Artemisia tridentata Nutt. ssp. tridentata, and ssp. vaseyana, along with natural hybrids of the two, are found in Salt Creek Canyon, near Nephi, Utah, USA. The two subspecies are separated by 1.1 km along the transect, and 85 m in elevation. Natural hybrids of the two occur on the same hill between the two parent populations. In 1993 seedlings from five populations along the transect were planted in three gardens. The upper, middle, and lower gardens allowed the five populations to grow in three different environments. Plant tissue was collected in triplicate from all five populations in each of the three gardens on 06 Nov. 1999. 5 mg (dry weight) of plant tissue were then combusted with Cu(II)O wireform, and Cu granular at 800C. CO2 from the combustion of the plant tissue was then extracted using cryogenic distillation methods. The CO2 was later analyzed in a mass spectrometer to measure the ratio of 13C/12C. This isotopic ratio yields a quantitative measurement of stress in the cumulative growth of the plant tissue. As stresses increase fractionation also increases and the ratio compared to a standard becomes more negative. The results of this analysis showed that, on average, stress/fractionation were highest in the upper garden and lowest in the lower garden. The environmental contribution to plant growth is clearly evidenced by the segregation of isotopic ratios between the gardens. The contribution of inheritance is also evident in the isotopic data. Stress/fractionation varies positively with the distance between the source location and the garden location. In addition to this variance, the hybrids exhibit lower levels of stress/fractionation in distant gardens than the parent populations. Mass spectroscopy is a powerful tool in looking at the contributions of both environment and inheritance in plant growth.

Key words: Artemisia tridentata, Carbon, mass spectroscopy, stable isotopes