Simulated global increases in atmospheric CO2 alter the tissue composition, but not the growth of some submerged aquatic plant bicarbonate users growing in DIC rich waters
2019
Hussner, Andreas | Smith, Rosali | Mettler-Altmann, Tabea | Hill, Martin P. | Coetzee, Julie
Current global change scenarios predict an increase in atmospheric CO₂ from the current 380 ppm to a value ranging from 540 ppm to 960 ppm by the year 2100. The effects of three air CO₂ levels (400, 600 and 800 ppm) on five submerged aquatic plants that utilize HCO₃⁻ were studied, using the elevated CO₂ Open Top Chamber facility at Rhodes University (Grahamstown, South Africa). Plants grew in water with two different initial dissolved inorganic carbon (DIC) concentrations of 1.5 and 3.0 mM. Overall, the growth rates and biomass allocation to roots were not affected by the initial DIC and air CO₂, even though differences between the species were found. Furthermore, no overall effects were found on net photosynthesis, chlorophyll and starch content, even though significant effects of CO₂ and DIC were observed in some species. In contrast, with increasing DIC and air CO₂ a significant global decline in leaf nitrogen content linked with an increased C:N molar ratio was observed. The results indicate that submerged aquatic HCO₃⁻ users will be less affected by atmospheric CO₂ increases when growing in DIC rich waters, in comparison to obligate CO₂ users growing under CO₂ limiting conditions as documented in previous studies. However, the changes found in plant nitrogen illustrate that atmospheric CO₂ increases will affect nitrogen absorption by submerged plants, with subsequent ecosystem level effects.
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