Skip to main content
ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #245131

Title: The potential impacts of nutrient and CO2 variations on ecosystem oxidative ratio

item GALLAGHER, M - Rice University
item HOCKADAY, W - Rice University
item MASIELLO, C - Rice University
item SNAPP, S - Rice University
item Polley, Herbert
item MCSWINEY, C - Michigan State University
item BALDOCK, J - Commonwealth Scientific And Industrial Research Organisation (CSIRO)

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/25/2009
Publication Date: 12/31/2009
Citation: Gallagher, M.E., Hockaday, W.C., Masiello, C.A., Snapp, S., Polley, H.W., Mcswiney, C.P., Baldock, J.A. 2009. The potential impacts of nutrient and CO2 variations on ecosystem oxidative ratio. In: Proceedings of the EOS Trans. American Geophysical Union, San Francisco, California. Paper No. 90(52):B21B-0339.

Interpretive Summary:

Technical Abstract: A fraction of fossil fuel carbon dioxide (CO2) emissions are being taken up by the terrestrial biosphere and the oceans. One particularly effective way of determining the sizes of these terrestrial biosphere and ocean carbon sinks is based on the measurements of changes in atmospheric oxygen (O2) and CO2 concentrations (Keeling et al. 1996). This method of carbon apportionment requires knowledge of total fossil fuel CO2 emissions, atmospheric O2 and CO2 concentrations, and the value of the terrestrial biosphere oxidative ratio (OR), which has historically been assumed to be constant at 1.10 (e.g. Prentice et al. 2001). OR is the ratio of moles of O2 per mole of CO2 in gas exchanges between the terrestrial biosphere and the atmosphere. An incorrect estimation of the biosphere’s OR results in misapportionment of CO2 between the terrestrial biosphere and ocean carbon sinks (Randerson et al. 2006). Understanding how OR can vary with changing environmental properties is therefore essential to accurately estimate the size of the terrestrial carbon sink. We estimate OR through its relationship with organic carbon oxidation state (Cox) measurements made using a 13C nuclear magnetic resonance spectrometer and a CHNSO elemental analyzer (Masiello et al. 2008; Hockaday et al. 2009). It is clear that ecosystem OR values frequently deviate from the assumed 1.10 (Masiello et al., 2008; Hockaday et al., 2009). Here we review what mechanisms drive shifts in OR, including: fire, climate (precipitation and temperature), land use change, atmospheric CO2 concentrations, and nutrient supply. We present data on the impact of nitrogen supply and elevated CO2 on ecosystem OR at two different field sites. We measure the effect of nitrogen supply on an agricultural ecosystem at the Kellogg Biological Station-Living Field Laboratory (KBS-LFL) in Michigan over a fertilization gradient (0 to 202 kg N/ha). We also measured the effect of atmospheric CO2 variation on ecosystem OR at a grassland site experiencing three atmospheric CO2 levels: pre-industrial, current, and projected (the USDA-Agricultural Research Service field site in Temple, Texas).