Climosequence approach to monitor the effects of exposure and altitude on physical, chemical and microbial properties of alpine soils.

To monitor the microclimate effects on soil microbial properties, it is of paramount importance to link two of the principal indicators of soil quality and functionality, i.e. microbial biomass and soil enzymatic activities. Up to now little is known about the aforementioned link in Alpine areas. This study focuses on a climosequence approach to evaluate the impact of both altitude (from 1000 m to 2400 m a.s.l.) and exposure (north and south facing slopes) on soil properties in ten alpine sites in Trentino (Val di Rabbi, Val di Sole, Italy). A total of 450 samples were collected in August 2012. Three plots (5x5 m) located at 50 m from each other were set-up in each site and five sub-samples were randomly collected at three soil depths (0-5 cm, 5-10 cm, 10-15 cm). We performed a multiple-enzymatic assay to detect eight hydrolases that are representative of the principal biogeochemical cycles. Soil microbial biomass was comparatively assessed by using two different DNA extraction methods followed by Picogreen based dsDNA quantifications: extraction-purification of soil DNA with a commercial kit (MP, Biomedical) to obtain a pure DNA for fingerprinting analysis; direct extraction-quantification of crude soil DNA. Soil microbial biomass, assessed by the second dsDNA approach, decreased significantly with soil depth. Furthermore, this method was also capable to reveal an increasing trend in south exposure respect to north exposure, representing a thermal signal. Thus, this method provided a reliable estimator of soil microbial biomass, without an underestimation derived from the unavoidable DNA loss (-34%) obtained during DNA purification required for downstream analysis. In line, enzymatic activities decreased significantly with soil depth, whereas altitude and exposure effects were often masked by the site effect. Moreover, our results suggested a significant and positive correlation between microbial biomass and all enzyme activities studied in the Alpine soils.