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Effect of Montmorillonite and Trace Elements on the Growth of Penicillium frequentans: II. Nitrate Nitrogen Source¹

ABSTRACT

The addition of montmorillonite to culture media has been shown to stimulate growth and metabolic activity of several soil fungi. The objective of this study was to determine if the growth stimulation of a common soil fungus, Penicillium frequentans, was due to montmorillonite supplying required trace elements when glucose and NaNO₃ were used as the C-energy and N sources, respectively.

The trace element treatments were (i) no trace elements, (ii) trace element solution 1, and (iii) trace element solution 2 which contained a 0.1M phosphate buffer plus trace elements. Either montmorillonite, at a concentration of approximately 500 mg/100 ml, or distilled water (controls) was added in dialysis tubing to the trace element solutions.

Without trace elements, the addition of clay increased biomass from 571 to 861 mg/100 ml, an increase of 51%. Biomass production in the controls of both trace element solutions was not significantly different than that produced in the no trace element solution with montmorillonite added. With the addition of clay to trace element solution 1, a 14% increase in biomass from 829 to 944 mg/100 ml was obtained. There was no significant increase in biomass in trace element solution 2, with the addition of clay. The montmorillonite maintained the pH of the medium at least 1.5 units greater than the controls in the no trace element and trace element 1 treatments. With trace element solution 2, a 0.5 pH unit increase after 6 days of growth resulted due to the montmorillonite. When clay was present in the medium, the Cu, Fe, and Mn content of the fungus was increased. As a result of fungal growth, the Zn and Cu contents of the montmorillonite were decreased from 51 to 28 and 37 to 28 µg/g, respectively.

A large portion of the stimulation in fungal growth due to montmorillonite was apparently due to the ability of the fungus to obtain trace elements from the clay. There was however, an increase in growth in trace element solution 1 which could not be attributed to trace elements when NO₃-N was used as a N source.

¹ Scientific Article no. 2471 and Contribution no. 5501 of the Maryland Agric. Exp. Stn., Dep. of Agronomy, College Park, MD 20742.

² Research Assistant and Associate Professor of Soil Science, respectively.

Received for publication June 23, 1978. Accepted for publication July 26, 1979.