AQUATIC HOMOGENOCENE Damming reduced the functional richness and caused the shift to a new functional state of the phytoplankton in a subtropical region Alfonso Pineda . Patrı ´cia Iatskiu . Susicley Jati . Aline C. M. Paula . Ba ´rbara F. Zanco . Claudia C. Bonecker . Geovani A. Moresco . Laura A. Ortega . Yasmin R. Souza . Luzia C. Rodrigues Received: 26 August 2019 / Revised: 16 May 2020 / Accepted: 25 May 2020 Ó Springer Nature Switzerland AG 2020 Abstract We analyzed the effect of damming on the temporal patterns of the composition and richness of phytoplankton Reynolds functional groups (RFG) from a subtropical floodplain, together with its drivers. We obtained data of environmental factors and presence–absence of RFG from sites at both a dammed and a non-dammed region, sampled at least twice a year for 19 years. Since damming decreases the effect of flooding in floodplains, as it isolates adjacent environments, changes environmental conditions, and decreases its temporal variation, we tested if, over time, damming could (i) decrease the richness, (ii) shift the functional structure, (iii) increase the spatial turnover, and (iv) decrease the within-year turnover. Only the dammed region showed changes over time, with a decrease in the richness and the shift to a new functional state, represented by flagellates. The low influence of flooding seemed to be the main driver of these changes by allowing the increase in nutrients (with negative effect on richness) and limiting the arrival of organisms from distant sites. By shifting the functional structure and causing the loss of RFGs, damming could trigger changes in the ecological interactions of floodplains and negatively affect the energy flux from the phytoplankton to superior trophic levels. Guest editors: Andre ´ A. Padial, Julian D. Olden & Jean R. S. Vitule / The Aquatic Homogenocene Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-020-04311-0) con- tains supplementary material, which is available to authorized users. A. Pineda (&) Programa de Po ´s-graduac ¸a ˜o Em Biologia Comparada – PGB, Universidade Estadual de Maringa ´ – UEM, Maringa ´, PR, Brazil e-mail: amanecce@gmail.com P. Iatskiu Á A. C. M. Paula Á B. F. Zanco Á C. C. Bonecker Á G. A. Moresco Á L. A. Ortega Á Y. R. Souza Á L. C. Rodrigues Programa de Po ´s-graduac ¸a ˜o em Ecologia de Ambientes Aqua ´ticos Continentais – PEA, Universidade Estadual de Maringa ´ – UEM, Maringa ´, PR, Brazil S. Jati Á C. C. Bonecker Á L. C. Rodrigues Nu ´cleo de Pesquisas em Limnologia e Aquicultura – Nupe ´lia, Universidade Estadual de Maringa ´ – UEM, Maringa ´, PR, Brazil 123 Hydrobiologia https://doi.org/10.1007/s10750-020-04311-0