|Rogers Jr, Hugo|
|Van Santen, Edzard|
|Prior, Stephen - Steve|
Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2001
Publication Date: 10/1/2001
Citation: Pritchard, S.G., Rogers, H.H., Davis, M.A.,Van Santen, E., Prior, S.A., and Schlesinger, W.H. 2001. The influence of elevated CO2 on fine root dynamics in an intact temperate forest. Global Change Biology 7:829-837. Interpretive Summary: Changes in patterns of root birth and death caused by rising atmospheric CO2 may increase storage of carbon in soil and could also impact ecosystem function. We quantified rooting in soil of a loblolly pine plantation exposed to elevated CO2 for one year. Exposure to elevated CO2 increased the total amounts of roots in soil, especially in the shallow soil underneath fallen leaves. This suggests that forest may play a role in capturing some of the extra carbon dioxide that is being emitted into the atmosphere. Furthermore, these results suggest that nutrient cycling may change in a high CO2 world.
Technical Abstract: Root dynamics are important for plant, ecosystem, and global carbon cycling. Changes in root dynamics caused by rising atmospheric CO2 can potentially alleviate further CO2 increases and affect forest function. We used FACE (Free-Air CO2 enrichment) to expose 13-year-old loblolly pine (Pinus taeda) forest plots (30 m diameter) to elevated (ambient +200 ppm) atmospheric CO2. Identical fully instrumented plots were implemented as controls (ambient air). We quantified root dynamics from October, 1998 to October, 1999 using minirhizotrons. Standing root crop (length and number) per minirhizotron was stimulated by high CO2 at the shallowest (0-7.7 cm) and intermediate (15.1-23.5 cm) soil depths generally resulting in greater total root length (+16%) and more roots (+24%) per tube. There was a significant CO2-by-depth interaction for live root diameters; at the shallowest depth, diameters under high CO2 were 35% greater than those under ambient conditions. Although not statistically significant, annual root production and mortality were 26 and 46% greater in elevated compared to ambient CO2. Mortality decreased with increasing depth and the slope of mortality with depth differed between elevated and ambient CO2. A trend indicating an increase in total annual root net primary productivity was observed under high CO2 (+30%). Relative root turnover (root flux/live root pool) was unchanged by elevated CO2. Results suggest increases in ecosystem-level root productivity in CO2 enriched environments. Such increases may represent a compensatory mechanism whereby mature forest trees can acquire nutrients to keep pace with enhanced photosynthesis in a high CO2 world.