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Title: Carbon dioxide exchange of Sahelian vegetation
Author: Levy, Peter E.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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Measurements of leaf and ecosystems scale CO2 flux were made at the millet, fallow and tiger bush sites at the HAPEX-Sahel Southern supersite. These were analysed in relation to biological and environmental variables. In the five species studied, leaf scale photosynthesis was strongly influenced by photosynthetic photon flux density (Q) and stomatal conductance, and was well described by the non-rectangular hyperbola model of Jarvis, Miranda and Muetzelfeldt (1985). Stem respiration was measured in two species, and increased exponentially with temperature. Stem respiration rates were higher in the wet season than in the dry season and this difference was used to separate growth and maintenance respiration. Effects of Q and sap flow on stem CO2 efflux were observed. A small number of soil respiration measurements were also made. Direct measurements of leaf area index, biomass and canopy structure were made at the millet and fallow sites. Two indirect methods of estimating leaf area index, from hemispherical photographs and measurements of transmitted Q, were used to all three sites. Together with measurements of canopy structure at each site, the measurements of leaf photosynthesis, stomatal conductance and stem soil respiration were used to parameterise two models which predict ecosystem net CO2 flux: a simple one-dimensional "big leaf" model and a complex three-dimensional model "MAESTRO". Model predictions were compared with independent ecosystem flux measurements made by eddy covariance. Generally, both models agreed well with measurements at all three sites. Differences between measurements and predictions were very small in millet and largest in tiger bush, and were attributed to the effect of canopy heterogeneity on eddy covariance measurements and the accuracy with which canopy structure parameters could be estimated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available