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Belowground factors mediating changes in methane consumption in a forest soil under elevated CO 2
Author(s) -
McLain Jean E. T.,
Kepler Thomas B.,
Ahmann Dianne M.
Publication year - 2002
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2001gb001439
Subject(s) - soil water , methane , environmental chemistry , soil carbon , atmospheric methane , cycling , water content , carbon cycle , environmental science , chemistry , carbon fibers , carbon dioxide , moisture , soil science , ecosystem , ecology , geology , forestry , geotechnical engineering , organic chemistry , biology , geography , materials science , composite number , composite material
The sustained increase in atmospheric CO 2 concentration observed over the past century, and projected to continue into the next, is of great significance for atmospheric CH 4 . Effects of elevated CO 2 on microbial methane cycling are potentially mediated by its effects on plant physiology, which include enhancement of carbon assimilation, belowground carbon allocation, and water use efficiency. To determine the importance of such changes for methane cycling, belowground factors impacting soil CH 4 consumption were investigated at the Free Air Carbon Transfer and Storage (FACTS)‐I site in the Duke Forest, North Carolina, in which plots have been exposed to ambient (370 ppm) or elevated (ambient + 200 ppm) CO 2 since August 1996. CH 4 fluxes at the soil surface, porespace concentrations of CH 4 , O 2 , and CO 2 , soil moisture, soil temperature, and soil pH were simultaneously measured over 24 months. Porespace CH 4 concentrations were highest (1.98 ± 0.25 ppm) at the soil surface and decreased to 0.65 ± 0.22 ppm at 30 cm, indicating that methanotrophic activity was depleting CH 4 in the upper soil layers and creating a gradient to draw atmospheric CH 4 into the soil. This was confirmed by surface CH 4 flux measurements, which averaged −1.54 ± 0.65 μmol/m 2 /h. Under elevated CO 2 , porespace CH 4 was 25–30% higher in the upper 70 cm of soils; CH 4 fluxes from the atmosphere into soil were diminished by ∼25%; soil CO 2 increased by 10–70%; and volumetric soil moisture was greater by up to 40% during some seasons. Statistical modeling revealed that soil moisture strongly predicted variability in surface CH 4 fluxes and that soil CO 2 and soil moisture both predicted variability in soil CH 4 . Results also indicated that a portion of the net CH 4 sink inhibition in elevated CO 2 soils could be attributable to alterations in soil biological processes, suggesting that changes in the CH 4 ‐cycling microbial ecology had taken place.