Soil carbon dioxide partial pressure and dissolved inorganic carbonate chemistry under elevated carbon dioxide and ozone

Document Type

Article

Publication Date

1-2005

Department

College of Forest Resources and Environmental Science

Abstract

Global emissions of atmospheric CO2 and tropospheric O 3 are rising and expected to impact large areas of the Earth's forests. While CO2 stimulates net primary production, O3 reduces photosynthesis, altering plant C allocation and reducing ecosystem C storage. The effects of multiple air pollutants can alter below-ground C allocation, leading to changes in the partial pressure of CO2 (pCO2) in the soil, chemistry of dissolved inorganic carbonate (DIC) and the rate of mineral weathering. As this system represents a linkage between the long- and short-term C cycles and sequestration of atmospheric CO 2, changes in atmospheric chemistry that affect net primary production may alter the fate of C in these ecosystems. To date, little is known about the combined effects of elevated CO2 and O3 on the inorganic C cycle in forest systems. Free air CO2 and O3 enrichment (FACE) technology was used at the Aspen FACE project in Rhinelander, Wisconsin to understand how elevated atmospheric CO2 and O 3 interact to alter pCO2 and DIC concentrations in the soil. Ambient and elevated CO2 levels were 360 ± 16 and 542 ± 81 μl l-1, respectively; ambient and elevated O 3 levels were 33 ± 14 and 49 ± 24 nl l-1, respectively. Measured concentrations of soil CO2 and calculated concentrations of DIC increased over the growing season by 14 and 22%, respectively, under elevated atmospheric CO2 and were unaffected by elevated tropospheric O3. The increased concentration of DIC altered inorganic carbonate chemistry by increasing system total alkalinity by 210%, likely due to enhanced chemical weathering. The study also demonstrated the close coupling between the seasonal δ13C of soil pCO 2 and DIC, as a mixing model showed that new atmospheric CO 2 accounted for approximately 90% of the C leaving the system as DIC. This study illustrates the potential of using stable isotopic techniques and FACE technology to examine long- and short-term ecosystem C sequestration.

Publication Title

Oecologia

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