Influence of Humic Acids on Iron Uptake by Fe-Deficient Tomato Plants

Iron deficiency in plants can lead to serious losses of yield and quality, including premature death of the plant, unless Fe-deficiency correction strategies are taken. A considerable amount of researches have been conducted over the past 80 years to determine the most effective and economical methods of correcting iron chlorosis. Among those methods, the use of Fe-EDDHA (Fe3+-ethylenediamine di-(o-hydroxyphenylacetate)) is considered the most effective fertilizer to relieve iron deficiency in plants. On the other hand, the influence of humic substances on plant growth and mineral nutrient accumulation have been also summarized by a lot of researches. Interactions of humic substances with biochemical mechanisms involved in the uptake of nutrients (i.e. ferric-chelate reductase, organic acid root accumulation, membrane permeability) have also been investigated, showing physiological effects. However, while natural humic substances have been extensively studied, little data is available for commercial humic substances although their use is quite common in agriculture. In the present study, the effects of humic acids extracted and purified from a commercial product obtained from lignites on iron deficient young tomato plants (Lycopersicon esculentum Mill 'Jaguar') in hydroponic culture were investigated. Parameters related to iron uptake (root organic anions content, ferric-reductase activity and membrane permeability), parameters related to plant growth (root and shoot fresh weight) and parameters related to iron levels in leaf (foliar Fe2+ content and chlorophyll levels) were studied. The results showed that the incorporation of humic acids to Fe-deficient tomato plants alleviated the symptoms of deficiency, improving growth and iron nutrition, by acting on iron uptake mechanisms.