ABSTRACT

FIGURE 3 Interacting effects of temperature and water potential on selection of microbial communities colonizing hair on a soil surface. Community 1 is dominated by Penicillium chrysogenum and P. frequentans; community 2 is predominantly P. citrinum and Asperfillus versicolor; community 3 is predominantly A. flavus, A. niger, and A. terreus. (From Griffin and Luard, 1979.)

It has been known for decades that wetting and drying cycles in soil have major influences on the turnover of carbon and other soil nutrients (Stevenson, 1956; Birch, 1958, 1959; Kieft et aI., 1987b; Cortez, 1989), with rates of organic matter degradation greater overall when a soil is alternately wetted and dried than if it is kept constantly moist. Desiccationinduced death of soil microbes releases carbon and other nutrients; rewetting of dried soils results in rapid growth and metabolism by the surviving microbes. Curiously, the rapid wetting of soil may be at least as stressful to microbes as the gradual drying, thereby contributing to the microbial death and recycling of immobilized cell material that occur as a result of wetting and drying cycles (Kieft et aI., 1987b).