Inorganic carbon shortage may limit the development of submersed macrophytes in habitats of the Paraná River basin

aim: in this investigation we carried out an experiment to assess whether the growth of egeria najas and e. densa (two rooted submersed hydrocharitacea, native to south america) are limited by inorganic carbon or not; methods: we measured the early plant growth in 3 l microcosms with alkalinities of 100 μm.l-1 and 500 μm.l-1. these alkalinites represent extremes which are typical of most waters in the upper paraná river basin and they represent low and high inorganic carbon (mainly bicarbonate) availabilities, respectively; results: the elongation of e. densa, and the relative growth rates and root development of both species were significantly higher when they grew in the high alkalinity treatment; conclusions: our results strongly suggest that in several habitats and during certain periods of the year, inorganic carbon shortage may limit the growth of both species. in this sense, phosphorus and nitrogen may assume a secondary role as controlling factors of these plants, because they assimilate these nutrients from sediment, where they are usually found in high concentrations. thus, controlling eutrofication as a strategy to reduce their biomass may not be successful.