Daily Change of Photosynthetic Properties of Rhododendron taishunense and R. latoucheae under Different Light Condition

In May 2021, five-year potted Rhododendron taishunense and R. latoucheae were treated under 85% shade and full light in nursery of Zhejiang Academy of Forestry, Hangzhou, and photosynthetic properties were measured by LI-6400 portable photosynthesize during 6:00-18:00 in late August 2021. The results showed that daily variation of Pn of two species showed a "single peak" under two light conditions. The Pn of R. taishunense under full light between 6:00 and 10:00 was greater than that under shade, but smaller than that under shade at 12:00-16:00. At 18:00, the PAR of R. taishunense received only 3.8 μmol CO2/m2/s, and Pn decreased to -0.4 μmol CO2/m2/s. It showed that R. taishunense needed proper shade when PAR was more than 1 154 μmol CO2/m2/s. Except at18:00, Pn of R. latoucheae under full light was larger than that under shade, and also larger than that of R. taishunense under full light. The daily variation of Tr of two species also showed a "single peak" under the two light conditions. Tr of R. taishunense was smaller than that of R. latoucheae under two light conditions. Shading caused Tr decline of 2 species. Under the two light conditions, Gs of R. taishunense gradually increased and then decreased, showing a "single peak". Under the two light conditions, the daily variation of Ci of two species showed a trend of gradual decline and then increase, but the overall change was relatively gentle, except for R. taishunense under full light, other treatments all reached the maximum value at 18:00. Ls of R. taishunense showed "single peak" under full light and "double peak" under shade. R. latoucheae show a "double peak" under full light and a "single peak" under shade. The relative content of chlorophyll of 2 species showed that the relative content of chlorophyll under shade was higher than that under full light, and the relative content of chlorophyll of R. latoucheae was higher than that of R. taishunense under both light environments. Leaves of two species showed yellow and chlorophyll contents decreased.