Changes in community composition of terrestrial gymnamoebae were analyzed in laboratory microcosms established with thoroughly mixed soil from a northeastern U. S. A. site taken during the onset of winter 2002-2003, when the soil temperature was 5degreesC. The temperature of one of the microcosms, maintained in constant temperature chambers, was increased from 5degreesC to 25degreesC at 5 intervals of two weeks each for a period of 10 weeks. Another microcosm was maintained for the 10 weeks at 5degreesC to serve as a control for the lapse of time and to assess the effects of prolonged treatment at 5degreesC simulating winter conditions. Small subsamples (0.01 g) of the microcosm soil were taken using a modified 1 cm(3) syringe with the tip cut off to make a cylindrical corer. Based on a culture enrichment technique, the morphospecies richness, heterogeneity of distribution within the samples (morphospecies uniqueness) and community patchiness were determined by microscopic observation of the morphospecies that grew out in the cultures of each 0.01 g sample. The data showed that with increasing temperatures up to 20degreesC, the richness and patchiness of morphospecies increased while the uniqueness did not change within statistical significance. Two-weeks treatment at 25degreesC simulating summer conditions, produced a marked decline in richness of morphospecies and a substantial increase in the percent that were encysted suggesting less favorable conditions for growth, perhaps resulting from thermal stress and depletion of nutrients and other resources. Overall, the evidence from this study indicated that release from cold stress during the transition from winter to spring produced increased richness of morphospecies and greater patchiness of the gymnamoeba communities. This "bloom," however, was followed by a period of less productivity and retrenchment with increasing numbers of encysted gymnamoebae, as the temperature was increased above 20degreesC.
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