Year‐Round Transpiration Dynamics Linked With Deep Soil Moisture in a Warm Desert Shrubland

• Published in: Water resources research Vol. 55; no. 7; pp. 5679 - 5695
• Main Authors: Szutu, D. J., Papuga, S. A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01-07-2019
• Subjects: Arid zones; Atmospheric models; Availability; Covariance; creosotebush; Dynamics; Ecohydrology; Ecosystems; Eddy covariance; evapotranspiration; Flow measurement; Hydrologic cycle; Hydrologic models; Hydrological cycle; Hydrology; Isotopes; Plant roots; plant water use; Precipitation; Seasonal variations; Shrublands; Soil; Soil dynamics; Soil moisture; Soil water; Soils; Temporal distribution; Transpiration; water‐use strategies
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2018WR023990

Ecohydrological processes in semiarid shrublands and other dryland ecosystems are sensitive to discrete pulses of precipitation. Anticipated changes in the frequency and magnitude of precipitation events are expected to impact the spatial and temporal distribution of soil moisture in these drylands, thereby impacting their ecohydrological processes. Recent field studies have shown that in dryland ecosystems, transpiration dynamics and plant productivity are largely a function of deep soil moisture available after large precipitation events, regardless of where the majority of plant roots occur. However, the strength of this relationship and how and why it varies throughout the year remains unclear. We present eddy covariance, soil moisture, and sap flow measurements taken over an 18‐month period in conjunction with an analysis of biweekly precipitation, shallow soil, deep soil, and stem stable water isotope samples from a creosotebush‐dominated shrubland ecosystem at the Santa Rita Experimental Range in southern Arizona. Within the context of a hydrologically defined two‐layer conceptual framework, our results support that transpiration is associated with the availability of deep soil moisture and that the source of this moisture varies seasonally. Therefore, changes in precipitation pulses that alter the timing and magnitude of the availability of deep soil moisture are expected to have major consequences for dryland ecosystems. Our findings offer insights that can improve the representation of drylands within regional and global models of land surface atmosphere exchange and their linkages to the hydrologic cycle.
Key Points
Shallow and deep soil moisture are isotopically distinct at this warm semiarid shrubland
Deep moisture tends to be isotopically similar to precipitation from previous season
Shrubs use deep moisture all year round