title: δ13C values of CO2from soil respiration on sites with crops of C3 and C4 type of photosynthesis.
abstract: Based on the differential discrimination between13CO2and12CO2during photosynthetic CO2fixation by C3 and C4 plants, the relative contribution of organic soil material of varying age can be checked by measuring the δ13C value of CO2evolved during soil respiration.The CO2from a soil cropped only with C3 plants for at least 7 years showed a δ13C value very close to that of C3 plant tissue. Correspondingly, a soil bearing the C4 plant maize for at least 6 years had a δ13C value for the respiratory CO2quite near to that of a typical C4 plant. A soil cropped with maize in the year of study only showed intermediate δ13C values, with a tendency towards C4. With soil standardised for cultivation and cropping, a quantification of the part that fresh organic matter and especially the last year plant residues play in soil respiration, can be achieved.
authors.affiliation: Institut für Botanik und Mikrobiologie der Technischen Universität, D-8000, München 2, Federal Republic of Germany.
authors.forename: Roswitha
authors.initials: R
authors.lastname: Schönwitz
authors.affiliation: Institut für Radiohydrometrie der Gesellschaft für Strahlen- und Umweltforschung mbH München, D-8042, Neuherberg, Federal Republic of Germany.
authors.forename: Willibald
authors.initials: W
authors.lastname: Stichler
authors.affiliation: Institut für Botanik und Mikrobiologie der Technischen Universität, D-8000, München 2, Federal Republic of Germany.
authors.forename: Hubert
authors.initials: H
authors.lastname: Ziegler