YURONG BIa's research while affiliated with Lanzhou University and other places

We studied the diurnal photosynthetic changes of Populus euphratica, a tree with distinct leaf shape polymorphism, in a typical desert environment. The photosynthetic CO2 assimilation rate in lanceolate leaves (LL), located at the bottom of the tree's canopy, is dependent on the diurnal changes in irradiation and reaches a maximum at 13:00 h, while a severe midday depression was observed in broad-ovate leaves (BOL) at the top of the tree's canopy at 13:00 h, most probably due to high temperature, irradiance, and water deficit. Though non-photochemical quenching increased dramatically at 13:00 h in BOL, the photosystem II (PS II) photochemical efficiency decreased. Western blot analysis showed that both PS II reaction center D1 protein and light harvesting complex II (LHC II) protein decreased when the midday depression occurred in BOL, which suggests that the decreased PS II proteins may account for the photosynthetic depression. Together with the low stomatal conductance observed, when this occurs, both stomatal and non-stomata] factors contribute to the midday depression in BOL. The physiological significance of leaf polymorphism is also discussed.