Genetic diversity of riverine reed stands indicating the water regime of the habitat

Although genetic diversity of reed stands developing in habitats with unchanged water levels have been frequently investigated, little is known about reed propagation along rivers, where fluctuating water levels may provide various conditions for germination and seedling development.The present paper evaluates genetic diversity of reed stands grown in (i) an oxbow with significant water level fluctuations related to the flood events in the main river; (ii) a separated oxbow which has lost connection to the main channel; and (iii) artificially controlled running water with low water level fluctuation. At each site, reed stands were investigated along transects parallel to the shore and multilocus phenotypes were determined by microsatellite analysis.The results demonstrated that genetic diversity of riverine reed stands can indicate the water regime of the habitat. Reed colonizes mostly by vegetative propagation where regular inundation can impede germination and seedling development and, therefore, genetic diversity is low in the whole stand. If a former oxbow becomes practically a lake, the clonal diversity and colonization processes are similar to those observed in regular lakes; clone number decreases toward the open water. When reed forms floating mats (i.e. the effect of water level fluctuation is excluded), generative reproduction prevails in the entire stand, resulting in high genetic diversity even at the open water edge of the stand.