Partitioning of evapotranspiration and its relation to carbon dioxide exchange in a Chihuahuan Desert shrubland
Article first published online: 25 SEP 2006
Copyright © 2006 John Wiley & Sons, Ltd.
Special Issue: Emerging Issues in Rangeland Ecohydrology
Volume 20, Issue 15, pages 3227–3243, 15 October 2006
How to Cite
Scott, R. L., Huxman, T. E., Cable, W. L. and Emmerich, W. E. (2006), Partitioning of evapotranspiration and its relation to carbon dioxide exchange in a Chihuahuan Desert shrubland. Hydrol. Process., 20: 3227–3243. doi: 10.1002/hyp.6329
- Issue published online: 25 SEP 2006
- Article first published online: 25 SEP 2006
- Manuscript Accepted: 4 OCT 2005
- Manuscript Received: 1 APR 2005
- National Science Foundation. Grant Numbers: EAR-9876800, NSF, DEB-041-5977 041-8134
- woody plant encroachment;
- net ecosystem exchange;
- Chihuahuan Desert;
- gross ecosystem exchange
Key to evaluating the consequences of woody plant encroachment on water and carbon cycling in semiarid ecosystems is a mechanistic understanding of how biological and non-biological processes influence water loss to the atmosphere. To better understand how precipitation is partitioned into the components of evapotranspiration (bare-soil evaporation and plant transpiration) and their relationship to plant uptake of carbon dioxide (CO2) as well as ecosystem respiratory efflux, we measured whole plant transpiration, evapotranspiration, and CO2 fluxes over the course of a growing season at a semiarid Chihuahuan Desert shrubland site in south-eastern Arizona. Whole plant transpiration was measured using the heat balance sap-flow method, while evapotranspiration and net ecosystem exchange (NEE) of CO2 were quantified using the Bowen ratio technique.
Before the summer rainy season began, all water and CO2 fluxes were small. At the onset of the rainy season, evapotranspiration was dominated by evaporation and CO2 fluxes were dominated by respiration as it took approximately 10 days for the shrubs to respond to the higher soil moisture content. During the growing season, periods immediately following rain events (<2 days) were dominated by evaporation and respiration while transpiration and CO2 uptake peaked during the interstorm periods. The surface of the coarse, well-drained soils dried quickly, rapidly reducing evaporation. Overall, the ratio of total transpiration to evapotranspiration was 58%, but it was around 70% during the months when the plants were active. Peak respiration responses following rain events generally lagged after the evaporation peak by a couple of days and were better correlated with transpiration. Transpiration and CO2 uptake also decayed rather quickly during interstorm periods, indicating that optimal plant soil moisture conditions were rarely encountered. NEE of CO2 was increasingly more negative as the growing season progressed, indicating a greater net uptake of CO2 and greater water use efficiency due mainly to decreases in respiration. Copyright © 2006 John Wiley & Sons, Ltd.