Mycorrhizal Ecology Research Articles

Clarifying the definition of common mycorrhizal networks

Abstract Common mycorrhizal networks (CMNs) are an enigmatic feature of soil and mycorrhizal ecology. The current use of the term ‘common mycorrhizal network’ stipulates a direct, continuous physical link between plants formed by the mycelium of mycorrhizal fungal genets. This means that a specific case (involving hyphal continuity) is used to define a much broader phenomenon of hyphae interlinking among roots of different plants. We here embrace a more inclusive definition of the CMN as a network formed by mycorrhizal fungal genets among roots of different plants, irrespective of the type of connection or interaction, and not limited to direct hyphal linkages. Implicitly, this broader version of the term has been used by many researchers already. We propose using the term ‘common mycorrhizal networks with hyphal continuity’ (CMN‐HC) to capture the more specific case of a continuous link via hyphae between the roots of different plants, which is important to study for some (notable carbon and nutrient exchange), but not all functions of a CMN (e.g. transfer of infochemicals or microbes). In addition, and becoming more general than CMN, we introduce the term ‘common fungal network’ (CFN) to include networks of any type of connection formed between different plants by any type of fungus; this includes also non‐mycorrhizal fungi, and indeed a combination of non‐mycorrhizal and mycorrhizal networks. We assert that this new conceptual framework incorporating three hierarchical terms (CMN‐HC, CMN and CFN), ranging from the most specific to the very broad, can usher in a period of new research activity on fungal networks. Read the free Plain Language Summary for this article on the Journal blog.

Mycorrhizal ecology would benefit from region-specific hypotheses

Most arbuscular mycorrhizal fungi exhibit global distributions but have been studied mostly in a specific region of the globe, mainly covering temperate and boreal habitats, where nitrogen is the most common nutrient limiting primary productivity. Yet, it is relatively common to extrapolate our understanding of temperate and boreal systems to other regions of the globe. While the physiology of mycorrhizal associations is unlikely to differ worldwide, there are good chances that environmental settings interact with the way mycorrhizas function across ecoregions. Here, we first argue that mycorrhizal ecologists should develop region-specific hypotheses. We subsequently identify likely differences in how mycorrhizas function in subtropical regions compared with better-studied temperate and boreal areas. We finally use the subtropical region of China to develop five geographically-focused hypotheses, envisaging that they will trigger the interest of the scientific community worldwide in understudied regions into studying mycorrhizas through a new lens. Expanding the range of hypotheses in mycorrhizal ecology to describe understudied regions of the world, has the potential to confer multifaceted benefits to both science and society. We advocate to do so, and present a roadmap on how to develop such hypotheses.

Mycorrhizal synthesis of <i>Tuber pseudohimalayense</i> with seven broad-leaved trees and <i>Pinus armandii</i>

Truffle cultivation is successfully applied throughout the world for several truffles of European origin. However, just two Chinese black truffles (Tuber indicum and T. himalayense) have been cultivated with a favorable outcome so far. Tuber pseudohimalayense is a black truffle of significant economic relevance in China, but little is known about its mycorrhizal ecology and it is not cultivated in orchards yet. Here, we selected seven broad-leaved tree species (Quercus fabrei, Q. aliena, Castanea mollissima, Carya illinoinensis, Q. glauca, Castanopsis orthacantha, Betula costata), and one coniferous tree (Pinus armandii), and inoculated them with T. pseudohimalayense spore suspension using axenically germinated seedlings under greenhouse conditions. The obtained mycorrhizae, well-developed, were analyzed from the morpho-anatomical and molecular points of view, and their main characteristics described. Synthesized T. pseudohimalayense mycorrhizae showed similar characters on all tree species, with a typical interlocking pseudoparenchymatous mantle and Hartig net, swollen appearance, yellow-brownish color, and long hyaline emanating hyphae with right-angle ramifications. These features are similar to those reported for mycorrhizae formed by related black truffle species. The successful mycorrhizal synthesis of T. pseudohimalayense on multiple trees species indicates that it has potential for cultivation in China.

