Fast mineralization of land-born C in inland waters: first experimental evidences of aquatic priming effect

In the context of global change, eroded soil carbon fate and its impact on aquatic ecosystems CO2 emissions are subject to intense debates. In particular, soil carbon mineralization could be enhanced by its interaction with autochthonous carbon, a process called priming effect, but experimental evidences of this process are scarce. We measured in a microcosm experiment simulating oligo-mesotrophic and eutrophic aquatic conditions how quickly soil organic matter (SOM) sampled in diverse ecosystems was mineralized as compared to mineralization within soil horizons. For both nutrient loads, C-13-glucose was added to half of the microcosms to simulate exudation of labile organic matter (LOM) by phytoplankton. Effects of LOM on soil mineralization were estimated using the difference in delta C-13 between the SOM and the glucose. After 45 days of incubation, the mean SOM mineralization was 63% greater in the aquatic context, the most important CO2 fluxes arising during the first days of incubation. Nutrients had no significant effect on SOM mineralization and glucose addition increased by 12% the mean SOM mineralization, evidencing the occurrence of a priming effect.