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Chemistry and long-term decomposition of roots from Douglas-fir grown at elevated atmospheric CO2 and warming conditions
Citation:
Chen, H., P. T. RYGIEWICZ, M. G. JOHNSON, M. E. Harmon, AND H. Tian. Chemistry and long-term decomposition of roots from Douglas-fir grown at elevated atmospheric CO2 and warming conditions. Presented at 4th USDA Greenhouse Gas Conference, Baltimore, MD, February 05 - 08, 2007.
Impact/Purpose:
Elevated atmospheric CO2 and warming may affect litter quality of plants and its subsequent decomposition in forested ecosystems.
Description:
Elevated atmospheric CO2 and warming may affect litter quality of plants and its subsequent decomposition in forested ecosystems. Little data are available to test this potential feedback on root tissues. In this study, we used the fine (diameter ≤ 2 mm) and small (2-10 mm) roots of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings grown for 4 years under ambient or elevated (+ 180 ppm) CO2, and under ambient or elevated (+3.5 0C) temperature in outdoor, sun-lit, terracosms for initial substrate quality analysis and subsequent field decomposition study. Four–years of exposure to elevated CO2 significantly increased water-soluble extractives (WSE) concentration of roots in addition to its significant effects on nonpolar extractives (NPE) concentration of roots, although elevated temperature virtually had no effect on the concentrations of N, cellulose, and lignin of root material. Elevated temperature treatment significantly affected WSE% and lignin% of fine roots. No significant interactive effects between CO2 and temperature treatments on substrate quality of roots except for WSE% of fine roots were observed. Field short-term root decomposition (≤ 9 months) indicated that the roots, with lowest WSE% from the control, showed the slowest decomposition than the roots from other treatments. However, the long-term root decomposition (9 to 36 months) was mainly influenced by incubation sites instead of the source of the roots. Our results suggest that a positive feedback of elevated CO2 and warming on root quality and subsequent decomposition exist in short-term period and the negative feedback of elevated CO2 changes is probably not important. The implications of this study for belowground carbon sequestration in coniferous forests at the Pacific Northwest were discussed.