A simple but substantial improvement in the way we currently represent leaf respiration in climate models

Institution: University of Exeter

Lead Supervisor: Dr Lina Mercado

Project Description

Plant respiration is a key component of the carbon cycle, and to make realistic projections of future climate predictions, it is fundamental to have a realistic representation of plant respiration within climate models. Climate models that are used to predict future climate change have rather simple representations of plant respiration, and what is worse, they over predict the observations at many sites (Mercado, unpublished work).  The representation of plant respiration in models is derived from observations taken during day time. However, recent evidence suggests that independent of their temperature sensitivity, leaf respiration during night time is lower than during day-time1.  The aim of this project is to collect data on leaf respiration under dark conditions, in order to gather more information to support our hypothesis. The main project outcome will be an empirically derived (from these data and few existing observations) model of leaf respiration that will appropriately represents respiration under day and night-time conditions. Publication of this work will have high impact on the vegetation and earth system modelling community as, the project output will represent a huge improvement into the way current models simulate leaf and plant respiration. This will form the basis of a PhD studentship project.

The project encompasses measuring leaf respiration under dark conditions (equipment, lab and desk space available), analysis of the data collected to produce a simple model of leaf respiration. The new model will be applied and compared to existing leaf respiration formulations in order to show the difference against the newly derived formulation. The supervisors Dr Lina Mercado–plant ecophysiologist and vegetation modeller and Prof Stephen Sitch –global vegetation modeller -will train the student on measuring techniques, data analysis and modelling. Project involves collaboration with Prof D. Bruhn from Aalborg University, Denmark.

1Bruhn et al (2008) Plant Biology, 10(2), 185-193.

Indicative timescale for project (subject to change)

Week 1-Week 2 Learning i) how to use the LI-6800, an instrument to measure leaf gas exchange and ii) how to measure leaf respiration, iii) practice in lab and on campus grounds during day and evening, iv) testing and refining measurement protocol v) reading on how leaf respiration is represented in models and current shortcomings

Week 2-Week 7 Data collection & data analysis: Taking leaf respiration measurements in the evening and early in the morning for 5 replicates per species for a variety of trees and shrubs across Exeter campus. Data analysis involves calculation of the Q10 temperature coefficient – which measures the rate of change in respiration as a consequence of increasing temperature by 100C – under light and under dark conditions for each individual measured.

Week 7-Week 10 Data analysis & simple modelling based on data analysis using either excel or any programming tool that student can use.

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