Antibiotic resistance profiles of soil bacterial communities over a land degradation gradient

This study profiled soils over a land degradation gradient to obtain formulae as integrative measures for describing the gradient as a result of deforestation in Thailand. We applied antibiotic resistance most-probable-number profiling to the soil bacterial communities, and then described the gradient. Soil samples were collected on the gradient represented by dry evergreen forest (the original vegetation), dry deciduous forest (moderately disturbed) and bare ground (the most degraded) in February (dry season), March (shortly after temporal precipitation) and June (rainy season) 2001. In the period of this study, the degradation was consistently shown as soil conditions like sandy texture, high bulk density, lower pH, high exchangeable acidity, poor mineral and organic nutrients and dryness. Soil fertility index and soil evaluation factor, as the integrative measures of the intensity of land degradation, were described by scores on the first or the second principal component derived from the soil bacterial community profiles for each sampling time (R > 0.457, p < 0.043) and by scores on the third and fourth principal components for the overall data set (R > 0.501, p < 0.001), suggesting great dry to moist seasonal effects. Further, the changes had significant relationships with gradients of soil moisture content, acidity and/or soil nitrogen content. The data sets on the soil bacterial community profiles had more complicated data structures than the physicochemical data sets, suggesting effects of the physicochemical changes on the soil bacterial community. The differences between the bacterial and the physicochemical aspects suggest that it is advantageous to observe multiple aspects of soil quality when describing a soil-related gradient of interest.