K. Guillaume et al., Does the timing of litter inputs determine natural abundance of C-13 in soil organic matter? Insights from an African tiger bush ecosystem, OECOLOGIA, 127(2), 2001, pp. 295-304
We investigated total primary production and natural abundance of C-13 in s
oil and plants in the landscape of tiger bush, Niger. Tiger bush is viewed
as a natural cyclic succession of several types of vegetation (grasses, liv
ing trees and senescent vegetation) occurring over very small areas, on soi
ls with similar chemical and physical characteristics. Under the pioneer fr
ont, production was 130 g m(-2) year(-1) of which 23% came from C-4 plants;
under the thicket of mature trees,grass production was 190 g m(-2) year(-1
) (all C-3 grasses) and under senescent vegetation, 40 g m(-2) year(-1) of
which 1.5% came from C-4 plants. Total above- and belowground primary produ
ction was estimated to be 890-4880 g m(-2) year(-1) of which 0.4-0.5% was c
ontributed by C-4 plants. From 29 to 45% of the soil organic carbon origina
ted from C-4 plants even though the contribution of C-4 grasses to total pr
imary production did not exceed 0.5%. We suggest that the order in which th
e different sources of organic matter entered the soil could lead to the ov
erlabelling of soil organic matter with a C-4 print. Because all C-4 plants
are grasses located in the pioneer front of tiger bush bands, their C-4 or
ganic matter enters the soil first and fixes onto clays. The C-3 organic ma
tter 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 activ
ity and quickly decomposes. We postulate that the repetition of this patter
n over many decades (incorporation of a pure C-4 material to soil, followed
by the incorporation of a C-3-dominated material), leads to the overaccumu
lation of C-4 compounds on the most protective sites.