Simulating leaf expansion and canopy development in potato as a function of nitrogen and CO₂

Dennis Timlin David Fleisher VR Reddy

The ability to simulate the effects of nitrogen on leaf growth and canopy development is important for potato simulation models that can be used to manage nitrogen applications. Most models simulate the effects of nitrogen on canopy growth at the whole plant level, i.e., the plant is viewed as a "big leaf".  Recently, more mechanistic, leaf level models of photosynthesis have been developed to better estimate carbon assimilation and evapotranspiration rates as a function of environmental and basic physiological variables.  In order to scale the simulations to the whole plant level, information on the growth of individual leaves is necessary. The objective of this study was to quantify leaf expansion rates in potato as a function of nitrogen application rate and CO₂ level. Two CO₂ levels were used to provide differences in carbon availability. The experiments were carried out using potted plants in outdoor, sunlit growth chambers with six levels of nitrogen (2, 4, 6, 8, 11, and 15 mmol l^-1) and two levels of CO₂. (370 and 700 mmol l^-1 air). The experiments were carried out in two consecutive periods in the summer of 2005.  Temperature was controlled at 23/18 C (day/night), nitrogen was applied every two to three days as a solution and carbon assimilation rates were measured. Leaf area was measured on selected mainstem and secondary stem branches. In general, leaf size increased with increasing N content for the same position on the mainstem.  Leaves higher on the mainstem tended to be larger for the ambient CO₂ treatment and lower leaves smaller. Elevated CO₂ plants had more and larger apical leaves then the ambient CO₂ plants at the same N content.  Equations were developed to describe leaf growth as a function of nitrogen content and added to a simulation model for potato.