Abstract
Rising atmospheric [CO2] has the potential to alter soil carbon (C) cycling by increasing the content of recalcitrant constituents in plant litter, thereby decreasing rates of decomposition. Because fine root turnover constitutes a large fraction of annual NPP, changes in fine root decomposition are especially important. These responses will likely be affected by soil resource availability and the life history characteristics of the dominant tree species. We evaluated the effects of elevated atmospheric [CO2] and soil resource availability on the production and chemistry, mycorrhizal colonization, and decomposition of fine roots in an early- and late-successional tree species that are economically and ecologically important in north temperate forests. Open-top chambers were used to expose young trembling aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees to ambient (36Â Pa) and elevated (56Â Pa) atmospheric CO2. Soil resource availability was composed of two treatments that bracketed the range found in the Upper Lake States, USA. After 2.5Â years of growth, sugar maple had greater fine root standing crop due to relatively greater allocation to fine roots (30% of total root biomass) relative to aspen (7% total root biomass). Relative to the low soil resources treatment, aspen fine root biomass increased 76% with increased soil resource availability, but only under elevated [CO2]. Sugar maple fine root biomass increased 26% with increased soil resource availability (relative to the low soil resources treatment), and showed little response to elevated [CO2]. Concentrations of N and soluble phenolics, and C/N ratio in roots were similar for the two species, but aspen had slightly higher lignin and lower condensed tannins contents compared to sugar maple. As predicted by source-sink models of carbon allocation, pooled constituents (C/N ratio, soluble phenolics) increased in response to increased relative carbon availability (elevated [CO2]/low soil resource availability), however, biosynthetically distinct compounds (lignin, starch, condensed tannins) did not always respond as predicted. We found that mycorrhizal colonization of fine roots was not strongly affected by atmospheric [CO2] or soil resource availability, as indicated by root ergosterol contents. Overall, absolute changes in root chemical composition in response to increases in C and soil resource availability were small and had no effect on soil fungal biomass or specific rates of fine root decomposition. We conclude that root contributions to soil carbon cycling will mainly be influenced by fine root production and turnover responses to rising atmospheric [CO2], rather than changes in substrate chemistry.
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Acknowledgements
This research was supported by DOE Program of Ecosystem Research (PER) grant number DE-FG02-93ER6166, the USDA Forest Service Northern Global Change Program, and USDA NRI Competitive Grants Program No. 2001-35107-11262. Logistical support for this project was provided by The University of Michigan Biological Station and is gratefully acknowledged. Dr. Chris Vogel helped install and maintain the CO2 control hardware, and Paul Higgins managed the field site and final harvest with a high level of efficiency and professionalism. Finally, we thank the many students who helped with various aspects of the project over the years.
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Communicated by Jim Ehleringer
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King, J.S., Pregitzer, K.S., Zak, D.R. et al. Fine root chemistry and decomposition in model communities of north-temperate tree species show little response to elevated atmospheric CO2 and varying soil resource availability. Oecologia 146, 318–328 (2005). https://doi.org/10.1007/s00442-005-0191-4
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DOI: https://doi.org/10.1007/s00442-005-0191-4
Keywords
- Trembling aspen
- Sugar maple
- Carbon-based secondary compounds
- Soil C cycling