PARENT SESSION
Oral Session # 77: Plant Ecology VI: Temperature and Water Stress.
Presiding: C Ford
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 102.

Differences in plant and soil water relations and nutrient status on contrasting sides of a cold desert ecotone.

Rosenthal, David^*,1, Ludwig, Fulco¹, Stiller, Volker², Donovan, Lisa¹, ¹ University of Georgia, Athens, GA² University of Utah, Salt Lake City, UT

ABSTRACT- In arid ecosystems, soil texture is an important determinant of plant available soil moisture. There is a rapid shift from active sandy soils to stabilized better developed soils along the ecotone between desert sand dunes and adjacent off dune habitats. In general, soil clay and nutrient content increase across this boundary. Plants on fine textured soils should exhibit more negative water potentials and increased resistance to cavitation than plants on coarser soils. At Little Sahara Sand Dunes, Utah, we studied plant available water and plant and soil nutrient content for three species of differing life forms that occur along a narrow sand dune/desert ecotone. For all species measured, seasonal plant predawn (pd) and midday (md) water potential were significantly higher on dunes than off dunes. Plants growing on active sand dunes maintained relatively high pd (> -1.5 MPa) throughout the summer season whereas plants growing off dunes were very water stressed from July on (pd < -1.5 MPa). Hardly any water was available for plants in shallow soils, but soil water potential increased with depth. Water was available for plants at 50 cm depth and below on dunes, but only below 75 cm depth off dunes. As predicted soil clay content was higher at off dune sites. Total soil N concentration was more than four times lower on dunes than off dunes. Overall soil P was similar across the ecotone. However, soil P increased with depth on the dunes while the trend was reversed off dunes. Plant N:P ratios were lower on the dunes. These findings suggest plants may not root at greater depths on the dunes. We tested the prediction that on dune plants have lower cavitation resistance by measuring percent loss of xylem conductivity as a function of xylem tension. Differences in cavitation resistance between congeners restricted to either side of the ecotone support the observed differences in plant water status for species that span the ecotone.

Key words: Desert Dunes, Hybridization, Water Relations, Helianthus