Ion Competition in Manganese Uptake by Barley Plants

Abstract

The recommended concentration of manganese in Hoagland's solution produces toxic symptoms in barley plants andl must be reduced substantially to avoid injury to the leaves. The suggested rate of 0.5 ppm Mln in this solution resulted in characteristic brown spots on the leaves and affected the yields adversely. When the concentration of Mn was reduced to 0.025 ppnm, this difficulty was overcome. Equally effective was the addition of 10 ppm silicon as sodium silicate to the solution (25). Another methodl of preventing manganese injury to barley leaves was that of increasing the total macro-nutrient strength of the solutions. This lowered the Mn content of the leaves, redluced the symptoms, and gave higher yieldIs (25). This report (leals primarily wvith subsequent experiments in wbhich the component ions of Hoagland's solution were manipulated to studly their individual effect on the uptake of Mn by barley. Materials & Methods Seedls of Atlas barley (Hordeium 7 vulgare L.) were germinated oln screens mounted on pyrex dishes containing distilled water. After 1 week, 5 seedlings Nvere placed in corks and transferred to 45-liter tanks in (luplicate filled with Hoagland's No. 2 solution, with modifie(d micrcnutrients (table I), and providled with gentle aeration. After growing for 6 weeks in the greenhouse, the plants were harvested, dried, weighed, and analyzed for Mln andl Fe. Manganese was (letermine(l colorinmetricall)' as permanganate after heating witlh periodate, and iron was complexed with o-phenanthroline. Results In the first experiment barley plants were grown in solutions covering a wide range of Mn concentrations comparing full-strength with one-fifth strength Hoagland macro-salts. MIicronutrients other than Mn were added uniformly to all cultures. The composition of the solutions used is given in table I. Analysis of the leaves showed an increase in Mn content with increasing concentration of M1n in solution, as would be expectedl. The MIn content of