title: Fine-root mortality rates in a temperate forest: estimates using radiocarbon data and numerical modeling.
abstract: * We used an inadvertent whole-ecosystem 14C label at a temperate forest in Oak Ridge, Tennessee, USA to develop a model (Radix1.0) of fine-root dynamics. Radix simulates two live-root pools, two dead-root pools, non-normally distributed root mortality turnover times, a stored carbon (C) pool, and seasonal growth and respiration patterns. * We applied Radix to analyze measurements from two root size classes (< 0.5 and 0.5-2.0 mm diameter) and three soil-depth increments (O horizon, 0-15 cm and 30-60 cm). * Predicted live-root turnover times were < 1 yr and approximately 10 yr for short- and long-lived pools, respectively. Dead-root pools had decomposition turnover times of approximately 2 yr and approximately 10 yr. Realistic characterization of C flows through fine roots requires a model with two live fine-root populations, two dead fine-root pools, and root respiration. These are the first fine-root turnover time estimates that take into account respiration, storage, seasonal growth patterns, and non-normal turnover time distributions. * The presence of a root population with decadal turnover times implies a lower amount of belowground net primary production used to grow fine-root tissue than is currently predicted by models with a single annual turnover pool.
authors.affiliation: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Riley
authors.affiliation: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.|Department of Environmental Studies, University of California, Santa Cruz, CA, USA.|Department of Integrative Biology, University of California, Berkeley, CA, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Gaudinski
authors.affiliation: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.|Energy and Resources Group, University of California, Berkeley, CA, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Torn
authors.affiliation: Belowground Forest Research, Apartado 104-5655, Santa Elena de Monteverde, Puntarenas, Costa Rica.
authors.forename: J D
authors.initials: JD
authors.lastname: Joslin
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Hanson
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes; D019069:Cell Respiration; D017753:Ecosystem; D007553:Isotope Labeling / Q000379:methods; D008954:Models, Biological; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism; D012621:Seasons; D013714:Tennessee; D013997:Time Factors; D014197:Trees / Q000254:growth & development* / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D002244:Carbon
references.citation: Aber JD, Melillo JM, Nadlehoffer KJ, McClaugerty CA, Pastor J. 1985. Fine root turnover in forest ecosystems in relation to the quantity and form of nitrogen availability: a comparison of two methods. Oecologia 66: 317-321.
references.citation: Bidartondo MI, Ek H, Wallander H, Soderstrom B. 2001. Do nutrient additions alter carbon sink strength of ectomycorrhizal fungi? New Phytologist 151: 543-550.
references.citation: Bird JA, Torn MS. 2006. Fine roots vs. needles: a comparison of C-13 and N-15 dynamics in a ponderosa pine forest soil. Biogeochemistry 79: 361-382.
references.citation: Bowling DR, Tans PP, Monson RK. 2001. Partitioning net ecosystem carbon exchange with isotopic fluxes of CO2. Global Change Biology 7: 127-145.
references.citation: Burton AJ, Pregitzer KS. 2002. Measurement carbon dioxide concentration does not affect root respiration of nine tree species in the field. Tree Physiology 22: 67-72.
references.citation: Burton AJ, Pregitzer KS, Ruess RW, Hendrik RL, Allen MF. 2002. Root respiration in North American forests: effects of nitrogen concentration and temperature across biomes. Oecologia 131: 559-568.
references.citation: Caldwell MM, Camp LB. 1974. Belowground productivity of 2 cool desert communities. Oecologia 17: 123-130.
references.citation: Carbone MS, Czimczik CI, McDuffee KE, Trumbore SE. 2007. Allocation and residence time of photosynthetic products in a boreal forest using a low-level C-14 pulse-chase labeling technique. Global Change Biology 13: 466-477.
references.citation: Clark DA, Brown S, Kicklighter DW, Chambers JQ, Thomlinson JR, Ni J. 2001. Measuring net primary production in forests: concepts and field methods. Ecological Applications 11: 356-370.
references.citation: Curtis PS, Hanson PJ, Bolstad P, Barford C, Randolph JC, Schmid HP, Wilson KB. 2002. Biometric and eddy-covariance based estimates of annual carbon storage in five eastern North American deciduous forests. Agricultural and Forest Meteorology 113: 3-19.
references.citation: Czimczik CI, Trumbore SE. 2007. Short-term controls on the age of microbial carbon sources in boreal forest soils. Journal of Geophysical Research-Biogeosciences 112 (G3): G03001.
references.citation: Edwards NT, Johnson DW, McLaughlin SB, Harris WR, eds. 1989. Carbon dynamics and productivity. Analysis of biogeochemical cycling processes in Walker Branch Watershed. New York, NY, USA: Springer Verlag.
