Bicarbonate and low iron level increase root to total plant weight ratio in olive and peach rootstock

Young plants obtained by micropropagation of olive (Olea europaea L. cv Picual) and peach rootstock GF677 (an hybrid of almond, Prunus amygdalus Batsch, and peach, Prunus persica L. Batsch) were grown in aerated basic nutrient solution for 35 days, with four treatments containing different concentrations of bicarbonate and iron as FeEDDHA, HCO3- (mM)/iron (Fe) (muM): 0/20, 5/5, 10/20, and 10/2.5. Chlorophyll content decreased with higher HCO3- and lower Fe level. The treatment 10/2.5 had a significant effect in reducing the number of new leaves and the weight of the shoot produced during the experiment. In spite of decreasing the shoot growth the treatments with HCO3- and low iron level maintained or increased the weight of the roots of both olive and GF677. The effect was more apparent when the ratio of root/total plant weight was obtained. This ratio increased from 28.1 to 43.5% in olive and from 23.4 to 40.4% in GF677, depending on treatment. The Fe concentration in leaves was related to the degree of chlorosis, reaching the lowest values in the most chlorotic plants from the treatment 10 mM HCO3-/2.5 muM Fe, and values near the control in the slightly chlorotic plants, from the treatment 10 mM HCO3-/20 muM Fe. In the treatments with bicarbonate the root mineral concentrations were altered, with a notable increase in phosphorus (P) and calcium (Ca) and an important reduction in Fe, manganese (Mn), and zinc (Zn), in relation to the control. The increased root to total plant weight ratio, with higher HCO3- or lower Fe level, is discussed in relation to both an increase in the PEP carboxylase activity in the roots and a higher assimilate partitioning to the roots.