title: Elevated CO2 stimulates net accumulations of carbon and nitrogen in land ecosystems: a meta-analysis.
abstract: The capability of terrestrial ecosystems to sequester carbon (C) plays a critical role in regulating future climatic change yet depends on nitrogen (N) availability. To predict long-term ecosystem C storage, it is essential to examine whether soil N becomes progressively limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. A critical parameter to indicate the long-term progressive N limitation (PNL) is net change in ecosystem N content in association with C accumulation in plant and soil pools under elevated CO2. We compiled data from 104 published papers that study C and N dynamics at ambient and elevated CO2. The compiled database contains C contents, N contents, and C:N ratio in various plant and soil pools, and root:shoot ratio. Averaged C and N pool sizes in plant and soil all significantly increase at elevated CO2 in comparison to those at ambient CO2, ranging from a 5% increase in shoot N content to a 32% increase in root C content. The C and N contents in litter pools are consistently higher in elevated than ambient CO2 among all the surveyed studies whereas C and N contents in the other pools increase in some studies and decrease in other studies. The high variability in CO2-induced changes in C and N pool sizes results from diverse responses of various C and N processes to elevated CO2. Averaged C:N ratios are higher by 3% in litter and soil pools and 11% in root and shoot pools at elevated relative to ambient CO2. Elevated CO2 slightly increases root:shoot ratio. The net N accumulation in plant and soil pools at least helps prevent complete down-regulation of, and likely supports, long-term CO2 stimulation of C sequestration. The concomitant C and N accumulations in response to rising atmospheric CO2 may reflect intrinsic nature of ecosystem development as revealed before by studies of succession over hundreds to millions of years.
authors.affiliation: Department of Botany and Microbiology, University of Oklahoma, Norman 73019, USA. yluo@ou.edu
authors.forename: Yiqi
authors.initials: Y
authors.lastname: Luo
authors.forename: Dafeng
authors.initials: D
authors.lastname: Hui
authors.forename: Deqiang
authors.initials: D
authors.lastname: Zhang
mesh_terms: D002244:Carbon / Q000032:analysis; D002245:Carbon Dioxide / Q000737:chemistry / Q000502:physiology*; D017753:Ecosystem; D009584:Nitrogen / Q000032:analysis; D018521:Plant Physiological Phenomena; D018517:Plant Roots / Q000737:chemistry; D018520:Plant Shoots / Q000737:chemistry; D010944:Plants / Q000737:chemistry*; D012987:Soil / Q000032:analysis
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen