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

The estimate of root and microbial respiration is subjected to additional errors, as the fluxes
are not estimated directly but are calculated from the other measurements, each subjected to its own
errors. We suggest establishing a large amount of partitioning plots to minimize the errors in
calculation of soil respiration components.
6.4.2. Combined SIR
Substrate induced respiration (SIR) is based on the response of microbial respiration to the
addition of glucose and the absence of response for root respiration (Panikov et al., 1991).
Combination of methods of substrate induced respiration and component integration into one
allowed moving the experiment from the laboratory to the field. The difference in the response and
comparison of CO2 efflux from soil with and without roots before and after glucose addition, in the
concentration much lower than the concentrations of the soluble carbohydrates in the root tissue,
allow calculating root and microbial respiration components. After the introduction of glucose the
respiration of microorganisms that was limited in the soil with C substrates increases several times
while the respiration of the living roots remains the same. In confront with the other methods used
in this study, combined SIR allows more exact separation of actual root respiration, from all the
other respiration sources by accounting a rhizomicrobial component as a part of microbial
respiration.
The applied glucose concentration (3mg/g of soil) is much lower than the concentration of
soluble carbohydrates in the roots observed for meadow grasses, which ranges from 5 to 50 mg/g of
root depending on the plant species and the growing period (Naumov, 1988), so the uptake of
glucose by roots couldn’ t have a significant effect on the respiration of the living roots.
Microbial respiration in the experiment was influenced significantly by the glucose
introduction. However, Larionova et al. (2006) showed that the coefficient of the respiration
increase (k) differs, depending on the source of microbial respiration: microbial decomposition of
dead roots, falloff, detritus or soil organic matter. The coefficient of decomposition of plant residues
(detritus, dead roots, litter) was as rule lower than the k in the soil. Experiments on roots showed
that the k increases two times already on the second day after the root destruction; however it
remains stable on different stages of decomposition (Larionova et al., 2006). This is the one of the
complications of the combined SIR technique: to determine exactly the k in the soil with the plant
residuals it is necessary to remove only the living root from the soil monolith. We have tried to
leave the litter and coarse dead plant residues in the soil sample used for k determination, however,
it was not possible to separate all dead and live root visually. This implies a certain underestimation
of the coefficient and further overestimation of microbial respiration. An alternative for future
studies could be the determination of the respiration response prior and after the glucose
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