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Foliar carbon isotope discrimination (Delta) is widely used as an integrator of physiological plant responses to environmental change. However, the relationship between foliar Delta and mineral nutrient accumulation is still not well-known. The foliar Delta, K, Ca, Mg, Si and ash contents of S. przewalskii Kom. (SP) and S. chinensis (Lin.) Ant. (SC), two over-winter trees distributed on high altitude plateaux and lower altitude plains, respectively, were measured at monthly intervals over two years under the same growing conditions to examine the genetic and seasonal variation in foliar nutrient concentrations in relation to foliar Delta. The foliar Delta, Mg, K and ash contents were markedly lower in SP than in SC, and the foliar Si content was significantly higher in SP than SC, while the differences in Ca contents between the two Sabina trees were not significant. There was higher foliar Delta in winter than in summer for both Sabina trees. Close negative correlations of foliar Delta with K and Mg content, and significant positive correlations between foliar Delta and Si contents, were observed in SP but not in SC. Thus, higher water-use efficiency of SP than of SC is related to higher Si and lower Mg and K contents that have positive effects on the reduction of transpiration rates or stomatal conductances. The results obtained by the present study will advance the understanding of the adaptive strategies of mineral nutrition and water use in harsh environments. Copyright (C) 2011 John Wiley & Sons, Ltd.