Objective Through the analysis of chlorophyll fluorescence phenotypes of Populus simonii in China, we can display the diversity of chlorophyll fluorescence phenotypes in P. simonii from multiple angles, laying a foundation for the exploration of related photosynthetic genetic mechanism.

Method According to the phenotypic data of chlorophyll fluorescence parameters of P. simonii in China, the variation law was explored by cluster analysis, phenotypic plasticity index and coefficient of variation calculation, dynamic fitting analysis and other methods.

Result (1) At a constant light intensity (same light intensity), k means clustering was applied to four chlorophyll fluorescence phenotypes of P. simonii, the optimal number of clusters was significantly influenced by light intensity. Four types of fluorescent phenotypes of P. simonii: the electron transfer rate (ETR) through photosynthetic system Ⅱ (PSⅡ), the actual light quantum yield (Yield), photochemical quenching coefficient (qP), non-photochemical quenching coefficient (qN) exhibited significant differences in different categories. (2) The calculation results of the phenotypic plasticity index and coefficient of variation of the four fluorescence parameters of P. simonii showed that the selected population had rich phenotypic plasticity under changeable resources, as the light intensity gradually increased, the phenotypic plasticity index of ETR, Yield and qN showed an overall trend of decreasing first, then increasing and then decreasing, while the phenotypic plasticity index of qN presented a decreasing trend in the whole process. This phenomenon might be related to the genetic control within each phenotype, and also reflected the different degree of response of different phenotypes to gradient light intensities; the coefficient of variation of ETR, Yield and qP showed a trend of decreasing initially and then rising with the increase of light intensity; the coefficient of variation of qN gradually decreased with the increase of light intensity, when the light intensity reached the maximum value, the coefficient of variation of all kinds of samples were less than 0.1. (3) Chlorophyll fluorescence phenotypes of P. simonii under different gradient (dynamic) light intensities can be divided into two categories after clustering. After fitting with the growth equation, it can be found that the phenotypic variation rate and the maximum (minimum) value of different categories of samples have significant differences.

Conclusion Chlorophyll fluorescence phenotypes of P. simonii vary widely and are significantly affected by light intensity. Through methods, such as cluster analysis, phenotypic plasticity and coefficient of variation calculation and growth equation fitting, we can explore the changing rule of chlorophyll fluorescence phenotypes effectively, lay a foundation for genetic analysis and photosynthesis mechanism, and provide scientific guidance for the cultivation of P. simonii.