Mass loss, fungal colonisation and nutrient dynamics of Phragmites australis leaves during senescence and early aerial decay

This study examined the mass loss, fungal biomass, and nutrient dynamics of standing Phragmites australis leaf blades during senescence and early decay in littoral reed stands of two hardwater lakes. Green living leaves were tagged at defined canopy heights in early autumn (late August or early September) and periodically collected until all leaf blades had fallen off the parent shoot. Samples were analysed for leaf dry mass remaining, fungal biomass associated with leaves (ergosterol concentrations), and nitrogen and phosphorus concentrations. Considerable mass loss of leaves occurred in the standing position (up to 28%). Nitrogen and phosphorus concentrations of leaves decreased substantially with time (by 39-77%), indicating that a major portion of these nutrients was translocated to the rhizome during senescence. Fungal biomass associated with leaves increased during the study period, reaching an estimated maximum of about 40 mg g(-1) of leaf dry mass. Fungal biomass was negatively correlated with leaf N and P concentrations. The observed patterns of leaf mass loss, nutrient dynamics, and fungal biomass were consistent with the successive senescence and death of leaves from the shoot base to its tip. The results of this study point to a notable mass loss of P. australis leaf blades in the standing position, which appears to be mediated by both plant and microbial processes. Nutrient dynamics, in contrast, appear to be largely governed by plant processes. (C) 2001 Elsevier Science B.V. All rights reserved.