SIMULATED DEW FORMATION AND MICROBIAL GROWTH IN SOIL OF A SEMIARID REGION OF WESTERN CANADA

Abstract

To simulate the effect of dew formation on microbial growth in semiarid soils, air-dry loam was exposed to moisture condensation by incubating soil in a sine wave temperature incubator in which the diurnal temperature was 27.5 and 4 C and the relative humidity was 45% at 27.5 C. In an open system, condensation increased the soil moisture from about 1.4 to 4% (by weight) which is equivalent to a moisture suction of −1,930 and −200 bars, respectively. Even at such high suctions, condensation caused marked increases in bacteria and actinomycetes as assessed by plate and direct counts. A pure culture of Arthrobacter oxidans, a typical nonsporeforming soil bacterium, responded in a manner similar to the natural bacterial flora. Neither temperature per se, spore germination, nor contamination by airborne microorganisms was responsible for these increases. It was hypothesized that at such high suctions, moisture distribution in the soil must be heterogenous in order to permit bacterial growth.