Simulation and validation of photosynthesis of greenhouse tomato based on temporal variation of sucrose yield

Abstract: Functional-structural model has been a new versatile tool in crop science in recent years, integrating by based on process model（BPM） and structural model (SM). However, the output of PBM and SM have not been well connected with each other, particularly when referred to dry matter and sucrose. Therefore, this work was dedicated to developing a novel functional-structural plant model for the photosynthesis of greenhouse tomato using sucrose. The experiments (marked as E1 and E2) were carried out at a venlo-type greenhouse in Jiangsu University of China from February 2017 to January 2018. The data from E1 was used to establish a photosynthesis model, and the data from E2 was applied to validate the model. In the experimental procedure, the tomato seedling with four leaves during the period of growth was transplanted into a cultivation barrel filled with perlites. Tomato seedling was watered by Hogland nutrient solution, 350ml twice a day. The temperature and humidity were controlled in the whole growth period at 15-32℃ and 60%-85%, respectively. The tomato plant was destructive sampling at 8:00, 10:00, 12:00, 14:00, and 16:00 at a sunny day under seedling, flowering, and harvest stage. After that, a high-performance liquid chromatography was utilized to determine the sucrose content of every leaf petiole after the fresh weight was measured. Interception of photosynthetically active radiation (PAR) was recorded using the 1:1 relative to greenness and normalized difference, where single leaf area was equal to the product of leaf length and width. Three submodels were included for the photosynthesis of single leaf, prediction of active leaf area (ALA), and total photosynthesis. Firstly, a mathematical submodel of sucrose production per unit leaf area was established using E1 data and PAR. Secondly, the concept of ALA was introduced to overcome the influence of leaving leaf on tomato leaf area, where the leaf area for photosynthetic effective radiation of tomato leaf interception was equivalent to that of top leaf interception. The single ALA was calculated by the single leaf area and intercepted PAR, and then the total ALA was the accumulation of single ALA. The ALA and Growth Degree days (GDD) were used to establish the prediction model of ALA. Thirdly, the photosynthesis submodel of single leaf and prediction model of ALA were fully integrated into a sucrose-based photosynthesis model of greenhouse tomato. The independent E2 data was used to verify the model. The results showed that the determination coefficient (R2) and the root mean squared (RMSE) between simulated and measured sucrose yield per unit leaf area were 0.98 and 0.95g/m2, respectively, indicating a high accuracy for the sucrose production per leaf, ALA, and total sucrose production. Specifically, the R2 and RMSE between simulated and measured ALA were 0.96 and 0.02 m2, respectively. Furthermore, the R2 and RMSE between the predicted and measured sucrose production per plant were 0.97 and 48.58mg/plant, respectively. It demonstrates that the photosynthesis model can preliminarily realize effectively integration of the process-based and structural model in crop science.