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Title: The contribution of photosynthesis and respiration to the net ecosystem exchange and ecosystem ¹³C discrimination of a sitka spruce plantation
Author: Wingate, Lisa
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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This thesis presents data collected from a Sitka spruce plantation in Scotland, UK during May and July 2001. Data are presented that quantify the daily pattern of environmental variables and their effect on rates of key physiological processes monitored from branches, soils and entire canopies using each method. A method was also developed to measure the carbon isotope composition of CO2 in air exchanged directly with branches. Daily patterns in instantaneous 13C discrimination (Dobs) and the d13C of respired CO2 were combined with continuous environmental and gas exchange data to explore theoretical models describing photosynthetic discrimination, D. This study demonstrated fractionation factors associated with respiratory processes and mesophyll conductance (gw) were important for explaining daily patterns in Dobs. Models were also developed and paramterised to predict daily cycles of instantaneous 13C discrimination and d13C of recently assimilated needle carbohydrates at the branch and canopy scale. This dynamically simulated the links between environmental conditions, canopy discrimination and the d13C branch respired CO2, providing both a method and model to directly test hypotheses concerning the environmental regulation of autotrophic respiration measured aboveground and from soil surfaces, potentially leading to a clearer understanding of temporal variability in observed ecosystem D and d13C of ecosystem respired CO2. Furthermore, these bottom-up estimates of canopy 13C discrimination provided a means of comparison with top-down estimates calculated from a recently developed approach incorporating the eddy covariance method and profiles of d13C and CO2 mole fraction. At the forest scale daily patterns and estimates of FA and FR were determined using the three approaches described above. Daily patterns of FA were comparable in magnitude and timing between methods and tightly coupled to environmental variables. Daily maximum uptake for FA ranged from -20 to -30 μmol m2 s-1 and were similar to other published studies for Sitka spruce plantations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available