[Effects of water stress on photosynthetic parameters of Phragmites australis in estuarine wetland of Yellow River Delta].

A pot experiment was conducted to study the effects of soil water content on the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 concentration (Ci), water use efficiency (WUE), and light use efficiency (LUE) of fresh water swamp Phragmites australis from estuarine wetland of Yellow River Delta, with the appropriate soil water condition approached. The results showed that the Pn, LUE, Tr, and WUE of fresh water swamp P. australis had obvious response thresholds on the alteration of soil water content. Waterlogged status was not the optimal water condition for fresh water swamp P. australis. To maintain the normal growth of fresh water swamp P. australis during its fast growth period, soil volumetric water content (Wv) should be above 25.7% (i.e., relative water content Wr > 66.6%), optimal Wv should be 36.9% (i.e., Wr = 95.6%), and the most deficient degree of Wv should be about 21.5% (i.e., Wr = 55.7%). Stomatal limitation was the main tolerance mechanism of fresh water swamp P. australis under water deficit. Under drought condition, the maximum net photosynthetic rate (P(n max)) and apparent quantum yield (AQY) of fresh water swamp P. australis declined obviously. In the meanwhile, fresh water swamp P. australis could reduce its dark respiration (Rd) to decrease the consumption of photosynthetic products, and improve its water use efficiency (WUE) to keep high photosynthetic rate.