A two-dimensional
micro-scale model of gas exchange during
photosynthesis in maize (Zea mays L.) leaves
Moges Retta1, Quang Tri Ho1 , Xinyou Yin2, Pieter Verboven1, Berghuijs Herman2, Bart M.
Nicolaï1, Paul C. Struik2
1
BIOSYST-MeBioS, Katholieke Universiteit Leuven, Willem de Croylaan 42, B-3001, Leuven,
Belgium
Centre for Crop Systems Analysis – Wageningen University, Droevendaalsesteeg 1, 6708
PB Wageningen, The Netherlands
2
Abstract
Gas exchange in leaves of C4 plants was investigated using a microscale model of combined gas
diffusion and C4 photosynthesis kinetics. Maize (Zea mays L.) leaf was chosen as the model
system. The actual 2-D microstructures of a leaf were incorporated into the microscale model.
The uptake of CO2 is facilitated by the carbonic anhydrase enzyme that converts it to bicarbonate
ions. This step is taken into account in the model by rewriting the kinetic equation for CO2
limited rate of phosphoenolpyruvate carboxylation using concentration of bicarbonate ions
instead of CO2 concentration. The model was validated using combined gas exchange and
chlorophyll fluorescence measurements on young, full-grown leaves and old leaves from plants
grown under high or low nitrogen levels. In general, there was good agreement between model
predictions of photosynthesis and experimental data. The model provided detailed insight into
CO2 exchange and photosynthesis. In addition, the effect of nitrogen supply on leaf
microstructure and, hence, gas exchange characteristics such as bundle sheath conductance was
quantified.
Key words: C4 photosynthesis, gas exchange, bundle sheath conductance, CO2 concentration
mechanism, leaf microstructure