| Plant and Soil 229 (2):259-270, February 2001. © Kluwer Academic Publishers Time-dependent responses of soil CO2 efflux components to elevated atmospheric [CO2] and temperature in experimental forest mesocosmsGuanghui LinLamont-Doherty Earth Observatory and Biosphere 2 Center of Columbia University, PO Box 689, Oracle, Arizona 85623, USA Corresponding author Paul T. Rygiewicz U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Corvallis, Oregon 97333, USA. James R. Ehleringer Stable Isotope Ratio Facility for Environmental Research, Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA. Mark G. Johnson U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Corvallis, Oregon 97333, USA. David T. Tingey U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Corvallis, Oregon 97333, USA. Abstract We previously used dual stable isotope techniques to partition soil CO_2 efflux into three source components (rhizosphere respiration, litter decomposition, and soil organic matter (SOM) oxidation) using experimental chambers planted with Douglas-fir [ Pseudotsuga menziesii (Mirb.) Franco] seedlings. The components responded differently to elevated CO_2 (ambient + 200 mmol mol^−1) and elevated temperature (ambient + 4 °C) treatments during the first year. Rhizosphere respiration increased most under elevated CO_2, and SOM oxidation increased most under elevated temperature. However, many studies show that plants and soil processes can respond to altered climates in a transient way. Herein, we extend our analysis to 2 years to evaluate the stability of the responses of the source components. Total soil CO_2 efflux increased significantly under elevated CO_2 and elevated temperature in both years (1994 and 1995), but the enhancement was much less in 1995. Rhizosphere respiration increased less under elevated temperature in 1995 compared with 1994. Litter decomposition also tended to increase comparatively less in 1995 under elevated CO_2, but was unresponsive to elevated temperature between years. In contrast, SOM oxidation was similar under elevated CO_2 in the 2 years. Less SOM oxidation occurred under elevated temperature in 1995 compared with 1994. Our results indicate that temporal variations can occur in CO_2 production by the sources. The variations likely involve responses to antecedent physical disruption of the soil and physiological processes. Keywords climate change, CO_2 enrichment, Douglas-fir forests, elevated atmospheric temperature, soil respiration, stable isotopes ISSN 0032-079X |
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