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

Abstract

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.Keywords: eutrophication, reservoirs, Egeria, bicarbonate, aquatic plants. Resumo: Objetivos:Nesse trabalho nós realizamos um experimento para avaliar se o crescimento de Egeria najas e E. densa (duas espécies de macrófitas aquáticas submersas da família Hydrocharitaceae, nativas da América do Sul) é limitado por carbono inorgânico; Métodos: Nós medimos os estágios iniciais de crescimento de fragmentos em microcosmos de 3 L com alcalinidade de 100 µM.L -1 e 500 µM.L -1 . Esses valores de alcalinidade foram escolhidos por representarem extremos típicos da maioria dos ecossistemas aquáticos da bacia do Alto rio Paraná e representaram baixa e alta disponibilidade de carbono (principalmente bicarbonato), respectivamente; Resultados: O alongamento de E. densa e o crescimento relativo e desenvolvimento de raízes de ambas as espécies foram significativamente maiores quando os fragmentos cresceram no tratamento de alta alcalinidade; Conclusões: Esses resultados indicam que em vários habitats da bacia do rio Paraná e durante certos períodos do ano, baixas concentrações de carbono inorgânico podem limitar o crescimento de ambas as espécies. Dessa forma, o fósforo e o nitrogênio podem assumir um papel secundário como fatores controladores do estabelecimento e crescimento dessas plantas, porque elas assimilam esses nutrientes do sedimento, onde os mesmos são encontrados em elevadas concentrações. Assim, somente o controle da eutrofização como uma estratégia para reduzir a biomassa dessas espécies pode não alcançar sucesso.Palavras-chave: eutrofização, reservatórios, Egeria, bicarbonato, plantas aquáticas. Biological Limnology 58Freitas, A. and Thomaz, SM. Acta Limnologica BrasiliensiaPositive influence of alkalinity on the occurrences of E. najas and E. densa were first suggested in the Paraná River basin in an investigation carried out in several...

Diversifying the technological strategies for recovering bioenergy from the two-phase anaerobic digestion of sugarcane vinasse: An integrated techno-economic and environmental approach

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Species identity and diversity effects on invasion resistance of tropical freshwater plant communities

“…Studies attributed the success of H. verticillata colonisation in that region to its ability to colonise habitats that other native plant species are not able to tolerate such as relatively deep sites (4.0-7.3 m) and sites highly disturbed by waves 36,37 . Inorganic carbon is another factor that has been considered limiting the growth and productivity of submerged plant species 38,39 . Previous studies on Cabomba genus and Utricularia genus show that these plants strictly use CO 2 as a source of inorganic carbon for photosynthesis whereas H. verticillata and E. densa can also use HCO 3 − 38,40,41 .…”

Diverse role of Macrophytes in aquatic ecosystems: A brief review

“…Starting from the edge with emerged plants, followed by plants with floating leaves until we found rooted submerged species. However, abiotic factors (i.e., depth, water temperature, light incidence, input of nutrients, and interspecific competition) may facilitate heterogeneous distribution (Middelboe & Markager, 1997;Freitas & Thomaz, 2011).…”