Modeling expansion of individual leaves in the potato canopy

A model to simulate expansion of individual leaves in potato (Solanum tuberosum cv. Kennebec) was developed by modifying a growth simulation routine from the model POTATO. Data for model development and testing were obtained from three soil-plant-atmosphere-research (SPAR) chamber experiments. The first experiment (D1) used six SPAR chambers with treatments of 14/10, 17/12, 20/15, 23/18, 28/23, or 34/29 °C day/night temperatures (16 h thermoperiod) at an elevated atmospheric carbon dioxide concentration ([CO₂]) of 740 μmol mol-1. Experiment D2 used two SPAR chambers at 23/18 °C at 740 μmol mol-1 [CO₂]. Experiment D3 duplicated the temperature treatments of D1 but at ambient [CO₂] (370 μmol mol-1). Potato leaf area expansion was sensitive to air temperature and [CO₂]. Maximum individual leaf area values were highest at cooler temperatures and elevated [CO₂]. Growth duration, defined as the time interval between leaf appearance and when 99% of final area was attained, was negatively correlated with increasing temperature. Growth duration increased by about 4 days at 14/10 and 34/29 °C at ambient [CO₂]. Temperature response and leaf physiological aging functions were developed from D1 and used to modify the existing growth model. D2 and D3 data were used to evaluate the modified model simulations during conditions of non-limited and limited carbohydrate availability. By varying an input to the model that simulates the effect of plant carbohydrate status on leaf expansion, the model was shown to be capable of reproducing leaf growth curves within 8% of the measured final area. The modified leaf expansion model is suitable for integration with existing potato models that simulate canopy leaf appearance. The expansion model provides an approach for coupling plant assimilate, water, and nutrient status with canopy expansion and the new response functions in the model can potentially be modified for use in different crop models.