Abstract: The diatom Phaeodactylum tricornutum was grown in matrixes of nitrogen repletion (882.35 μmol·L^-1) and limitation (40 μmol·L^-1) to investigate the effects of nitrogen limitation on photosystem Ⅱ photochemistry reaction and resistance to high light intensity. Results showed that nitrogen limitation reduced the growth rate, decreased the chlorophyll a content, and accelerated the photoinhibition in P. tricornutum. The analyses of the polyphasic rise of fluorescence transients demonstrated that nitrogen limitation inhibited the electron transfer from Q_A^- to Q_B, and high light treatment led to further accumulation of Q_A^-. In addition, under the nitrogen limitation condition, the active reaction centers were closed partially, and the energy fluxes for absorption (ABS/RC), trapping (TR_o/RC), and dissipation (DI_o/RC) per reaction center were increased. The combination of high light treatment and nitrogen limitation resulted in further inactivation of PSII reaction center. Our results indicated that nitrogen limitation could modify the PSII photochemistry, and reduce the resistance of P. tricornutum to high light intensity.

Key words: Tibet Plateau, PDO, vegetation growth, structural equation model (SEM), seasonal response, climate change.