title: Global patterns and controls of soil organic carbon dynamics as simulated by multiple terrestrial biosphere models: Current status and future directions.
abstract: Soil is the largest organic carbon (C) pool of terrestrial ecosystems, and C loss from soil accounts for a large proportion of land-atmosphere C exchange. Therefore, a small change in soil organic C (SOC) can affect atmospheric carbon dioxide (CO2) concentration and climate change. In the past decades, a wide variety of studies have been conducted to quantify global SOC stocks and soil C exchange with the atmosphere through site measurements, inventories, and empirical/process-based modeling. However, these estimates are highly uncertain, and identifying major driving forces controlling soil C dynamics remains a key research challenge. This study has compiled century-long (1901-2010) estimates of SOC storage and heterotrophic respiration (Rh) from 10 terrestrial biosphere models (TBMs) in the Multi-scale Synthesis and Terrestrial Model Intercomparison Project and two observation-based data sets. The 10 TBM ensemble shows that global SOC estimate ranges from 425 to 2111 Pg C (1 Pg = 1015g) with a median value of 1158 Pg C in 2010. The models estimate a broad range of Rh from 35 to 69 Pg C yr-1with a median value of 51 Pg C yr-1during 2001-2010. The largest uncertainty in SOC stocks exists in the 40-65°N latitude whereas the largest cross-model divergence in Rh are in the tropics. The modeled SOC change during 1901-2010 ranges from -70 Pg C to 86 Pg C, but in some models the SOC change has a different sign from the change of total C stock, implying very different contribution of vegetation and soil pools in determining the terrestrial C budget among models. The model ensemble-estimated mean residence time of SOC shows a reduction of 3.4 years over the past century, which accelerate C cycling through the land biosphere. All the models agreed that climate and land use changes decreased SOC stocks, while elevated atmospheric CO2and nitrogen deposition over intact ecosystems increased SOC stocks-even though the responses varied significantly among models. Model representations of temperature and moisture sensitivity, nutrient limitation, and land use partially explain the divergent estimates of global SOC stocks and soil C fluxes in this study. In addition, a major source of systematic error in model estimations relates to nonmodeled SOC storage in wetlands and peatlands, as well as to old C storage in deep soil layers.
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Hanqin
authors.initials: H
authors.lastname: Tian
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Chaoqun
authors.initials: C
authors.lastname: Lu
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Jia
authors.initials: J
authors.lastname: Yang
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Kamaljit
authors.initials: K
authors.lastname: Banger
authors.affiliation: School of Earth Sciences and Environmental Sustainability Northern Arizona University Flagstaff Arizona USA; Department of Civil Engineering, Construction Management, and Environmental Engineering Northern Arizona University Flagstaff Arizona USA.
authors.forename: Deborah N
authors.initials: DN
authors.lastname: Huntzinger
authors.affiliation: Department of Civil Engineering, Construction Management, and Environmental Engineering Northern Arizona University Flagstaff Arizona USA; Center for Ecosystem Science and Society Northern Arizona University Flagstaff Arizona USA.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Schwalm
authors.affiliation: Department of Global Ecology Carnegie Institution for Science Stanford California USA.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Michalak
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute Oak Ridge National Laboratory Oak Ridge Tennessee USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Cook
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement Gif sur Yvette France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute Oak Ridge National Laboratory Oak Ridge Tennessee USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hayes
authors.affiliation: Atmospheric Sciences and Global Change Division Pacific Northwest National Laboratory Richland Washington USA.
authors.forename: Maoyi
authors.initials: M
authors.lastname: Huang
authors.affiliation: National Institute for Environmental Studies Tsukuba Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Ito
authors.affiliation: Department for Atmospheric Sciences University of Illinois at Urbana-Champaign Urbana Illinois USA.
authors.forename: Atul K
authors.initials: AK
authors.lastname: Jain
authors.affiliation: Department of Hydraulic Engineering Tsinghua University Beijing China.
authors.forename: Huimin
authors.initials: H
authors.lastname: Lei
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute Oak Ridge National Laboratory Oak Ridge Tennessee USA.
authors.forename: Jiafu
authors.initials: J
authors.lastname: Mao
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Shufen
authors.initials: S
authors.lastname: Pan
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute Oak Ridge National Laboratory Oak Ridge Tennessee USA.
authors.forename: Wilfred M
authors.initials: WM
authors.lastname: Post
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement Gif sur Yvette France.
authors.forename: Shushi
authors.initials: S
authors.lastname: Peng
authors.affiliation: Department of Ecology Montana State University Bozeman Montana USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Poulter
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Ren
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute Oak Ridge National Laboratory Oak Ridge Tennessee USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Ricciuto
authors.affiliation: National Snow and Ice Data Center Boulder Colorado USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Schaefer
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute Oak Ridge National Laboratory Oak Ridge Tennessee USA.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Shi
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Tao
authors.affiliation: Ames Research Center, National Aeronautics and Space Administration Mountain View California USA.
authors.forename: Weile
authors.initials: W
authors.lastname: Wang
authors.affiliation: Environmental Sciences Division and Climate Change Science Institute Oak Ridge National Laboratory Oak Ridge Tennessee USA.
authors.forename: Yaxing
authors.initials: Y
authors.lastname: Wei
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Qichun
authors.initials: Q
authors.lastname: Yang
authors.affiliation: International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences Auburn University Auburn Alabama USA.
authors.forename: Bowen
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Department of Atmospheric and Oceanic Science University of Maryland College Park Maryland USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Zeng
keywords: belowground processes; heterotrophic respiration (Rh); mean residence time (MRT); soil carbon dynamics model; soil organic carbon (SOC); uncertainty