Journal
OECOLOGIA
Volume 128, Issue 2, Pages 237-250Publisher
SPRINGER
DOI: 10.1007/s004420100656
Keywords
northern forests; global change; carbon sequestration; soil respiration; dissolved organic carbon; soil pCO(2)
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Rising atmospheric CO2 may stimulate future forest productivity, possibly increasing carbon storage in terrestrial ecosystems, but how tropospheric ozone will modify this response is unknown. Because of the importance of fine roots to the belowground C cycle, we monitored fine-root biomass and associated C fluxes in regenerating stands of trembling aspen, and mixed stands of trembling aspen and paper birch at FACTS-II, the Aspen FACE project in Rhinelander, Wisconsin. Free-air CO2 enrichment (FACE) was used to elevate concentrations of CO2 (average enrichment concentration 535 mul l(-1)) and O-3 (53 nl l(-1)) in developing forest stands in 1998 and 1999. Soil respiration, soil pCO(2), and dissolved organic carbon in soil solution (DOC) were monitored biweekly. Soil respiration was measured with a portable infrared gas analyzer. Soil pCO(2) and DOC samples were collected from soil gas wells and tension lysimeters, respectively. at depths of 15, 30, and 125 cm. Fine-root biomass averaged 263 g m(-2) in control plots and increased 96% under elevated CO2. The increased root biomass was accompanied by a 39% increase in soil respiration and a 27% increase in soil pCO(2). Both soil respiration and pCO(2) exhibited a strong seasonal signal, which was positively correlated with soil temperature. DOC concentrations in soil solution averaged similar to 12 mg l(-1) in surface horizons, declined with depth, and were little affected by the treatments. A simplified belowground C budget for the site indicated that native soil organic matter still dominated the system, and that soil respiration was by far the largest flux. Ozone decreased the above responses to elevated CO2, but effects were rarely statistically significant. We conclude that regenerating stands of northern hardwoods have the potential for substantially greater C input to soil due to greater fine-root production under elevated CO2 Greater fine-root biomass will be accompanied by greater soil C efflux as soil respiration, but leaching losses of C will probably be unaffected.
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