The Photosynthetic Characteristics And Photochemical Response To Salinity Stress Of Branch Cortex Of Salix Matsudana

Corticular photosynthesis refixes the CO2 released by branch respiration, which increases carbon use efficiency and reduces the degree of acidification in the bark. In this study, we used a female Salix matsudana to study the photosynthetic characteristics of branches cortex using techniques of the sucrose density gradient centrifugation, gas change and chlorophyll fluorescence. We also studied the photochemical response mechanism of corticular photosynthesis in Salix under salinity stress.The separated chloroplasts from cortex and mature leaves were tested for structure integrity by Hill reaction. The light saturation point of the corticular chloroplasts was 300μmol·m-2·s-1 and the maximum photosynthetic rate was 35.5816μmolO2·mgChl-1·h-1, which were lower than those of leaves. The Fv/Fm and Fv/Fo of PSⅡwas 0.23 and 0.25 respectively, for cortex chloroplasts, higher than from leaves.The cortex of branches had lower light saturation point and net photosynthetic rate than leaves, which was 200μmol·m-2·s-1 and 0.26μmol·m-2·s-1, respectively. The CO2 refixing rate was up to 87.53%. The total chlorophyll, chlorophyll a/b value, and carotenoid content of cortex was 0.14±0.01, 1.85±0.03, and 0.04±0.00 mg·g-1FW, respectively. All were lower than that from leaves. Moreover, the cortex Fv/Fm, Fv/Fo, ΦPSⅡ and the ETR were all lower than that from leaves.Under salinity stress at 1.5% NaCl, the maximum refixing rate and the capability of light response in coetex decreased. Furthermore, the total chlorophyll content in cortex decreased by 28.57% as a result of salinity treatment, while the carotenoid content showed no change.In conclusion, cortex exhibited high photosynthetic efficiency corresponding to the intenal low light intensity, low concentration of CO2, while leaf chloroplasts were more sensitive to the change of environment. Under salt stress, the synthesis of chlorophyll of cortex was restrained, and the efficiency of energy conversion of PSⅡ in cortex was reduced. Nevertheless, the carotenoid had no significantly change reflected that the protective adaptation of the corticular photosynthesis in adversity environment.