Abstract: To further understand light reaction of Pinus (pine) species, the fast chlorophyll fluorescence induction curves and parameters of four species (P. armandii, P. bungeana, P. tabuiaeformis, P. densiflora) were compared with that of two Populus (poplar) species (P. tomentosa, P. euramericana) chosen as representatives of angiosperm trees in this study. The main differences in the fast chlorophyll fluorescence induction kinetics between the two kinds of trees were summarized as the follow. The chlorophyll fluorescence induction curves of the two poplar species were typical OJIP induction curves, while the OJIP induction curves of Pinus species exhibited relatively lower J phase, obscure I phase and earlier P phase. Light reaction characteristics of the four pine species were demonstrated by fluorescence parameters in detail. The RC (RC: PSⅡ reaction centre) density per excited cross section (CS) of pine trees leaves was lower than poplar trees, which led to more energy fluxes per RC (ABS/RC, TR_o/RC, ET_o/RC, DI_o/RC) of pine trees. However the primary photochemistry rate (M_o) had no difference between the two kinds of trees. Electron transport efficiency of Q_A (ψ_ET) in pine trees was even higher than poplar trees. Pine needles had greater values in relative variable fluorescence of I phase (V_i), which indicated that pine trees had lower efficiency of electron transport fluxes from Q_B to PSI acceptors (ψ_RE). Meanwhile, pine trees had smaller plastoquinone pool (S_m) and less turn-over number of Q_B (N), along with the faster plastoquinone pool redox rate (S_m/T_fm). These results could be the major cause of obscure I phase and earlier P phase appeared on the OJIP induction curve of pine trees, which further caused smaller values of performance index ( PI_CSm), quantum yield of electron transport flux until PSI (φ_Ro) and bigger values of dissipated energy ratio of PSⅡ (K_n, F_o/F_m) in pine trees. The results above suggested that the density of RC per excited cross section and the size of plastoquinone pool would be the two major factors that affected light reaction activity of pine trees, so as to affected photosynthetic function of pine trees.

Key words: Populus species, Pinus species, the fast chlorophyll fluorescence induction kinetics, light reaction