den Austausch von Nährstoffen und Sekundärmetabo-liten automatisch profitieren, ist sicher zu simpel. Beide Partner müssen ihre " Interessen " lau-fend austarieren, damit es zu keiner einseitigen Ausbeutung kommt. Es gibt unter beiden Partnern Generalisten und Spezialisten, und es scheint, dass über eine Ver-netzung der Hyphen ein mutualistisches Konsortium geformt wird, das plastisch auf Heraus-forderungen sich dauernd verändernder Umweltbedingungen reagieren kann. Dies würde erklären, warum unsere Wald-Ökosysteme relativ stabil bzw. erholungsfähig sind, trotz teils harscher Klimabedingungen. Wir sind noch weit davon entfernt, diese Phänomene im Einzelnen zu verstehen. Die hier ange-schnittenen Hypothesen bedürfen deshalb weiterer Bestätigung, also Forschung.
... The interest in the specificity phenomenon is not simply theoretical. It ultimately affects how each mycorrhizal fungus can create and maintain mycelial networks ‫ء‬ in complex plant communities and on how these linkages can possibly alter resource allocation and communication among individuals, two research venues vigorously pursued by scientists worldwide (Simard et al. 2015;Horton 2015). ...
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Over the last decade, we have witnessed extraordinary progress in the understanding of molecular dialogues between the partners in plant root mutualisms and, as such, a considerable amount of new information now needs to be integrated into an already significant body of literature. The topic of symbiosis has become difficult to explore in a teaching venue, as there is seemingly so much to discuss, and yet students are truly interested in the discipline because of its potential applications in conservation, sustainable agriculture, and forestry. In this minireview targeted to instructors, senior students, and scientists, we offer a means of teaching the symbioses between mycorrhizal fungi and vascular plants, whereby we propose a conceptual staircase with three levels of incremental learning difficulty. At the first level, we describe the fundamentals of mycorrhizas with special emphasis on the plant–fungus interface. At the second level, we focus on the pre-communication between the two partners. At the third level, we discuss the physiology of the interface in terms of agriculture and forestry. At the end of each level, we provide a short summary where the most important concepts have been outlined for an instructor. As well, throughout the text, we raise questions of interest to the field at large.
... If terrestrial fungi have similar values, this would restrict evaporation, even at low external relative humidity, depending on the radius of the pores and wettability of the walls (79). While the role of matric potentials is well understood for the soil-plant-atmosphere continuum (79), we are only at the beginning of understanding water fluxes through the more complex soil-mycorrhiza-plant-atmosphere or soil-saprotroph-atmosphere systems (76,94). ...
Article
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The Mycelium as a Network, Page 1 of 2 Abstract The characteristic growth pattern of fungal mycelia as an interconnected network has a major impact on how cellular events operating on a micron scale affect colony behavior at an ecological scale. Network structure is intimately linked to flows of resources across the network that in turn modify the network architecture itself. This complex interplay shapes the incredibly plastic behavior of fungi and allows them to cope with patchy, ephemeral resources, competition, damage, and predation in a manner completely different from multicellular plants or animals. Here, we try to link network structure with impact on resource movement at different scales of organization to understand the benefits and challenges of organisms that grow as connected networks. This inevitably involves an interdisciplinary approach whereby mathematical modeling helps to provide a bridge between information gleaned by traditional cell and molecular techniques or biophysical approaches at a hyphal level, with observations of colony dynamics and behavior at an ecological level.
... Cortinarius spp. have high-biomass growth forms, medium-distance exploration types, and enhanced capacities to degrade complex organic matter, thus securing access to limiting N (Simard et al., 2015), and it is possible that a release from grazing favoured an increased investment in this type of C-demanding, yet nutrient-uptake efficient mycorrhizae, due to an increase in competition. In boreal forests, high abundance of cord-forming ectomycorrhizal fungi, such as Cortinarius species, was linked to rapid turnover of mycelial biomass and low C sequestration, while ericoid mycorrhizal ascomycetes facilitated long-term humus build-up through production of melanized hyphae that resist decomposition (Clemmensen et al., 2015). ...
Thesis
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Arctic and alpine ecosystems are experiencing fundamental changes in vegetation composition due to increasing temperatures. One of the most palpable of these changes is the expansion of shrubs on the treeless tundra, which has been reported from many sites throughout the Arctic. An increase in tall deciduous shrub cover has been hypothesized to have profound implications for ecosystem processes, e.g. through increasing snow trapping in winter, which can raise soil temperatures and accelerate nutrient turnover rates. In spring, taller shrub canopies can lower albedo and speed up spring thaw, thus prolonging the growing season. An increase in low evergreen shrubs, on the other hand, may decrease turnover rates through the production of more recalcitrant litter. The effect of herbivory on different shrub species may therefore be of major importance. The aim of this thesis was to investigate how vegetation has changed in the Scandes forest-tundra ecotone over the past two decades and how large herbivores have influenced these changes. 16-year old reindeer exclosures, in several different vegetation types in the Scandes mountain range, were used to study how plant community composition, mycelia production and nutrient allocation patterns within plants were affected by grazing. The comparative effects of reindeer and hare browsing on tall shrubs were also examined. Low evergreen shrubs, such as mountain crowberry and heather, had increased dramatically at both shrub heath and mountain birch forest sites, and were not influenced by large herbivores. Deciduous shrub cover, mainly consisting of dwarf birch, had increased to a far lesser extent but was significantly greater and taller inside exclosures. Tall shrub cover was, in turn, negatively correlated with summer soil temperatures, while winter soil temperatures tended to be higher in exclosures. Despite this, no effects of grazing on diversity were found. At a grass heath site, a similar expansion of ericoid shrubs was seen, whereas at a more productive low herb meadow, grazer exclusion had triggered an advancement of willow species, which had grown tall inside the exclosures. Outside the exclosures, low evergreen shrubs had increased, suggesting that, in the absence of herbivores, this group was outcompeted by tall deciduous shrubs. Furthermore, not only reindeer but also mountain hares were found to substantially affect tall shrubs. Apart from plant community composition, herbivory also affected carbon content and isotopic composition of a perennial herb, as well as the overall production of ectomycorrhizal mycelia. Surprisingly, contrasting effects on mycelia production were found in the mountain birch forest, where mycelia biomass was larger inside exclosures, and in the shrub heath, where mycelia biomass was larger outside exclosures. By holding back the expansion of deciduous shrubs, herbivores can decelerate turnover rates. Furthermore the increase in more recalcitrant litter and ericoid mycelia associated with evergreen shrubs may slow down nutrient cycling further. Hence, the unexpected finding that the major vegetation shift was an increase in ericoid shrubs, rather than tall deciduous shrubs as many other studies have reported, may have far-reaching consequences for ecosystem functioning and soil carbon stocks.
... We now know that MNs can influence plant establishment (Dickie et al. 2002;Nara 2006), survival (Horton and Bruns 2001;Teste et al. 2009;Bingham and Simard 2011), physiology (Wu et al. 2001(Wu et al. , 2002, growth (Teste et al. 2010) and defence chemistry (Song et al. 2010(Song et al. , 2014Babikova et al. 2013). This influence is thought to occur because the MN serves either as a pathway for interplant exchange of resources and stress molecules or as a source of fungal inoculum ( Fig. 1) (see reviews by Simard et al. 2012Simard et al. , 2013Simard et al. , 2015. For instance, anastomosis with existing MNs of established plants is considered the most common mechanism for mycorrhizal fungal colonization of regenerating plants in situ (van der Heijden and Horton 2009; Kariman et al. 2012). ...
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Adaptive behavior of plants, including rapid changes in physiology, gene regulation and defense response can be altered when linked to neighbouring plants by a mycorrhizal network. Mechanisms underlying the behavioral changes include mycorrhizal fungal colonization by the mycorrhizal network or interplant communication via transfer of nutrients, defense signals or allelochemicals. We focus this review on our new findings in ectomycorrhizal ecosystems, but also review recent advances in arbuscular mycorrhizal systems. We have found that the behavioral changes in ectomycorrhizal plants can depend on environmental cues, the identity of the plant neighbor and the characteristics of the mycorrhizal network. The hierarchical integration of this phenomenon with other biological networks at broader scales in forest ecosystems, and the consequences we have observed when it is interrupted, indicates that underground 'tree talk' is a foundational process in the complex adaptive nature of forest ecosystems. Published by Oxford University Press on behalf of the Annals of Botany Company.
Book
This Element follows the development of humans in constantly changing climates and environments from Homo erectus 1.9 million years ago, to fully modern humans who moved out of Africa to Europe and Asia 70,000 years ago. Biosemiotics reveals meaningful communication among coevolving members of the intricately connected life forms on this dynamic planet. Within this web hominins developed culture from bipedalism and meat-eating to the use of fire, stone tools, and clothing, allowing wide migrations and adaptations. Archaeology and ancient DNA analysis show how fully modern humans overlapped with Neanderthals and Denisovans before emerging as the sole survivors of the genus Homo 35,000 years ago. Their visions of the world appear in magnificent cave paintings and bone sculptures of animals, then more recently in written narratives like the Gilgamesh epic and Euripides' Bacchae whose images still haunt us with anxieties about human efforts to control the natural world.
