Response of leaf photosynthetic characteristics of Syringa oblata and Syringa reticulata var. mandshurica to chilling stress

Syringa species not only have good ornamental properties but also play an important role in the landscaping and environmental purification of cities. To investigate the chilling stress resistance of Syringa oblata Lindl. and Syringa reticulata var. mandshurica and provide theoretical grounds for the practical cultivation of Syringa species, in vitro leaves were used to study photosynthetic gas exchange parameters and chlorophyll fluorescence parameters. After nine hours of chilling, decreasing rates of net photosynthesis, stomatal conductance, and transpiration in S. reticulata var. mandshurica leaves were significantly greater than that of the S. oblata, while intercellular CO2 concentrations in S. oblata leaves were higher than those in S. reticulata var. mandshurica. The quantum yield of PSII reaction center (CYRILLIC CAPITAL LETTER EFPSII) declined in S. reticulata and light capture efficiency (F-v '/F-m ') was stable. However, reduction percentages of F-v '/F-m ', CYRILLIC CAPITAL LETTER EFPSII, and F-v/F-m in S. oblata were significant higher than those of S. reticulata var. mandshurica. After nine hours of chilling, the relative variable fluorescence of V-J and V-I of S. oblata increased and the increasing rate of V-J was greater than V-I. In contrast, the change of V-J and V-I in S. reticulata var. mandshurica leaves was relatively small. This suggests that chilling primarily damaged the electron transport process of Q(A) to Q(B) at the receptor site of the PSII reaction center. Photosynthetic capacity of S.oblata was more sensitive to chilling stress compared to S. reticulate var. mandshurica, which the limitations were mainly due to non-stomatal factors such as the decrease in electron transport efficiency, activity in the PSII reaction center, and the destruction of the photodamage defense system.