Rhizome age structure of three populations of Phragmites australis (CAV.) TRIN. ex STEUD.: Biomass and mineral nutrient concentrations

The rhizome age structure for populations of Phragmites australis (CAV.) TR IN. ex STEUD. was determined at three sites of the Trebon Biosphere Reserve (Czech Republic). These sites were classified according to plant species c omposition and phosphorus availability as oligotrophic (Branna), mesotrophi c (Rozmberk East) and hypertrophic (Rozmberk West). P. australis stands at these sites were expanding, stabilized and retreating, respectively. Rhizom es 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 i n the branching hierarchy and to supplementary morphological criteria. The analysis of the branching pattern revealed that at the sites studied, the r hizomes typically branch only once a year. The longest life span of rhizome s (six years) was found for the stable reed population at Rozmberk East. Th e reduced rhizome life span at Rozmberk West (four to five years), accompan ied by a reduced branching frequency of horizontal rhizomes, was ascribed t o a greater incidence of anaerobic conditions associated with the permanent flooding of the hypertrophic organic soil. The maximum life span of the Br anna population (four years) probably corresponds to the total age of the r eed population. The concentrations of nitrogen, phosphorus, and potassium i n the tissue decreased with rhizome age while those of calcium and magnesiu m increased. The effect of rhizome age on mineral-nutrient concentrations w as more pronounced than the effect of site on these concentrations. The min eral nutrient concentrations were not closely associated with reed performa nce.