Dynamic carbohydrate supply and demand model of vegetative growth

We previously developed a steady-state model of vegetative growth based on the hypothesis that growth is the minimum of the supply of non-structural carbohydrate (NSC) from photosynthesis and the demand for NSC to synthesize new tissue. Here, we incorporate sink inhibition of photosynthesis in a dynamic model of growth hour by hour, and assume that starch synthesis and breakdown provide sufficient NSC for growth and respiration during both day and night. It is not clear whether photosynthesis inhibition changes within the photoperiod or only from one day to the next. When this dynamic model was applied to tomato plants which had been pre-adapted under high or low light, respiration in darkness was first predicted to be constant, and then decreased with time, when NSC fell below the value needed for maximum growth. When predicting growth for tomato seedlings in a growth chamber at various temperatures between 9 and 36 degrees C, the correlation between predicted and actual minimum values of NSC was greater for the dynamic model (R-2= 0.83) than the steady-state model (R-2= 0.65). A large fraction of photosynthesis must be inhibited to predict NSC accurately under demand-limited conditions, in contrast with little inhibition under supply-limited conditions. This combination could be achieved only by relating inhibition to the minimum NSC content over a diurnal cycle, rather than NSC hour by hour during the day.