Effects of Humic Acid on Root Development and Nutrient Uptake of Vicia faba L. (Broad Bean) Seedlings Grown under Aluminum Toxicity

Interactions of humic acid with development and uptake by seedlings of Vicia faba L., (cv. Eresen 87) grown in conditions of aluminium toxicity have been investigated in pot experiments in a controlled greenhouse environment. The objective of the study was to investigate whether humic acid moderates aluminum toxicity. The seedlings were treated with solutions of aluminum chloride (AlCl3) prepared in Hoagland control nutrient solution (HO) and 50 and100 mu M and humic acid + Hoagland (HA) solutions, respectively. The 50 and100 mu M HA solutions increased root fresh (RFW) and dry (RDW) weights, where the RFW differed significantly from controls (HO) after statistical evaluation by NCSS (NCSS, Kaysville, Utah) with two-sample T-test range at the 5% level. The results of the current experiment suggested that humic acid had suppressed or counteracted the toxic effect of aluminum (Al3+) on both main and lateral root growth. Humic acid seems to block the effect of Al3+ on nutrient uptake, as tested by atomic absorption spectrophotometry (AAS) and flame photometery (FP). Al3+ content in the roots was significantly decreased by 219% in 50-mu M HA and by 49% in 100-mu M HA treatments respectively. Potassium (K+), sodium (Na+), and iron (Fe3+) were recorded as the other elements taken up in the greatest amounts among the tested nutrients, in addition to Al3+. Humic acid increased the contents of Na+, K+, manganese (Mn2+), and zinc (Zn2+) significantly in both concentrations of HA treatment compared to controls. The Fe3+ content in the roots decreased, in both treatments of HA, application by 252% and 32% respectively. The reduction in the former was significant