Importance of seedling recruitment for regeneration and maintaining genetic diversity of Cyperus papyrus during drawdown in Lake Naivasha, Kenya

•Estimated seed number of Cyperus papyrus umbel ranged from 98,022 to 337,536.•Drawdown-flooding phases resulted in seedling recruitment, zonation and dispersal.•PCoA revealed genotypes in seedlings and parent stand belong to single gene pool.•Seedlings had more private allelic diversity than parent stands.•Spatial genetic structuring was detected at 100 m distance in parent stands.

Drawdown-flooding cycles occur commonly in many water bodies and influence plant succession in many ways including the expansion of macrophytes through seedling recruitment. We investigated a regeneration event of Cyperus papyrus in Lake Naivasha and documented seed production, seedling recruitment, zonation progression, dispersal and establishment in relation to evidence from genetic relatedness between seedlings and mature stands using microsatellite loci. Seed estimate counts in five papyrus umbels reached high values between 98,000 and 337,000. The drawdown drying phase led to desiccation accompanied by cracking of mudflat soils, and the oxidation and demise of littoral aquatic plants. Reflooding led to distinct zones of young papyrus and hygrophilous ephemerals. In the final flooding phase when the lake reached normal water levels, hygrophilous ephemerals died off while papyrus survived. Young floating papyrus mats dispersed through wind and wave action joined existing mature stands or spread into formerly unoccupied shoreline areas.Microsatellite analysis of seedlings in the drawdown zone and a neighboring stand of mature and juvenile shoots reveals high overall gene diversity (Ho = 0.476, He = 0.576, Ae = 2.8) reflecting an underlying sexual reproduction. A large overlap of genotypes was found in seedling and parent stands indicating a single gene pool. A total of 40 alleles were observed across 3 life stages (clonal juvenile, mature and seedlings), however, more private alleles and higher allelic diversity were detected in seedlings than in the parent individuals, showing their contribution to an increase in the local gene pool. Fine-scaled spatial genetic structuring was detected at about 100 m distance in parent stands for both juvenile and mature life stages indicating a potential influence caused by local seed rain.