Salt tolerance in Phragmites australis populations from coastal Mediterranean marshes

Responses to salt in soil interstitial water were studied experimentally fo r nine populations of Phragmites australis (Cav.) Trin. ex Steud. from coas tal Mediterranean marshes in France. The effects of exposure to salinity ra nging 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 sal inity above 10 parts per thousand. Variation in germination among populatio ns was small in freshwater (ranging from 89 to 99% on average) but saline c onditions 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 p er thousand. The effects on the number and length of shoots from a 25-day t emporary exposure at 25 parts per thousand followed by recovery in freshwat er were measured. Growth decreased with increasing salinity (50% decrease a t 7.5 parts per thousand when compared to freshwater) and 7-100% mortality depending on population, occurred at 15 and 20 parts per thousand. Cumulati ve shoot length and biomass production varied significantly among populatio ns in freshwater but the difference was small in saline conditions, signifi cant for biomass but not for length. The 25-day exposure at 25 parts per th ousand 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 no t different between exposed seedlings and controls. The temporary stress su ppressed the differences among populations but they were restored during su bsequent growth in freshwater. None of the variation patterns observed duri ng the experiment were related to the present condition of the site of orig in. (C) 2001 Elsevier Science B.V. All rights reserved.