Modification and validation of the theory of phenology model — A case study of maize in China

Based on the progress made in stress biology and epigenetics, the current theoretical framework of phenology model, which only considers the response mechanism of developmental rate to the environment factors, is being revised and validated to incorporate mechanisms of response, adaptation, and memory. The adaptation mechanism is taken as an example and the day of year (DOY) of the beginning of the growth period is proposed as the factor to characterize the adaptability, which is then integrated with linear temperature response functions to establish a phenology model coupled with both Response and Adaptation Mechanisms (RAM). The specific implementation of RAM is in the form of: R_i=a+(c+d×DOY₀)×T_i. RAM model is calibrated and validated using phenology observations during the vegetative growth period (VGP) and reproductive growth period (RGP) of maize at 194 agrometeorological observation sites across China. Results show that DOY is generally positively correlated with developmental rate over all the sites during the development periods. The collinearity of DOY and temperature in the two development periods at all sites are within the acceptable range. Compared with the linear temperature response model, the RAM model improves the interpretation rate of the observed data by 0.213 and 0.274 in the VGP and RGP, respectively. Compared with the typical fully calibrated bilinear (WOFOST) and nonlinear (Gao) models, RAM can reduce the RMSE by 0.4 and 0.4 d during VGP, respectively, and by 1.6 and 0.7 d during RGP, respectively in the calibration process. In the validation process, RAM can reduce the RMSE by 0.1 and 0.4 d during VGP, respectively, and by 1.1 and 0.4 d during RGP, respectively. In addition, RAM mode has the advantage of a simple parameterization process. Our results show that the modified phenology model framework may have promising prospects in theoretical research and practical application.