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Effects of inorganic carbon source on photosynthetic rates of Egeria najas Planchon and Egeria densa Planchon (Hydrocharitaceae)
Pierini, S.A.; Thomaz, S.M. (2004). Effects of inorganic carbon source on photosynthetic rates of Egeria najas Planchon and Egeria densa Planchon (Hydrocharitaceae). Aquat. Bot. 78(2): 135-146. dx.doi.org/10.1016/j.aquabot.2003.09.007
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

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Keywords
    Carbon cycle; Dissolved gases; Inorganic carbon; P effects; Photosynthesis; Uptake; Egeria densa; Egeria najas; Brazil, Parana, Itaipu Reservoir; Fresh water

Authors  Top 
  • Pierini, S.A.
  • Thomaz, S.M.

Abstract
    The ability of two submerged freshwater macrophyte species, Egeria najas Planchon and Egeria densa Planchon to use HCO3 as a source of inorganic carbon for photosynthesis was assessed by a pH drift experiment. The pH values and different HCO3 concentrations were set up at the beginning of the experiments, in low and high alkalinities (ca. 100 and 800µmol). Results of pH drift experiment and [CT]/Alk quotient indicated that both species used HCO3 and were adapted to low inorganic carbon availability. Nevertheless, different efficiencies of HCO3 use were evident based on the photosynthesis rates and pH values attained at the end of the experiments. Higher photosynthesis rates and pH values were observed in the presence of E. najas both at low and high alkalinities. Both species used more efficiently HCO3 in high alkalinity. The results suggest that the efficiency in using HCO3 depends on the concentration of this ion in water uptake ability of these species. Both E. najas and E. densa preferred CO2 in both alkalinities. By adjusting the data with a Michaelis-Menten equation, it was shown that E. najas is slightly more efficient in using CO2 than E. densa, when the concentrations of this dissolved gas in water are low. Thus, the low CO2 concentrations characteristic of several Brazilian freshwater ecosystems may be advantageous to the colonization of E. najas, compared to E. densa.

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