Chapter
Functional traits are widely recognized as a useful framework for testing mechanisms underlying species community assemblage patterns and ecosystem processes. While botanists have developed this field during the past 20 years, mycology still needs to catch up. Only during recent years, ecological research has begun to recognize the fundamental role of fungi in virtually all ecosystems. For this role, the mechanistic background needs to be uncovered, which is tightly intertwined with fungal functional traits. These traits are of morphological, physiological, and behavioral nature. In this article, current knowledge is presented, and gaps to be closed are analyzed.
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Mycorrhizal fungi are key components of soil biodiversity that offer potential to provide sustainable solutions for land management, notably in agriculture and forestry. Several studies conducted in controlled environments show that key functional attributes of common mycorrhizal networks (CMNs), which inter-link different plants, are influenced by management practices. Here, we highlight the need to consider how land management affects the ubiquity and function of CMNs in nature to maximize the role of mycorrhizal fungi in enhancing ecosystem services. We emphasize that CMNs can sometimes negatively affect aspects of plant performance, but there remain major gaps in understanding before explicit consideration of CMN management can be delivered. Summary Most mycorrhizal fungi have the capacity to develop extensive extraradical myce-lium, and thus have the potential to connect multiple plants and form a 'common mycorrhizal network'. Several studies have shown that these networks can influence plant establishment, nutrition, productivity and defense, nutrient distribution and storage, and multitrophic interactions. However, many of these studies have focused on the importance of common mycorrhizal networks in ecological contexts and there has been less emphasis in managed systems, including croplands, grassland, agrofor-estry and forestry, on which humankind relies. Here we review the evidence of the potential importance of common mycorrhizal networks in managed systems, and provide insight into how these networks could be managed effectively to maximize the functions and outputs from managed systems. We also emphasize possible negative effects of common mycorrhizal networks on plant performance and question popular views that mycorrhizal networks may offer a panacea for enhancing ecosystem services. We highlight the need to gain greater insight into the ubiquity, functioning, and response to management interventions of common mycorrhizal networks and, critically, the need to determine the extent to which these networks can add value to the promotion of mycorrhizal colonization. K E Y W O R D S agroecosystems, forestry, land management, plant to plant signaling, restoration, soil biodiversity, sustainable agriculture
Research
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Plant competition belowground is a crucial factor that determines plant fitness and shapes plant communities. It has been shown that roots possess the ability to recognize between self and non-self individuals and modify their growth patterns accordingly. Roots may also be further able to discriminate between kin and non-kin roots. Competition is stronger with non-kin than kin neighbors, but whether root growth patterns determined by kin interactions are modified in stressful environments is largely unexplored. In this study we used two different experimental setups to confirm whether the clonal species Glechoma hederacea exhibits kin recognition between roots, and how water limitation modifies this response. A split-root design was conducted using a focal clonal fragment of G. hederacea placed onto the ridge that separated two adjacent containers: either square petri-dishes boxes with 200 ml of soil or 400 ml clear pots. Focal plants were randomly allocated to either growing alone or in competition with another G. hederacea ramet (of similar size taken from the same stolon as the focal plant) or a non-kin individual (a ramet selected from a different population). A water limitation treatment was applied to both experiments. Five root parameters were measured during the experiment using boxes: the maximum depth and the maximum width of the deepest root, the depth and the maximum width of the widest root, and the total number of roots visible. All plants were harvested after 36 days and several final root measurements were taken and analyzed using GiaRoots. Our results show that G. hederacea roots have kin recognition mechanisms, showing a significant tendency to avoid growing toward a non-kin neighbor but not avoiding the roots of a kin plant, even though the presence of a kin plant modifies root distribution within the soil. As expected, water limitation significantly affected plant growth and root parameters, but this effect was not related to neighbor kin identity. Taken together, our results confirm the existence of root recognition in this species and suggest that the mechanisms of kin recognition are probably related to a root-derived chemical cues, as recognition took place before physical contact occurred.
Article
Belowground ectomycorrhizal (ECM) fungal communities are affected by the dominant tree species of aboveground vegetation. We investigated ECM-fungal communities in the boundary between secondary broad-leaved forests dominated by ECM trees and cypress plantations consisting of arbuscular trees. ECM root tips were collected from soil cores and seedlings at a small scale within 20 m of the boundary. We used molecular analysis of internal transcribed spacer regions of rDNA to identify ECM-fungal species. Of the 104 molecular taxonomic units detected from soil cores and seedlings, the estimated ECM-fungal species richness in broad-leaved forests was higher than that in the cypress plantations. More than half of the ECM-fungal species detected in cypress plantations were shared with adjacent broad-leaved forests. In particular, Russulaceae and Thelephoraceae were dominant in broad-leaved forests and cypress plantations. However, low-frequency occurrence taxa in broad-leaved forests were mostly absent in cypress plantations, at a distance of more than 10 m from the boundary. ECM-fungal species associated with seedlings tended to differ between broad-leaved forests and cypress plantations. Furthermore, Cenococcum geophilum shared soil cores and seedlings in both stands. These results indicated that ECM-fungal communities in cypress plantations were affected by adjacent broad-leaved forests, and this effect likely involved distance from the boundary.
Article
1. Mycorrhizal networks are conduits for the transfer of resources between hosts. While ectomycorrhizal networks (EMN) are known to influence seedlings, their effect on adult tree growth remains unknown and may have important implications for forest responses to future climates. 2. We used annual basal area increment of trees and previously described Rhizopogon vesiculosus and Rhizopogon vinicolor EMNs to examine an association between the number of connections between trees through an EMN and the growth of adult interior Douglas-fir. We compared this relationship for the year the networks were mapped, in 2008, with eight years previous and eight years afterward. We also compared the variation in standardized growth (2000–2016) to examine the association between growth variability and EMN variables. 3. Greater growth was positively associated with 1) the number of connections to other trees via a Rhizopogon vinicolor EMN, and 2) the number of genets of Rhizopogon vesiculosis by which a tree was colonized. Variation of growth (2000–2016) was negatively associated with increasing number of connections to other trees via Rhizopogon vinicolor. Synthesis. These findings, for the first time, indicate that EMNs may positively influence the growth of adult trees. The difference in tree growth response between the sister fungal species highlights a novel avenue to identify interspecific and intraspecific differences between species occurring at different depths in the soil. Our study has important implications when considering the role of EMNs in influencing forest health and mitigating stress from environmental conditions.
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Bioelectricity from ecosystems of living plants and their associated soil electric-generating microorganisms is an innovative source of alternative energy. The bioelectro-productivity of forests ecosystems, marshy areas and agro-ecosystems of orchards and plantations of agricultural crops was assessed in situ in three parts of the Western Ukraine in the north, in the Polissia, in the central part, in the Opillia and in the south, on the border of the Pokutsko-Bukovina Carpathians and Chornogora. The bioelectric potential was determined in the most spread and typical microbial-plant associations of forests, swampy meadows and agro-ecosystems of the Western Ukraine using the two-electrode system, which was located stationary in the soil in the zone of association of the plant root system and electric-generating microorganisms during 150 days - from the beginning of summer to late autumn. The highest rates of bioelectricity were recorded in phyto-microbiocenoses of forests. The average level of bioelectric potential of forests was 1080.5 mV. In the gardens and wetlands, bioelectric performance was slightly lower, 1055.3 mV and 1051.2 mV, respectively. The bioelectric potential of the most agricultural crops was significantly lower, except for the Z. mays crop, which was characterized by high average values of bioelectric potential at the level of garden shrubs. It was found that the daily level of bioelectricity fluctuates slightly with slight decrease at the end of the light day in the some samples. We observed small fluctuations in the parameters of bioelectric potential, because the level of photosynthesis and, accordingly, the degree of accumulation of organic compounds that are substrates for the development of electroactive microorganisms, depending on meteorological conditions, physicochemical soil factors are specific to each ecosystem and each new day. The seasonal fluctuations in the level of bioelectric potential during June – October in the studied microbial-plant associations were statistically insignificant. The influence of humidity on the generation of the bioelectrical potential of phyto-microbocenoses was studied. The positive effect of soil moisture on the bioelectric potential generation was revealed. With increase in humidity of soil from 15% to 55% the level of bioelectric potential of forest and garden microbial-plant associations also increased significantly. The increasing of the bioelectric potential of forest and garden microbial-plant associations of P. silvestris and M. domestica was 159.3 mV and 115.4 mV, respectively in these conditions. The increasing of bioelectric potential in dry soils was determined, due to active photosynthesis and moisture accumulation by plants. With the decrease in humidity of soil from 55% to 25%, the level of bioelectric potential increased significantly in agricultural and garden microbial-plant associations of R. rubrum and B. oleracea, the increase in bioelectric potential was 96.3 and 81.7 mV, respectively. High and stable average values of the bioelectric potential of microbial-plant associations of forests and wetland meadows, orchards and some crops observed for the period from June to October, the rise of potential even in arid conditions were revealed their prospects as an important source of renewable energy. Forests and wetlands, which occupy a significant part of the territory of Western Ukraine, could become an additional environmentally friendly source of energy, both large-scale and local in case of further development of electro-biotechnology.
