Effects of hydrology and salinity on chlorophyll fluorescence parameters of Scirpus nipponicus Makino

To evaluate the effects of hydrology and salinity on chlorophyll fluorescence parameters of Scirpus nipponicus Makino in Momoge National Nature Reserve, we conducted a controlled experiment with six different levels of salinity (300, 1000, 2000, 3000, 4000, and 5000 mg/L) and six different water depths (-10, 0, 20, 40, 60, and 80 cm). A SPAD-502 plus portable chlorophyll content tester and Junior-PAM modulated chlorophyll fluorometer were used to measure chlorophyll content and fluorescence parameters, respectively. Results showed that as the water level increased, chlorophyll content increased and chlorophyll fluorescence parameters (i.e., potential activity of PSⅡ, maximal quantum yield of PSⅡ, actual quantum yield of PSⅡ in light, photosynthetic electron transfer rate, photochemical quenching, and non-photochemical quenching) increased at first and then decreased. Furthermore, F_v/F_o, F_v/F_m, and q_N were higher in the low-water range (-10 - 20 cm), while yield, ETR, and q_P were higher in high-water range (40 - 80 cm). The chlorophyll content and fluorescence parameters of S.nipponicus initially increased with increasing salinity but decreased when the salt concentration reached 3000 mg/L. These results indicate that S. nipponicus is suitable for growing in high water level environments (40 - 80 cm) and exhibits a certain tolerance for salinity, with the higher water levels alleviating damage caused by salt stress to allow photosynthesis and improve tolerance to high salt environments.