Modelling maize photosynthesis and light utilization based on a 3D maize canopy model

Light distribution and leaf photosynthesis characteristics are highly heterogeneous within a crop canopy. Maize canopy photosynthesis model based on a 3D canopy structure is an important approach to accurately evaluating radiation use efficiency for cultivars. In this study, we built a maize photosynthetic production model 3DMaizeCaP via coupling canopy 3D architecture model, radiative flux distribution model, leaf photosynthesis model and radiation utilization model. In this study, three cultivars with different plant architecture, i.e., AD268, JK968 and ZD958, and two typical weather conditions, i.e., a sunny day and an overcast day were used. In order to unravel the responses of canopy photosynthesis rate and radiation use efficiency to cultivar and environment, a simulation study combined with field experiment was performed. The results showed that the maximum photosynthesis rate and dark respiration rate decreased linearly with decreasing leaf rank for AD268, JK968 and ZD958. The distribution of both the maximum photosynthesis rate and dark respiration rate of individual leaves showed a vertical profile from the top to the bottom of the maize canopy. The AD268 had the highest maximum photosynthesis rate and the lowest dark respiration rate among three cultivars. The diurnal course of canopy photosynthesis rate was characterized evidently that canopy photosynthesis rate increased in the morning and reached the maximum value at 12:00 of noon on an overcast day and at 11:00 on a sunny day and then decreased in the afternoon for all cultivars. The maximum canopy photosynthesis rate of AD268 was 21.6 μmol CO2/(m2•s) on an overcast day and was 26.2 μmol CO2/(m2•s) on a sunny day, which were significantly higher than that of JK968 (20.8 μmol CO2/(m2•s) and 24.9 μmol CO2/(m2•s)) and of ZD958 (19.6 μmol CO2/(m2•s) and 24.4 μmol CO2/(m2•s)). The daily net assimilated CO2 of AD268 was significantly (P<0.05) higher than that of ZD958. In comparison with ZD958, the daily net assimilated CO2 increased by 14.8% and 12.4% on a sunny and an overcast day respectively. The plant architecture of AD268 was significantly different with other cultivars (P<0.05). However, there was no significant difference in the daily intercepted photosynthetic absorbed radiation between cultivars (P>0.05). The leaf at 16th main stem phytomer rank produced the highest daily net assimilated CO2 among individual leaves at the leaf level. The radiation use efficiency of AD268 was 3.22 and 3.03 g/MJ under a sunny and an overcast condition, respectively, indicating a 4.5% and a 5.6% increase compared to JK968 and a 7.7% and a 7.8% compared to ZD958. The canopy radiation use efficiency of maize was more sensitive to the initial slope of light response curve than to the maximum photosynthesis rate (P<0.05). From the point view of improving canopy radiation use efficiency for maize, designing a maize ideotype that has a more compact plant architecture and higher leaf photosynthetic capacity was suggested for breeding in the future. This study could provide not only an approach for quantitatively estimating canopy photosynthesis rate of maize but also an evaluation basis as well as a phenotyping technique for breeding cultivars with high photosynthetic efficiency.