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Soil microorganisms and their symbiotic relationships with plants are fundamental to nutrient cycling in temperate forest ecosystems. This highly diverse microbiome contains up to a quarter of Earth’s biodiversity, but our understanding of how this affects the function of forests is not well understood. This thesis investigated the role of plant symbionts on the allocation of C to belowground microbial symbionts and to ground vegetation via microbial symbionts. Radio-isotope pulse labelling was used to determine the belowground C dynamics of these highly complex systems by allowing us to quantify pools and fluxes within the plant-microbe-soil continuum. In Chapter 3, the role of arbuscular and ecto-mycorrhizal fungi in belowground allocation of C in three temperate tree species was investigated by destructive harvesting of trees 336 days after a pulse label had been applied. The results suggested that Alnus glutinosa and Betula pendula allocated C belowground to microbes, whereas Castanea sativa transferred the C to the soil where it was sequestered. In Chapter 4, inter- and intra-specific C transfer was studied using trees connected via a common mycorrhizal network (CMN), the results suggested that more C was transferred between inter- than intra-specific species combinations. In Chapter 5, C transferred via three “donor” tree species to the root nodules of A. glutinosa “receiver” tree connected with a CMN was investigated using the methodology pioneered in Chapter 3. The plant: fungal amalgam preferentially allocated C from the donor trees to the root nodules of the receiver A. glutinosa tree. We postulated that this was due to the considerable energetic demands of nitrogen-fixation by Frankia alni in the root nodule creating a strong C sink. In Chapter 6, the transfer of C from 13-year-old coppiced A. glutinosa and C. sativa trees to ground vegetation via CMN was investigated. 14C activity in the ground vegetation under the A. glutinosa trees was expected to be greatest, as A. glutinosa share arbuscular mycorrhizal partnerships with the ground vegetation. No difference in 14C activity was found in the hyphae, soil solution or ground vegetation under A. glutinosa. We postulated that this could be due to root grafting, mycorrhizal types exchanging nutrients, or reabsorption of tree rhizodeposits. Overall this study suggests that the plant: microbe symbiosis that is ubiquitous across the temperate biome is both important for nutrient cycling and C storage, but also that the sharing of resources via CMNs could be altering plant competition dynamics that have previously been based on the assumption that plants are not physically connected and actively sharing resources. Further work to determine how plants or mycorrhizae control belowground resource sharing could lead to a paradigm shift in our understanding of competition and facilitation in plant community dynamics.
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Background It is well established that the functioning of terrestrial ecosystems depends on biophysical and biogeochemical feedbacks occurring at the soil-plant-atmosphere (SPA) interface. However, dynamic biophysical and biogeochemical processes that operate at local scales are seldom studied in conjunction with structural ecosystem properties that arise from broad environmental constraints. As a result, the effect of SPA interactions on how ecosystems respond to, and exert influence on, the global environment remains difficult to predict.ScopeWe review recent findings that link structural and functional SPA interactions and evaluate their potential for predicting ecosystem responses to chronic environmental pressures. Specifically, we propose a quantitative framework for the integrated analysis of three major plant functional groups (evergreen conifers, broadleaf deciduous, and understory shrubs) and their distinct mycorrhizal symbionts under rising levels of carbon dioxide, changing climate, and disturbance regime. First, we explain how symbiotic and competitive strategies involving plants and soil microorganisms influence scale-free patterns of carbon, nutrient, and water use from individual organisms to landscapes. We then focus on the relationship between those patterns and structural traits such as specific leaf area, leaf area index, and soil physical and chemical properties that constrain root connectivity and canopy gas exchange. Finally, we use those relationships to predict how changes in ecosystem structure may affect processes that are important for climate stability.Conclusions On the basis of emerging ecological theory and empirical biophysical and biogeochemical knowledge, we propose ten interpretive hypotheses that serve as a primary set of hierarchical relationships (or scaling rules), by which local SPA interactions can be spatially and temporally aggregated to inform broad climate change mitigation efforts. To this end, we provide a series of numerical formulations that simplify the net outcome of complex SPA interactions as a first step towards anticipating shifts in terrestrial carbon, water, and nutrient cycles.
Article
Purpose Based on the significance of ectomycorrhizae (ECM) and increased publication activity on this subject, it was decided to carry out a bibliometric analysis of scientific outputs in this area. The purpose of this study is to reveal the research trends of scientific outputs on ECM for the past 30 years and provide a potential guide for future research. Design/methodology/approach A method of bibliometric analysis was performed, based on the online version of the Science Citation Index Expanded, Web of Science, from 1986 to 2017. The authors evaluated the publication types, languages, source countries, journals, the patterns of publication outputs, most-cited articles, most-productive authors, institutional distributions, subject categories, high-frequency keywords and keywords plus and high-frequency terms in the title and abstract of ectomycorrhizal research. Keywords, keywords plus and high-frequency terms in the title and abstract were analyzed via VOSviewer to illustrate the extent of co-occurrence. This study further describes the recent research priority or hotspots and reveals the research trends. Findings From 1986 to 2017, the publication output on ECM showed a rising trend; the number of articles has rapidly increased after 2003. Based on co-occurrence analysis for keywords, keywords plus and terms in the title and abstract, “ectomycorrhizal fungi” is the most popular keyword and keywords plus; “concentration” is the most high-frequency terms in the title and abstracts. Plant biology, mycology and ecology are the hotspots in the ectomycorrhizal research. Ectomycorrhizal taxonomy, the molecular mechanisms of ectomycorrhizal symbioses and the common mycorrhizal networks are the future direction. Originality/value A bibliometric analysis has been carried out to analyze the trends of ECM research with 30 years. This study provides a potential guide for future research related to ectomycorrhizae.
Chapter
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 neurotransmitters. 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.
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Background Mycorrhizal strategies are very effective in enhancing plant acquisition of poorly-mobile nutrients, particularly phosphorus (P) from infertile soil. However, on very old and severely P-impoverished soils, a carboxylate-releasing and P-mobilising cluster-root strategy is more effective at acquiring this growth-limiting resource. Carboxylates are released during a period of only a few days from ephemeral cluster roots. Despite the cluster-root strategy being superior for P acquisition in such environments, these species coexist with a wide range of mycorrhizal species, raising questions about the mechanisms contributing to their coexistence. Scope We surmise that the coexistence of mycorrhizal and non-mycorrhizal strategies is primarily accounted for by a combination of belowground mechanisms, namely (i) facilitation of P acquisition by mycorrhizal plants from neighbouring cluster-rooted plants, and (ii) interactions between roots, pathogens and mycorrhizal fungi, which enhance the plants’ defence against pathogens. Facilitation of nutrient acquisition by cluster-rooted plants involves carboxylate exudation, making more P available for both themselves and their mycorrhizal neighbours. Belowground nutrient exchanges between carboxylate-exuding plants and mycorrhizal N2-fixing plants appear likely, but require further experimental testing to determine their nutritional and ecological relevance. Anatomical studies of roots of cluster-rooted Proteaceae species show that they do not form a complete suberised exodermis. Conclusions The absence of an exodermis may well be important to rapidly release carboxylates, but likely lowers root structural defences against pathogens, particularly oomycetes. Conversely, roots of mycorrhizal plants may not be as effective at acquiring P when P availability is very low, but they are better defended against pathogens, and this superior defence likely involves mycorrhizal fungi. Taken together, we are beginning to understand how an exceptionally large number of plant species and P-acquisition strategies coexist on the most severely P-impoverished soils.
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Ectomycorrhizal (EM) networks provide a variety of services to plants and ecosystems include nutrient uptake and transfer, seedling survival, internal cycling of nutrients, plant competition, and so on. To deeply their structure and function in ecosystems, we investigated the spatial patterns and nitrogen (N) transfer of EM networks using ¹⁵N labelling technique in a Mongolian scotch pine (Pinus sylvestris var. mongolica Litv.) plantation in Northeastern China. In August 2011, four plots (20 × 20 m) were set up in the plantation. 125 ml 5 at.% 0.15 mol/L ¹⁵NH4¹⁵NO3 solution was injected into soil at the center of each plot. Before and 2, 6, 30 and 215 days after the ¹⁵N application, needles (current year) of each pine were sampled along four 12 m sampling lines. Needle total N and ¹⁵N concentrations were analyzed. We observed needle N and ¹⁵N concentrations increased significantly over time after ¹⁵N application, up to 31 and 0.42%, respectively. There was no correlation between needle N concentration and ¹⁵N/¹⁴N ratio (R² = 0.40, n = 5, P = 0.156), while excess needle N concentration and excess needle ¹⁵N/¹⁴N ratio were positively correlated across different time intervals (R² = 0.89, n = 4, P < 0.05), but deceased with time interval lengthening. Needle ¹⁵N/¹⁴N ratio increased with time, but it was not correlated with distance. Needle ¹⁵N/¹⁴N ratio was negative with distance before and 6th day and 30th day, positive with distance at 2nd day, but the trend was considerably weaker, their slop were close to zero. These results demonstrated that EM networks were ubiquitous and uniformly distributed in the Mongolian scotch pine plantation and a random network. We found N transfer efficiency was very high, absorbed N by EM network was transferred as wide as possible, we observed N uptake of plant had strong bias for ¹⁴N and ¹⁵N, namely N fractionation. Understanding the structure and function of EM networks in ecosystems may lead to a deeper understanding of ecological stability and evolution, and thus provide new theoretical approaches to improve conservation practices for the management of the Earth’s ecosystems.
