Spatio-temporal dynamics and plasticity of clonal architecture in Potamogeton perfoliatus

Aboveand below-ground clonal growth architecture was compared for two neighbouring patches of Potamogeton perfoliatus L. in Lake Constance, representing typical sparse and dense growth types. A detailed map of individual ramets and their corresponding rhizome network was produced and the seasonal development of ramet sprouting and rhizome growth was reconstructed. Rhizomes extended at rates ranging between 40 and 63 cm per year, and added a new shoot for every 1–20 cm of rhizome produced. The main rhizome axis grew in a semi-linear fashion, with deviation means of 15 and 24◦, and developed 0–0.5 branches per plant, with an insertion angle from 15–90◦. Total rhizome length of all plants amounted to 5 and 11 m m−2 at the two sites. The total biomass produced at the two sites differed by 10-fold. The neighboring patches also showed different allocation patterns which are interpreted as foraging. Contrary to the prediction of the foraging hypothesis, there was only a small difference in mean spacer length between sites. On the other hand, the spacer length was plastic relatively to total biomass. We propose that spacer length is not an independent part of the foraging strategy, but rather a result of overall productivity and biomass allocation. Phosphorus content of plant tissue at the more productive site was two-fold higher than that at the less productive site which suggests that the different growth types may be due to differences in sediment nutrient availability: in situ fertilization of a less productive site increased the P content to those levels of the productive site. In situ fertilization also resulted in higher ramification, lower root allocation and decreased spacer length and confirmed the foraging capability of P. perfoliatus. © 2004 Elsevier B.V. All rights reserved.