Fig 1.
(a) Two-layer soil moisture framework for a natural dryland system: plant productivity is enhanced by deep (>20 cm) soil moisture following large (>8 mm) rains. (b) Soil moisture conditions under different irrigation styles: passive irrigation provides deep soil moisture during small rain events (<8 mm) whereas active irrigation provides perennial deep soil moisture.
Fig 2.
Aerial photographs were Reprinted from (https://imagery.library.arizona.edu) under a CC BY license, with permission from Pima Association of Governments, original copyright 2015. (a) semiarid city of Tucson, AZ; (b) passive irrigation treatment where a bioswale directs stormwater (blue arrows) into the soil surrounding an urban mesquite tree; (c) the active irrigation site with eight mesquite trees (i.e. AI 1—AI 8); (d) the passive irrigation site with eight mesquite trees (i.e. PI 1—PI 8; asterisks indicate ‘PIstreet’ trees, which are the trees whose accompanying bioswales are connected to the adjacent road and thus receive appreciable impervious runoff illustrated by blue arrows).
Fig 3.
(a) Soil water content reflectometers to measure volumetric water content at 10 cm and 30 cm under each tree; (b) sap flow sensors on mesquite trunks where insulating wrap encloses the thermal dissipation probes; (c) hemispherical photography of mesquite canopy; (d) daily phenocam photo where black box indicates region of interest for greenness analysis.
Fig 4.
Data from both passive (PI) and active (AI) irrigation sites: (a) precipitation; (b) air and soil temperature; (c) VWCshallow and VWCdeep; (d) Vsap; (e) normalized LAI; (f) Gn.
Fig 5.
Alternating passive irrigation (PI) and active irrigation (AI) for annual, spring, and summer season (a) VWCshallow; (b) VWCdeep; (c) Vsap; (d) Gn.
Fig 6.
Deep soil moisture closer look.
Time series of daily average VWCdeep values under the PI, PIstreet, and AI treatments.
Fig 7.
Deep soil moisture regressions.
Linear regressions between (a-d) VWCdeep and Vsap; (e-h) VWCdeep and Gn; gray circles are passive irrigation (PI) and black circles are active irrigation (AI). Blocks are separated into spring and summer seasons. All regressions show statistical significance (Table 1).
Table 1.
Coefficient of Determination (R2) and slope values resulting from linear regression of Gn and Vsap as a function of VWCshallow and VWCdeep; and Gn as a function of Vsap (greenness efficiency; GE).
Fig 8.
Linear regression of Gn as a function of Vsap for (a) passive irrigation (PI) and (b) active irrigation (AI); dots represent spring; circles represent summer; x’s represent the remainder of the year.