Sources and sinks of carbonyl sulfide in an agricultural field in the Southern Great Plains

Authors

Kadmiel Maseyk, Université Pierre et Marie CurieFollow
Joseph A. Berry, Carnegie Institution, Stanford, CAFollow
David P. Billesbach, University of Nebraska-LincolnFollow
John Elliott Campbell, Sierra Nevada Research Institute, University of California, Merced, CAFollow
Margaret S. Torn, Lawrence Berkeley National LaboratoryFollow
Mark Zahniser, Aerodyne Research Inc., Billerica, MAFollow
Ulli Seibt, University of California, Los AngelesFollow

Document Type

Article

Date of this Version

6-24-2014

Citation

PNAS (June 24, 2014), vol. 111, no. 25, pp. 9064–9069
doi: 10.1073/pnas.1319132111

Comments

Copyright (c) 2014 NAS. Used by permission.

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.

Includes Supplementary files.