Effects of abiotic conditions on Phragmites australis along geographic gradients in Lake Burullus, Egypt

Stand structure and biomass production of Phragmites australis (Cav.) Trin. ex Steud. were analyzed along north-south and east-west transects in the Burullus coastal lagoon (N Egypt, 410 km2) at monthly intervals over a period of 1 year (February 2003 until January 2004). For this purpose, young and old stands were selected at eight different locations in the lagoon. It was found that the north-south transect mainly represented a fertility gradient (207-286 mg l-1 TN, 30-106 mg l-1 TP), while the east-west transect was associated with significantly decreasing salinity (7-4 ppt). All morphological and biomass variables of P. australis were significantly different between young and old stands. On average, the old (7.3 ± 0.2 kg DW m-2) accumulated three times more total above-ground biomass than the young stands (2.5 ± 0.1 kg DW m-2). Shoot height, diameter and shoot dry weight significantly increased by 25-50% with increasing fertility along the north-south transect. Shoot density significantly decreased from north to south, while it almost doubled in the north sites from 109 ± 6 to 216 ± 7 shoots m-2 along the west-east transect. In separate stepwise multiple regressions, variation in water quality explained 34-63% of the variation in morphology and total above-ground biomass in the old stands (salinity and water level were most important for biomass, transparency also for height and density) while it explained 16-42% of variation in young stands (mainly transparency). © 2009 Elsevier B.V. All rights reserved.