Physiological responses of Phragmites australis to the combined effects of water and salinity stress

A pot culture experiment with four levels of soil water content (waterlogged condition, 90%, 75% and 60% of field capacity) and five levels of sodium chloride (NaCl) concentration (0, 60, 120, 180 and 240mM) was conducted to examine the physiological responses of salt meadows Phragmites australis to soil water content and NaCl salinity in the Yellow River Delta, China. Results indicated that (i) the combined effects of soil water and NaCl salinity had significant influences on the light-saturated photosynthetic rate (P-n max, F=719, P<001), intercellular CO2 concentration (C-i, F=2492, P<001) and stomatal conductance (g(s), F=1816, P<001) at light saturation of this species. The light-saturated photosynthetic rate (P-n max) was the largest at 90% of field capacity with 60mM NaCl salinity treatment (1310mu mol CO(2)m(-2)s(-1), SD +/- 046) and decreased with the increase of NaCl salinity and water deficit. Under severe water and salinity stress, P-n max decreased with C-i rising substantially, which means the non-stomatal limitations of P. australis occur; (ii) stress resistance in the salt meadow P. australis was closely related to the retention of a relatively higher water status and a higher content of potassium (K+) in leaves; and (iii) both content of sodium (Na+) and proline were significant increased by water stress and NaCl salinity stress, and the leaf proline content was positively correlated with the leaf Na+ content (r=0837, n=60). Copyright (c) 2013 John Wiley & Sons, Ltd.