title: Sources and sinks of carbonyl sulfide in an agricultural field in the Southern Great Plains.
abstract: Net photosynthesis is the largest single flux in the global carbon cycle, but controls over its variability are poorly understood because there is no direct way of measuring it at the ecosystem scale. We report observations of ecosystem carbonyl sulfide (COS) and CO2 fluxes that resolve key gaps in an emerging framework for using concurrent COS and CO2 measurements to quantify terrestrial gross primary productivity. At a wheat field in Oklahoma we found that in the peak growing season the flux-weighted leaf relative uptake of COS and CO2 during photosynthesis was 1.3, at the lower end of values from laboratory studies, and varied systematically with light. Due to nocturnal stomatal conductance, COS uptake by vegetation continued at night, contributing a large fraction (29%) of daily net ecosystem COS fluxes. In comparison, the contribution of soil fluxes was small (1-6%) during the peak growing season. Upland soils are usually considered sinks of COS. In contrast, the well-aerated soil at the site switched from COS uptake to emissions at a soil temperature of around 15 °C. We observed COS production from the roots of wheat and other species and COS uptake by root-free soil up to a soil temperature of around 25 °C. Our dataset demonstrates that vegetation uptake is the dominant ecosystem COS flux in the peak growing season, providing support of COS as an independent tracer of terrestrial photosynthesis. However, the observation that ecosystems may become a COS source at high temperature needs to be considered in global modeling studies.
authors.affiliation: Institute of Ecology and Environmental Sciences, Université Pierre et Marie Curie, Grignon Campus, 78850 Thiverval-Grignon, France; kadmiel.maseyk@upmc.fr useibt@ucla.edu.
authors.forename: Kadmiel
authors.initials: K
authors.lastname: Maseyk
authors.affiliation: Department of Global Ecology, Carnegie Institution, Stanford, CA 94305;
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Berry
authors.affiliation: Biological Systems Engineering Department, University of Nebraska, Lincoln, NE 68583;
authors.forename: Dave
authors.initials: D
authors.lastname: Billesbach
authors.affiliation: Sierra Nevada Research Institute, University of California, Merced, CA 95343;
authors.forename: John Elliott
authors.initials: JE
authors.lastname: Campbell
authors.affiliation: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
authors.forename: Margaret S
authors.initials: MS
authors.lastname: Torn
authors.affiliation: Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., Billerica, MA 01821; and.
authors.forename: Mark
authors.initials: M
authors.lastname: Zahniser
authors.affiliation: Institute of Ecology and Environmental Sciences, Université Pierre et Marie Curie, Grignon Campus, 78850 Thiverval-Grignon, France;Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095 kadmiel.maseyk@upmc.fr useibt@ucla.edu.
authors.forename: Ulli
authors.initials: U
authors.lastname: Seibt
mesh_terms: D017753:Ecosystem; D008954:Models, Biological; D009825:Oklahoma; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism*; D013461:Sulfur Oxides / Q000378:metabolism*; D014908:Triticum / Q000254:growth & development / Q000378:metabolism*
chemical_list: D013461:Sulfur Oxides; C010063:carbonyl sulfide
keywords: ERU; LRU; carbonic anhydrase; flux partitioning; soil metabolism