Rhizome age structure of three populations ofPhragmites australis (Cav.) Trin. ex Steud.: Biomass and mineral nutrient concentrations

Abstract

The rhizome age structure for populations ofPhragmites australis (Cav.) Trin. exSteud. was determined at three sites of the Třeboň Biosphere Reserve (Czech Republic). These sites were classified according to plant species composition and phosphorus availability as oligotrophic (Branna), mesotrophic (Rožmberk East) and hypertrophic (Rožmberk West).P.australis stands at these sites were expanding, stabilized and retreating, respectively. Rhizomes were sampled within the terrestrial parts of the reed stands (at a water depth of about 10 cm). The rhizomes were dated according to the position in the branching hierarchy and to supplementary morphological criteria. The analysis of the branching pattern revealed that at the sites studied, the rhizomes typically branch only once a year. The longest life span of rhizomes (six years) was found for the stable reed population at Rožmberk East. The reduced rhizome life span at Rožmberk West (four to five years), accompanied by a reduced branching frequency of horizontal rhizomes, was ascribed to a greater incidence of anaerobic conditions associated with the permanent flooding of the hypertrophic organic soil. The maximum life span of the Branna population (four years) probably corresponds to the total age of the reed population. The concentrations of nitrogen, phosphorus, and potassium in the tissue decreased with rhizome age while those of calcium and magnesium increased. The effect of rhizome age on mineral-nutrient concentrations was more pronounced than the effect of site on these concentrations. The mineral nutrient concentrations were not closely associated with reed performance.