Variation in Water Use Strategies of Riparian Velvet Mesquite

Abstract

In the semi-arid to arid Sonoran and Chihuahuan deserts, mesquite trees are fixtures across the landscape occupying diverse habitats. Mesquite plays a pivotal ecological role, influencing hydrological processes and contributing to the overall biodiversity of the region. This is especially true in riparian areas, where an understanding of the adaptive water use strategies they employ is essential to understanding the ecohydrology of these important ecosystems. This study investigates the water use strategies of riparian mesquite trees (Prosopis velutina) in southern Arizona across two water years. We explore the impact of age, size, and density of mesquite stands on source water use, with a focus on understanding how these trees access both deep groundwater and shallow soil moisture. We found that despite differences in stand characteristics (e.g. mature, young thicket, and thinned thicket), riparian P. velutina opportunistically used both deep and shallow water sources, depending on the time of year. We also examined leaf water potential to assess seasonal water stress, and found increasing water stress over the growing season, even after the onset of monsoon rains. Despite differences in monsoon precipitation over the study period, leaf water potential remained similar between the two years, suggesting the significance of winter precipitation preceding drier monsoons. The study highlights the anisohydric strategy of riparian P. velutina, emphasizing carbon assimilation over water loss and opportunistic patterns in source water use.