Responses of Six Crop Species to Solution Zinc2+ Activities Buffered with HEDTA
Zinc contamination has long hampered the use of conventional nutrient solutions for attaining reproducible and severe Zn deficiencies. Chelator-buffered solutions show promise for precisely imposing micronutrient deficiencies, but further studies are needed to fully evaluate the method and to develop methods to avoid Zn-deficiency-induced P toxicity. In a greenhouse study, seedlings of maize (Zea mays L. ‘Golden Cross Bantam’), wheat (Triticum aestivum L. ‘Yecora Rojo’), tall wheatgrass (Elytrigia pontica [Podp.] Holub ‘Orbit’), alfalfa (Medicago sativa L. ‘Germain's WL-320’), soybean (Glycine max [L.] Merr. ‘Vinton 81’), and tomato (Lycopersicon esculentum L. ‘Jackpot’) were grown for 16 to 29 d in solutions containing 0.4 to 12 µM total Zn. Computed Zn2+ activities were buffered at 4 to 123 pmol L−1 by a 50-µM excess of HEDTA, and solution P was maintained at 10 ± 3 µM. Zinc deficiencies ranged from mild to severe, dry matter yield minima ranged from 32 to 89% of controls, and critical Zn2+ activities for the onset of deficiency ranged from approximately 10 to 65 pmol L−1. The relative sensitivity of the six species to low Zn was maize > tomato > wheat > alfalfa ≈ tall wheatgrass > soybean. Shoot Zn concentrations were consistent with the widely reported critical range of 15 to 20 mg kg−1. Zinc deficiency in the three grass species led to hyperaccumulation of P to phytotoxic levels, and leaf symptoms largely reflected this toxicity. Leaf P concentrations in the three dicots tended to be lower, but may have been within the phytotoxic range. Thus, even with P concentrations that approach soil solution values, the P toxicity that often accompanies Zn deficiency in solution-culture experiments was not eliminated. The effects of Zn deficiency on shoot concentrations of nutrients other than P were variable, although divalent cations tended to be elevated in Zn-deficient shoots.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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