Comparative Study on Photosynthetic Characteristics of Hybrid Lagerstroemia indica (Red Rocket ♀ × Sichuan Pink Flower ♂) F1 Generation and Its Parents

Exploring the differences in photosynthetic specificity between F1 generation L. indica and its parents, the photosynthetic pigment content and light response curves of Red Rocket (♀), Sichuan Pink Flower (♂) and F1 generation L. indica species were measured under natural growth conditions. The results showed that the relationship between Chl a, Chl b, Car, and Chl content of the L. indica species was as follows: F1 generation >Red Rocket >Sichuan Pink Flower; The size relationship of P_n is: F1 generation >Sichuan Pink Flower >Red Rocket; The size relationship of G_s is: F1 generation > Sichuan Pink Flower >Red Rocket; LUE is: F1 generation >Red Rocket >Sichuan Pink Flower; When PAR<1000 μmol·m⁻²·s⁻¹, T_r is as follows: F1 generation>Sichuan Pink Flower >Red Rocket. When PAR>1200 μmol·m⁻²·s⁻¹, T_r is as follows: Red Rocket>F1 generation>Sichuan Pink Flower; WUE peaks appear at PAR values of 500~600 μmol·m⁻²·s⁻¹ and 1400~1500 μmol·m⁻²·s⁻¹. Prior to the first peak, the WUE of Red Rocket was higher. After the first peak, the WUE of Sichuan Pink Flower and F1 generation was higher; F1 generation has the highest P_{n max}, as well as the highest LSP, lowest LCP, and lowest R_d. Therefore, the F1 generation of hybrid crape myrtle (Red Rocket × Sichuan Pink Flower) has the greatest P_{n max} and a wider range of light ecology, which could be in relatively weak light of the forest window and the understory of the sparse forest, and also in the strong light of the roadside and the garden. It is more suitable to Red Rocket on the shady side of the drought-prone backlight, and it is more suitable to plant Sichuan Pink flower the sunny side of the drought-prone area.