Diversity of indigenous arbuscular mycorrhizal fungi in rhizosphere of upland rice (Oryza sativa L.) varieties in Southwest Nigeria

Diversity of indigenous arbuscular mycorrhizal fungi in rhizosphere of upland rice (Oryza sativa L.) varieties in Southwest Nigeria

Stepping forward from relevance in mycorrhizal ecology.

This article is a Commentary on Fernandez et al., 226: 569–582.

Arbuscular mycorrhiza has little influence on N2O potential emissions compared to plant diversity in experimental plant communities.

Denitrification is an ecosystem process linked to ongoing climate change, because it releases nitrous oxide (N2O) into the atmosphere. To date, the literature covers mostly how aboveground (i.e. plant community structure) and belowground (i.e. plant-associated soil microbes) biota separately influence denitrification in isolation of each other. We here present a mesocosm experiment where we combine a manipulation of belowground biota (i.e. addition of Rhizophagus irregularis propagules to the indigenous mycorrhizal community) with a realized gradient in plant diversity. We used a seed mix containing plant species representative of mesophytic European grasslands and by stochastic differences in species establishment across the sixteen replicates per treatment level a spontaneously established gradient in plant diversity. We address mycorrhizal-induced and plant-diversity mediated changes on denitrification potential parameters and how these differ from the existing literature that studies them independently of each other. We show that unlike denitrification potential, N2O potential emissions do not change with mycorrhiza and depend instead on realized plant diversity. By linking mycorrhizal ecology to an N-cycling process, we present a comprehensive assessment of terrestrial denitrification dynamics when diverse plants co-occur.

Global imprint of mycorrhizal fungi on whole-plant nutrient economics

Mycorrhizal fungi are critical members of the plant microbiome, forming a symbiosis with the roots of most plants on Earth. Most plant species partner with either arbuscular or ectomycorrhizal fungi, and these symbioses are thought to represent plant adaptations to fast and slow soil nutrient cycling rates. This generates a second hypothesis, that arbuscular and ectomycorrhizal plant species traits complement and reinforce these fungal strategies, resulting in nutrient acquisitive vs. conservative plant trait profiles. Here we analyzed 17,764 species level trait observations from 2,940 woody plant species to show that mycorrhizal plants differ systematically in nitrogen and phosphorus economic traits. Differences were clearest in temperate latitudes, where ectomycorrhizal plant species are more nitrogen use- and phosphorus use-conservative than arbuscular mycorrhizal species. This difference is reflected in both aboveground and belowground plant traits and is robust to controlling for evolutionary history, nitrogen fixation ability, deciduousness, latitude, and species climate niche. Furthermore, mycorrhizal effects are large and frequently similar to or greater in magnitude than the influence of plant nitrogen fixation ability or deciduous vs. evergreen leaf habit. Ectomycorrhizal plants are also more nitrogen conservative than arbuscular plants in boreal and tropical ecosystems, although differences in phosphorus use are less apparent outside temperate latitudes. Our findings bolster current theories of ecosystems rooted in mycorrhizal ecology and support the hypothesis that plant mycorrhizal association is linked to the evolution of plant nutrient economic strategies.

Marcel van der Heijden.

Marcel van der Heijden.