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Adaptive behavior of plants, including rapid changes in physiology, gene regulation and defense response can be altered when linked to neighbouring plants by a mycorrhizal network. Mechanisms underlying the behavioral changes include mycorrhizal fungal colonization by the mycorrhizal network or interplant communication via transfer of nutrients, defense signals or allelochemicals. We focus this review on our new findings in ectomycorrhizal ecosystems, but also review recent advances in arbuscular mycorrhizal systems. We have found that the behavioral changes in ectomycorrhizal plants can depend on environmental cues, the identity of the plant neighbor and the characteristics of the mycorrhizal network. The hierarchical integration of this phenomenon with other biological networks at broader scales in forest ecosystems, and the consequences we have observed when it is interrupted, indicates that underground 'tree talk' is a foundational process in the complex adaptive nature of forest ecosystems. Published by Oxford University Press on behalf of the Annals of Botany Company.
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Microautoradiographic studies were carried out to examine the distribution and exchange of phosphate and labeled carbohydrates in mycorrhizal roots of Populus tremula x Populus alba L. following application of P-33-orthophosphate (P-i) and (CO2)-C-14. Labeled P-i was not homogeneously distributed along the mycorrhizal longitudinal axis. The fungal sheath and the Hartig net contained more P-33(i) in the median parts of the root than in the apical or basal root zones, indicating that uptake and transfer of P-i to the host plant was localized mainly in this area. The P-i was translocated by the Hartig net and the interfacial apoplast to the host plant. It was distributed by way of the stele within the plant. Young leaves and meristematic tissue in the shoot tip were the main sinks for P-i. In plants that were left in the dark for 5 days before P-33(i) application, the reduced carbohydrate supply caused a decrease in P-i absorption by mycorrhizal roots. Microautoradiography of mycorrhizal roots after assimilation of (CO2)-C-14 revealed that: (1) the fungal partner had a high capacity to attract photosynthates; (2) the main transfer of carbohydrates was localized in the median zone of a mycorrhizal root; (3) carbohydrates that were absorbed by the mycorrhizal fungus were translocated to the fungal sheath and were homogeneously distributed; and (4) in the main exchange zone, cortical cell nuclei showed a high sink capacity, indicating increased metabolic activity in these cells. We postulate that (1) the phosphate demand of the host plant regulates absorption of P-i by the fungus, and (2) a bidirectional transfer of carbohydrates and P-i occurs across the same interface structure in ectomycorrhizal roots of Populus.
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Arbuscular mycorrhizal (AM) fungi are mutualistic symbionts living in the roots of 80% of land plant species, and developing extensive, belowground extraradical hyphae fundamental for the uptake of soil nutrients and their transfer to host plants. Since AM fungi have a wide host range, they are able to colonize and interconnect contiguous plants by means of hyphae extending from one root system to another. Such hyphae may fuse due to the widespread occurrence of anastomoses, whose formation depends on a highly regulated mechanism of self recognition. Here, we examine evidences of self recognition and nonself incompatibility in hyphal networks formed by AM fungi and discuss recent results showing that the root systems of plants belonging to different species, genera and families may be connected by means of anastomosis formation between extraradical mycorrhizal networks, which can create indefinitely large numbers of belowground fungal linkages within plant communities.
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Extensive regions of interior Douglas-fir (Pseudotsuga menziesii var. glauca, IDF) forests in North America are being damaged by drought and western spruce budworm (Choristoneura occidentalis). This damage is resulting from warmer and drier summers associated with climate change. To test whether defoliated IDF can directly transfer resources to ponderosa pine (Pinus ponderosae) regenerating nearby, thus aiding in forest recovery, we examined photosynthetic carbon transfer and defense enzyme response. We grew pairs of ectomycorrhizal IDF 'donor' and ponderosa pine 'receiver' seedlings in pots and isolated transfer pathways by comparing 35 μm, 0.5 μm and no mesh treatments; we then stressed IDF donors either through manual defoliation or infestation by the budworm. We found that manual defoliation of IDF donors led to transfer of photosynthetic carbon to neighboring receivers through mycorrhizal networks, but not through soil or root pathways. Both manual and insect defoliation of donors led to increased activity of peroxidase, polyphenol oxidase and superoxide dismutase in the ponderosa pine receivers, via a mechanism primarily dependent on the mycorrhizal network. These findings indicate that IDF can transfer resources and stress signals to interspecific neighbors, suggesting ectomycorrhizal networks can serve as agents of interspecific communication facilitating recovery and succession of forests after disturbance.
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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 vesiculosus and 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 x 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 sub-network 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.This article is protected by copyright. All rights reserved.
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BC's forests have already faced two simultaneous, globally significant, epidemics linked to climate change; the Doth-istroma needle blight epidemic in NW BC and the massive mountain pine beetle epidemic throughout the BC Interior. Building on these experiences, we have compiled our best estimates of how we believe other forest health agents may behave as climate change continues to influence our forests. We have drawn on literature from around the world but have focused on the situation in BC. We have made management recommendations based on what we have seen so far and what we expect to come. RÉSUMÉ Les forêts de la C.-B. ont déjà subi simultanément deux épidémies significativement importantes liées aux changements climatiques: la brûlure en bande rouge à l' état d' épidémie dans le nord-ouest de la C.-B. et l'infestation massive par le den-droctone du pin ponderosa relevé partout dans la zone intérieure de la C.-B. À partir de ces situations, nous avons bâti nos meilleurs estimés de ce qu'il nous semble sera le comportement d'autres ravageurs forestiers alors que les changements climatiques continuent de modifier nos forêts. Nous avons consulté des documents de partout dans le monde, mais nous nous sommes attardés à la situation vécue en C.-B. Nous avons établi des recommandations portant sur l'aménagement d'après ce que nous avons constaté à ce jour et selon ce que nous prévoyons pour l'avenir.
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Greater understanding of positive interspecific interactions in nutrient-poor soils is a priority, particularly in phosphorus- (P) limited ecosystems where plants with contrasting nutrient-acquiring strategies co-occur. It is also relevant to agro-ecosystems, since global P stocks are being depleted. In this study, we assess positive interactions between sympatric plants with contrasting nutrient-acquiring strategies from highly P-impoverished soils from the biodiversity hotspot of south-western Australia. Four plant species (Banksia menziesii, Eucalyptus marginata, Verticordia nitens, and Melaleuca preissiana) that are non-mycorrhizal (cluster rooted), ectomycorrhizal (EM), arbuscular (AM), or dual AM/EM, respectively, were grown together in a specially-designed ‘common garden’ microcosm with nutrient-poor or fertilised soil, with or without root intermingling and fungal hyphae contact. We measured growth, mycorrhizal colonisation, root intermingling, and nutrient uptake to determine positive or negative growth patterns among the various plant assemblies. Growth of the AM/EM host was best when interacting with both the EM host and a non-mycorrhizal nutrient-mining plant with cluster roots (Banksia) in microcosms where root intermingling was not possible. Growth promotion was only seen in pots with nutrient-poor soils, where the better growth of Melaleuca coincided with higher shoot P, manganese, calcium, iron and boron content, whereas an increase in soil nutrient status through fertiliser addition resulted in a decrease in nutrient sharing between co-occurring species. Furthermore, the dual AM/EM Melaleuca exhibited enhanced EM colonisation and favoured EM over AM fungi when grown beside Eucalyptus and Banksia. We surmise that mycorrhizal networks were instrumental in the variation in both mycorrhizal type and colonisation levels. We conclude that complementarity of plant nutrient-acquisition strategies can promote growth of neighbour species. The results show a synergistic effect between EM hyphal scavenging and mobilisation of limiting nutrients by cluster roots. The positive and negative interactions enable coexistence to go far beyond the traditional view that plants interact mainly through resource depletion. This study improves our understanding of how root interactions could shape plant communities and promote species diversity and packing in nutrient-impoverished habitats. This article is protected by copyright. All rights reserved.
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Fungi are sessile, highly sensitive organisms that actively compete for environmental resources both above and below the ground. They assess their surroundings, estimate how much energy they need for particular goals, and then realise the optimum variant. They take measures to control certain environmental resources. They perceive themselves and can distinguish between ‘self’ and ‘non-self’. They process and evaluate information and then modify their behaviour accordingly. These highly diverse competences show us that this is possible owing to sign(aling)- mediated communication processes within fungal cells (intraorganismic), between the same, related and different fungal species (interorganismic), and between fungi and non-fungal organisms (transorganismic). Intraorganismic communication involves sign-mediated interactions within cells (intracellular) and between cells (intercellular). This is crucial in coordinating growth and development, shape and dynamics. Such communication must function both on the local level and between widely separated mycelium parts. This allows fungi to coordinate appropriate response behaviors in a differentiated manner to their current developmental status and physiological influences. This book will orientate further investigations on how fungal ecosphere inhabitants communicate with each other to coordinate their behavioral patterns and whats the role of viruses in this highly dynamic interactional networks. Additionally this book will serve as an appropriate tool to transport an integrated depiction of this fascinating kingdom.
