Response of terrestrial CH4 uptake to interactive changes in precipitation and temperature along a climatic gradient

We determined the response of terrestrial methane (CH₄) uptake to 4 years of full-factorial manipulations of precipitation and temperature in four ecosystems along a 50 km warm and dry to cold and wet climatic gradient (desert grassland, pinyon-juniper woodland, ponderosa pine forest, and mixed conifer forest). Our goals were to determine whether ecosystem-specific, intraannual, and interactive responses to altered precipitation and warming are quantitatively important. Passive collectors and interceptors increased (+50% per event) and reduced (−30% per event) the quantity of precipitation delivered to experimental plant–soil mesocosms, and downward transfer along the elevation gradient warmed mesocosms by 1.8°C on average. Methane uptake in the colder and wetter ecosystems along the gradient decreased with increasing precipitation, especially during the wet season. The warmer and drier ecosystems, however, responded more strongly to warming, exhibiting less CH₄ uptake with increasing temperature. We found no interaction between altered precipitation and warming in any ecosystem. Soil CH₄ consumption in the laboratory was a strong predictor of ecosystem differences in field CH₄ consumption, but was a poor predictor of the effects of climatic change observed in the field. Based on our results, future climate scenarios that are wet and warm will cause the largest reduction in terrestrial CH₄ uptake across ecosystem types.