Reduction of the temperature sensitivity of minerotrophic fen methane emissions by simulated glacial atmospheric carbon dioxide starvation

Abstract

Variations to the global wetland CH 4 source strength in response to changes in orbital insolation patterns and atmospheric CO 2 concentration ([CO 2 ] a) are hypothesized to play an important role in determining glacial-interglacial variations in atmospheric CH 4 concentration ([CH 4 ] a). Here the interactive effects of temperature, a major controlling variable determining wetland CH 4 flux, and the low [CO 2 ] a of glacial intervals are investigated for the first time. We measured the temperature dependence of CH 4 emissions from replicated mesocosms (n = 8 per CO 2 treatment) collected from a minerotrophic fen and an ombrotrophic bog incubated in either ambient (c. 400 ppm) or glacial (c. 200 ppm) [CO 2 ] a located in the United Kingdom. CH 4 fluxes were measured at 5°C, 10°C, 15°C, 20°C, and 25°C and then in reverse order over a 20 day period under each [CO 2 ] a treatment. Results showed that the Q 10 temperature response of CH 4 emissions from the Carex/Juncus-dominated fen declined significantly by approximately 39% under glacial [CO 2 ] a (ambient [CO 2 ] a = 2.60, glacial [CO 2 ] a = 1.60; P < 0.01). By contrast, the response of CH 4 emissions from the Sphagnum-dominated bog remained unaltered (ambient [CO 2 ] a = 3.67, glacial [CO 2 ] a = 3.67; P > 0.05). This contrasting response may be linked to differences in plant species assemblage and the varying impact of CO 2 starvation on plant productivity and carbon availability in the rhizosphere. Furthermore, our results provide empirical evidence to support recent model-based indications that glacial-interglacial variations in [CH 4 ] a may be explained by changes in wetland CH 4 source strength in response to orbitally forced changes in climate and [CO 2 ] a. © 2013. American Geophysical Union. All Rights Reserved.