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Mycelial fungi grow as indeterminate adaptive networks that have to forage for scarce resources in a patchy and unpredictable environment under constant onslaught from mycophagous animals. Development of contrast-independent network extraction algorithms has dramatically improved our ability to characterise these dynamic macroscopic networks and promises to bridge the gap between experiments in realistic experimental microcosms and graph-theoretic network analysis, greatly facilitating quantitative description of their complex behaviour. Furthermore, using digitised networks as inputs, empirically-based minimal biophysical mass-flow models already provide a high degree of explanation for patterns of long-distance radiolabel movement, and hint at global control mechanisms emerging naturally as a consequence of the intrinsic hydraulic connectivity. Network resilience is also critical to survival and can be explored both in silico by removing links in the digitised networks according to particular rules, or in vivo by allowing different mycophagous invertebrates to graze on the networks. Survival depends on both the intrinsic architecture adopted by each species and the ability to reconnect following damage. It is hoped that a comparative approach may yield useful insights into not just fungal ecology, but also biologically inspired rules governing the combinatorial trade-off between cost, transport efficiency, resilience and control complexity for self-organised adaptive networks in other domains.
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Ectomycorrhizal (EM) networks are hypothesized to facilitate regeneration under abiotic stress. We tested the role of networks in interactions between P. menziesii var. glauca trees and conspecific seedlings along a climatic moisture gradient to: (1) determine the effects of climatic factors on network facilitation of Pseudotsuga menziesii (Mirb.) Franco var. glauca (Mayr) seedling establishment, (2) infer the changing importance of P. menziesii var. glauca parent trees in conspecific regeneration with climate, and (3) parse the competitive from facilitative effects of P. menziesii var. glauca trees on seedlings. When drought conditions were greatest, seedling growth increased when seedlings could form a network with trees in the absence of root competition, but was reduced when unable to form a network. Survival was maximized when seedlings were able to form a network in the absence of root competition. Seedling stem natural abundance δ13C increased with drought due to increasing water use efficiency, but was unaffected by distance from tree or network potential. We conclude that P. menziesii seedlings may benefit from the presence of established P. menziesii trees when growing under climatic drought, but that this benefit is contingent upon the establishment of an EM network prior to the onset of summer drought. These results suggest that networks are an important mechanism for EM plants establishing in a pattern consistent with the stress-gradient hypothesis, and therefore the importance of EM networks to facilitation in regeneration of EM trees is expected to increase with drought.
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The objective of this study was to determine whether interior Douglas-fir (Pseudotsuga menziesii var. glauca) seedling establishment is affected by the presence of an ectomycorrhizal network (MN), and whether this varies by regional climate, seed provenance and seedling life history. We examined how MN facilitation varied with seedling provenance by planting interior Douglas-fir seed and nursery-grown seedlings near the crown edge of mature conspecific trees along a climatic stress gradient. Survival of outplanted nursery seedlings was greatest for the medium moisture provenance, but decreased with drought more rapidly than the wet or dry provenances. The driest provenance performed best under severe drought, but the survival of all provenances was still less than 35% under severe drought. Survival, growth and δ13C of seedlings grown from seed or in the nursery were not affected by MNs. We conclude that seedling genetic and life history effects outweigh benefits that MNs may incur upon Douglas-fir seedling performance under conditions of severe drought. Selection of appropriate provenances and robust growing stock will become of increasing importance for regenerating sites where drought is expected to increase with climate change.
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Mycorrhizal networks, defined as a common mycorrhizal mycelium linking the roots of at least two plants, occur in all major terrestrial ecosystems. This review discusses the recent progress and challenges in our understanding of the characteristics, functions, ecology and models of mycorrhizal networks, with the goal of encouraging future research to improve our understanding of their ecology, adaptability and evolution. We focus on four themes in the recent literature: (1) the physical, physiological and molecular evidence for the existence of mycorrhizal networks, as well as the genetic characteristics and topology of networks in natural ecosystems; (2) the types, amounts and mechanisms of interplant material transfer (including carbon, nutrients, water, defence signals and allelochemicals) in autotrophic, mycoheterotrophic or partial mycoheterotrophic plants, with particular focus on carbon transfer; (3) the influence of mycorrhizal networks on plant establishment, survival and growth, and the implications for community diversity or stability in response to environmental stress; and (4) insights into emerging methods for modelling the spatial configuration and temporal dynamics of mycorrhizal networks, including the inclusion of mycorrhizal networks in conceptual models of complex adaptive systems. We suggest that mycorrhizal networks are fundamental agents of complex adaptive systems (ecosystems) because they provide avenues for feedbacks and cross-scale interactions that lead to self-organization and emergent properties in ecosystems. We have found that research in the genetics of mycorrhizal networks has accelerated rapidly in the past 5 y with increasing resolution and throughput of molecular tools, but there still remains a large gap between understanding genes and understanding the physiology, ecology and evolution of mycorrhizal networks in our changing environment. There is now enormous and exciting potential for mycorrhizal researchers to address these higher level questions and thus inform ecosystem and evolutionary research more broadly.
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The authors manipulated light, temperature, and nutrients in moist tussock tundra in Alaska to determine how global changes might affect community and ecosystem processes. Some of these manipulations altered nutrient availability, growth-form composition, net primary production, and species richness in less than a decade, indicating arctic vegetation at this site is sensitive to climatic change. In general, short-term (3-yr) responses were poor predictors of longer term (9-yr) changes in community composition. The longer term responses showed closer correspondence to patterns of vegetation distribution along environmental gradients. Nitrogen and phosphorus availability tended to increase with elevated temperature and in response to light attenuation. Nutrient addition increased biomass and production of deciduous shrubs but reduced growth of evergreen shrubs and nonvascular plants. Light attenuation reduced biomass of all growth forms. Elevated temperature enhanced shrub production but reduced production of nonvascular plants. The contrasting responses to temperature increase and to nutrient addition by different growth forms {open_quotes}canceled out{close_quotes} at the ecosystem level, buffering changes in ecosystem characteristics such as biomass, production, and nutrient uptake. The major effect of elevated temperature was to speed plant response to changes in soil resources and, in long term (9 yr), to increase nutrient availability. Species richness was reduced 30-50% by temperature and nutrient treatments. Declines in diversity occurred disproportionately in forbs and in mosses. During our 9-yr study (the warmest decade on record in the region), biomass of one dominant tundra species unexpectedly changed in control plots in the direction predicted by our experiments and by Holocene pollen records. This suggests that regional climatic warming may already be altering the species composition of Alaskan arctic tundra. 73 refs., 9 figs., 4 tabs.
Article
The arbuscular mycorrhizal (AM) symbiosis is responsible for huge fluxes of photosynthetically fixed carbon from plants to the soil. Carbon is transferred from the plant to the fungus as hexose, but the main form of carbon stored by the mycobiont at all stages of its life cycle is triacylglycerol. Previous isotopic labeling experiments showed that the fungus exports this storage lipid from the intraradical mycelium (IRM) to the extraradical mycelium (ERM). Here, in vivo multiphoton microscopy was used to observe the movement of lipid bodies through the fungal colony and to determine their sizes, distribution, and velocities. The distribution of lipid bodies along fungal hyphae suggests that they are progressively consumed as they move toward growing tips. We report the isolation and measurements of expression of an AM fungal expressed sequence tag that encodes a putative acyl-coenzyme A dehydrogenase; its deduced amino acid sequence suggests that it may function in the anabolic flux of carbon from lipid to carbohydrate. Time-lapse image sequences show lipid bodies moving in both directions along hyphae and nuclear magnetic resonance analysis of labeling patterns after supplying ¹³C-labeled glycerol to either extraradical hyphae or colonized roots shows that there is indeed significant bidirectional translocation between IRM and ERM. We conclude that large amounts of lipid are translocated within the AM fungal colony and that, whereas net movement is from the IRM to the ERM, there is also substantial recirculation throughout the fungus.
Book
The roots of most plants are colonized by symbiotic fungi to form mycorrhiza, which play a critical role in the capture of nutrients from the soil and therefore in plant nutrition. Mycorrhizal Symbiosis is recognized as the definitive work in this area. Since the last edition was published there have been major advances in the field, particularly in the area of molecular biology, and the new edition has been fully revised and updated to incorporate these exciting new developments. . Over 50% new material . Includes expanded color plate section . Covers all aspects of mycorrhiza . Presents new taxonomy . Discusses the impact of proteomics and genomics on research in this area.
