CR2025_47 Nutrient Impacts and Microbiochemical Controls on Carbon Storage in Forest Soils

Lead Supervisor: Liz Shaw, Department of Geography and Environmental Sciences, University of Reading

Email: e.j.shaw@reading.ac.uk

Co-supervisors: Elena Vanguelova, Forest Research; Brian Pickles, Department of Ecology and Evolutionary Biology, University of Reading; Rodica Pena, Department of Sustainable Land Management, University of Reading

Temperate forests and woodlands play a vital role in storing carbon, much of which is held in the soil. This natural carbon storage helps to offset the effects of climate change. However, the ability of forests to sequester carbon depends on several factors, including the availability of key soil nutrients like nitrogen (N) and phosphorus (P). These nutrients influence the processes by which carbon is added to the soil through plant growth and lost through microbial activity as organic matter decomposes.

Traditionally, N has been considered the primary macronutrient element governing carbon accumulation in forests and woodlands. However, evidence suggests a significant shift, both in Europe and globally, where historical N limitations are giving way to P limitations due to increased atmospheric N deposition. This transition raises questions about the role of P and its potential constraints on microbial activity in the soil.

This PhD project therefore aims to investigate how and why changing macronutrient availability influences the breakdown of organic matter and, in turn, carbon storage in temperate forest and woodland soils. Central to this study are the extracellular enzymes released by soil microbes and plant roots to break down complex organic molecules, releasing nutrients in forms microbes and plants can use. The project will explore how changes in absolute and relative (to nitrogen) phosphorus availability affect the production and balance of these enzymes, and their subsequent feedback to nutrient availability and carbon cycling in soils.

The research will primarily focus on farmland woodlands in the UK, crucial components of the nation’s net-zero strategy. These woodlands are exposed to varying levels of nitrogen deposition due to nearby agricultural activities, providing an ideal setting for conducting “natural experiments” that investigate biogeochemical responses under varying nitrogen and phosphorus availabilities.

To test assumptions about (substrate supply or resource demand) regulation of microbial enzyme expression, laboratory experiments will simulate various nitrogen and phosphorus inputs to test their effects on microbial enzyme production and persistence. ¹³C isotopic tracing will be used to understand how varying N:P influences the fate of litter carbon during decomposition. The research will therefore involve both fieldwork “natural experiments” and laboratory experimentation. To support and extend the insights from field and lab experiments, there will be opportunities to incorporate an ecological modelling approach, to simulate carbon, nitrogen, and phosphorus-acquiring enzyme activities. This will enable an exploration of how soil microbes adjust enzyme production based on nutrient needs, and the resulting impacts on soil carbon storage, under current and potential future scenarios with changing nutrient levels.

This research, at the intersection of soil biogeochemistry and forest ecology, will contribute to a better understanding of nutrient-driven soil carbon cycling in forests and woodlands, supporting strategies for effective ecosystem management and science-based recommendations for global climate action.

Training opportunities: 

This project combines field monitoring, lab work, and process-based modelling in partnership with Forest Research (FR), GB’s principal forestry research organization, providing access to woodland monitoring networks, experiments, and datasets. Field training includes soil survey, sampling design, in situ nutrient measurements. Lab training covers soil C:N:P analysis, isotope tracing, microbial and biochemical assays. A placement at FR’s Alice Holt station (~25 miles from Reading) provides facilities, training, and opportunities for research translation with the Forestry Commission. Alternative approaches – using archived samples, existing datasets, and virtual placement – can substitute fieldwork or in-person placements based on individual circumstances. 

Student profile:

This project would be suitable for students with a background in Environmental Science, Plant Science, Forestry, (Micro)Biology, Biochemistry or Ecology. Applicants should preferably hold an MSc in a relevant subject and at minimum an upper 2nd class degree or equivalent. 

Co-Sponsorship details: 

This project will receive a CASE award from Forest Research.

References:

• Du E, van Doorn M and de Vries W (2021) Spatially divergent trends of nitrogen versus phosphorus limitation across European forests. Science of The Total Environment 771, 2021,145391.
• Forstner, SJ, Wechselberger, V, Stecher, S, Muller, S, Keiblinger, KM, Wanek, W, Schleppi, P, Gundersen, P, Tatzber, M, Gerzabek, MH, Zechmeister-Boltenstern, S (2019) Resistant soil microbial communities show signs of increasing phosphorus limitation in two temperate forests after long-term nitrogen addition. Frontiers in Forests and Global Change 2, 73.
• Sinsabaugh, R. L., & Follstad Shah, J. J. (2012). Ecoenzymatic stoichiometry and ecological theory. Annual Review of Ecology, Evolution, and Systematics, 43, 313-343.
• Zheng HF, Vesterdal L, Schmidt IK and Rousk J (2022) Ecoenzymatic stoichiometry can reflect microbial resource limitation, substrate quality, or both in forest soils. Soil Biology & Biochemistry 167, 1879-3428.
• Manzoni, S., Arjun, C, Spohn, M, Lindahl, B (2021) Modelling microbial adaptations to nutrient limitation during litter decomposition. Frontiers in Forests and Global Change. DOI:10.3389/ffgc.2021.686945