references.citation: Fahey TJ, Bledsoe CS, Day FP, Ruess R, Smucker AJM. 1999. Fine root production and demography. In: Robertson GP, Coleman DC, Sollins P, eds. Standard soil methods for long term ecological research. New York, NY, USA: Oxford University Press, 437-455.
references.citation: Gaudinski JB, Torn MS, Riley WJ, Swanston C, Trumbore SE, Joslin JD, Majdi H, Dawson TE, Hanson PJ. 2009. Use of stored carbon reserves in growth of temperate tree roots and leaf buds: analyses using radiocarbon measurements and modeling. Global Change Biology doi: DOI: 10.1111/j.1365-2486.2008.01736.x
references.citation: Gaudinski JB, Trumbore SE, Davidson EA, Cook AC, Markewitz D, Richter DD. 2001. The age of fine-root carbon in three forests of the eastern United States measured by radiocarbon. Oecologia 129: 420-429.
references.citation: Gaudinski JB, Trumbore SE, Davidson EA, Zheng S. 2000. Soil carbon cycling in a temperate forest: radiocarbon-based estimates of residence times, sequestration rates and partitioning of fluxes. Biogeochemistry 51: 33-69.
references.citation: Guo DL, Li H, Mitchell RJ, Han WX, Hendricks JJ, Fahey TJ, Hendrick RL. 2008. Fine root heterogeneity by branch order: exploring the discrepancy in root turnover estimates between minirhizotron and carbon isotopic methods. New Phytologist 177: 443-456.
references.citation: Guo DL, Mitchell RJ, Hendricks JJ. 2004. Fine root branch orders respond differentially to carbon source-sink manipulations in a longleaf pine forest. Oecologia 140: 450-457.
references.citation: Hanson PJ, Nelson TE, Tschaplinski TJ, Wullschleger SD, Joslin JD. 2003a. Estimating the net primary and net ecosystem production of a southern upland quercus forest from an 8-year biometric record. In: Hanson PJ, Wullschlegger SD, eds. Changing precipitation regimes and terrestrial ecosystems: North American perspective. New York, NY, USA: Springer, 378-395.
references.citation: Hanson PJ, Todd DE, Johnson DW, Joslin JD, O’Neill EG. 2003b. Responses of eastern deciduous forests to precipitation change. In: Hanson PJ, Wullschlegger SD, eds. Changing precipitation regimes and terrestrial ecosystems: North American perspective. New York, NY, USA: Springer, 164-179.
references.citation: Hanson PJ, Todd DE, Joslin JD. 2003c. Canopy production. In: Hanson PJ, Wullschlegger SD, eds. Changing precipitation regimes and terrestrial ecosystems: North American perspective. New York, NY, USA: Springer, 164-179.
references.citation: Hendrick RL, Pregitzer KS. 1992. The demography of fine roots in a northern hardwood forest. Ecology 73: 1094-1104.
references.citation: Hogberg P, Nordgren A, Buchmann N, Taylor AFS, Ekblad A, Hogberg MN, Nyberg G, Ottosson-Lofvenius M, Read DJ. 2001. Large-scale forest girdling shows that current photosynthesis drives soil respiration. Nature 411: 789-792.
references.citation: Hogberg P, Read DJ. 2006. Towards a more plant physiological perspective on soil ecology. Trends in Ecology & Evolution 21: 548-554.
references.citation: Horwath WR, Pregitzer KS, Paul EA. 1994. C-14 Allocation in tree soil systems. Tree Physiology 14: 1163-1176.
references.citation: Houghton JT, Ding Y, Griggs DJ, Noguer M, Van Der Linden PJ, Dai X, Maskell K, Johnson CA, eds. 2001. Climate Change 2001: the scientific basis. Contribution of Working Group 1 to the Third Assessment Report of the Intergovernmental Panel on Climate Change. New York, NY, USA: Cambridge University Press.
references.citation: Jackson RB, Mooney HA, Schulze ED. 1997. A global budget for fine root biomass, surface area, and nutrient contents. Proceedings of the National Academy of Sciences 94: 7362-7366.
references.citation: Johnson DW, Van Hook RI. 1989. Analysis of biogeochemical cycling process in Walker Branch Watershed. New York, NY, USA: Springer-Verlag New York Inc.
references.citation: Johnston C, Groffman P, Breshears D, Cardon Z, Currie W, Emanuel W, Gaudinski J, Jackson R, Lajtha K, Knadelhoffer K et al . 2004. The frontier below: carbon cycling in soil. Frontiers in Ecology and the Environment 2: 522-528.
references.citation: Joslin JD, Gaudinski JB, Torn MS, Riley WJ, Hanson PJ. 2006. Fine-root turnover patterns and their relationship to root diameter and soil depth in a C-14-labeled hardwood forest. New Phytologist 172: 523-535.
references.citation: Joslin JD, Wolfe MH. 2003. Fine-root growth response. In: Hanson PJ, Wullschleger SD, eds. North American temperate deciduous forest responses to changing precipitation regimes. New York, NY, USA: Springer-Verlag, Inc., 274-302.
