Lead Supervisor: Liz Shaw, Department of Geography and Environmental Science, University of Reading
Email: e.j.shaw@reading.ac.uk
Co-supervisors: Elena Vanguelova, Forest Research; Mark Tibbett, School of Agriculture Policy, and Development, University of Reading
Forests and woodlands serve as key carbon reservoirs, with a substantial portion of the carbon stored as soil organic matter. The capacity of forests to sequester carbon depends, among other factors, on the availability of the soil macronutrients, nitrogen and phosphorus. These nutrients influence both carbon input into the soil and carbon loss through the stimulation of primary productivity and microbial respiration, respectively.
Traditionally, nitrogen has been considered the primary nutrient governing carbon accumulation in forests and woodlands. However, evidence suggests a significant shift, both in Europe and globally, where historical nitrogen limitations are giving way to phosphorus limitations due to increased atmospheric nitrogen deposition. This transition raises questions about the role of phosphorus and its potential constraints on microbial activity in the soil.
This PhD research project therefore aims to unravel the soil macronutrient biogeochemistry governing soil carbon sequestration in temperate forest and woodland systems contributing to understanding of their role in mitigating climate change.
Central to this study are extracellular enzymes, which microorganisms (and plant roots) release into the soil. These enzymes play a pivotal role in converting complex forms of nitrogen and phosphorus into bioavailable nutrients for plants and microorganisms. Microbial enzyme expression and metabolism is thought to be regulated by availability of organic substrate relative to resource demand, connecting elemental stoichiometry of microbial biomass and leaf-litter derived SOM substrates. The project will explore how fluctuations in nutrient availability impact the activities of key extracellular enzymes involved in nutrient transformations and their subsequent feedback to nutrient availability and effects on 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. There is opportunity to understand these biogeochemical constraints under both current conditions and potential future scenarios with declining nitrogen deposition. The research will involve the fieldwork “natural experiments” and also laboratory experimentation. Lab experiments will involve manipulations to test assumptions about extracellular enzyme regulation and persistence in woodland soil types.
Training Opportunities
This project combines field and laboratory work, collaboration with Forest Research (Great Britain’s principal organisation for forestry and tree-related research) who will provide access to existing woodland monitoring networks, experiments and background datasets. There are opportunities to gain field practical skills in soil survey, sampling design and in situ nutrient measurements. Lab-based training includes analysis of soil carbon quantity and quality, isotopic C tracing and assays for extracellular enzyme activities. A placement opportunity at Forest Research’s Alice Holt station (< 1 hour from Reading), offers access to facilities and training schemes, including research translation in collaboration with the Forestry Commission.
Student Profile
This project would be suitable for students with a background in Environmental Science, Plant Science, Forestry, (Micro)Biology and/or Ecology. Applicants should preferably hold an MSc in a relevant subject and at minimum an upper 2nd class degree or equivalent.
Funding Particulars
This project has CASE support 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.