title: Does the timing of litter inputs determine natural abundance of (13)C in soil organic matter? Insights from an African tiger bush ecosystem.
abstract: We investigated total primary production and natural abundance of (13)C in soil and plants in the landscape of tiger bush, Niger. Tiger bush is viewed as a natural cyclic succession of several types of vegetation (grasses, living trees and senescent vegetation) occurring over very small areas, on soils with similar chemical and physical characteristics. Under the pioneer front, production was 130 g m(-2) year(-1) of which 23% came from C4 plants; under the thicket of mature trees, grass production was 190 g m(-2) year(-1) (all C3 grasses) and under senescent vegetation, 40 g m(-2) year(-1) of which 1.5% came from C4 plants. Total above- and belowground primary production was estimated to be 890-4880 g m(-2) year(-1) of which 0.4-0.5% was contributed by C4 plants. From 29 to 45% of the soil organic carbon originated from C4 plants even though the contribution of C4 grasses to total primary production did not exceed 0.5%. We suggest that the order in which the different sources of organic matter entered the soil could lead to the overlabelling of soil organic matter with a C4 print. Because all C4 plants are grasses located in the pioneer front of tiger bush bands, their C4 organic matter enters the soil first and fixes onto clays. The C3 organic matter enters the soil several years later and is also fixed by the clays but in a lower proportion. Therefore it is less protected from microbial activity and quickly decomposes. We postulate that the repetition of this pattern over many decades (incorporation of a pure C4 material to soil, followed by the incorporation of a C3-dominated material), leads to the overaccumulation of C4 compounds on the most protective sites.
authors.affiliation: Ecole Normale Supérieure, Laboratoire d'Ecologie, UMR 7625, 46 rue d'Ulm, 75230, Paris Cedex 05, France.
authors.forename: K
authors.initials: K
authors.lastname: Guillaume
authors.affiliation: Ecole Normale Supérieure, Laboratoire d'Ecologie, UMR 7625, 46 rue d'Ulm, 75230, Paris Cedex 05, France.
authors.forename: M
authors.initials: M
authors.lastname: Huard
authors.affiliation: Ecole Normale Supérieure, Laboratoire d'Ecologie, UMR 7625, 46 rue d'Ulm, 75230, Paris Cedex 05, France.
authors.forename: J
authors.initials: J
authors.lastname: Gignoux
authors.affiliation: Laboratoire de Biogéochimie Isotopique, UMR 7618, Université Pierre et Marie Curie, case no 120, 4 place Jussieu, 75252, Paris Cedex 05, France.
authors.forename: A
authors.initials: A
authors.lastname: Mariotti
authors.affiliation: Ecole Normale Supérieure, Laboratoire d'Ecologie, UMR 7625, 46 rue d'Ulm, 75230, Paris Cedex 05, France.
authors.forename: L
authors.initials: L
authors.lastname: Abbadie