Abstract
Enhancing root-zone (RZ) dissolved inorganic carbon (DIC) levels of plants grown hydroponically and aeroponically can increase biomass accumulation but may also alter plant nutrient uptake. These experiments investigated how bicarbonate (HCO3−) added to a hydroponic nutrient solution and CO2 gas added to an aeroponic system affected biomass and nutrient concentrations of lettuce and pepper plants. Applying high RZ HCO3− concentrations (20 mM) to lettuce plants grown hydroponically decreased foliar N, P, Cu, K, Mn and Zn concentrations, concurrent with decreased biomass accumulation (50% less than control plants). On the contrary, 1 mM RZ HCO3− promoted biomass accumulation (10% more than control plants), but this could not be attributed to higher tissue nutrient concentrations. While elevated RZ CO2 did not alter biomass accumulation and nutrient concentrations in pepper grown aeroponically, it decreased foliar Mg and S concentrations in lettuce grown aeroponically even though nutrient contents (concentration x biomass) did not differ between treatments, due to 22% more biomass than control plants. In addition, elevated RZ CO2 enhanced N, P, Cu and Zn contents relative to control plants, indicating greater uptake of those elements. Nevertheless, there was no consistent relationship between plant growth promotion and altered plant nutrition, suggesting alternative mechanisms of growth regulation.
Highlights
Atmospheric CO2 is the main form of inorganic carbon assimilated by terrestrial photosynthetic organisms
Since plant growth and development largely depend on the combination and concentration of mineral nutrients available in the RZ, this study aims to understand how HCO3 − added to hydroponic nutrient solution or CO2 gas into the RZ of lettuce and pepper plants grown aeroponically affects foliar and root tissue nutrient concentrations
1 mM and 5 mM HCO3 − increased shoot fresh weight, shoot dry weight and leaf area by ~10%, while root dry weight was significantly lower in control plants and those exposed to 1 mM
Summary
Atmospheric CO2 is the main form of inorganic carbon assimilated by terrestrial photosynthetic organisms. As water percolates through the soil, it becomes enriched with CO2 from plant and microbial respiration. Some of this CO2 can be dissolved in the soil, producing dissolved inorganic carbon (DIC), which is controlled by the partial pressure of CO2 (pCO2 ), pH and temperature [1]. The soil inorganic carbon comprises CO2 in the gas phase, the liquid phase solution containing bicarbonate (HCO3 − ) and CO3 − and the carbonate in the solid phase. It is well known that CO2 is absorbed through the stomata in the leaf, many studies have observed that roots are able to take up dissolved inorganic carbon (DIC) contained in soils as well as gaseous CO2 respired by the roots
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