The fate of C-4 and C-3 macrophyte carbon in central Amazon floodplain waters : insights from a batch experiment Mortillaro, J. M. Passarelli, C. /Abril, Gwenaël Hubas, C. Alberic, P. Artigas, L. F. Benedetti, M. F. Thiney, N. /Moreira Turcq, Patricia Perez, M. A. P. Vidal, L. O. Meziane, T. Central amazon Floodplains Fatty acids Stables isotopes Macrophytes Degradation The central Amazon floodplains are particularly productive ecosystems, where a large diversity of organic carbon sources are available for aquatic organisms. Despite the fact that C-4 macrophytes generally produce larger biomasses than C-3 macrophytes, food webs in the central Amazon floodplains appear dominantly based on a C-3 carbon source. In order to investigate the respective fate and degradation patterns of C-4 and C-3 aquatic plant-derived material in central Amazon floodplains, we developed a 23-days batch experiment. Fatty acid and carbon concentrations as well as stable isotope compositions were monitored over time in 60 L tanks. These tanks contained Amazon water, with different biomasses of C-3 and C-4 macrophyte, representative of in situ densities occurring in central Amazon floodplains. In the C-4 Paspalum repens treatments, organic (POC, DOC) and inorganic carbon (DIC) got rapidly enriched in C-13, whereas in the C-3 Salvinia auriculata treatments, POC and DOC showed little change in concentration and isotopic composition, and DIC got depleted in C-13. The contribution of P. repens to POC and DOC was estimated to reach up to 94.2 and 70.7%, respectively. In contrast, no differences were reported between the C-3 S. auriculata and control treatments, an observation attributed to the lower C-3 biomass encountered in the field, to a slower degradation rate of C-3 compared to C-4 compounds, and to similar isotopic compositions for river POC and DOC, and C-3 compounds. The C-13 enrichments of POC, DOC, and DIC from P. repens treatments were attributed to an enhanced bacterially-mediated hydrolysis and mineralization of C-4 material. Evolutions of bacterial abundance and branched fatty acid concentrations confirmed the role of heterotrophic microbial communities in the high P. repens decomposition rate. Our experiment highlights the predominant role of C-4 aquatic plants, as a large source of almost entirely biodegradable organic matter available for heterotrophic activity and CO2 outgassing to the atmosphere. 2016 text https://www.documentation.ird.fr/hor/fdi:010067718 fdi:010067718 Mortillaro J. M., Passarelli C., Abril Gwenaël, Hubas C., Alberic P., Artigas L. F., Benedetti M. F., Thiney N., Moreira Turcq Patricia, Perez M. A. P., Vidal L. O., Meziane T.. The fate of C-4 and C-3 macrophyte carbon in central Amazon floodplain waters : insights from a batch experiment. 2016, 59, 90-98 EN BRESIL