Biometric variation in Phragmites australis affecting convective ventilation and amino acid metabolism

Parameters of convective ventilation and amino acid patterns in basal culm internodes of Phragmites australis (Cav.) Trin. ex Steud. were studied at f our sites in the Danube Delta (Romania) in May 1997. The considerable stand -specific differences in shoot diameter, length and density were related to ventilation efficiency. Tall shoots with high diameters were able to induc e higher gas flow rates per generated pressure differential, than those wit h smaller diameters. However, if the flow rates of single culms were relate d to the corresponding shoot densities, stands with thinner shoots but high er densities achieved significantly higher ventilation efficiencies per m(2 ) reed stand. These differences in the rate at which rhizomes can be flushe d with air were reflected in amino acid patterns in basal culm internodes. The fractions of Ala, Ser and gamma-aminobutyric acid of total amino acid c ontent were significantly increased at stands with tall, thick shoots but l ow densities. The contents of these amino acids were correlated with parame ters of convective ventilation, and may indicate hypoxic conditions in basa l and below-ground plant parts of P. australis. In conclusion, biometric pa rameters of reed stands can be decisive for determining the efficiency of c onvective ventilation. (C) 1999 Elsevier Science B.V. All rights reserved.