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Effect of the Sol-Gel Transformation in Clay-Water Systems on Biological Activity: I. Seed Germination and Bacterial Thermogenesis¹

ABSTRACT

Gels containing 4, 6 and 8% Na- or Na/Al-clay (Na-clay with hydrous aluminum oxide impurity) were extruded through a 20-gauge hypodermic needle into petri dishes. Half of the petri dishes were tapped on the laboratory bench to disturb the gels within them. Then all of the gel surfaces were smoothed with a spatula and lettuce (Lactuca sativa L.) seeds were placed on them. It was found that the lettuce seeds germinated faster on the disturbed gels.

In a second experiment, gels containing 4% Na- or Na/Al-clay were mixed with nutrient medium and inoculated with the bacterium Streptococcus faecalis. Then the inoculated gels were extruded through a 20-gauge hypodermic needle into pairs of calorimetric cells. Before inserting the cells into the Calvert calorimeter, one member of each pair was tapped to disturb the gel within it. It was found that bacterial heat production was greater in the disturbed gels than in the undisturbed ones.

In a third experiment, Na- or Na/Al-clay sols and gels were mixed with nutrient medium, inoculated and, extruded into pairs of calorimetric cells, as before. This time, neither cell was tapped to disturb its contents. But the concentration of clay in one was different from that in the other. It was found that there was a difference in heat production within the cells when one contained a sol and the other a gel. Other work has shown that a disturbance tends to transform a clay gel to a clay sol. Hence, the present experiments indicate that biological activity is different in a clay gel than in a clay sol.

¹ Journal Paper no. 3680, Purdue Univ. Agr. Exp. Sta. Contribution from the Dept. of Agronomy. This research was supported by the National Aeronautics and Space Administration.

² Formerly Post-Doctoral Research Associates and Professor of Soil Chemistry, respectively. The first-named author is at the Dept. of Biochemistry, Purdue Univ. The second-named author is at the Dept. of Soil Science, Univ. of Sydney, Sydney, Australia.

Received for publication April 29, 1969. Accepted for publication September 4, 1969.