Geostatistical analysis of the distribution of NH4+ and NO2--oxidizing bacteria and serotypes at the millimeter scale along a soil transect

Soil is known to be heterogeneous for different activities at several spati al scales. Most studies have focused on macro- and meso-scales but micro-sc ales are rarely addressed. Hence, the spatial structure of NH4+- and NO2--o xidizers and of various serotypes of the latter was studied along two trans ects of approximately 10 cm, with two micro-samples taken from each millime ter. The presence of NH4- and NO2-- oxidizers in a micro-sample was detecte d using colorimetric tests for the presence or absence of NO2- in cultures of the micro-samples. Geostatistics was used to determine the range of spat ial influence of the bacterial types. For both types, semi-variograms indic ated a nonrandom spatial pattern. The spatial dependence ranged from 2 to 4 mm for NO2- and NH4+-oxidizers respectively, and the two bacterial types w ere not independently spatially located. Among the six serotypes of NO2--ox idizers, only one exhibited a spatial dependence. The existence of a spatia l structure at the millimeter scale suggests that micro-scale sampling shou ld be employed for soil studies. Therby, data on bacterial populations and activities can be referred to a spatial scale which is meaningful to these organisms. (C) 2000 Federation of European Microbiological Societies. Publi shed by Elsevier Science B.V. All rights reserved.