Quantitative study on leaf color dynamics of winter wheat

Chinese. 【目的】模拟小麦叶色变化的动态过程,为实现小麦生长的可视化表达奠定基础。【方法】以不同施氮水平下不同类型小麦品种的两个生长季田间试验为基础,通过连续测量不同处理条件下小麦主茎和分蘖不同叶位叶片的SPAD值,综合分析小麦叶片SPAD值随生育进程的变化规律及其与RGB值的关系,进而构建基于SPAD的冬小麦叶色变化动态的模拟模型。【结果】模型采用分段函数描述叶片SPAD值随生育进程的动态变化过程：第1阶段为基于二次曲线的叶色增强过程;第2阶段为相对稳定的功能期叶色维持过程;第3阶段为基于二次曲线的叶色减弱过程;并基于叶片氮含量表达了氮素供应水平对叶片SPAD值变化规律的影响,同时用线性方程描述了叶片SPAD值与RGB值之间的定量关系。利用独立的小麦田间试验资料对所建模型进行了测试和检验,显示不同时刻主茎和分蘖叶片SPAD预测值的平均RMSE分别为11.60%和9.03%。【结论】本模型具有较强的动态预测性和可靠性,为进一步建立虚拟小麦生长系统奠定了基础。

English. [ Objective] Modeling leaf color dynamics in wheat is of significant importance for realizing virtual wheat plant growth. [Method] Based on time-course observations on leaf SPAD value on main stem and tillers under different nitrogen rates and winter wheat cultivars in two growing seasons, the change patterns of leaf SPAD with growth progress and environmental factors were characterized, and the relationship between leaf SPAD and RGB was analyzed. Using systematic analysis method and dynamic modeling technology, a SPAD-based leaf color dynamic model was developed to simulate time-course change characters of leaf SPAD on wheat plant. [ Result ] The leaf color dynamic could be described with three phases in SPAD. The first phase in SPAD during leaf growth period was based on the quadratic relationship of leaf color to growing degree days （GDD）, the second phase during leaf function period was represented with a relative stable SPAD, and the third phase during leaf senescence period was described in a quadratic equation between SPAD and GDD. In addition, the effect of nitrogen status on leaf SPAD was quantified by the value of leaf nitrogen concentration, and the relationship between SPAD and RGB was described with linear equation. The model was validated with the independent field experiment data of different winter wheat cultivars. The average RMSEs of time-course leaf SPAD on stem and tiller were ll.60% and 9.03%, respectively. [Conclusion] Thus, the present model has a good performance in predicting leaf color on wheat plant, laying a foundation for further constructing virtual leaf growth system of wheat.