Oliver, Rebecca Joy
Predicting the yield and water-use of poplar short rotation coppice under a future climate.
University of Southampton, School of Biological Sciences,
Under the current climate there is significant spatial variation in the yield and water-use of
bioenergy crops such as poplar short rotation coppice (SRC). Marked changes in patterns
of precipitation and temperature are predicted globally as a result of anthropogenic climate
change. This is likely to significantly impact on the yield and transpiration of poplar SRC.
The response of poplar SRC to future climate change is unknown and represents a
significant knowledge gap in the path to a sustainable future.
This thesis used a land-surface scheme, JULES, to investigate the response of poplar SRC
yield and transpiration to the interaction between changes in atmospheric CO2
concentration and changes in climate. Empirical work generated poplar SRC specific
parameter values for use JULES. It was found that Vmax, a key model photosynthetic
parameter, was significantly lower when estimated under the assumption of infinite leaf
internal conductance to CO2. This invalidated the assumption that internal CO2 transfer has
a negligible impact on the drawdown of CO2 from ci to cc. The photosynthesis model in
JULES is based on this assumption; however, inclusion of this additional CO2 transfer
pathway in the model did not impact on the accuracy of the simulated carbon assimilation,
because the value of Vmax used in the model compensated for the presence/absence of this
pathway. It was concluded that, given the model’s high sensitivity to Vmax, it is essential to
calibrate the model with a parameter value estimated under assumptions appropriate for the
model. Further modification, calibration and validation enabled JULES to simulate the
dynamic growth and water-use of poplar under a managed SRC cycle, which is a novel
application for the model. Changes in climate were simulated using an ensemble of GCM
anomalies and atmospheric CO2 concentration was simulated using the SRES A1B
emissions scenario. Results of this work highlighted the influence of climate in modifying
the yield and transpiration responses to elevated concentrations of atmospheric CO2.
Additionally, for a future climate scenario, these simulations indicated higher yields but
also higher water-use of poplar SRC, although the magnitude and direction of response
was highly spatially variable.
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