Response of chlorophyll fluorescence characteristics to a water gradient in the leaves of Deyeuxia angustifoli from wetland in Sanjiang Plain

In this study, changes in the function of PSII (Photosystem II) in the leaves of Deyeuxia angustifolia across a water gradient were analyzed using a chlorophyll fluorescence technique with leaf samples from three typical wetland types from a plain in Sanjiang. The three wetland types were marshes (perennial ponding), marshland meadows (seasonal ponding), and meadows (no ponding on the surface). The results showed that the two indices for the Deyeuxia angustifolia leaves, PSII maximum photochemical efficiency (F_v / F_m) and photosynthetic performance (PI_ABS) based on the absorption of light energy, increased by varying degrees after a decrease in soil moisture in the marshland meadow and the other meadows when compared to the marshes. This indicates that PSII photochemical activity in the leaves from the marshland meadow and the other meadows was significantly higher than that of the leaves from the marshes. According to the OJIP curves for the Deyeuxia angustifolia leaves that were standardized across the water gradient, we found that OEC (oxygen evolving complex) activity of the PSII donor side and the electron transport capacity of the PSII receptor side were significantly higher in the leaves from the marshland meadows and the other meadows than that of the leaves from the marshes. The actual photochemical efficiency (Ф_PSⅡ) and electron transport rate (ETR) of the leaves from the marshland meadows and the other meadows with high light intensities were also significantly higher than that of the leaves from the marshes. Furthermore, the study on light energy utilization by Deyeuxia angustifolia leaves across the water gradient revealed that the proportion of light energy absorbed and consumed, in the form of ineffective heat by PSII in the leaves from the marshland meadows and other meadows, was reduced, and the proportion of distribution to the inactivation reaction center while the light energy was being absorbed was used more in the photochemical reaction center to improve the photochemical function in the PSII reaction center. There was no significant difference in PSII function between the leaves from the marshland meadows and the other meadows, which indicates the PSII function of Deyeuxia angustifolia leaves has a strong adaptability across a water gradient.