title: Forest productivity under elevated CO₂ and O₃: positive feedbacks to soil N cycling sustain decade-long net primary productivity enhancement by CO₂.
abstract: The accumulation of anthropogenic CO₂ in the Earth's atmosphere, and hence the rate of climate warming, is sensitive to stimulation of plant growth by higher concentrations of atmospheric CO₂. Here, we synthesise data from a field experiment in which three developing northern forest communities have been exposed to factorial combinations of elevated CO₂ and O₃. Enhanced net primary productivity (NPP) (c. 26% increase) under elevated CO₂ was sustained by greater root exploration of soil for growth-limiting N, as well as more rapid rates of litter decomposition and microbial N release during decay. Despite initial declines in forest productivity under elevated O₃, compensatory growth of O₃ -tolerant individuals resulted in equivalent NPP under ambient and elevated O₃. After a decade, NPP has remained enhanced under elevated CO₂ and has recovered under elevated O₃ by mechanisms that remain un-calibrated or not considered in coupled climate-biogeochemical models simulating interactions between the global C cycle and climate warming.
authors: School of Natural Resource & Environment and Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA. drzak@umich.edu
authors: Donald R
authors: DR
authors: Zak
authors: Kurt S
authors: KS
authors: Pregitzer
authors: Mark E
authors: ME
authors: Kubiske
authors: Andrew J
authors: AJ
authors: Burton
mesh_terms: D031002:Acer; D029662:Betula; D018533:Biomass; D002245:Carbon Dioxide / Q000494:pharmacology*; D058458:Nitrogen Cycle; D009587:Nitrogen Isotopes / Q000032:analysis; D010126:Ozone / Q000494:pharmacology*; D032107:Populus; D012987:Soil / Q000032:analysis; D014197:Trees / Q000187:drug effects*
chemical_list: D009587:Nitrogen Isotopes; D012987:Soil; D002245:Carbon Dioxide; D010126:Ozone