Plant responses to an edaphic gradient across an active sand dune/desert boundary in the great basin desert

In arid ecosystems, variation in precipitation causes broad-scale spatial heterogeneity in soil moisture, but differences in soil texture, development, and plant cover can also create substantial local soil moisture heterogeneity. The boundary between inland desert sand dunes and adjacent desert habitats exhibits abrupt changes in soil and vegetation characteristics that may be associated with differences in plant-available water and nutrients. We hypothesized that differences in plant water status between habitats would mirror changes in soil texture and vegetation cover. Because the dunes have higher water availability, we predicted that plants on dunes would have higher plant water potential ( C) and be less water use efficient than plants off dunes. We tested these predictions for three species -Psoralidium lanceolatum (a C-3 perennial N-fixing subshrub), Stipa hymenoides (a C-3 perennial bunchgrass), and Salsola iberica (a C-4 annual)-on actively moving desert dunes and adjacent stabilized dunes at Little Sahara Dunes, Utah. Plants on the dunes maintained higher predawn (Psi(pd)) water potentials (>-1.5 MPa) throughout the summer season, whereas off-dune plants were water stressed from July on (Psi(pd) < -1.5 MPa). Midday water potential (Psi(md)) generally mirrored Psi(pd). As predicted, off-dune plants were more water use efficient, on the basis of leaf carbon isotope ratios (delta C-13) for the C-3 species. The observed differences in soil particle size, soil water content, and the concomitant effect on soil Psi likely explain the observed differences in Psi(pd). Soil N was significantly lower on dunes, while soil P was similar across habitats. In contrast, leaf N was similar across habitats, but leaf P was significantly higher on dunes, possibly because of species-specific differences in nutrient relations or differences in habitat nutrient availability. Abrupt changes in water and nutrient availability associated with soil texture are likely to be important selective forces shaping plants' strategies in this and other desert boundary communities.