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Titel Isotopic composition of soil CO2 to evaluate microbial availability of organic carbon
VerfasserIn J. Pausch, Y. Kuzyakov
Konferenz EGU General Assembly 2012
Medientyp Artikel
Sprache Englisch
Digitales Dokument PDF
Erschienen In: GRA - Volume 14 (2012)
Datensatznummer 250069028
 
Zusammenfassung
The production of CO2 in soil strongly depends on microbial availability of organic carbon (C). It is obvious, that C that entered the soil recently is more easily available for microorganisms in comparison to older C: However, only very few approaches allow for a quantitative estimation of microbial availability of C in relation to the time it is entering the soil. We hypothesized that δ13C values of CO2 and of soil organic matter (SOM) after a C3 to C4 vegetation change will enable us to calculate the relative availability of younger and older C sources for microorganisms. Soil CO2 was sampled over one vegetation period at depths of 10, 40-50 and 60-70 cm at three treatments: a C3 reference (wheat), a C4/fallow (fallow after one year of maize cropping), and a C4/C4 (two years of maize cropping). Based on the δ13C of CO2 purified from the admixture of atmospheric CO2 by the Miller/Tans model and on the δ13C values of SOM, the contributions of younger (C4) and older (C3) C sources to CO2 and SOM were assessed. Depending on soil depth and the presence of living roots, the contribution of C4-C to soil CO2 ranged from 20 to 60 %, but that of C4-C to SOM was less than 5 %. By comparing the contributions of C3-C and C4-C to CO2 and SOM, we found that the relative availability of organics recently introduced into the soil was about 10 times higher than the availability of C stabilized in soil for longer than one year. We concluded that simultaneous analysis of the δ13C values of both SOM and of CO2 allows not only for the quantification of the CO2 sources, but also for the estimation of the microbial availability of soil C pools of different age.