Article
The objective of the study was to determine whether nutrient fluxes mediated by hyphae of vesicular‐arbuscular mycorrhizal (VAM) fungi between the root zones of grass and legume plants differ with the legume's mode of N nutrition. The plants, nodulating or nonnodulating isolines of soybean [Glycine max (L.) Merr.], were grown in association with a dwarf maize (Zea mays L.) cultivar in containers which interposed a 6‐cm‐wide root‐free soil bridge between legume and grass container compartments. The bridge was delimited by screens (44 μm) which permitted the passage of hyphae, but not of roots and minimized non VAM interactions between the plants. All plants were colonized by the VAM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. The effects of N input to N‐sufficient soybean plants through N2‐fixation or N‐fertilization on associated maize‐plant growth and nutrition were compared to those of an N‐deficient (nonnodulating, unfertilized) soybean control. Maize, when associated with the N‐fertilized soybean, increased 19% in biomass, 67% in N content and 77% in leaf N concentration relative to the maize plants of the N‐deficient association. When maize was grown with nodulated soybean, maize N content increased by 22%, biomass did not change, but P content declined by 16%. Spore production by the VAM fungus was greatest in the soils of both plants of the N‐fertilized treatment. The patterns of N and P distribution, as well as those of the other essential elements, indicated that association with the N‐fertilized soybean plants was more advantageous to maize than was association with the N2‐fixing ones.
Chapter
In developed forests and secondary successional sites, host plants can readily access ectomycorrhizal (ECM) fungi because of the ubiquitous ECM mycelia and spores in soil, but this is not the case in some primary successional sites. In a volcanic desert on Mt Fuji, Japan, most of the area is non-mycorrhizal habitat and has poorly developed soil spore-banks. ECM habitat, i.e. pioneer willow shrubs and a small surrounding area containing ECM mycelia, are quite sparsely distributed, accounting for about 1 % of the ground surface in total. Such unique conditions provide us an interesting opportunity to explore the magnitude and role of direct mycelial connections between plants, i.e. ECM networks, in the field. It is difficult to observe individual ECM mycelial spread in soil, but the distribution of sporocarps and ECM roots having the same genotype indicate the spread of a mycelium in soil. We applied microsatellite markers to genotype sporocarps and ECM tips, and found that genets of two pioneer Laccaria species were small in size (mostly <1 m) and ephemeral. In contrast, genets of Scleroderma included some long-lived large genets (>10 m). These results indicate that ECM networks could vary considerably in size and longevity, even in the same site and associated with the same host species. Field transplanting experiment revealed that current-year willow seedlings rarely formed ECM associations in most habitats of the desert and showed poor growth. ECM infection from spores did not significantly improve seedling growth, indicating a small isolated mycelium on a tiny seeding may not be enough to acquire sufficient nutrients from extremely nutrient poor scoria. In contrast, seedlings transplanted near the pre-established willow shrubs, where ECM networks are available, readily formed ECM associations and grew well. Moreover, artificially reproduced ECM networks in previously non-mycorrhizal habitats significantly improved the growth of connected seedlings in 10 of 11 ECM fungal species in this desert. Therefore, ECM networks appear to be mostly positive and could be critical to seedling establishment, at least in this primary successional setting. Some previously proposed mechanisms may be less relevant to the observed positive effect of ECM networks on seedling establishment. For example, plant-to-plant carbon transfer through ECM networks might work for seedlings in dark forest floor, but not in primary successional settings characterized by strong sun light. More relevant mechanisms should include rapid ECM colonization with low costs, larger absorbing surface area than a solitary mycelium, and nutrient translocation within a network from nutrient rich soil patches to most demanding parts, often seedlings.
Chapter
The soil–plant–fungal matrix is inherently complex. There are thousands of species, highly variable environments in time and space, multiple interactions within a range of resources, and exchanges between multiple trophic levels. Here, we look at the structure of that complexity to see if there are emergent properties that allow us to understand that complexity. We emphasize our work from Mediterranean-type ecosystems in California and Oregon, but the perspective is valid across biomes. We examine a diversity of mycorrhizal types, with an emphasis on interactions of arbuscular mycorrhizae (AM) and ectomycorrhizae (EM) with host plants. These taxonomically different fungi differ in structural and biochemical properties including hyphal growth patterns and enzymatic capabilities. Because the symbionts are fungi, their hyphae connect multiple plants, forming networks. Materials (C, N, P, and water) are exchanged between plants through mycorrhizal networks. Importantly, networks themselves have structural properties that confer stability or instability and control the directions of flows. Thus, network theory has the ability to resolve patterns of elemental transfers and exchanges, and thus the outcomes for plant community dynamics. Also importantly, hyphae and fine roots have limited life spans, making interactions highly dynamic. Together, these dynamic interactions will help us unravel the complex relationships and the evolutionary histories that result in community and ecosystem dynamics.
Article
Terrestrial fungi are commonly studied in the laboratory, growing on artificial media in which nutrients are typically homogeneously distributed and supplied in superabundance, the environment is sterile and microclimate (temperature, moisture, gaseous regime) usually relatively constant. This contrasts with the natural environment, in which: nutrients are often patchily and sparsely distributed or not readily available, because they are locked in recalcitrant material (e.g. lignin); many other organisms are encountered, including other fungi, bacteria and invertebrates; and microclimate is constantly changing, both temporally and spatially. This chapter explores the ways in which fungi cope with environmental heterogeneity. Similar situations are faced by macroorganisms and analogies are drawn. Emphasis is placed on basidiomycetes, not only because they have been studied in most detail, but because of their dominant role as decomposers and mutualistic symbionts (Boddy & Watkinson, 1995; Smith & Read, 1997) and because they are better adapted to respond to environmental heterogeneity over scales ranging from micrometres to many metres than are other fungi. Both saprotrophic and ectomycorrhizal Basidiomycota form extensive mycelial systems in woodland soil and litter, but it is the former that are the focus of this review. Saprotrophic, cord-forming Basidiomycota that ramify at the soil–litter interface, interconnecting disparate litter components, provide most examples. The key feature of these fungi that fits them for growth in environments where resources are heterogeneously distributed is that they are non-resource-unit restricted, i.e. they can grow out of one resource in search of others. © Cambridge University Press 2007 and Cambridge University Press, 2009.
Article
The roots of most plants are colonized by symbiotic fungi to form mycorrhiza, which play a critical role in the capture of nutrients from the soil and therefore in plant nutrition. Mycorrhizal Symbiosis is recognized as the definitive work in this area. Since the last edition was published there have been major advances in the field, particularly in the area of molecular biology, and the new edition has been fully revised and updated to incorporate these exciting new developments. . Over 50% new material . Includes expanded color plate section . Covers all aspects of mycorrhiza . Presents new taxonomy . Discusses the impact of proteomics and genomics on research in this area.
Article
The role of arbuscular mycorrhizas in the transfer of N and P between pea (Pisum sativum L.) and barley (Hordeum vulgare L.) plants was studied in a controlled environment. The plants were grown together in PVC containers, either in symbiosis with Glomus intraradices Schenck and Smith or as non-mycorrhizal controls, and with their root systems separated by an intermediate buffer zone (2 cm), confined by fine nylon mesh. The pea donor plants were supplied simultaneously with 15N and 32P, using a split-root labelling technique, in order to follow the flow of N and P to the barley receiver plants during 60 d of growth. In half of the containers, the donor-plant shoot was removed 42 d after the start of labelling and the roots were left in the soil to decompose. The reverse transfer of N and P, from barley donor to pea receiver plants was also measured to allow calculation of the net transfer through hyphae between mycorrhizal donor and receiver plants. No significant transfer of N was detected from intact pea donor plants to the barley receiver plants in the non-mycorrhizal controls. Mycorrhizal colonization slightly increased the transfer of N. However, the net transfer of N was almost insignificant since N was also transferred in the reverse direction, from barley to pea. Removal of the pea donor-plant shoots increased the N transfer to 4% of the donor-root N in the non-mycorrhizal controls. Contrastingly, 15% of the donor-root N was transferred to the receiver plants, when plants were colonized by G. intraradices. The results for P transfer followed the same patterns as was observed for N, although in smaller proportions. The results indicate that arbuscular mycorrhizas may play a significant role in the flow of N and P between two plants interconnected by hyphae, when the root system of one of the plants is decomposing.
Chapter
Mycorrhizal fungi are involved in the uptake of nutrients in exchange for C from host plants, and possibly in the transfer of C and nutrients between plants. Ecto-mycorrhizal fungi (EMF) increase uptake rates of nutrients by a variety of mechanisms, including increased physical access to soil, changes to mycorrhizosphere or hyphosphere chemistry, and alteration of the bacterial community in the mycorrhizosphere. They influence mycorrhizosphere chemistry through release of organic acids and production of enzymes. Movement of nutrients within an ecto-mycorrhizal (EM) mycelial network, as well as exchange of C and nutrients between symbionts, appear to be regulated by source-sink relationships. Estimates of the quantity of plant C partitioned belowground (to roots and EMF) varies widely (40–73%) depending on the methodology used and ecosystem studied, and is affected by several factors such as the identity of plant and fungal species, plant nutrient content, and EM age.
