Résumé
1. As soils store more carbon (C) than the Earth’s atmosphere and
terrestrial biomass together, the balance between soil C uptake in the
form of soil organic matter and release as CO2 upon its decomposition is a
critical determinant in the global C cycle regulating our planet’s
climate. Although plant litter is the predominant source of C fueling both
soil C build-up and losses, the issue of how litter chemistry influences
this balance remains unresolved. 2. As a contribution to solving that
issue, we traced the fate of C during near-complete decomposition of
13C-labelled leaf and root litters from 12 plant species in a
coarse-textured soil. We separated the soil organic carbon (SOC) into
mineral-associated organic matter (MAOM) and particulate organic matter
(POM) pools, and investigated how 14 litter chemical traits affected novel
SOC formation and native SOC mineralization (i.e., the priming effect) in
these soil fractions. 3. We observed an overall net increase in SOC due to
the addition of litter, which was stronger for root than for leaf litters.
The presumed stable MAOM-C pool underwent both substantial stabilization
and mineralization, whereas the presumably less stable POM-C pool showed
substantial stabilization and reduced mineralization. Overall, the initial
increase in soil C mineralization was fully counterbalanced by a later
decrease in native soil C mineralization. POM-C formation as well as
MAOM-C formation and mineralization were positively related to the initial
litter lignin concentration and negatively to that of the nitrogen
leachates, whereas the opposite was observed for POM-C mineralization. 4.
Synthesis. Our results highlight the importance of litter chemical traits
for SOC formation, and stabilization, destabilization, and mineralization.
In our coarse-textured soil, the amount of MAOM-C did not change despite
large C fluxes through this pool. The litter chemical traits that drove
these processes differed from those frequently reported for fine-textured
soils far from mineral-associated C saturation. To account for these
discrepancies, we propose an integrative perspective in which litter
quality and soil texture interactively control soil C fluxes by modulating
several SOC stabilization and destabilization mechanisms. Irrespective,
our results open new critical perspectives for managing soil C pools
globally.