From mycorrhizal fungal traits to ecosystem properties – and back again

Abstract Mycorrhizal fungi are known for their functional importance in plant growth and nutrition, and because these symbiotic fungi represent a fundamental linkage between plants and soils, they likely underpin a number of biogeochemical processes in ecosystems. However, our ability to isolate and quantify their role in ecosystems has remained a challenge. This special feature presents seven new studies that advance our understanding of how mycorrhizal fungi contribute to ecosystem function. We specifically highlight two complementary approaches by which ecologists are gaining insight: focusing on mycorrhizal fungal traits to target the biological mechanisms that scale up to the ecosystem, and capturing patterns and processes across ecosystems to understand the net effect of complex plant–fungal–soil interactions. The studies in our special feature provide evidence that traits both within and across species of mycorrhizal fungi can contribute to ecosystem processes, and that disturbance from global change and management may result in altered mycorrhizal traits and lead to compromised ecosystem function. From a broader perspective, studies also demonstrate that key ecosystem properties vary over gradients of mycorrhizal dominance and time, suggesting that mycorrhizal effects emerge from complex interactions within ecosystems Synthesis. Employing complementary approaches to the study of mycorrhizal ecology may allow us to isolate the mycorrhizal traits that matter most for ecosystem properties, as well as the suite of ecosystem properties that result from mycorrhizal fungi, thus converging on biogeochemical mechanisms that underpin terrestrial ecosystem function.

Shroomroot: An Action-Based Digital Game to Enhance Postsecondary Teaching and Learning about Mycorrhizae

The majority of terrestrial plants associate with fungi in symbiotic resource-exchange relationships called mycorrhizae. Because of the importance of these mycorrhizal systems to ecosystem functioning, it is crucial that future resource managers and scientists have a solid understanding of mycorrhizal ecology. Limited interest of postsecondary students in plants and fungi compared with animals, combined with difficulties visualizing below-ground processes, present challenges for learning mycorrhizal concepts. To address this, we created the digital, plant-ecology-centric, action-based game Shroomroot for use in a second year, postsecondary Introduction to Soil Science course. We then assessed effects of Shroomroot on students’ knowledge acquisition and engagement with the topic of mycorrhizal ecology using a pre- and post-test evaluation. Students’ knowledge of mycorrhizal ecology increased significantly after playing Shroomroot, and tended to increase more for items related to Shroomroot gameplay than in rewards-based game content. Student engagement with mycorrhizal content tended to increase after gameplay. These results suggest positive potential for action-based, plant-ecology-oriented digital games in a postsecondary science curriculum. Furthermore, greater understanding of mycorrhizae has the potential to improve our multifaceted relationships with the ecosystems upon which we depend.

Seeing networks for what they are in mycorrhizal ecology

Abstract Networks tools are being increasingly used in the study of plant-fungus interactions and likely to provide new insights in the way plant-fungus interactions are structured. At the same time, they raise new questions and challenges. Here, I highlight the most important problems and outline how network tools can be effectively used in mycorrhizal ecology. Network-based tools can be used to explore and visualize mycorrhizal interaction patterns: this can pave the way towards further empirical work and hypothesis testing. However, network-based tools cannot, by themselves alone, provide much insight about the ecological mechanisms driving the establishment of mycorrhizal interactions, because many mechanisms can yield a given network-level pattern. They also cannot help predicting the future dynamics of mycorrhizal communities, because modelling studies need to be conducted using parameters and rules that are relevant to the mycorrhizal symbiosis, which is not currently done. Also, drawing analogies between mycorrhizal networks and other types of networks must be made with caution, taking into account all the potential similarities, but also discrepancies, between these kinds of unrelated networks. I think that keeping the above issues in mind will be critical to keep the network-based approach viable and useful in mycorrhizal ecology.

Orchid re-introductions: an evaluation of success and ecological considerations using key comparative studies from Australia