Article
Loblolly pine (Pinus taeda L.) seedlings were grown axenically in mycorrhizae synthesis cultures with either the symbiont Pisolithus tinctorius (Pers.) Coker and Couch or Thelephora terrestris (Ehrh.) Fr. Glassware was designed to allow synthesis of mycorrhizae on two seedlings physically separated except for a bridge formed between the two root systems by mycorrhizal fungus mycelium. Glucose-C^1^4 and sucrose-C^1^4 were used as tracers to investigate movement of labeled compounds from mycorrhizal roots to external mycelium, from external mycelium to roots and from one root system to the other via shared mycelium. Whether applied to foliage as glucose-C^1^4 or sucrose-C^1^4, C^1^4 was readily translocated to pine roots. Transport of C^1^4 from mycorrhizal roots to external hyphae of T. terrestris up to a distance of 12 cm was shown, but only slight movement of C^1^4 occurred into external hyphae of P. tinctorius. The introduction of glucose-C^1^4 and sucrose-C^1^4 to isolated strands of T. terrestris resulted in the movement of C^1^4 from strands to roots. Movement of isotope from one seedling to the other via mutually-shared mycelium did not occur in the synthesis cultures; however, C^1^4 movement between root systems artifically linked by mycelial strands indicated that interplant exchange can take place. Evidence suggests that mycorrhizal fungi such as T. terrestris could be effective in the exchange of organic and possibly other materials between root systems in an ecosystem.
Article
1. Previously there have been studies of rates of movement of 32P between tillers within grass plants, and other studies of rates of 32P movement between plants. This paper describes an experiment to compare these rates of transfer, using mycorrhizal and non-mycorrhizal plants. 2. Two plants of Lolium perenne were grown per pot of soil, and carrier-free 32P was fed to one leaf of one of the plants. 32P was measured in new leaf tips every few days and in the whole shoots after 7 weeks. 3. The rate of 32P transfer between mycorrhizal plants was about 2-5% of that between tillers within a plant; between non-mycorrhizal plants it was slower. The half-time for 32P equilibration between tillers was about 1-2 months, which is the same order of magnitude as the half-lives of leaves of some perennial grasses, but shorter than the half-lives of tillers. For 32P equilibration between plants the half-times were about 2 years if they were mycorrhizal and 6 years if non-mycorrhizal, which is longer than the half-lives of leaves or tillers. 4. These results suggest that phosphorus movement between plants, even when they are mycorrhizal, is too slow to influence substantially the nutrient status of the shoots.
Article
Mycorrhizal networks which allow carbon compounds and mineral nutrients to be passed between individual plants, even members of different species, are potentially of great ecological importance. The evolution of such systems is of particular interest as they appear to need a group selectionist explanation. I suggest that such explanations are not necessary to explain the evolution of these systems as gene level explanations can be provided which appear to be sufficient to explain their evolution. Such explanations are to be preferred since they are less open to problems with cheating by the symbionts and therefore more stable.
Article
We examined how simulated herbivory, fungicide, and genet affect the magnitude and direction of net carbon transfer between paired mycorrhizal Lotus corniculatus. One plant in each pair was labeled with C-14, and C-14 levels in the unlabeled plant were quantified. Without fungicide, the roots of unlabeled plants received significantly more C-14 when the labeled partner was clipped than when the unlabeled plant was clipped, indicating that net carbon flow was away from clipped plants and toward unclipped plants. Because the specific activity of donor roots was unaffected by simulated herbivory, fungicide, and genet, significant differences in net carbon flow were not simply due to differences in C-14 uptake by labeled plants. Clipping did not affect carbon transfer between plants in trays treated with the fungicide benomyl, which probably reduced but did not eliminate VAM colonization. The three genets did not differ. The median C-14 levels of unlabeled root samples were only 1.2% the C-14 levels of labeled plants' roots and thus constituted a very small portion of their carbon budget. C-14 levels in stems of unlabeled plants were never above background, suggesting that the fungal symbiont retained most of the transferred carbon. Although clipping can affect net carbon flow, we failed to detect significant differences in the amount of C-14 leaking from the roots of clipped vs unclipped plants. This study suggests that grazed mycorrhizal plants are unlikely to gain significant amounts of carbohydrates from neighbors and may actually experience a net loss.
Article
The contribution of hyphae to water transport in ectomycorrhizal (ECM) white spruce (Picea glauca) seedlings was examined by altering expression of a major water-transporting aquaporin in Laccaria bicolor. Picea glauca was inoculated with wild-type (WT), mock transgenic or L. bicolor aquaporin JQ585595-overexpressing (OE) strains and exposed to root temperatures ranging from 5 to 20°C to examine the root water transport properties, physiological responses and plasma membrane intrinsic protein (PIP) expression in colonized plants. Mycorrhization increased shoot water potential, transpiration, net photosynthetic rates, root hydraulic conductivity and root cortical cell hydraulic conductivity in seedlings. At 20°C, OE plants had higher root hydraulic conductivity compared with WT plants and the increases were accompanied by higher expression of P. glauca PIP GQ03401_M18.1 in roots. In contrast to WT L. bicolor, the effects of OE fungi on root and root cortical cell hydraulic conductivities were abolished at 10 and 5°C in the absence of major changes in the examined transcript levels of P. glauca root PIPs. The results provide evidence for the importance of fungal aquaporins in root water transport of mycorrhizal plants. They also demonstrate links between hyphal water transport, root aquaporin expression and root water transport in ECM plants.
Article
The role of arbuscular mycorrhizas in the transfer of N and P between pea (Pisum sativum L.) and barley (Hordeum vulgare L.) plants was studied in a controlled environment. The plants were grown together in PVC containers, either in symbiosis with Glomus intraradices Schenck and Smith or as non-mycorrhizal controls, and with their root systems separated by an intermediate buffer zone (2 cm), confined by fine nylon mesh. The pea donor plants were supplied simultaneously with 15N and 32P, using a split-root labelling technique, in order to follow the flow of N and P to the barley receiver plants during 60 d of growth. In half of the containers, the donor-plant shoot was removed 42 d after the start of labelling and the roots were left in the soil to decompose. The reverse transfer of N and P, from barley donor to pea receiver plants was also measured to allow calculation of the net transfer through hyphae between mycorrhizal donor and receiver plants. No significant transfer of N was detected from intact pea donor plants to the barley receiver plants in the non-mycorrhizal controls. Mycorrhizal colonization slightly increased the transfer of N. However, the net transfer of N was almost insignificant since N was also transferred in the reverse direction, from barley to pea. Removal of the pea donor-plant shoots increased the N transfer to 4% of the donor-root N in the non-mycorrhizal controls. Contrastingly, 15% of the donor-root N was transferred to the receiver plants, when plants were colonized by G. intraradices. The results for P transfer followed the same patterns as was observed for N, although in smaller proportions. The results indicate that arbuscular mycorrhizas may play a significant role in the flow of N and P between two plants interconnected by hyphae, when the root system of one of the plants is decomposing.
Article
Changes in the natural abundance of 13C were used to quantify carbon transfer between C3 and C4 plants in a common mycorrhizal network. Experiments using two mesh sizes to either prevent (0.45 μm) or allow (20 μm) mycorrhizal connections between Plantago lanceolata (C3) and Cynodon dactylon (C4) plants were run. Root and shoot samples were taken for δ13C determinations.It could not be assumed that all the pairs of plants were linked; therefore non-parametric statistical tests were used. In order to measure transfer between pairs of plants the shoot δ13C value was used as a reference and the deviation of the root δ13 C value from this as a measure of carbon transfer. As the C. dactylon root δ13 C value became more negative with the 20 μm mesh present, the root-shoot difference increased. In P. lanceolata both the root and shoot δ13C values became less negative but the root-shoot difference did increase gradually. When the root-shoot difference in C. dactylon was plotted against root δ13C value the relationship was ≈unity, suggesting that transferred carbon remained in the roots and fungal material did not move into the shoots. In P. lanceolata the results showed that the slope of the relationship between root-shoot difference and root δ13C value was ≈0.5. This suggests any transferred carbon moved into both the root and shoot material.The root-shoot difference can be used to estimate % carbon transfer. For individual C. dactylon plants the results varied from 0 to 41% with most values falling at 10% or below. It was not possible to calculate % transfer amounts for P. lanceolata. This range of variation could have important implications for plant interactions in communities.
Article
Nitrogen (N) transfer between plants has been found where at least one plant can fix N2. In nutrient-poor soils, where plants with contrasting nutrient-acquisition strategies (without N2 fixation) co-occur, it is unclear if N transfer exists and what promotes it. A novel multi-species microcosm pot experiment was conducted to quantify N transfer between arbuscular mycorrhizal (AM), ectomycorrhizal (EM), dual AM/EM, and non-mycorrhizal cluster-rooted plants in nutrient-poor soils with mycorrhizal mesh barriers. We foliar-fed plants with a K15NO3 solution to quantify one-way N transfer from ‘donor’ to ‘receiver’ plants. We also quantified mycorrhizal colonisation and root intermingling. Transfer of N between plants with contrasting nutrient-acquisition strategies occurred at both low and high soil nutrient levels with or without root intermingling. The magnitude of N transfer was relatively high (representing 4 % of donor plant N) given the lack of N2-fixation. Receiver plants forming ectomycorrhizas or cluster roots were more enriched, compared to AM-only plants. We demonstrate N transfer between plants of contrasting nutrient-acquisition strategies, and a preferential enrichment of cluster-rooted and EM plants compared to AM plants. Nutrient exchanges between plants are potentially important in promoting plant coexistence in nutrient-poor soils.
