Sparks, J., and J.R. Ehleringer. 1997. Leaf carbon isotope discrimination and nitrogen content for riparian trees along elevational transects. Oecologia 109:362-367.

Leaf carbon isotope discrimination (D), seasonal estimates of the leaf-to-air water vapor gradient on a molar basis (omega), and leaf nitrogen contents were examined in three riparian tree species (Populus fremontii, Populus angustifolia, and Salix exigua) along elevational transects in northern and southern Utah USA (1500 - 2670 m and 600 - 1820 m elevational gradients, respectively). The omega values decreased with elevation for all species along transects. Plants growing at higher elevations exhibited lower values than plants at lower elevations (P. fremontii, 22.9 and 19.5, respectively; P. angustifolia, 23.2 and 19.2, respectively; and S. exigua, 21.1 and 19.1, respectively). Leaf nitrogen content increased with elevation for all species, suggesting that photosynthetic capacity at a given intercellular carbon dioxide concentration was greater at higher elevations. Leaf and nitrogen content values were highly correlated, implying that leaves with higher photosynthetic capacities also had lower intercellular carbon dioxide concentrations. No significant interannual differences were detected in carbon isotope discrimination.