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What are the effects of exotic tree introduction in British forests on soil nitrogen cycle processes?

Project Description

Project Highlights:
• Exotic tree species are projected to become commonplace in Britain’s forests throughout the next century
• You will assess whether these exotic tree species influence a significant change in the soil microbiome as well as production of nitrogenous gases
• This project will allow you to use field-based soil surveying, soil gas measurements, laboratory microcosms, and molecular analysis of soil.

Recent reports have noted that Britain’s forests of the future will be comprised of many exotic species that are well adapted to projected climate scenarios1. While this is a necessary preventative measure to ensure continued carbon capture by our forests, there may be unforeseen consequences. Many of these exotic species, which include Ginko and Araucaria, make root associated with arbuscular myccorhizal (AM) fungi. This is in contrast to oaks, beech, and pine which make similar associations with ectomycorrhizal (ECM) fungi. In addition to different fungal symbionts, AM trees select for completely different soil microbiomes relative to ECM trees. One biogeochemical consequence of these divergent microbiomes is in the production of nitrogenous gases (e.g., N2O and NOy ≡ NO, NO2, HONO), with the AM soil producing significantly more of these gases relative to the ECM soil2. These gases are of great importance as they contribute directly to the greenhouse effect (N2O) and strongly influences the oxidative capacity of the atmosphere (NOy).
Because of the potential large-scale incorporation of AM tree species throughout British forests, there is a great need to parameterize the role of tree species composition in mitigating or contributing to the flux of nitrogenous gases. Thus, a multidisciplinary approach, including atmospheric chemistry, biogeochemistry, and microbiological techniques is needed to fully elucidate potential fluxes of these important trace gases from individual tree species as well as from mixed forest stands. Using greenhouse experiments, laboratory microcosms, and field-based measurements we propose to quantify fluxes of N2O and NOy to determine if exotic tree proliferation will lead to altered soil microbiomes as well as an increase in nitrogenous gas flux from soil.

We will establish sampling plots in forest stands that are AM-dominant, ECM-dominant, and mixed AM/ECM as well as stands that have been modified with exotic species (both AM and ECM species). In those plots we will make seasonal nitrogen gas measurements as well as evaluate the soil microbial community. To assess the individual impact of tree species on gas production, we will grow saplings of tree species known to associate with AM or ECM fungi (both native and exotic) in pots containing soils collected from AM- and ECM-dominated stands. AM and ECM saplings will be planted in ECM and AM soils (reciprocal transplant) which will allow us to estimate how soil origin (AM vs. ECM) affect nitrogen gas flux when AM trees are planted in ECM soils (and vice versa).

Training and skills:
Training during this fellowship includes a wide range of molecular techniques and analyses (microbial culturing, DNA extraction from soil, PCR, sequencing, and bioinformatics) as well as analytical chemistry (nitrogen oxide quantification, reactive oxygen extraction from soil and subsequent quantification, and building sampling mesocosms). Field-based sampling and measurements from forest ecosystems will also be emphasized.

Partners and collaboration:
Both Dr. Mushinski and Professor Bending have substantial expertise in nitrogen cycle biogeochemistry as well as plant-soil-microbe interactions, evidenced by publications in the Proceedings of the National Academy of Sciences, New Phytologist, and Soil Biology and Biochemistry. The UK Forestry Commission may be an avenue for partnership on this project.

Possible timeline:
Year 1: Conduct field measurements of N2O and NOy fluxes from AM-dominated, ECM-dominated, AM/ECM mixed, and exotic species soils throughout the UK.
Year 2: Assess how individual AM- and ECM-associated trees influence the production of nitrogenous gases and explore whether these responses depend on plant vs. soil characteristics.
Year 3: Utilize genomic tools to better discriminate sources of N2O and NOy produced during nitrogen cycling.

Funding Notes

This funding provides full tuition fees at the Home/EU rate, pays an annual stipend in line with UK Research Councils (currently £15,009) and a research training support grant (RTSG) of £8,000


Further reading:
[1] Horton, H. (2019) ‘Britain's forests of the future will be filled with foreign species in attempt to address climate change, head of Forestry Commission reveals’, Available at:

[2] Mushinski, R.M. et al. (2019) ‘Microbial mechanisms and ecosystem flux estimation for aerobic NOy emissions from deciduous forest soils’, Proceedings of the National Academy of Sciences, 116 (6) 2138-2145.

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