Riparian forests are prone to biotic invasion by non-native plants. Non-native plants can alter ecosystem-level nutrient dynamics by differing from native species in key physical or physiological traits.  Few studies have examined the effects of non-native species on nutrient cycling in riparian zones.  This study compared the influence of native Populus deltoides ssp. wislizenii (Rio Grande cottonwood) and non-native Tamarix chinensis (salt cedar) on soil nitrogen cycling in riparian forests along the middle Rio Grande of New Mexico.  This study demonstrated that native and non-native riparian plants of semi-arid regions consume organic forms of N, in addition to mineral forms. T. chinensis and P. deltoides were similar with respect to nitrogen preferences, rates of nitrogen uptake, root surface enzyme activity, and leaf stoichiometry, despite differences in mycorrhizal associations. Potential rates of net nitrogen mineralization were similar across species. Greater retranslocation of nutrients prior to leaf senescence by P. deltoides resulted in lower quality litter relative to T. chinensis.   However, higher litter production within stands of P. deltoides provided increased nitrogen inputs to soils and thus supported greater pools of soil nitrogen as compared to stands of T. chinensis.  Functional similarities in nitrogen acquisition and allocation between T. chinensis and P. deltoides indicate that T. chinensis invasion does not substantially alter ecosystem nitrogen recycling or retention.