With global biodiversity in decline, there is now an urgent requirement to take ameliorative action for endangered species in the form of re-introductions. For the highly diverse orchid family, many species face imminent extinction. Successful re-introductions that result in self-sustaining populations require not only an understanding of existing threats, but an in-depth understanding of species ecology. Increasingly, translocations, ranging from re-introductions to assisted colonisation, are being adopted as recovery actions. Do these translocations mitigate threatening processes and account for the two key ecological attributes for orchid survival; pollinator and mycorrhizal presence? Here, we conducted a literature review identifying the known threats to orchid survival and their necessary mitigation strategies. Next, we evaluated the success of 74 published international orchid translocations on 66 species against a consideration of orchid ecological attributes. Lastly, we empirically tested an additional 22 previously unpublished re-introductions on 12 species undertaken since 2007 against a re-introduction process that accounts for identified threats and orchid ecological attributes. We identified habitat destruction, weed invasion, herbivory, illegal collection, pollinator decline, pathogens and climate change as critical threats to orchid survival. In our global review based on published translocations, the average survival rate, 1-year post translocation was 66 % yet only 2.8 % of studies reported natural recruitment in field sites. Although survival of translocated orchids is clearly being achieved, these programmes did not relate orchid growth and development to key ecological requirements of orchid population resilience, pollinator and mycorrhizal ecology. Ensuring pollinator and mycorrhizal presence shows that these two factors alone are key factors influencing survival and persistence in an Australian review of 22 previously unpublished orchid re-introductions. In the Australian review flowering in the year following, out-planting was observed for 81 % of the re-introductions with seed set occurring in 63 % of re-introductions within the length of the study. Recruitment was observed in 18 % of the Australian re-introduced populations indicating a degree of population resilience. As orchid re-introductions will be a major strategy for wild orchid conservation in the future, we present a framework for orchid re-introductions, including criteria for success. We recommend symbiotic propagation and, for specialised pollination syndromes, the study of pollinator interactions prior to site selection and re-introduction of plants.

Using molecular biology to study mycorrhizal fungal community ecology: Limits and perspectives

Molecular tools have progressively replaced morphological approaches to characterize microbial communities in nature. Arbuscular mycorrhizal (AM) fungi are no exception to this rule. Yet, one challenge posed by these symbionts is that they colonize simultaneously both plant roots and soil, which complicates their detection and quantification. In most studies conducted to date, AM fungal communities have been characterized from roots only, soil only or spores only. Here, we discuss the pitfalls associated to drawing ecological inferences using such datasets. We also conclude by arguing that molecular biology will contribute most to advance knowledge in AM fungal ecology if it is integrated into broader perspectives taking into account the natural history of these organisms. This calls for a better merging of molecular and morphological approaches, and the establishment of intensive, long-term research programs.

International Congress on Mycorrhizae: mycorrhizal symbiosis a key factor for improving plant productivity and ecosystems restoration.

The Mycorrhizae and Mediterranean Ecosystems Group (MYCOMED), the African Network on Mycorrhiza (AFRINOM) and the French Mycorrhizologist Network (RAMYF) co-organized an International Congress on BMycorrhizal Symbiosis a Key Factor for Improving Plant Productivity and Ecosystems Restoration^ in Marrakech, Morocco, October 15–17, 2014. Three hundred participants from 45 different countries attended the congress, which included 65 oral presentations and 100 posters. Abstracts of all talks and posters can be found at the website (http://icmycorrhizae2014.uca.ma) of Cadi Ayyad University. The congress was an international forum for exchange of knowledge and expertise between scientists developing fundamental and applied mycorrhizal research as well as companies commercializing mycorrhizal inoculum. The objectives were to update scientific and technical knowledge on mycorrhizal fungi as providers of key ecological services, to valorize the mycorrhizal symbiosis in practices in the socioeconomic environment of Mediterranean and tropical areas and to share the experiences of scientists with young researchers, policy makers and end-users. The contents addressed included three topics: (i) biology, ecology and diversity of mycorrhizal fungi in tropical and Mediterranean environments; (ii) mycorrhizal symbiosis and plant tolerance to biotic and abiotic stresses and (iii) valorization and transfer of mycorrhizal biotechnologies in agro-ecological engineering strategies and the socio-economic environment of tropical and Mediterranean areas. In the opening conference on the role of arbuscular mycorrhiza for plant health, Prof. Paola Bonfante (Italy) provided an overview on the cellular and molecular mechanisms which allow plants to take up essential minerals in model legume plants, and revealed how mycorrhiza may have a systemic impact on the fruit transcriptomics and nutrient content in agricultural important crops such as tomato. Dr. Marc Buee (France) introduced topic (i) by raising the fundamental question of how to connect metagenomics and mycorrhizal fungal ecology. Through various examples, spanning from local to large-scale studies using biogeographic approaches, he presented the advantages and risks of highthroughput sequencing to investigate ectomycorrhizal fungal ecology, with unprecedented scales of sampling, and illustrated how fungal genome resources feed metagenomics to increase knowledge on the ecology of mycorrhizal fungal communities and assemblages. In introducing topic (ii), Prof. Guillaume Becard (France) talked about plant mechanisms that discriminate beneficial and pathogenic microorganisms via microbial signals. These molecular signals are involved in the processes of nodulation, mycorrhization, root development and basal plant immunity. They could have a huge potential for sustainable agriculture because of their implication in enhancing plant nutrition, growth and defense against pathogens and pests. Dr. Silvio Gianinazzi (France) introduced topic (iii) by presenting the domestication of beneficial soil microorganisms as an innovative technology for agriculture. He suggested that Mohamed Hafidi, Ahmed Qaddoury, Robin Duponnois, Daniel Wipf, Mohamed Hijri and Amadou Bâ contributed equally to this work.

