OOS 27-2 - Ozone at AspenFACE: Effects on plant productivity and ecosystem carbon storage

Wednesday, August 10, 2011: 1:50 PM
17A, Austin Convention Center
Alan F. Talhelm, Department of Forest Ecology and Biogeosciences, University of Idaho, Moscow, ID, Courtney E. Campany, Forest, Rangeland, and Fire Sciences, University of Idaho, Moscow, ID, Kurt S. Pregitzer, Natural Resources, University of Idaho, Moscow, ID, Donald R. Zak, School of Natural Resources & Environment, University of Michigan, Ann Arbor, MI and Mark E. Kubiske, Northern Research Station, USDA Forest Service, Rhinelander, WI
Background/Question/Methods

Concentrations of tropospheric ozone (O3) and atmospheric carbon dioxide (CO2) are both predicted to increase in coming decades. Although increases in CO2 are hypothesized to enhance forest productivity and soil carbon (C) storage, O3 is phyto-toxic to many species and genotypes and is thought to reduce soil C storage.  In order to examine the effects of these gases on forest productivity and soil C storage, here we present the results of a comprehensive forest harvest in three young northern temperate forest communities exposed to elevated O3 and/or elevated CO2 for 12 years.

Results/Conclusions

As factorial effects, total forest biomass was increased 64% by elevated CO2 (P = 0.008) and decreased 23% by elevated O3 (P = 0.077). For both CO2 and O3, these effects were larger aboveground (CO2: +76% and P = 0.007, O3: -27% and P = 0.058) than belowground (CO2: +33% and P = 0.022, O3: -9% and P = 0.342).  No significant interactions between CO2 and O3 or between these gases and community types were observed in our analysis of these forest biomass pools. Although the changes in aboveground biomass matched hypotheses for the effects of CO2 and O3, our results suggest that models cannot simply extrapolate the changes in aboveground biomass to belowground biomass pools. For soil C, we sampled the top 50 cm of soil in 10 cm increments. As factorial effects, CO2 and O3 reduced soil C storage in the top 50 cm by 7% and 5%, respectively, but these effects were not statistically significant (P > 0.35). However, elevated O3 significantly reduced soil C storage in the top 10 cm of soil (-11%, P = 0.042), while elevated CO2 significantly reduced soil C storage in the 10-20 cm increment (-18%, P = 0.034). For elevated O3, the observed changes in soil C pools are consistent with simple conceptual models which predict that reduced plant productivity will translate to lower soil C storage. However, changes in productivity under elevated CO2 do not appear to have the same effect. For elevated CO2, other research suggests that the increased acquisition of soil N to support greater forest productivity may be responsible for the lack of soil C storage.

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