CR2025_35 Unravelling how mycorrhizal and decomposer fungi in forest soils effect wood and litter decomposition and may mitigate climate change

Lead Supervisor: Mark Tibbett, Department of Sustainable Land Management, University of Reading

Email: m.tibbett@reading.ac.uk

Co-supervisors: Dan Eastwood, Department of Biosciences, Swansea University; Elena Vanguelova, Forest Research; Rodica Pena, Department of Sustainable Land Management, University of Reading

Forest soils are part of the solutions to global climate change by sequestering carbon (C) to compensate for anthropogenic carbon dioxide (CO₂) emissions, which are the major cause of rising global temperatures. Soil C-sequestration depends on two contrasting processes: soil organic matter (SOM) decomposition which results in C-loss to atmosphere, and SOM stabilisation that results in C-storage in soil.

Fungi are the dominant decomposers in forest ecosystems responsible for the decomposition of dead wood and litters in soils. Two major fungal groups, saprotrophic (SAP) and ectomycorrhizal (EM), play key roles in the decomposition process, interacting and competing for contrasting resources across soil, wood, and litter. SAP fungi primarily obtain carbon from decomposing wood and litter, while EM fungi, which form symbiotic associations with tree roots, depend on photosynthate carbon from their hosts, playing a substantial role in plant-derived carbon sequestration in forest soils. Within the soil environment, these two groups of fungi compete for contrasting resources, with resource size and structure shaping their strategies. EM fungi prioritise the acquisition of nutrients (e.g. nitrogen) rather than the breakdown of litter and wood for carbon. SAP fungi, in contrast, employ different strategies: some complete their life-cycle within a resource (resource unit limited), and others form mycelial networks within the soil linking sources of nutrition (non-resource unit limited) where nitrogen is translocated based on C:N ratio dynamics. The balance between these nutritional strategies may substantially alter decomposition and hence CO₂ release from forest soils. This effect, known as the “Gadgil effect” (Figure 1), reflects the competitive interactions between these fungal types and their impact on soil CO₂ emissions during decomposition. If true, this phenomenon represents a potential mechanism for climate change mitigation through enhanced carbon sequestration in soils. However, the mechanism by which SAP and EM fungi interact in carbon cycling remains controversial and poorly understood, with inconsistent evidence.

In this project, you will determine whether the interactions between SAP and EM fungi could be a neglected component of forest soil ecology that may be manipulated to augment soil C-sequestration in forests. You will be part of a research team investigating these phenomena and will access established field experiments across forests in east and south England.  Here, soil plots have been isolated from the photosynthate supply from trees restricting access of EM in favour of SAP fungi (alongside controls plots: no restriction). These plots offer opportunities for novel studies, including the decomposition rate of various substrates, such as litters and wood. The decomposition of larger woody debris, particularly in contrast to litter decay, remain unknown. Analysis might include advanced high-throughput or MinION sequencing. You will also have access to new measurement techniques and training that have not applied in this field, including FTIR spectroscopy and enzyme assays for carbon and nitrogen cycling.

The study will be developed collaboratively by the student and supervisors. The overall aim is to determine whether the “Gadgil effect” can be measured and to characterise the ecological processes that define it. We hypothesise that leaf litter and smaller woody resources initially support a more diverse community including EM fungi, while larger wood substrates on the forest floor will be targeted by SAP decay specialists. Further assessments may explore long-term fungal succession and substrate structural change due to decay or investigate nutrient dynamics using carbon and nitrogen stable isotopes to track movement and sequestration following decay under differing treatments.     

To achieve the project goals, at least two experimental interventions will be applied to the existing plots. Interventions will involve arranging different resource types within experimental plots designed to measure the Gadgil effect:

1. Litter and wood shavings: investigate the effect of Gadgil treatments (EM exclusion) by comparing the decomposition rate of leaf litter with those of smaller lignified biomass (twigs, roots, shavings) resources.
2. Wood disc (~30 cm diameter) baits: characterise the community colonisation and succession over time using molecular community analysis.

Decomposition of all substrate types will be integrated into an overarching synthesis that will set the benchmark in our understanding of resource size effects and fungal nutritional strategy on forest decay systems.

 Training opportunities:

Forest research will not only assist in the maintenance and field sampling work but also will provide training in key areas. The student will be working as part of an interdisciplinary team working on current experimental sites and have access to FR laboratories.

Training at Swansea will focus on fungal interaction dynamics and molecular analyses involving both sequencing and chemical analysis/

At the university of Reading training will be given specialist training enzyme assay and FTIR use and interpretation

Most importantly, the partnership combines national expertise in SAP and EM fungal biology, uniquely, in the UK. 

Student profile: 

This project would be suitable for students with a degree in biology, microbiology, ecology, soil science, environment science or a closely related science degree.

Co-Sponsorship details: 

The project will receive a CASE award from Forest Research.