Depth to ground water affects riparian tree water uptake and physiological condition.
HORTON, J.L.*, S.C.HART and T.E.KOLB
Northern Arizona University, Flagstaff, AZ 86011-5018 1
In order to effectively manage riparian ecosystems, it is important to understand the water requirements of native riparian tree species. We investigated water uptake and physiological condition of two native species, Populus fremontii and Salix gooddingii, and one invasive exotic species, Tamarix chinensis, along the unregulated Hassayampa River in Arizona. We established seven transects along a gradient of surface flow and depth to ground water. Depth to ground water and soil water content were monitored during both the 1997 and 1998 growing seasons. Leaf gas exchange, 13C, water potential, and canopy condition were measured on all species in both years. Source and xylem waters were collected for stable isotope analysis to determine plant water sources. Ground water was deep and highly variable in the ephemeral reach in 1997. Predawn water potential decreased with increasing depth to ground water for both native species, but not for Tamarix in 1997. Preliminary stable isotope analysis of ecosystem water sources suggests a shift in water uptake sources as depth to ground water increased in all species. This shift was associated with decreased leaf gas exchange and twig xylem water potential, and increased in canopy dieback in the native species, but not in Tamarix. In contrast, ground water was shallower and more constant in 1998 than in 1997, due to the occurrence of a strong El Nino event. Predawn water potential was unrelated to depth to ground water for all three species, and there was no apparent change in water uptake sources for any species over the narrow range of depth to ground water observed in 1998. In addition all species had higher rates of leaf gas exchange, greater branch elongation, and lower canopy dieback in 1998 than in 1997.
Keywords: riparian, water source use, ground water
This abstract is being presented at: 9:45 AM in session:
Oral Session #20: Riparian Ecology.