The effects of litter on growth and plasticity of Phragmites australis clones originating from infertile, fertile or eutrophicated habitats

In many European countries a strong decline of Phragmites australis (Cav.) Trin. Ex Steudel (common reed) has been observed. In some instances this decline has been related to the accumulation of litter. A greenhouse experiment was conducted with P. australis cuttings from different stable and die-back populations in the Czech Republic and the Netherlands, which were grown in sand (oxidised substrate) and a mixture of sand and litter (reduced substrate). The stable populations were from fertile and infertile habitats, and the die-back populations from originally infertile and now eutrophicated habitats. It was hypothesised that (i) clones from stable populations in fertile habitats are better adapted to accumulated litter (reduced substrate) than those in infertile habitats, and (ii) clones from die-back populations in eutrophicated habitats are more similar to those from stable populations in infertile than fertile habitats, and (iii) the allocation and morphological traits induced in the different environments are adaptive i.e. result in a higher total dry weight (as a measure of fitness) in a particular environment. No significant population × substrate type interaction terms were present, therefore, populations did not differ in their responses to accumulated litter. Population differences in total dry weight, allocation and morphological traits could not be related to adaptations to accumulated litter. Therefore, the different hypotheses were rejected. Generally, clones from infertile habitats were more similar and less plastic than those from the fertile and eutrophicated habitats. Some of these latter clones had a significantly higher total dry weight in sand, but others in sand–litter. Although substrate-type had no overall effect on total dry weight, it affected almost all other plant traits. Clones growing in sand–litter had a higher dry matter allocation to leaves, leaf weight ratio, specific leaf weight ratio, and number of shoots than plants growing in sand, whereas the allocation of dry matter to stems and roots, shoot length and the distance between shoots was lower for clones growing in sand–litter than in sand. Between substrate-types no differences in dry matter of rhizomes were present, however, clones growing in sand–litter produced longer, but thinner rhizomes than those in sand. It was concluded that responses of P. australis to accumulated litter were directed towards a high input of oxygen into a small volume of substrate. It was co