The effect of experimental ecosystem warming on CO2 fluxes in a montane meadow
Climatic change is predicted to alter rates of soil respiration and assimilation of carbon by plants. Net loss of carbon from ecosystems would form a positive feedback enhancing anthropogenic global warming. We tested the effect of increased heat input, one of the most certain impacts of global warming, on net ecosystem carbon exchange in a Rocky Mountain montane meadow. Overhead heaters were used to increase the radiative heat flux into plots spanning a moisture and vegetation gradient. We measured net whole-ecosystem CO2 fluxes using a closed-path chamber system, relatively nondisturbing bases, and a simple model to compensate for both slow chamber leaks and the CO2 concentration-dependence of photosynthetic uptake, in 1993 and 1994. In 1994, we also measured soil respiration separately. The heating treatment altered the timing and magnitude of net carbon fluxes into the dry zone of the plots in 1993 (reducing uptake by 100 g carbon m2), but had an undetectable effect on carbon fluxes into the moist zone. During a strong drought year (1994), heating altered the timing, but did not significantly alter the cumulative magnitude, of net carbon uptake in the dry zone. Soil respiration measurements showed that when differences were detected in dry zone carbon fluxes, they were caused by changes in carbon input from photosynthesis, not by temperature-driven changes in carbon output from soil respiration. When differences were detected in dry-zone carbon fluxes, they were caused by changes in carbon input from photosynthesis, not by a temperature-driven changes in carbon output from soil respiration. Regression analysis suggested that the reduction in carbon inputs from plants was due to a combination of two soil moisture effects: a direct physiological response to decreased soil moisture, and a shift in plant community composition from high-productivity species to low-productivity species that are more drought tolerant. These results partially support predictions that warming may cause net carbon losses from some terrestrial ecosystems. They also suggest, however, that changes in soil moisture caused by global warming may be as important in driving ecosystem response as the direct effects of increased soil temperature.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director. Office of Science. Office of Basic Energy Sciences (US)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 841890
- Report Number(s):
- LBNL-43995; GCBIFE; R&D Project: 468107; TRN: US200515%%767
- Journal Information:
- Global Change Biology, Vol. 5, Issue 2; Other Information: Journal Publication Date: February 1999; PBD: 1 Jul 1997; ISSN 1354-1013
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
CARBON
CLIMATIC CHANGE
DROUGHTS
ECOSYSTEMS
FEEDBACK
GREENHOUSE EFFECT
HEAT FLUX
HEATERS
HEATING
MOISTURE
PHOTOSYNTHESIS
PLANTS
REGRESSION ANALYSIS
RESPIRATION
ROCKY MOUNTAINS
SOILS
TERRESTRIAL ECOSYSTEMS
CARBON FLUX CLIMATE CH CO2 FEEDBACK GREENHOUSE GAS MONTANE MEADOW SOIL RESPIRATION