Abstract: Leaf area index (LAI) is one of the most important crop parameters in photosynthesis- driving crop growth simulation model and canopy evapotranspiration simulation model, while air temperature and radiation are the important climate factors affecting crop leaf growth. In this paper, experiments with different sweet pepper (Capsicum annuum L.) cultivars and sowing dates were conducted in greenhouse to quantitatively analyze the relationships of the number of unfolding leaves per plant, the number of old leaves removed per plant, and the length of each leaf with air temperature and radiation. Based on these quantitative relationships, a leaf area simulation model for greenhouse sweet pepper was developed, and the independent experimental data were used to validate the model. The results showed that the number of unfolding leaves per plant was a positive exponential function of the product of thermal effectiveness and PAR (TEP) accumulated after emergence, and the length of each leaf was a negative exponential function of the TEP accumulated after emergence. The coefficient of determination (R²) and the root mean squared error (RMSE) between simulated and measured leaf number, leaf length, and LAI were 0.94, 0.89, and 0.93, and 3.4, 2.15, and 0.15, respectively. The model could use air temperature, radiation, planting density, and emergence date to satisfactorily predict the LAI of greenhouse sweet pepper, and supply required LAI information for the sweet pepper growth and canopy evapotranspiration simulation models.

Key words: tree, biotic factor, abiotic factor, temporal scale, non-structural carbohydrate, spatial scale