Prof David Johnson

Chair in Soil Microbial Ecology

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Tel: 0161 2751555

Research in my group focuses on understanding biological interactions in the terrestrial environment, particularly among plants, soils, mycorrhizal fungi and herbivores. Much of this research concerns the role of biological interactions in the context of carbon and mineral nutrient cycling, and therefore my group often uses isotopic tracers to quantify nutrient fluxes. A key research focus is on the ecology of symbiotic mycorrhizal fungi that inhabit the roots of most plants and are ideal models for testing ecological theory, and crucial in regulating biogeochemical cycling and plant fitness. Our research is applied to tropical and temperate forests, peatlands, grasslands and agri-ecosystems.

BBSRC-funded PhD 2021 entry:

Quantifying greenhouse gas emissions in agri-ecosystems across multiple scales

This exciting project will provide training for careers in sustainable agriculture. The project will develop new understanding of how grazed grassland management practices influence and mitigate greenhouse gas emissions. The focus will be on upland grasslands and experiments will make fine scale measurements of greenhouse gas fluxes at high temporal resolution using our novel mobile laboratory (‘GasLab’). Additionally, the use of stable isotope tracers will enable detailed investigation of the mechanisms contributing to these fluxes, including the soil biological pathways of denitrification, which is a major pathway for the production of the potent greenhouse gas nitrous oxide (N2O). The student will gain training in a range of disciplines related to plant and soil science and agro-ecology, and will gain a thorough understanding of the factors that contribute to greenhouse gas emissions in grasslands. The work will be of direct policy relevance (and will require close collaboration with Natural England) and will lead to several important publications and outputs.


Self-funded PhDs:

I am interested in self-funded PhD students on projects related to plant-soil interactions including "The functional importance of plant-fungal interactions in agri-ecosystems". 

In this exciting project, we will investigate how different land management strategies, such as fertiliser use and reseeding, affect the ability of plants to interact with mycorrhizal fungi. We will test hypotheses concerning reciprocal exchange of nutrients between plants and mycorrhizal fungi, how so-called ‘common mycorrhizal fungal networks’, which connect many individual plants simultaneously, can facilitate plant growth, nutrition and fitness, and how the symbiosis affects interactions with common agricultural pests. The project will use state-of-the-art isotopic analysers and manipulation experiments to quantify nutrient flows and test how fungal mycelium regulates plant performance. The work will be analysed in the context of the need to develop sustainable food security strategies.


Underground fungal networks - their role in plant to plant signalling and seedling growth

Testing how common mycorrhizal fungal networks facilitate plant growth and transmission of signals related to defence against herbivory

Greenhouse gas emissions from grasslands

Using cutting-edge technology (e.g. our GasLab mobile van) to measure fluxes of nitrous oxide from soils in relation to agricultural management

Our new NERC-funded mobile laboratory (Gladiss the GasLab) is used to quantify fluxes of greenhouse and trace gases (N2O, CH4, CO2, NH3) in situ, and also enables quantification of the isotope ratios of some of these gases (15N2O, 13CO213CH4) in real time using automated chambers and the latest laser absorption spectrometers. Meteorological data are also collected. The 4x4 vehicle can operate remotely and is available for hire to the scientific community.


Active research projects

  1. NERC Standard Discovery (Feb 2019-Feb 2022) “Disentangling mechanisms of co-adaptation between trees and soil food webs in response to environmental perturbations.” PI: D Johnson. £793k        NE/S002189/1 
  2. NERC International Opportunities Fund (Feb 2018-Jan 2020) “Plant-soil feedbacks as drivers of seedling establishment in tropical and sub-tropical forests”. £48793. NE/R004986/1
  3. NERC-NSF Standard Discovery (April 2017-2020). “Mycorrhizal drivers of SOM formation and decomposition” PI: Jens Subke, Stirling. NSFDEB-NERC. £443k. NE/P011098/1  
  4. NERC Standard Discovery (Feb 2017-2020). “Social networking in soil: Biodiversity as a selective force for inter-plant signalling”. PI: D Johnson. £625k. NE/P001823/1
  5. NERC Standard Discovery (October 2016-April 2020). “Will more productive arctic ecosystems sequester less soil carbon? PI: Phil Wookey, Heriot Watt, CoI: D Johnson. £794k. NE/P002722/2.
  6. NERC Capital Equipment “Isotope trace gas laboratory” £500k. PI: Y Teh
  7. NERC Capital Equipment “In situmobile isotope trace gas laboratory” £590k. PI: D Johnson 
  8. “What makes a specialist special? The physiology of ecological specialization in plant-fungal mutualisms”. May 2015-2018. NERC Standard. £630k. PI: D Johnson. NE/M015653/1.


Areas of expertise

  • QK Botany - Mycorrhiza, Ecology, Soil Science, Biodiversity, Biogeochemical cycling, Sustainable agriculture, Ecosystem processes, Plant science

Biology, Medicine and Health (BMH) Domains

Education / academic qualifications

  • 1998 - Doctor of Philosophy, Changes in soil microbial biomass & activities and plant nutrition in response to simulated pollutant nitrogen deposition, The University of Sheffield

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