title: Redefining fine roots improves understanding of below-ground contributions to terrestrial biosphere processes.
abstract: Fine roots acquire essential soil resources and mediate biogeochemical cycling in terrestrial ecosystems. Estimates of carbon and nutrient allocation to build and maintain these structures remain uncertain because of the challenges of consistently measuring and interpreting fine-root systems. Traditionally, fine roots have been defined as all roots ≤ 2 mm in diameter, yet it is now recognized that this approach fails to capture the diversity of form and function observed among fine-root orders. Here, we demonstrate how order-based and functional classification frameworks improve our understanding of dynamic root processes in ecosystems dominated by perennial plants. In these frameworks, fine roots are either separated into individual root orders or functionally defined into a shorter-lived absorptive pool and a longer-lived transport fine-root pool. Using these frameworks, we estimate that fine-root production and turnover represent 22% of terrestrial net primary production globally - a c. 30% reduction from previous estimates assuming a single fine-root pool. Future work developing tools to rapidly differentiate functional fine-root classes, explicit incorporation of mycorrhizal fungi into fine-root studies, and wider adoption of a two-pool approach to model fine roots provide opportunities to better understand below-ground processes in the terrestrial biosphere.
authors.affiliation: Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China.
authors.forename: M Luke
authors.initials: ML
authors.lastname: McCormack
authors.affiliation: Bio-Protection Research Centre, Lincoln University, Canterbury, New Zealand.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Dickie
authors.affiliation: Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Eissenstat
authors.affiliation: Department of Natural Resources, Cornell University, Ithaca, NY, 14853, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Fahey
authors.affiliation: Department of Plant Biology, University of Minnesota, St Paul, MN, 55108, USA.
authors.forename: Christopher W
authors.identifier: http://orcid.org/0000-0002-6310-6027
authors.initials: CW
authors.lastname: Fernandez
authors.affiliation: Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China.
authors.forename: Dali
authors.initials: D
authors.lastname: Guo
authors.affiliation: Department of Forest Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Heljä-Sisko
authors.initials: HS
authors.lastname: Helmisaari
authors.affiliation: Earth Systems Research Center, University of New Hampshire, Durham, NH, 03824, USA.
authors.forename: Erik A
authors.initials: EA
authors.lastname: Hobbie
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors.forename: Colleen M
authors.initials: CM
authors.lastname: Iversen
authors.affiliation: Department of Earth System Science, Stanford University, Stanford, CA, 94305, USA.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Jackson
authors.affiliation: Department of Forest Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Jaana
authors.initials: J
authors.lastname: Leppälammi-Kujansuu
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Norby
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN, 47405, USA.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Phillips
authors.affiliation: Department of Forest, Rangeland, and Fire Sciences, University of Idaho, Moscow, ID, 83844, USA.
authors.forename: Kurt S
authors.initials: KS
authors.lastname: Pregitzer
authors.affiliation: Department of Biology, College of Charleston, Charleston, SC, 29401, USA.
authors.forename: Seth G
authors.initials: SG
authors.lastname: Pritchard
authors.affiliation: Institute of Forest Ecology, University of Natural Resources and Life Sciences, Vienna, Austria.
authors.forename: Boris
authors.initials: B
authors.lastname: Rewald
authors.affiliation: Institute of Dendrology, Polish Academy of Sciences, Kórnik, 62-035, Poland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Zadworny
mesh_terms: D018533:Biomass; D017753:Ecosystem; D038821:Mycorrhizae / Q000502:physiology; D018517:Plant Roots / Q000502:physiology*; D019655:Quantitative Trait, Heritable
keywords: below ground; ecosystem; ecosystem modeling; fine-root order; mycorrhizal fungi; net primary productivity (NPP); plant allocation; plant traits