references.citation: Joslin JD, Wolfe MH, Hanson PJ. 2001. Factors controlling the timing of root elongation intensity in a mature upland oak stand. Plant & Soil 228: 201-212.
references.citation: Keel SG, Siegwolf RTW, Korner C. 2006. Canopy CO2 enrichment permits tracing the fate of recently assimilated carbon in a mature deciduous forest. New Phytologist 172: 319-329.
references.citation: King JS, Albaugh TJ, Allen HL, Buford M, Strain BR, Dougherty P. 2002. Below-ground carbon in put to soil is control led by nutrient availability and fine root dynamics in loblolly pine. New Phytologist 154: 389-398.
references.citation: Luo YQ. 2003. Uncertainties in interpretation of isotope signals for estimation of fine root longevity: theoretical considerations. Global Change Biology 9: 1118-1129.
references.citation: Majdi H, Andersson P. 2005. Fine root production and turnover in a Norway spruce stand in northern Sweden: effects of nitrogen and water manipulation. Ecosystems 8: 191-199.
references.citation: Majdi H, Pregitzer K, Moren A, Nylund J, Agren G. 2005. Measuring fine root turnover in forest ecosystems. Plant and Soil 276: 1-8.
references.citation: Matamala R, Gonzalez-Meler MA, Jastrow JD, Norby RJ, Schlesinger WH. 2003. Impacts of fine root turnover on forest NPP and soil C sequestration potential. Science 302: 1385-1387.
references.citation: McClaugherty CA, Aber JD, Melillo JM. 1982. The role of fine roots in the organic-matter and nitrogen budgets of two forested ecosystems. Ecology 63: 1481-1490.
references.citation: McLaughlin SB, McConathy RK, Barnes RL, Edwards NT. 1980. Seasonal-changes in energy allocation by white oak (Quercus alba). Canadian Journal of Forest Research-Revue Canadienne de Recherche Forestiere 10: 379-388.
references.citation: Milchunas DG, Lauenroth WK, Singh JS, Cole CV, Hunt HW. 1985. Root turnover and production by C-14 dilution - implications of carbon partitioning in plants. Plant and Soil 88: 353-365.
references.citation: Pregitzer KS. 2002. Fine roots of trees - a new perspective. New Phytologist 154: 267-270.
references.citation: Pregitzer KS, Kubiske ME, Yu CK, Hendrick RL. 1997. Relationships among root branch order, carbon, and nitrogen in four temperate species. Oecologia 111: 302-308.
references.citation: Pregitzer KS, Laskowski MJ, Burton AJ, Lessard VC, Zak DR. 1998. Variation in sugar maple root respiration with root diameter and soil depth. Tree Physiology 18: 665-670.
references.citation: Press W, Flannery B, Teukolsky S, Vetterling W. 1989. Numerical recipes (FORTRAN). Cambridge, UK: Cambridge University Press.
references.citation: Schuur EAG, Trumbore SE. 2006. Partitioning sources of soil respiration in boreal black spruce forest using radiocarbon. Global Change Biology 12: 165-176.
references.citation: Stuiver M, Polach HA. 1977. Reporting of C-14 data - discussion. Radiocarbon 19: 355-363.
references.citation: Tierney GL, Fahey TJ. 2002. Fine root turnover in a northern hardwood forest: a direct comparison of the radiocarbon and minirhizotron methods. Canadian Journal of Forest Research-Journal Canadien de la Recherche Forestiere 32: 1692-1697.
references.citation: Tierney GL, Fahey TJ, Groffman PM, Hardy JP, Fitzhugh RD, Driscoll CT, Yavitt JB. 2003. Environmental control of fine root dynamics in a northern hardwood forest. Global Change Biology 9: 670-679.
references.citation: Trumbore S, Da Costa ES, Nepstad DC, De Camargo PB, Martinelli L, Ray D, Restom T, Silver W. 2006. Dynamics of fine root carbon in Amazonian tropical ecosystems and the contribution of roots to soil respiration. Global Change Biology 12: 217-229.
references.citation: Trumbore SE, Gaudinski JB. 2003. The secret lives of roots. Science 302: 1344-1345.
references.citation: Trumbore SE, Gaudinski JB, Hanson PJ, Southon JR. 2002. Quantifying ecosystem-atmosphere carbon exchange with a 14C label. EOS, Transactions, American Geophysical Union 83: 265-268.
references.citation: Vogt KA, Persson H. 1991. Measuring growth and development of roots. In: Lassoie JP, Hinckley TM, eds. Techniques and approaches in forest tree ecophysiology. Boca Raton, FL, USA: CRC, 477-501.
references.citation: Wells CE, Eissenstat DM. 2001. Marked differences in survivorship among apple roots of different diameters. Ecology 82: 882-892.