LIFE-HISTORY TRAITS - A POSSIBLE CAUSE FOR THE HIGHER FREQUENCY OF OCCURRENCE OF ZANNICHELLIA-PEDUNCULATA THAN OF ZANNICHELLIA-OBTUSIFOLIA IN TEMPORARY MARSHES

Zannichellia pedunculata Reichenb. and Zannichellia obtusifolia Talavera, Garcia-Murillo & Smit have been recorded in the marshes of the Camargue (south of France). Of these species, Z. pedunculata is very common, but Z. obtusifolia is rare. In three neighbouring marshes, Z. pedunculata and Z. obtusifolia occur regularly together. These two species have a similar morphology. Some of their life history traits were compared experimentally in natural and artificial habitats. At the two concentrations of Cl- studied (0 and 2 g l-1), the percentage germination of Z. obtusifolia (100% and 96%, respectively) is equal to or higher than that of Z. pedunculata (100% and 38%, respectively) when the seeds are not allowed to dry out. In contrast, when the seeds have undergone desication, the percentage germination of Z. pedunculata is higher (94% and 64%, respectively) than that of Z. obtusifolia (88% and 56%, respectively at the two concentrations of Cl-, 0 and 2 g l-1). Salinity and the date of flooding were found to affect the biomass of both species of Zannichellia similarly. After flooding in autumn, Zannichellia pedunculata is capable of producing fruit before the winter, but Z. obtusifolia does not do so until the following spring. The inability to reproduce in the autumn, and the negative influence of desiccation on the rate of germination and percentage germination, can explain why Z. obtusifolia is uncommon in the Camargue marshes which are subject to frequent and irregular periods of drying out.