The Effect of pH Level and CaCO₃ Content in Tissue Culture Medium on Roots, Biomass and Mineral Uptake of Blueberry

Blueberry production has undergone a dramatic increase in the last decades in the best-suited soils for this crop; therefore new plantations are expanding into unfavorable soils (pH>5.5). Under such conditions, it has been widely suggested that uptake of the micronutrients Fe, Mn and Zn become the limiting factors for the plant’s growth. The objective of this work was to study the effect of pH and CaCO₃ on the root development and mineral uptake under controlled conditions of tissue culture. Ochlockonee Cv. plantlets were grown in tissue culture medium at different pH levels: 5, 6, 7 and 8 controlled by buffers and additional treatment of 1% CaCO₃ (pH~7). Shoots and roots dry biomass decreased as the pH increased. The dry biomass of the CaCO₃ treatment was 50% of that without CaCO₃ at the same pH. Mineral concentrations in plant organs weren`t affected significantly by pH. The concentrations in shoots of most of the minerals were higher in the plants grown with CaCO₃ than without CaCO₃ at the same pH level. The uptake per fresh root weight of most of the minerals, especially Ca, and Ca accumulation in the roots, were higher in the plants grown with CaCO₃ treatment than without CaCO₃ at same pH level. These results are in agreement with our results obtained from blueberry plants grown hydroponically, which showed that Ca accumulated on the root surface and inside the root tissue under alkaline-neutral pH conditions. We assume that Ca accumulates on roots and inside the plant organs as oxalate and citrate salts. These results and our results obtained in a pot experiment, suggest that excess Ca uptake plays a major role in the negative response of blueberry plants to base-neutral pH conditions and to high CaCO₃ content in the growth medium.