Regenerative strategies of aquatic plants in disturbed habitats: the role of the propagule bank

Recovery of plants from disturbance is frequently associated with the prese nce of an extensive seed bank. In a cut-off channel of the Rhone River subj ected to fluctuating water levels and scouring forces during flash floods, regenerative strategies of aquatic plants were investigated through the stu dy of the sediment propagule bank and its comparison with the established v egetation. Within this channel, the zone disturbed only by scouring floods (zone F) had a small propagule bank (as assessed by greenhouse germination trials), whereas more propagules regrew in zone FE which was subjected to b oth scouring floods and episodic sediment emersion. There, regrowth was mos tly from sexual propagules, with the stonewort Chara vulgaris being the dom inant component. In zone F, no relationship between propagule bank composit ion and established vegetation was demonstrated. In zone FE, a strong posit ive relationship between vegetative propagules (buds + rhizomes + fragments ) and the established vegetation occurred. The disturbance history of the s ite indicated that the flowering and seed production of most species was di srupted by the flood regime, the result being that only one third of the hy drophyte species present in the established vegetation were present in the seed bank. Consequently, in this habitat, resistance type regenerative stra tegies, involving fragments and rhizomes, were adopted by most species. Res ilience regenerative strategies involving seed- or bud-banks, together with resistance strategies involving the development of a terrestrial growth fo rm, were adopted by plants that had to face both floods and sediment emersi ons. The precise nature of disturbance appears to affect regenerative strat egies of aquatic plants and merits greater attention in studies of trait-en vironment relationship. The diversity of regenerative strategies within and between aquatic plant species is likely to contribute significantly to the underlying stability of vegetation in flood disturbed habitats.