Several environmental factors potentially influence the stable isotope compositions of plants, depending on species and local environment. Although several studies have discussed these aspects in C-3 and C-4 plants, only a few have attempted to identify the major drivers of delta C-13, delta O-18, and delta N-15 in CAM plants. In this study, stable isotopic ratios of CAM plants collected along an altitudinal transect in the Chisos Mountains/USA during two growth seasons, are used to understand major factors governing isotopic variability. A strong and significant relationship between delta C-13 and altitude, positive for agave at <1700 m and negative for both agave and cacti at >1500 m, suggests variable carbon isotope fractionation at different altitudes, which may be unique to CAM plants. Our data suggest that temperature primarily governs delta C-13 of the studied plants. The significant negative correlations observed between the delta O-18 of agaves and the recorded air temperature (0.59 parts per thousand/degrees C) are similar to the delta O-18 of precipitation vs. temperature variability in global data. The delta N-15 variations suggest a similar N-source for both agaves and cacti, and reflect progressive changes in the dominant N-source across desert-grassland-woodland zones. We conclude that the stable carbon and oxygen isotope composition of agave reflects the climatic conditions along the elevation transect. (C) 2013 Elsevier Ltd. All rights reserved.