THE EFFECTS OF BORON ON THE UPTAKE OF VARIOUS MINERAL ELEMENTS BY LOQUAT PLANTS

A hydroponic experiment was carried out in order to study the effects of high boron (B) concentrations in nutrient solution on the uptake of various mineral elements by plants of loquat (Eriobotrya japonica Lindl.). Six-month-old seedlings were grown in a sand:perlite (1:2) medium and irrigated with Hoagland’s nutrient solutions with various B concentrations (25, 50, 100, 200 or 400 μΜ). The control treatment was a solution containing 25 μΜ B. Sixty-nine days after the beginning of treatments, plants were harvested and separated into leaves, stems and roots. All plant parts were oven-dried and weighted. Dried samples were milled to a fine powder and the concentrations of B, P, K, Ca, Mg, Fe, Mn, Zn and Na were determined. Afterwards, the total nutrient content per plant was calculated by multiplying the concentrations of each nutrient in each plant part by the corresponding dry weights. The increase of B concentration in the nutrient solution did not result in a corresponding linear increase of total amount of B absorbed by plant (r=0.343, P>0.05). High B concentrations (400 μΜ) significantly reduced K, P, Ca, Mg, Zn, Fe and Mn plant uptake. Furthermore, the uptake of all the elements was inversely related to B concentration in the nutrient solution, with r values ranging between -0.654 (P<0.001) for P and -0.744 (P<0.01) for K. Regarding the Na, although its total uptake was not affected significantly by the various B treatments, a significant mild negative correlation between Na uptake and B concentration in the nutrient solution was found (r=-0.421, P<0.05). In conclusion, loquat plants are very susceptible to B excess, especially when they are grown in media containing more than 50 μΜ B (≈0.55 ppm B). Moreover, the uptake of almost all the elements studied is limited when loquat plants grow extensively under a solution with excessive B concentrations (400 μΜ Β).