Early growth characteristics of Potamogeton pectinatus L.: the significance of the tuber

Abstract

A germination experiment was done with tubers of Potamogeton pectinatus L. originating from Californian (U.S.A.) irrigation canals. After 14 days it was found that: (a) the tubers germinated readily upon detachment from the mother plant, so no innate dormancy was present; (b) when the tubers remained attached to the mother rhizome, however, no germination was observed; (c) larger tubers germinated earlier than smaller ones; and (d) the proportion of a clutch from one motherplant that germinated after detachment was larger for larger clutches.

In a second experiment, plant development from the moment of tuber germination was followed in detail for 30 days, using two weight classes of tubers: small (36.4 ± 0.8 g fresh weight, mean ± standard error) and large (130.7 ± 5.4). Fitted exponential tuber depletion curves as well as logistic growth curves were significantly different for the two weight classes.

A carbon balance model was calibrated to these growth data and fitted the data reasonably well. The model made up mass balances with a time step of one day and had the following general form: Tuber import + photosynthetic production = maintenance respiration + growth respiration + growth. Major assumptions had to be made on the conversion efficiency of reallocated tuber carbon. The calibrated model showed that contribution to the total carbon pool by the smaller tubers became less than 10% after 14 days, whilst for the larger ones this was so only after 18 days. A final residual tuber weight of 10% below which no further depletion was apparently possible, was reached after about 20 days for the smaller tubers. For the larger tubers, this final constant weight was probably not yet reached during the experiment.