Amino acids as indicators of physiological stress in common reed Phragmites australis affected by an extreme flood

The effects of extreme flooding at Lake Constance on the content and composition of amino acids in Phragmites australis were studied at nine reed stands with different degrees of damage. Following the flood damage, we discovered a complex die-back syndrome which is characterised by a decrease in total culm density from 32 to 4 culms m(-2), an increase in percentage of secondary shoots by 70% and decline in mean culm biomass by 27 g dry wt. Furthermore, a reduction of total carbohydrates by 60%, starch by 56-70% and soluble sugars by 49-59% in the vertical and horizontal storage rhizomes was found, together with changes in the composition of amino acids in the basal culm internodes. Within primary shoots from extremely damaged reed stands we found a significant increase in the total content of amino acids (150 versus 40 mumol amino acid g(-1) dry wt. in undamaged stands). Asparagine (Asn) contributed one of the largest fractions to total amino acids, on average about 25% in undamaged reed stands. In contrast, the main amino acid of primary shoots from extremely damaged reeds was not Asn (15%) but gamma-aminobutyric acid (Gaba). Its share was 36% in primary shoots and 48% in insect-infested primary shoots, respectively. This is the highest Gaba content reported in P. australis. The significant increase in the share of gamma-aminobutyric acid in shoots from extremely damaged reed stands was accompanied by an increase in alanine. These changes in the composition of amino acids are discussed with respect to the significance of certain amino acids acting as stress indicators, such as oxygen deprivation, causing a hypoxic metabolic state in R australis stands. (C) 2004 Elsevier B.V. All rights reserved.