Article
Stomata regulate rates of carbon assimilation and water loss. Arbuscular mycorrhizal (AM) symbioses often modify stomatal behavior and therefore play pivotal roles in plant productivity. The size of the AM effect on stomatal conductance to water vapor (g s ) has varied widely, has not always been apparent, and is unpredictable. We conducted a meta-analysis of 460 studies to determine the size of the AM effect under ample watering and drought and to examine how experimental conditions have influenced the AM effect. Across all host and symbiont combinations under all soil moisture conditions, AM plants have shown 24 % higher g s than nonmycorrhizal (NM) controls. The promotion of g s has been over twice as great during moderate drought than under amply watered conditions. The AM influence on g s has been even more pronounced under severe drought, with over four times the promotion observed with ample water. Members of the Claroideoglomeraceae, Glomeraceae, and other AM families stimulated g s by about the same average amount. Colonization by native AM fungi has produced the largest promotion. Among single-AM symbionts, Glomus deserticola, Claroideoglomus etunicatum, and Funneliformis mosseae have had the largest average effects on g s across studies. Dicotyledonous hosts, especially legumes, have been slightly more responsive to AM symbiosis than monocotyledonous hosts, and C3 plants have shown over twice the AM-induced promotion of C4 plants. The extent of root colonization is important, with heavily colonized plants showing ×10 the g s promotion of lightly colonized plants. AM promotion of g s has been larger in growth chambers and in the field than in greenhouse studies, almost ×3 as large when plants were grown under high light than low light, and ×2.5 as large in purely mineral soils than in soils having an organic component. When AM plants have been compared with NM controls given NM pot culture, they have shown only half the promotion of g s as NM plants not given anything at inoculation to control for associated soil organisms. The AM effect has been much greater when AM plants were larger or had more phosphorus than NM controls. These findings should assist in further investigations of predictions and mechanisms of the AM influence on host g s .
Article
Extramatrical mycelia (EMM) of ectomycorrhizal (ECM) fungi are potentially extensive in soil and receive significant allocations of plant-derived carbon. Although losses from living EMM occur via respiration and exudation, EMM represents a considerable biomass component and potential carbon sink in many forest soils. ECM root tips and rhizomorphs may persist in soil for many months, but interactions between grazing arthropods and decomposers probably facilitate more rapid turnover of diffuse EMM. Elevated atmospheric CO2 concentration [CO2] is likely to increase carbon allocation to ECM fungi by their tree hosts. This will probably increase root colonization by ECM fungi and drive changes in their communities in soil. The likely effects of elevated [CO2] and other climate change factors on the production and turnover of EMM production are difficult to predict from current evidence, and this hampers our understanding of their potential value as future carbon sinks. Responses of grazing soil arthropods to future climate change will have a strong influence on EMM turnover, along with the abilities of ECM fungi to store carbon in below-ground, and this should be seen as a priority area for future research.
Article
Anthropogenic nitrogen (N) deposition alters ectomycorrhizal fungal communities, but the effect on functional diversity is not clear. In this review we explore whether fungi that respond differently to N deposition also differ in functional traits, including organic N use, hydrophobicity and exploration type (extent and pattern of extraradical hyphae). Cortinarius, Tricholoma, Piloderma, and Suillus had the strongest evidence of consistent negative effects of N deposition. Cortinarius, Tricholoma and Piloderma display consistent protein use and produce medium-distance fringe exploration types with hydrophobic mycorrhizas and rhizomorphs. Genera that produce long-distance exploration types (mostly Boletales) and contact short-distance exploration types (e.g., Russulaceae, Thelephoraceae, some athelioid genera) vary in sensitivity to N deposition. Members of Bankeraceae have declined in Europe but their enzymatic activity and belowground occurrence are largely unknown. Bankeraceae produce a distinct hydrophobic mat exploration type that may also be important in N acquisition under conditions of low N availability.
Article
It is well known from laboratory studies that a single mycorrhizal fungal isolate can colonize different plant species, form interplant linkages, and provide a conduit for interplant transfer of isotopic carbon, nitrogen, phosphorus, or water. There is increasing laboratory and field evidence that the magnitude and direction of transfer is influenced by physiological source-sink gradients between plants. There is also evidence that mycorrhizal fungi play a role in regulating transfer through their own source-sink patterns, frequency of links, and mycorrhizal dependency. Although it is plausible that connections are extensive in nature, field studies have been hampered by our inability to observe them in situ and by belowground complexity. In future, isotopic tracers, morphological observations, microsatellite techniques, and fluorescent dyes will be useful in the study of networks in nature. Mycorrhizal networks have the potential to influence patterns of seedling establishment, interplant competition, plant diversity, and plant community dynamics, but studies in this area are just beginning. Future plant community studies would benefit from concurrent experimental use of fungal network controls, isotopic labeling, direct observation of interplant linkages, and long-term observation in the field. In this paper, we review recent literature on mycorrhizal networks and interplant carbon transfer, suggest future research directions, and highlight promising scientific approaches.
Article
Experiments were carried out to investigate the possibility that vesicular-arbuscular (VA) mycorrhizal infection of grass (Lolium perenne L.) and clover (Trifolium repens L.) roots can enhance the exchange of nitrogen between the root systems of nitrogen-fixing pasture legumes and associated grasses. The results showed higher rates of transfer of 15N applied as (15NH4)2SO4 to the clover plants to companion grass plants when the roots were mycorrhizal. In some cases but not all the grass grew better in the mycorrhizal treatments. An experiment in which the clover and grass roots were separated by a 60 μm (mean pore size) nylon mesh screen showed that translocation of the nitrogen was probably along the mycorrhizal hyphae. It was not clear from the data whether transfer was mediated by a common hyphal net or some other less direct means.
Article
summaryPinus sylvestris L. and Larix eurolepis Henry seedlings were grown together in non–sterile laboratory microcosms containing functional mycelial networks of one of three different ectomyeorrhizal Fungi. The fungi used were Suillus bovinus (Fr.) O. Kuntze, and two Fungi which are commonly considered to be specific to Larix spp., Suillus grevillei (Klotzsch) Sing, and Boletirms cavipes (Opat.) Kalchbr. Patterns of mycorrhizal infection, transport of labelled assimilate and phosphorus uptake within the microcosms were studied in order to evaluate tine functional attributes of associations formed between P. sylvestris and the two‘larch specific’fungi. Fungal colonization of lateral roots and accumulation of labelled assimilate from adjacent plants fed with 14CO2 was significantly greater in the roots of Pinus plants when the ectomycorrhizal fungus was S. bovinu, and significantly greater in Larix roots when the fungus was V. grevillei or li. cavipes. Kctomycorrhizas formed between P. sylvestris and Ii, cavipes were fully functional in terms of transfer of labelled assimilate to the fungal mycelium. In mixed communities infected by B. caripes, myeclial uptake and translocation of 32P-labelled orthophosphate was significantly greater to Larix plants than to Pinus plants. Formation of sheathed lateral roots on the Pinus plants was low. There was some autoradiographic evidence of phosphorus translocation from mycorrhizal pine roots to stem and leaf tissue hut levels of activity in the shoots were low, indicating limited translocation across the host-fungus interface.
Article
Using perspex observation chambers, the uptake, translocation and distribution of 32P-labelled phosphorus was studied in ectomycorrhizal mycelial networks of Suillus bovinus (Fr.) O. Kuntze interconnecting plants of Pinus contorta Dougl. ex Loud and Pinus sylvestris L. Label was fed either directly to the cut ends of individual mycelial strands, to plant roots, or to the unsterile peat in the vicinity of advancing mycelial fans. Where 32P was fed to individual strands or mycelial fans it was taken up and translocated through the mycelium, over distances exceeding 40 cm, to all host plants connected to the mycelial network. Ectomycorrhizal roots acted as major sinks for phosphate but the label did not move exclusively towards the plant and was distributed throughout the mycelial system. Calculated translocation rates and flux rates suggest that transport is primarily by symplastic flow rather than turgor driven bulk flow. The amount of label accumulated by each plant was significantly related both to the size of the plant shoot and to the number of mycorrhizal root tips but did not appear to be influenced by the transpiration rates of individual plants. Phosphorus supplied directly to plant roots did not move to other plants via the mycelial connections suggesting that movement of phosphorus between the fungus and host is unidirectional.
Article
Ammonia assimilation has been followed in ectomycorrhizal roots of Fagus sylvatica. The absorption of ammonium ions was associated with a rapid synthesis of free amino acids in mycorrhizal tissues, glutamine being the most prominent. In the presence of [15N]ammonium, glutamate, glutamine and alanine became the most strongly labelled metabolites of ectomycor-rhizas. Nitrogen-15 nuclear magnetic resonance spectroscopy demonstrated that the glutamine amide-N was the most highly enriched component of the extracts. Methionine sulphoximine and albizine, inhibitors of glutamine synthetase and glutamate synthase, almost completely blocked the incorporation of 15N label into amino acids and induced an accumulation of NH4+. These observations suggest that in the ammonia-fed beech ectomycorrhizas, ammonia assimilation occurs mainly via the glutamine synthetase/glutamate synthase pathway, and that glutamate dehydrogenase plays little, if any, part in this process. Alternative models for the nitrogen assimilation pathways in fungal and host tissues are presented.