Effect of the filling season on aquatic plants in Mediterranean temporary ponds

Aims Pond environmental conditions may differ among years with regards to the season in which ponds begin to fill.We experimen-tally evaluated how seedling emergence,plant growth and phe-nology differed among years in which filling occurred in winter,autumn or spring.Methods We collected sediments from a natural temporary pond and located them in aquariums.They were placed in a climatic chamber that simulated annual variation in field environmental temperatures and light conditions.Aquariums were assigned to one of three treat-ments,which differed in the date on which they were filled with water(autumn,winter and spring).We counted the number of seed-lings of different species emerged and recorded data about the pres-ence of flowers,seeds or spores every week.The experiment was finished in June,when we harvested the plants and estimated their biomass.Important Findings In most species,seedling emergences were primarily related to time after filling,and thus synchronized their life cycles with the unpre-dictably timed wet phase of the ponds.Autumn filling resulted in the highest numbers of seeds/spores.However,winter filling pro-moted plant growth the most.In the spring filling treatment,more terrestrial plant seedlings emerged and fewer seeds/spores were produced.When ponds are flooded earlier,plants may produce a higher number of propagules.However,in years when inundation is delayed to spring and hydroperiods are short,seedling emergence deplete the seed bank and there is little to no seed production,while terrestrial monocots are able to colonize pond basin.