Imaging the Response of Woody Vegetation Ecosystems of the Northern Chihuahuan Desert to Short Simulated Precipitation Pulses: Implications for the Resiliency of Arid Ecosystems and the Water Balance of Desert Landscapes

In the southwestern United States, and within the larger Chihuahuan desert, keystone species such as Creosote shrub (Larrea tridentata) and Honey Mesquite (Prosopis glandulosa), exhibit vegetation activity year-round, even at times when water availability is severely limited. For that reason, these species dominate vegetation productivity (i.e. carbon sequestration from the atmosphere for plant tissue growth), and control to a large extent the magnitude and rate of water fluxes from precipitation into and out of the soils. Hence, playing a fundamental role in modulating the amounts of water that can lead to groundwater recharge of vast arid lands. However, despite the importance of these plants on regulating the water and carbon cycles on the deserts of North America, little is known on their water sourcing strategies and their response rates for short precipitation pulses typical of the region, as well as the role that the physical structure of desert soils imprint on their physiologic adaptations to cope with extreme heat and dry climates. This work aims to fill important gaps of knowledge on the dynamics of water sourcing from short precipitation pulses for Creosote shrubs and Honey Mesquite. Short precipitation pulses were artificially simulated by irrigating small plots (~4x4m) containing Creosote and Mesquite vegetation with water with a known isotopic composition. The vegetation inside the plots was sampled hourly previous, during and after the irrigation events to assess their response to the sudden availability of extra moisture. Concurently, continuous 3D soil tomographies of the shallow soil (~2m depth) in time lapse mode were obtained using electrical resistivity meter surveys to image the changes in soil moisture content. Changes in isotopic signature of the xylem water in the plants and moisture conditions of the shallow soils under their canopies during and after the simulated precipitation pulses, reveal the strategies of both plants for taking advantage of these short influxes of moisture. Comparisons to longer time series of the isotopic signature of the same plants' water allows us to draw a conceptual model of woody vegetation water sourcing in this arid environment to help predict the ecosystem's responses to expected shifts in rainfall patterns and variability.