An investigation into the effects of nitrogen on growth and morphology of stable and die-back populations of Phragmites australis

In many European countries a strong decline of Phragmites australis (common reed) populations has been observed during the past two decades. This has become known as die-back or reed regression. A greenhouse growth experiment was performed with P. australis cuttings from stable and die-back populations from The Czech Republic and The Netherlands. The stable populations were from fertile and infertile environments, and the die-back populations were originally from infertile but now eutrophicated habitats. It was hypothesised that (i) stable P. australis populations from fertile and infertile habitats would show inherent differences in biomass (allocation) and N-content in response to nitrogen loading, and (ii) die-back populations would be more similar to stable populations from infertile as opposed to fertile habitats in terms of biomass (allocation) and N-content. The stable Czech populations showed an increase in dry weight with increasing fertility of the habitat. This was not related, however, to leaf area ratio (LAR), specific leaf area (SLA) or nitrogen use efficiency (NUE). The dry weight of the stable Dutch populations did not vary with fertility, although the population from the infertile habitat showed a higher allocation of dry matter and nitrogen to the below-ground parts as compared to the fertile habitat population. Total dry weight of the die-back Czech population did not differ from that seen for stable populations from the infertile habitats, and no differences were found between the Dutch populations. Die-back populations did not show a higher resemblance with stable populations from infertile as opposed to fertile habitats with respect to plant traits involved in the capture of Light and/or nitrogen. Most plant traits were affected by nitrogen, irrespective of habitat fertility, and populations did differ in morphology and dry matter allocation. However, since performance of populations could not be related to the fertility of the habitat, both hypotheses were rejected. The importance of other selectional processes is discussed. (C) 1998 Elsevier Science B.V.