Effect of Water Stress on Photosynthesis, Chlorophyll Fluorescence Parameters and Water Use Efficiency of Common Reed in the Hexi Corridor

Water stress is the major environmental stress that affect agricultural production worldwide, especially in arid and semi-arid regions. This research investigated the effect of water stress on common reed (Phragmites australis (Cav.) Trin. ex Steud.) grown in the West Lake Wetland of Zhangye City, China. We designed with four water treatments (100, 95, 85 and 75% of water field capacity, i.e. CK (100%), mild (95%), moderate (85%) and severe (75%) water deficit regimes). The effect of water stress on photosynthesis and chlorophyll fluorescence parameters was investigated. There was a midday depression in net photosynthetic rate (Pn) for CK, mild and moderate drought, but not for severe drought. Stomatal limitation was dominant for mild treatment. But under severe drought stomatal limitation to photosynthesis was dominating in the morning and nonstomatal limitation was dominating in the afternoon. Compared with CK treatment, Pn, stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate (E) and water use efficiency (WUE) were always lower at drought stress. This result suggests that water stress caused the photosynthesis of common reed to be completely blocked and the common reed was a drought-sensitive plant. We found 75% is the moisture threshold for common reed. The decrease in Fm, Fv, Fv/Fm and increase F0 suggested that Rubisco activity reduced and PSII partially inactivated during the day under drought. However, part of this inactivation of PSII might be alleviated under mild or moderate drought, but severe drought cannot. Drought stress also affected the photosynthesis Pn-PAR response curve. Drought stress increased LCP, RD and decreased LSP, Pmax and AQY. This indicates that when common reed suffers from drought, the utilization range of light intensity become narrowed and photosynthetic ability or adaptability to light reduced.