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Forests for climate mitigation – how does tree-derived nitrogen influence soil greenhouse gas production?


School of Geosciences

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Dr L Street , Prof Elizabeth Baggs , Dr M Perks No more applications being accepted Competition Funded PhD Project (Students Worldwide)

About the Project

Summary: How does the capture and transport of nitrogen by forest trees influence the key microbial processes driving greenhouse gas emissions from soils? Answering this question will help us understand how forests can contribute to climate mitigation under changing environmental conditions.

Background: Afforestation is widely seen as a natural climate solution – multiple national and international initiatives promote tree planting for climate mitigation. However, recent work in the UK suggests that in some circumstances afforestation can promote carbon losses from soils which more than offset the carbon gained in tree biomass. The cause of these losses is not fully understood, but may be explained by a shift in soil microbial function in the presence of tree roots as forests establish. It is critically important that tree planting policy is supported by a strong evidence base, to avoid ineffective or even counterproductive measures. Understanding how forest trees influence soil biogeochemistry is crucial; this PhD project will focus on the key role of organic nitrogen.

We know plants influence the biogeochemistry of the soil in multiple ways; for example by taking up nutrients plants can limit nutrient availability for the activity of soil microbes. On the other hand, exudation of plant-derived molecules from the root surface can increase the availability of organic compounds in the soil which can stimulate microbial activity. There are large gaps in our understanding of how these two aspects of plant function influence carbon and nitrogen cycling in soils – and thus the key ecosystem services that forests provide, such as soil carbon sequestration, biomass production and downstream water quality. The role of tree-derived organic nitrogen (small peptides and amino acids) in soils is particularly uncertain and presents an opportunity for novel, cutting-edge research.

This project will examine the dynamics of organic nitrogen in forest soils, specifically the utilisation of plant-derived nitrogen in key microbial processes, how this influences nitrogen uptake by trees and soil greenhouse gas production. Understanding the processes underpinning plant-mediated cycling of organic nitrogen will help inform our understanding of forest ecosystems’ role in climate mitigation and the response of future forests to environmental change.

Key research questions:
1. What is the fate of tree-derived nitrogen in conifer and broadleaved woodland soils?
2. How does tree-derived nitrogen influence microbial processing of carbon and nitrogen in soil?
3. Do forests take up or ‘recycle’ their own nitrogen?
4. What role do ectomycorrhizal fungi play in the cycling of organic nitrogen?

Funding Notes

Funding covers stipend, fees and research costs.

References

Friggens, NL, et al. (2020) Tree planting in organic soils does not result in net carbon sequestration on decadal timescales. Global Change Biology. 21, 5178– 5188. doi: 10.1111/gcb.15229
Jonard M, et al. (2014). Tree mineral nutrition is deteriorating in Europe. Global Change Biology 21, 418-3. doi: 10.1111/gcb.12657
Nair R, et al. (2016) Does canopy nitrogen uptake enhance carbon sequestration by trees? Global Change Biology 22, 875–888. doi: 10.1111/gcb.13096
Van der Linde S, (2018). Environment and host as large-scale controls of ectomycorrhizal fungi. Nature 558, 243–248. doi: 10.1038/s41586-018-0189-9
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