Litter decomposition in peatlands is promoted by mixed plants

Fabien Leroy (1, 2) , Sébastien Gogo (1, 2) , Alexandre Buttler (3) , Luca Bragazza (3) , Fatima Laggoun-Défarge (1, 2)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 Biogéosystèmes Continentaux - UMR7327
3 LCE - Laboratoire Chrono-environnement (UMR 6249)

Purpose: The carbon sink function of peatlands is primarily driven by a higher production than decomposition of the litter Sphagnum mosses. The observed increase of vascular plants in peatlands could alter the decomposition rate and the carbon (C) cycle through a litter mixing effect, which is still poorly studied. Here, we examine the litter mixing effect of a peat moss (Sphagnum fallax) and two vascular plants (Pinus uncinata and Eriophorum vaginatum) in the field and laboratory-based experiment. Materials and methods: During the laboratory incubation, mass loss, CO2 production, and dissolved organic carbon concentration were periodically monitored during 51 days. The collected data were then processed in a C dynamics model. The calculated enzymatic activity was correlated to the measured β-glucosidase activity in the litter. In the field experiment, mass loss and CO2 production from litter bags were annually measured for 3 years. Results and discussion: Both laboratory and field experiments clearly show that the litter mixture, i.e., Sphagnum-Pinus-Eriophorum, had a synergistic effect on decomposition by enhancing the mass loss. Such enhanced mass loss increased the water extractable C and CO2 production in the litter mixture during the laboratory experiment. The synergistic effect was mainly controlled by the Sphagnum-Eriophorum mixture that significantly enhanced both mass loss and CO2 production. Although the β-glucosidase activity is often considered as a major driver of decomposition, mixing the litters did not cause any increase of the activity of this exo-enzyme in the laboratory experiment suggesting that other enzymes can play an important role in the observed effect. Conclusions: Mixing litters of graminoid and Sphagnum species led to a synergistic effect on litter decomposition. In a context of vegetation dynamics in response to environmental change, such a mixing effect could alter the C dynamics at a larger scale. Identifying the key mechanisms responsible for the synergistic effect on litter decomposition, with a specific focus on the enzymatic activities, is crucial to better predict the capacity of peatlands to act as C sinks.

Mots clés: β-glucosidase; Dissolved organic carbon; Litter mixture effect; Carbon dynamics models; CO2 production; Catalysis

Domaines: Ecosystèmes; Interfaces continentales, environnement; Sciences de l'environnement

Fabien Leroy, Sébastien Gogo, Alexandre Buttler, Luca Bragazza, Fatima Laggoun-Défarge. Litter decomposition in peatlands is promoted by mixed plants. Journal of Soils and Sediments, 2018, 18, pp.739-749. ⟨10.1007/s11368-017-1820-3⟩. ⟨insu-01598365⟩