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Forest soil carbon oxidation state and oxidative ratio responses to elevated CO 2
Author(s) -
Hockaday William C.,
Gallagher Morgan E.,
Masiello Caroline A.,
Baldock Jeffrey A.,
Iversen Colleen M.,
Norby Richard J.
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg003010
Subject(s) - soil carbon , carbon cycle , carbon sink , environmental chemistry , carbon dioxide , soil respiration , soil organic matter , environmental science , sink (geography) , carbon fibers , chemistry , carbon dioxide in earth's atmosphere , biosphere , total organic carbon , ecosystem , soil water , ecology , soil science , biology , materials science , cartography , organic chemistry , composite number , composite material , geography
The oxidative ratio (OR) of the biosphere is the stoichiometric ratio (O 2 /CO 2 ) of gas exchange by photosynthesis and respiration—a key parameter in budgeting calculations of the land and ocean carbon sinks. Carbon cycle‐climate feedbacks could alter the OR of the biosphere by affecting the quantity and quality of organic matter in plant biomass and soil carbon pools. This study considers the effect of elevated atmospheric carbon dioxide concentrations ([CO 2 ]) on the OR of a hardwood forest after nine growing seasons of Free‐Air CO 2 Enrichment. We measured changes in the carbon oxidation state (C ox ) of biomass and soil carbon pools as a proxy for the ecosystem OR. The OR of net primary production, 1.039, was not affected by elevated [CO 2 ]. However, the C ox of the soil carbon pool was 40% higher at elevated [CO 2 ], and the estimated OR values for soil respiration increased from 1.006 at ambient [CO 2 ] to 1.054 at elevated [CO 2 ]. A biochemical inventory of the soil organic matter ascribed the increases in C ox and OR to faster turnover of reduced substrates, lignin and lipids, at elevated [CO 2 ]. This implicates the heterotrophic soil community response to elevated [CO 2 ] as a driver of disequilibrium in the ecosystem OR. The oxidation of soil carbon pool constitutes an unexpected terrestrial O 2 sink. Carbon budgets constructed under the assumption of OR equilibrium would equate such a terrestrial O 2 sink to CO 2 uptake by the ocean. The potential for climate‐driven disequilibriua in the cycling of O 2 and CO 2 warrants further investigation.