Salt tolerance in Phragmites australis populations from coastal Mediterranean marshes

Responses to salt in soil interstitial water were studied experimentally for nine populations of Phragmites australis (Cav.) Trin. ex Steud. from coastal Mediterranean marshes in France. The effects of exposure to salinity ranging from 0 to 25 parts per thousand were measured on germination of seeds collected in each site. Germination was up to 100% and was affected by salinity above 10 parts per thousand. Variation in germination among populations was small in freshwater (ranging from 89 to 99% on average) but saline conditions increased the contrast (5-60% at 25 parts per thousand). Growth of seedlings in shoot and biomass production were measured during a a-month exposure to constant saline solutions, ranging from 0 to 20 parts per thousand. The effects on the number and length of shoots from a 25-day temporary exposure at 25 parts per thousand followed by recovery in freshwater were measured. Growth decreased with increasing salinity (50% decrease at 7.5 parts per thousand when compared to freshwater) and 7-100% mortality depending on population, occurred at 15 and 20 parts per thousand. Cumulative shoot length and biomass production varied significantly among populations in freshwater but the difference was small in saline conditions, significant for biomass but not for length. The 25-day exposure at 25 parts per thousand stopped growth and plants recovered after flushing with freshwater. The stress effect was significant for shoot length but not for shoot number. Twenty-five days after the treatment ended, the numbers of shoots were not different between exposed seedlings and controls. The temporary stress suppressed the differences among populations but they were restored during subsequent growth in freshwater. None of the variation patterns observed during the experiment were related to the present condition of the site of origin. (C) 2001 Elsevier Science B.V. All rights reserved.