Abstract: A pot experiment was conducted to study the effects of soil water cont ent on the net photosynthetic rate (Pn), transpiration rate (Tr), st omatal conductance (Gs), intercellular CO2 concentration (Ci), wat er use efficiency (WUE), and light use efficiency (LUE) of fresh water s wamp Phragmites australis from estuarine wetland of Yellow River Delta, with the appropriate soil water condition approached. The results showed that the P n, LUE, Tr , and WUE of fresh water swamp P. australis had o bvious 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 i ts fast growth period, soil volumetric water content (Wv ) should be above 257% (i.e., relative water content Wr>666%), opt imal Wv should be 369% (i.e., Wr=956%), and the most deficie nt degree of Wv should be about 215% (i.e., Wr=557%). Stomat al limitation was the main tolerance mechanism of fresh water swamp P. austral is under water deficit. Under drought condition, the maximum net photosyntheti c rate (Pn max) and apparen t quantum yield (AQY) of fresh water swamp P. australis declined obvious ly. In the meanwhile, fresh water swamp P. australis could reduce its dark r espiration (Rd) to decrease the consumption of photosynthetic products, an d improve its water use efficiency (WUE) to keep high photosynthetic rate.

Key words: sand-fixing plant, configuration mode, plant community characteristics, water relation, gas exchange.