Measuring and modelling plant-driven soil carbon dynamics

Lead Research Organisation: Cranfield University
Department Name: School of Water, Energy and Environment

Abstract

One of the most pressing problems in environmental science is the possibility of a feedback loop between atmospheric CO2 levels, global warming and soil carbon emissions. The land surface is currently a net sink for rising CO2 as vegetation grows faster, but as warming continues, soil microbes will turn over carbon faster, and it is predicted that the land will become a net source of CO2 at some point resulting in a feedback loop.
However understanding of the underlying processes is poor and they are poorly represented in models. This PhD will exploit a unique experimental facility at Cranfield - the Wolfson Field Laboratory - to study plant root-soil interactions affecting soil carbon turnover so as to develop better soil carbon models. The facility contains large soil monoliths linked to instruments for measuring carbon fluxes and their stable-isotope composition. The isotope composition allows partitioning of the fluxes between plant and soil sources, giving detailed datasets for modelling. We will exploit this data using model-data fusion techniques to develop and test new models of the underlying processes.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
NE/M009106/1 01/10/2015 31/03/2024
1818447 Studentship NE/M009106/1 03/10/2016 31/12/2020
 
Description Travel grant
Amount £500 (GBP)
Organisation British Society of Soil Science 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2019 
End 08/2019
 
Title Sampling and analysis system for separating plant and soil carbon fluxes under field conditions 
Description A major obstacle to developing a better understanding and improved models of plant-driven soil C dynamics is a lack of datasets representative of conditions in the field. Due to the inherent difficulty involved in distinguishing between plant and soil C fluxes under natural environmental conditions most studies assessing rhizosphere priming have been short-term and lab- or pot-based. Our method uses large (0.8 m diameter, 1 m deep) lysimeters containing two C3 soils and sown with a C4 grass (Bouteloua dactyloides), using differences in the C isotope ratios of CO2 produced by C4 plant respiration and C3 SOM decomposition to partition net C fluxes. Previous studies under field conditions have struggled to separate these fluxes as differences between plant and SOM isotope ratios are small. Using a novel C3 to C4 plant change allows us to exploit differences in C isotope fractionation between these two photosynthetic pathways to create a larger distinction. Gas flux measurements are made thrice daily from 24 planted lysimeters using cavity ring-down spectroscopy, using an automated system which allowed us to continually monitor fluxes for over 6 months. Flux measurements have been coupled with near-continuous soil moisture and temperature measurements at multiple depths. We have demonstrated that this system enables successful partitioning of soil and plant C fluxes under field conditions. Results from the initial growing season show clear patterns to both plant and soil C dynamics at both diurnal and seasonal timescales. 
Type Of Material Improvements to research infrastructure 
Year Produced 2018 
Provided To Others? No  
Impact This research method and setup enables the generation of field-scale datasets of seperated plant and soil respiration fluxes. These are much needed to improve models of soil carbon dynamics, and better integrate the impacts of root activity on soil C cycling.