Radiocaesium activity concentrations in macrofungi from Galicia (NW Spain): Influence of environmental and genetic factors

Radiocaesium (137Cs) is an artificial radionuclide that can be captured from the soil through the mycelium of fungi. However, in Spain there are few data on its presence in edible mushrooms. 137Cs activity concentrations were determined using 54 samples of wild and cultivated mushrooms and 18 samples of soil, all of them collected in Galicia (NW Spain) during 2010. Samples were analyzed by gamma spectroscopy with a High-Purity Germanium (HPGe) detector. The average activity concentration of 137Cs in wild mushrooms was 249.2Bqkg−1 dry weight (dw) and about 24.9Bqkg−1 fresh weight (fw). Genetic factors (species) influenced the uptake of 137Cs, highlighting Hydnum repandum as the greatest accumulator of all wild species (1016.4Bqkg−1 dw), while cultivated species showed much lower levels (1.6Bqkg−1 fw). Accumulation was also favored by fungal mycorrhizal ecology, whose mycelium was distributed in contaminated soil horizons. The mean levels detected in soils were 14Bqkg−1 fw. Although some species behaved as bioexclusors of radiocaesium, the transfer factors (TF) suggest that mushrooms preferentially bioaccumulate 137Cs. No sample reached the limit of 600Bqkg−1 fw (about 6000Bqkg−1 dw) indicated in the European legislation. In conclusion, the consumption of mushrooms harvested from the investigated areas poses no toxicological risk to human health due to radiocaesium.

Evolving insights to understanding mycorrhizas

Evolving insights to understanding mycorrhizas

Mycorrhizal ecology and evolution: the past, the present, and the future.

Almost all land plants form symbiotic associations with mycorrhizal fungi. These below-ground fungi play a key role in terrestrial ecosystems as they regulate nutrient and carbon cycles, and influence soil structure and ecosystem multifunctionality. Up to 80% of plant N and P is provided by mycorrhizal fungi and many plant species depend on these symbionts for growth and survival. Estimates suggest that there are c. 50 000 fungal species that form mycorrhizal associations with c. 250 000 plant species. The development of high-throughput molecular tools has helped us to better understand the biology, evolution, and biodiversity of mycorrhizal associations. Nuclear genome assemblies and gene annotations of 33 mycorrhizal fungal species are now available providing fascinating opportunities to deepen our understanding of the mycorrhizal lifestyle, the metabolic capabilities of these plant symbionts, the molecular dialogue between symbionts, and evolutionary adaptations across a range of mycorrhizal associations. Large-scale molecular surveys have provided novel insights into the diversity, spatial and temporal dynamics of mycorrhizal fungal communities. At the ecological level, network theory makes it possible to analyze interactions between plant-fungal partners as complex underground multi-species networks. Our analysis suggests that nestedness, modularity and specificity of mycorrhizal networks vary and depend on mycorrhizal type. Mechanistic models explaining partner choice, resource exchange, and coevolution in mycorrhizal associations have been developed and are being tested. This review ends with major frontiers for further research.

