Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 10, 4937-4956, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
23 Jul 2013
Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland
J. H. Shim1, H. H. Powers1, C. W. Meyer1, A. Knohl2, T. E. Dawson3, W. J. Riley4, W. T. Pockman5, and N. McDowell1 1Earth and Environmental Sciences Division, Los Alamos National Laboratory, MS-J495, Los Alamos, NM 87545, USA
2Chair of Bioclimatology, Georg-August University of Göttingen, Göttingen, Germany
3Department of Integrative Biology, University of California, Berkeley, CA, USA
4Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
5Department of Biology, University of New Mexico, Albuquerque, NM 87131-0001, USA
Abstract. We conducted high frequency measurements of the δ18O value of atmospheric CO2 from a juniper (Juniperus monosperma) woodland in New Mexico, USA, over a four-year period to investigate climatic and physiological regulation of the δ18O value of ecosystem respiration (δR). Rain pulses reset δR with the dominant water source isotope composition, followed by progressive enrichment of δR. Transpiration (ET) was significantly related to post-pulse δR enrichment because the leaf water δ18O value showed strong enrichment with increasing vapor pressure deficit that occurs following rain. Post-pulse δR enrichment was correlated with both ET and the ratio of ET to soil evaporation (ET/ES). In contrast, the soil water δ18O value was relatively stable and δR enrichment was not correlated with ES. Model simulations captured the large post-pulse δR enrichments only when the offset between xylem and leaf water δ18O value was modeled explicitly and when a gross flux model for CO2 retro-diffusion was included. Drought impacts δR through the balance between evaporative demand, which enriches δR, and low soil moisture availability, which attenuates δR enrichment through reduced ET. The net result, observed throughout all four years of our study, was a negative correlation of post-precipitation δR enrichment with increasing drought.

Citation: Shim, J. H., Powers, H. H., Meyer, C. W., Knohl, A., Dawson, T. E., Riley, W. J., Pockman, W. T., and McDowell, N.: Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland, Biogeosciences, 10, 4937-4956,, 2013.
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