[Effects of flash scheme on maximum chlorophyll fluorescence under illumination and its derived parameters]

The maximum chlorophyll fluorescence yield under illumination (F_m') is one of the most important parameters in plant eco-physiological research, and usually was estimated with rectangular flush scheme (RF). However, the estimation accuracy of RF for F_m' was affected by the rapid turnover of photosystem 2 (PS2). In order to eliminate the effect of the rapid turnover of photosystem 2 (PS2), the multiphase flush scheme (MPF) based on the linear relationship between the flush (Q') and chlorophyll fluorescence (F') is proposed to estimate F_m' at infinite irradiance. Leaf gas exchange and chlorophyll fluorescence of three woody species (Castanopsis sclerophylla, Cyclobalanopsis glauca, and Sapium sebiferum) were respectively measured with RF and MPF, F_m' and the derived parameters [the quantum efficiency of PS2 (Φ_PSII), the electron flux through PS2 (J), the maximum electron transfer rate (J_max), mesophyll conductance (g_m) and chloroplast CO₂ concentration (C_c)] were compared between the two different schemes, and the effects of RF and MPF on these parameters were analyzed. The results showed that no significant difference was found in the parameters for the three species between RF and MPF at the light intensity lower than 200 μmol·m^-2·s^-1. F_m' estimated with MPF for the three species were 3.5%-5.2%, 11.7%-18.0%, and 3.2%-7.1% higher than those with RF, respectively, at the light intensity higher than 200 μmol·m^-2·s^-1. The derived parameters (Φ_PSII, J and J_max) estimated with MPF for the three species were higher than those with RF, while the derived parameters(g_m and C_c) estimated with MPF were lower at the light intensity higher than 200 μmol·m^-2·s^-1. In conclusion, estimates of parameters (F_m', Φ_PSII, and J) were not significantly affected by the two different schemes at the light intensity lower than 200 μmol·m^-2·s^-1. The estimates of parameters (F_m', Φ_PSII, J, J_max, g_m, and C_c) were significantly affected by the two different schemes at the light intensity higher than 200 μmol·m^-2·s^-1. Compared with MPF, parameters of F_m', Φ_PSII, J and J_max estimated with RF were underestimated, while parameters of g_m and C_c were overestimated.