MEGAN L. PURCHASE

Environmental Researcher

Welcome

I'm a third year PhD candidate at the University of Warwick. I'm interested in soil health and the effects of land use change and human input on the biogeochemistry of soils. Please enjoy having a look at some of my work and feel free to contact me if you have any questions - I'm always happy to talk about soil.


Research Themes

BIOGEOCHEMISTRY


LAND-USE CHANGE AND URBANISATION

MICROBIOLOGY


Current Projects

Resolving soil sourced atmospheric pollution across a land-use continuum

Connecting cicada emergence to forest emissions of greenhouse gases

Our lab studies environmental processes that occur within the terrestrial biosphere. We link plants and microbes to the flow of carbon and nutrients in natural and managed ecosystems.

Our research focuses on the structure and ecosystem functions of microbial communities.

Latest News

Conferences & Symposiums

AGU Annual Meeting 2023

San Francisco, CA - December 2023

eLightning Presentation

British Society of Soil Science Early Career Travel Grant

Abstract

Volatile reactive nitrogen oxides (NOy) are significant atmospheric pollutants, including NOx (nitric oxide [NO] + nitrogen dioxide [NO2]), and NOz (nitrous acid [HONO] + nitric acid [HNO3] + nitrogen trioxide [NO3] + ...). NOy species are products of nitrogen (N) cycle processes such as nitrification and denitrification. Biogenic sources, including soil, account for over 50% of natural NOy emissions to the atmosphere, yet emissions from soils are generally not included in atmospheric models due to a lack of mechanistic data. This work is a unique investigation of NOy fluxes on a landscape scale, taking a comprehensive set of land-use types, human influence, and seasonality into account to determine large-scale heterogeneity to provide a basis for future modelling and hypothesis generation. By coupling 16S rRNA amplicon sequencing and quantitative PCR, we have linked significant differences in functional potential and activity of nitrifying and denitrifying soil microbes across a gradient of urbanisation and land-use to NOy emissions from soil. We have assessed soil physicochemical properties characteristic of different land-use types, and as a result of anthropogenic influence. Further, we have identified the response of soil NOy emissions from varying land-use types to N deposition and found soils subject to more human influence to be less microbially active despite increased available N, potentially as a result of poor soil health from anthropogenic pollution. Structural equation modelling suggests human influence on soils to be a more significant effector of soil NOy emissions than land-use type. Results show significant seasonal variation of rates of N cycle processes and reactive N fluxes, demonstrating a need for temporal scale to be considered in future investigations.

Abstract

Nitrous oxide (N2O) is a potent greenhouse gas with more warming potential than carbon dioxide (CO2) and soils are known to be the dominant source of atmospheric N2O. N2O is produced and emitted during microbial transformations of nitrogen (N) species that make up the N cycle. The synchronous emergence of periodical cicadas represents one of the largest insect emergence events. The year 2021 saw the emergence of the 17-year “Brood X” cicadas (Magicicada septendecim, M. cassinii, and M.Septendecula). The exoskeletons of cicadas are primarily made up of chitin, a polymer of N-acetylglucosamine (GlcNac). The aboveground lifespan of cicadas is just ~6 weeks, after which the large deposition of low C:N content cicada carcasses is a significant N-rich input into the environment, particularly to forest soils. 

Decomposition of insect carcasses occurs more readily than decomposition of other organic material, making insects an important and currently understudied input of N to soils that can contribute to emissions of N species from soils.It has been found that emissions of N2O are enhanced when cicada carcasses are added to soil chambers. We have examined the soil microbiome, and the cicada necrobiome using quantitative PCR (qPCR) and 16S rRNA amplicon sequencing to elucidate the potential microbial source of these enhanced emissions. We suggest a currently unknown microbial pathway for the decomposition of cicada chitin and the resulting enhanced N cycle processes that lead to “hotspots” of N2O emissions from forest soils following cicada emergence. Future work will involve time-series experiments to ascertain the links between decomposition state, microbial community of the soil and carcasses, and N2O emissions.


CENTA Conference 2023 

University of Warwick - September 2023

Organising Committee

Short Talk - 2nd Place

PGR Symposium 2023 

University of Warwick - March 2023

School of Life Sciences Best Research Poster Award for presenting one of the five best posters at the SLS Postgraduate Research Symposium

MMEG Conference 2022

University of Strathclyde

Abstract

Volatile reactive nitrogen oxides (NOy) are significant atmospheric pollutants, including NO + NO2 (NOx) and HONO + HNO3 + NO3(NOz). Biogenic sources, including soil, account for over 50% of natural NOy emissions to the atmosphere. Despite their importance, NOy emissions from soils are generally not included in atmospheric models due to a lack of mechanistic data.

Spatial heterogeneity amongst landscapes and across population gradients likely influences NOy fluxes due to differences in atmospheric deposition rates and anthropogenic soil modifications – likely altering microbial and abiotic cycling of NOy; however, this has not been explored in mechanistic detail. Here, we link nitrifying and denitrifying soil microbes, across a gradient of urbanisation and land-use, to NOy gas fluxes from soil. To resolve temporal discrepancies, soil sampling (0-10 cm) occurred seasonally.

Results show significant changes in relative abundances of microbial orders associated with nitrification, denitrification and nitrogen fixation across a human population gradient, and between land-use types, suggesting anthropogenic impact on soil microbiology. From structural equation modelling (SEM), we see NOy and NO fluxes significantly affected by land-use type. Soil physicochemistry is a major influence on other measured variables and is therefore likely to be an important predictor of soil NOy fluxes. 

 

Keywords: Soil, Biogeochemical cycling, Anthropogenic impacts


CENTA Conference 2022

National Space Centre, UK




Net Zero     Doctoral Summer Showcase 2022

Loughborough University, UK

Poster -  1st Place


‘Science of Future Food' Event 2022

University of Warwick, Stratford Innovation Campus

Poster


Training News

FAAM Experience Flight 

Facility for Atmospheric and Airborne Measurements, Cranfield University, August 2023

Thanks to  Doug Anderson, Chris Reed, and the everyone at FAAM

Fundamentals of Build-It-Yourself Environmental Sensors

Kings College London, May 2023, funded by NERC

Thanks to  Dr Daniel Schillereff, Dr Michael Chadwick, Dr Kristofer Chan, Professor Mark Mulligan, Dr Kate Olde, Dr Francis O'Shea, Nathan Oo, Reagan Pearce

Introduction to Earth Observation Data

Cranfield University, May 2023, funded by NERC

Thanks to  Dr Abdou Khouakhi, Dr Jacqueline Hannam, Dr Toby Waine, Dr Daniel Simms, Ann Holden, Ian Truckell

Contact Me