drivers of soil respiration of root and microbial ... - Unitus DSpace

2.2.4. Biochemical analyses
Microbial Biomass C
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Soil sampling was performed twice in the year 2006: in the middle of the growing season, in
June and in the end of the growing season, in October. For each sampling date 8 soil cores were
collected.
For MBC determination the Fumigation Extraction method (Vance et al., 1987) was used. In
brief, two portions of moist soil (20 g oven-dry soil) were weighed, the first one (non fumigated)
was immediately extracted with 80 ml of 0.5M K 2 SO 4 for 30 min by oscillating shaking at 200 rpm
and filtered with filter paper (Whatman n. 42); the second one was fumigated for 24h at 25 °C with
ethanol-free CHCl3 and then extracted as described above. Organic C in the fumigated and non
fumigated extracts was determined after oxidation with 0.4 N K 2 Cr 2 O 7 at 100°C for 30 min.
Microbial C was calculated as a difference between C content in fumigated and non fumigated
extracts divided by a conversion factor (KEC: 0.38).
2.2.5. Statistics
Each measurement plot of soil respiration was considered as experimental unit, the replicate
measurements were averaged for further analyses, so that soil CO2 efflux for each date represents
the average of all the plots. Standard error (SE) of mean was calculated to provide a measure of the
variance for aboveground and belowground biomass and soil respiration flux measurements.
Multiple linear regression analysis was used to evaluate the contribution of GPP of various times
after the measurements to soil CO2 efflux from soil. Nonlinear regression analyses were performed
to estimate the effect of temperature and soil water content on soil respiration of different origin.
The significant of all the regression coefficients were tested using STATISTICA (Stat Soft).