title: Fine root heterogeneity by branch order: exploring the discrepancy in root turnover estimates between minirhizotron and carbon isotopic methods.
abstract: Fine roots constitute a large and dynamic component of the carbon cycles of terrestrial ecosystems. The reported fivefold discrepancy in turnover estimates between median longevity (ML) from minirhizotrons and mean residence time (MRT) using carbon isotopes may have global consequences. Here, a root branch order-based model and a simulated factorial experiment were used to examine four sources of error. Inherent differences between ML, a number-based measure, and MRT, a mass-based measure, and the inability of the MRT method to account for multiple replacements of rapidly cycling roots were the two sources of error that contributed more to the disparity than did the improper choice of root age distribution models and sampling bias. Sensitivity analysis showed that the rate at which root longevity increases as order increases was the most important factor influencing the disparity between ML and MRT. Assessing root populations for each branch order may substantially reduce the errors in longevity estimates of the fine root guild. Our results point to the need to acquire longevity estimates of different orders, particularly those of higher orders.
authors.affiliation: Department of Ecology, College of Environmental Sciences, Peking University, Beijing 100871, China.
authors.forename: Dali
authors.initials: D
authors.lastname: Guo
authors.affiliation: USDA Forest Service Southern Research Station, Center for Forested Wetlands Research, 2730 Savannah Highway, Charleston, SC 29414, USA.
authors.forename: Harbin
authors.initials: H
authors.lastname: Li
authors.affiliation: Joseph W. Jones Ecological Research Center at Ichauway, Rt. 2, Box 2324, Newton, GA 39870, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Mitchell
authors.affiliation: Department of Ecology, College of Environmental Sciences, Peking University, Beijing 100871, China.
authors.forename: Wenxuan
authors.initials: W
authors.lastname: Han
authors.affiliation: Department of Biology, University of West Georgia, Carrollton, GA 30118, USA.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Hendricks
authors.affiliation: Department of Natural Resources, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Fahey
authors.affiliation: Warnell School of Forest Resources, University of Georgia, Athens, GA 30602, USA.
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Hendrick
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism; D003198:Computer Simulation; D017753:Ecosystem; D008954:Models, Biological; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism; D010944:Plants / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D002244:Carbon