N deposition and elevated CO_2 on methane emissions: differential responses of indirect effects through litter chemistry feedback compared to direct effects

VERONICA ANDREA PANCOTTO; VAN BODEGOM, PETER; VAN HAL, JURGEN; VAN LOGTESTIJN, RICHARD; BLOKKER, PETER; TOET, SYLVIA; AERTS, RIEN

JOURNAL OF GEOPHYSICAL RESEARCH

AMER GEOPHYSICAL UNION

Año: 2009

0148-0227

Increases in atmospheric CO2 concentration and N deposition are expected to affect methane (CH4) production in soils and emission to the atmosphere, directly through increased plant litter production and indirectly through changes in substrate quality. We examined how CH4 emission responded to changes in litter quality under increased N and CO2, beyond differences in CH4 resulting from changes in litter production. We used senesced leaves from 13C-labeled plants of Molinia caerulea grown at elevated and ambient CO2 and N-fertilization to carry out two experiments: a laboratory litter incubation and a pot experiment. N-fertilization increased N and decreased C concentrations in litter whereas elevated CO2 decreased litter quality as reflected in litter C and N concentrations and in the composition of lignin and saturated fatty acids within the litter. In contrast to our expectations, CH4 production in the laboratory incubation decreased when using litter from N-fertilized plants as substrate, whereas litter from elevated CO2 had no effect, compared to the control without N or CO2. Due to high within-treatment variability in CH4 emissions, none of the treatment effects were reflected in the pot experiment. C-mineralization rates were not affected by any of the treatments. Thus, the experiments showed that indirect effects of N availability through litter quality changes (described here for the first time) contrast direct effects of N fertilization on CH4 production. The complex interaction of direct effects with indirect effects of increased N on litter quality may potentially result in a net decrease in CH4 emissions from wetlands in the long-term.