林木外生菌根菌研究进展及应用前景

菌根学理论研究日新月异，已引起世界各国学者的广泛关注。菌根化应用技术研究逐渐发展，大量文献表明：菌根研究在农、林生产上的具有广泛的应用前景，尤其促进林木生长发育具有不可替代的作用，为此，本文在较为全面的介绍了我国外生菌根真菌资源研究状况，并从菌根营养学、菌根生态学与环境生态效益，以及应用技术等方面的研究进展进行综合论述，同时探讨了我国菌根研究与应用等方面存在的主要问题，并展望今后的研究的热点与趋势，以期为我国菌根学在林木研究提供下一步发展的目标和思路。 The theory of Mycorrhizology is changing for the better day by day, which has caused wide attention of scholars in the world. The research on the application technology of mycorrhizal is gradually developed, and a lot of literatures show that the application prospect of mycorrhizal research in the development of agriculture and forestry is wide. In particular, the function that promotes growth and development for forest is not substituted. And that the research status of Ectomycorrhizal fungi in China is comprehensive introduced in this paper. And the research progress of mycorrhizal nutrition, mycorrhizal ecology and environmental ecological benefits and Application Technology and so on was comprehensively discussed. At the same time, the main problems existing in our country’s about mycorrhizal research and application etc. were analyzed. The study of focus and trends in the future was prospected, in order to provide the objective and thinking of the next step development of the mycorrhiza in Forest Research for our country.

On the importance of details in arbuscular mycorrhizal research

Most journals require authors to provide sufficient experimental detail in their publications to enable other scientists to reproduce the studies presented. However, my personal experience when reading papers in my research field suggests that many details that could be considered important are commonly overlooked. I analysed the work published during 2013 within the field of arbuscular mycorrhizal ecology, assessing whether 15 important details from 5 fundamental criteria were reported about (1) the experimental treatment, (2) the abiotic growing conditions, (3) the soil nutrient concentrations, (4) the duration of the study and (5) a description of the methodology employed to collect the data. Only 26% of the 171 publications analysed reported all 5 of the most important criteria. The need of including more details when reporting research is discussed and recommendations about which details should be included are provided.

A meta-analysis of arbuscular mycorrhizal effects on plants grown under salt stress.

Salt stress limits crop yield and sustainable agriculture in most arid and semiarid regions of the world. Arbuscular mycorrhizal fungi (AMF) are considered bio-ameliorators of soil salinity tolerance in plants. In evaluating AMF as significant predictors of mycorrhizal ecology, precise quantifiable changes in plant biomass and nutrient uptake under salt stress are crucial factors. Therefore, the objective of the present study was to analyze the magnitude of the effects of AMF inoculation on growth and nutrient uptake of plants under salt stress through meta-analyses. For this, data were compared in the context of mycorrhizal host plant species, plant family and functional group, herbaceous vs. woody plants, annual vs. perennial plants, and the level of salinity across 43 studies. Results indicate that, under saline conditions, AMF inoculation significantly increased total, shoot, and root biomass as well as phosphorous (P), nitrogen (N), and potassium (K) uptake. Activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase also increased significantly in mycorrhizal compared to nonmycorrhizal plants growing under salt stress. In addition, sodium (Na) uptake decreased significantly in mycorrhizal plants, while changes in proline accumulation were not significant. Across most subsets of the data analysis, identities of AMF (Glomus fasciculatum) and host plants (Acacia nilotica, herbs, woody and perennial) were found to be essential in understanding plant responses to salinity stress. For the analyzed dataset, it is concluded that under salt stress, mycorrhizal plants have extensive root traits and mycorrhizal morphological traits which help the uptake of more P and K, together with the enhanced production of antioxidant enzymes resulting in salt stress alleviation and increased plant biomass.