What makes a specialist special? The physiology of ecological specialization in plant-fungal mutualisms

Lead Research Organisation: University of Manchester
Department Name: Earth Atmospheric and Env Sciences


Ecological specialization is the process whereby an organism adapts to a narrower range of conditions than a generalist, and the process is central to the distribution and maintenance of global biodiversity. Yet, theory underpinning the evolution of ecological specialization has failed to i) fully consider situations where both generalist and specialist organisms form close associations with the same partner, and ii) identify the physiological mechanisms that lead to specialization in organisms that form mutually-beneficial relationships. The situation in (i) is prevalent in the widespread and globally-important mutualism that occurs between many tree roots and soil-borne 'ectomycorrhizal' fungi. Thus our understanding of the factors that drive the evolution of specialists and generalists in ectomycorrhizal symbioses is presently inadequate.

In this proposal, we will test the hypothesis that differences in resource transfer between plants and ectomycorrhizal fungi (carbon from plants to fungi, and nitrogen and phosphorus from fungi to plants) are key fitness consequence of specialization. We predict that specialist ectomycorrhizal fungi, i.e. those that often associate with just one genus of host plant) transfer more mineral nutrients to host plants for a given unit of carbon received from the host plant compared to generalists (i.e. they have a more favourable 'resource exchange rate'). We predict this efficiency in resource exchange makes them better competitors, however, we expect competitive advantage to be seen only under a limited breadth of niches. For example, such a situation may occur when specialist and generalist fungi are competing for resources from litter belonging to the 'specialist' host plant. We will also test the hypothesis that the spatial distribution of generalist and specialist ectomycorrhizal fungi on individual root systems affects acquisition of carbon from plants, and its subsequent allocation to external mycelium, and thus their ability to coexist.

To test these hypotheses, we will establish microcosms in which plants are colonised by host specialist and generalist ectomycorrhizal fungi in which the spatial distribution and scope for competition between the fungi is manipulated. We will also introduce different litter types to provide substrates that differ in suitability for the specialist. Stable and radioisotope tracers will be used to quantify resource exchange between partners and the efficiency of carbon use by ectomycorrhizal fungi relative to mineral nutrient transfer. These experiments will be complemented by field-based bioassays using seedlings inoculated with specialist and generalist ectomycorrhizal fungi, which are transplanted to environments that are deemed either favourable or unfavourable for specialists and generalists.

Planned Impact

We aim to engage the general public through educational activities associated with the project (see Pathways to Impact). We think the general public is a crucial group to inform, especially given the general lack of awareness of the key roles fungi play in many processes. Our Pathways to Impact exploits the proximity of the Cruickshank Botanic Gardens to achieve this aim.

We also aim to engage local science secondary school teachers, who have the responsibility of enthusing at an early age the next generation of ecologists. This aim is particularly important and timely given the recent change to the national curriculum (Curriculum for Excellence). To achieve this we will liaise with professional staff very closely involved with school teacher training at the University's Natural History Centre.

The rationale for the work we propose is ostensibly quite academic in nature, in that it deals with fundamental questions about the consequences of the evolution of specialization using ectomycorrhizal trees as models to test our hypotheses. However, these consequences have important implications for a range of stakeholders. The Forestry Commission will be particularly interested in the role of ectomycorrhizal fungi in affecting biogeochemical cycles. Current environmental policies aim to both maintain and enhance biodiversity and yet reduce losses of carbon and nutrients, and it is possible for these two aims to conflict.

The Forestry Commission will also be further interested in how the presence of different types of ectomycorrhizal fungi affects tree productivity. They have a strong interest in achieving maximum crop yield and we will determine whether this is affected by varying the ectomycorrhizal fungal communities. The Forestry Commission also has a key role in maximising soil carbon storage because of the vast area of forests that they manage. Increasing carbon storage is a central part of UK legislation and out data will provide the evidence-base to develop effective management strategies that optimise carbon storage. This aim requires a better understanding of the carbon cycle more generally in forests, and a key component of our work quantifies the flux of carbon into soils, and its release as CO2.

Other stakeholders include: Scottish Natural Heritage (SNH) who will be interested because they have a statutory requirement to protect and enhance UK's biodiversity, including fungi. Our results will help demonstrate the key roles ectomycorrhizal biodiversity plays in enhancing ecosystem functioning.

Inter-agency Plant Conservation Working Group; this is a multi-agency group based in the UK aiming to develop plant conservation good practice.

Other conservation groups are also increasingly interested in the role ectomycorrhizal fungal diversity and their effects on plants (e.g. Plantlife International, Trees for Life). Indeed, there has been a recent move to strengthen the profile of fungi across the UK that has involved groups like Plant Life, British Mycological Society, and the UK Fungal Conservation Forum.

The needs of the UK Biodiversity Research Advisory Group (UK BRAG) who highlight the urgent need to understand the link between plant and microbial functional diversity.


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Ardanuy A (2021) Tripartite symbioses regulate plant-soil feedback in alder in Functional Ecology

Description Understanding the relationship between ectomycorrhizal fungi (EMF) and their host tree communities is essential for developing knowledge on community resilience and afforestation. Different tree communities will likely harbour different EMF communities with some EMF specialising on a particular tree genus and others being generalists. However, the consequences of such interactions for seedling recruitment, EMF diversity and wider ecosystem processes are poorly resolved. Here we test how monoculture and mixed forest stands affect seedling growth, and EMF community composition on seedling roots and in decomposing litter.
We grew Betula pendula and Pinus sylvestris seedlings in soil from B. pendula, P. sylvestris monocultures and a 50:50 B. pendula:P. sylvestris mixed woodland established in 1961. We measured mycorrhizal colonisation and growth of seedlings, and the EMF community composition on their roots. In addition, we established a reciprocal litter transplant experiment in the field and measured the community composition of EMF colonising litter using High Throughput Sequencing (HTS).
Of 257 experimental seedlings,139 formed ectomycorrhizas at the end of the study. Betula pendula were more likely to be mycorrhizal when grown on home soil vs P. sylvestris soil. Pinus sylvestris seedlings were also more likely to be mycorrhizal when grown on B. pendula soil rather than home soil. Mycorrhizal status had a greater impact on biomass and C:N ratio than soil origin.
NMDS analysis showed that the stand type rather than seedling species affected the EMF community composition, with the P. sylvestris stand communities being more distinct from the B. pendula and mixed communities. From molecular analyses,102 EMF Operational Taxonomic Units were identified. The NMDS revealed clustering via litter type rather than by stand type.

Our findings show that stand composition and associated litter affected EMF colonisation and community composition, which has consequences for seedling recruitment and resilience.
Exploitation Route Testing the mechanisms by which mixtures select for particular species of ectomycorrhizal fungi
Sectors Agriculture, Food and Drink,Energy,Environment

Description Short-circuiting the terrestrial phosphorus cycle: symbiotic control of organic phosphorus mineralisation and uptake
Amount £662,184 (GBP)
Funding ID NE/W000350/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 02/2022 
End 07/2025
Description Public Talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Talk to the Cheshire Wildlife Trust on mycorrhizal fungi
Year(s) Of Engagement Activity 2018