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

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All diurnal measurements of root and microbial-derived respiration performed in various
months of 2007 were plotted together against changes in soil temperature (Fig. 7). Microbial
respiration clearly increases with increase in the soil temperature: starting from November,
September to June. Out of the general trend are the days of July and August with the low microbial
activity under the high values of temperature, this period is however characterized by a low SWC.
Root-derived respiration didn’ t show such a clear dependence on seasonal changes in temperature
and SWC, with relatively high values also during the driest days of July and August. However, the
maximum efflux was observed as for microbial respiration in June.
2.3.2. Seasonal variation of soil respiration of different origin
Although we have found that the diurnal variation in soil respiration was not strongly
correlated with soil temperature, increasing the time scale to seasonal level changes a picture. We
assessed sensitivity of soil CO2 efflux of different origin by fitting exponential function to the data
from individual treatments.
Rx=aexp bTs
where Rx is soil respiration from the source, Ts is a soil temperature ( o C) and a is the intercept of
respiration when temperature is 0 o C (basal respiration rate) and b represents temperature sensitivity
of soil CO2 efflux. The b values were used to calculate a respiration quotient (Q10), which describes
change in fluxes over a 10 o C in soil temperature. As the winter measurements were not possible in
2006-2007, we assumed respiration rate, measured in 2008 under 0 o C soil temperature as a basal
respiration and applied this value to all the other years.
Q10=exp 10/b
During the period with SWC>20% total and microbial-derived soil respiration were quite
well correlated with seasonal changes in soil temperature at 5 cm depth (Fig. 8), increasing
exponentially with increasing of Ts. The exponential relationship in the absence of the water stress
accounted for approximately 82% of flux variability for Rs; 80% for Rh and 60% for Ra (Fig. 8,
Table 1). The overall Q10 values for the years 2006-2007-2008 are represented in Table 1. Including
in the analyses periods with lower SWC resulted in the significant decrease of the Q10’ s and loss of
the correlation with temperature.
Root-derived respiration was less sensitive to changes in soil temperature, the correlation
was not strong and under temperatures higher than 15 o C and favourable soil humidity (SWC>20%)
the shape of the regression curve was reaching a plateau, without a characteristic exponential
increase, observed for Rh and Rs (Fig. 8).