Iron Chelate Photodegradation in Fertilizer and Nutrient Solutions Affect Iron Acquisition

in HortScience
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  • 1 Dept. of Horticulture, Clemson Univ., Clemson, SC 29634-0375

Iron chelate photodegradation is a problem in tissue culture where limited soluble Fe in agar reduces callus tissue growth. Our objectives were to determine if Fe chelate photodegradation occurs in commercial fertilizers used in greenhouse plant production and, if so, the effects on plant Fe acquisition. Commercial 20N–10P–20K soluble fertilizers containing Fe-EDTA were prepared as 100x stocks based on a 100 mg N/liter (1x) concentration. A modified Hoagland's solution with Fe-DTPA was prepared as a 10x stock based on a 200 mg N/liter (1x) concentration. Samples then were kept in darkness or were irradiated with 500 μmol·m–2·s–1 from fluorescent and incandescent sources for ≤240 hours. Soluble Fe in the irradiated commercial fertilizer solutions decreased 85% in 240 h. Soluble Fe in the Hoagland's solution, prepared in the lab, decreased 97% in 72 h. There was no loss in soluble Fe in any dark-stored treatment; demonstrating photodegradation of Fe-chelates under commercial settings. Excised roots of marigold (Tagetes erecta L.), grown hydroponically in the irradiated solutions, had Fe(III)-DTPA reductase activity 2 to 6 times greater than roots of plants grown in solutions kept in darkness. Plants growing in irradiated solutions acidified the rhizosphere more than plants growing in solutions kept dark. The increase in Fe reductase activity and rhizosphere acidification are Fe-efficiency reactions of marigold responding to the photodegradation of Fe-chelates and subsequent decrease in soluble Fe in both commercial fertilizers and lab-prepared nutrient solution.

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