Environmental controls on photosynthesis and N-cycling in Welwitschia mirabilis are evaluated through delta13C and delta15N analyses of leaf material from 26 individuals in the southermost population of this long-lived gymnosperm, which is endemic to the Namib Desert. The coastal Namib Desert in southwestern Africa is hyperarid in terms of rainfall, but receives up to 100 days of fog each year. This climate regime leads to interesting water relations in the Namib flora and fauna. Among many enigmatic characteristics, photosynthesis in W. mirabilis has puzzled researchers since the 1970's. Although it is predominantly a C3 plant, delta13C ranges from -17.5 to -23.50/00 in natural habitats, and can be as enriched as -14.40/00 under artificial growing conditions. Recently the CAM pathway has been confirmed, but the driver for CAM utilization has not been identified. In this study we incorporate new delta13C compositions for plants in the middle of the 100 km aridity gradient which spans the natural distribution of W. mirabilis. Initial results show an enriched delta13C signal (-200/00) in the more exposed individuals compared with those in a sandy drainage depression (-220/00). In addition, the documented correlation between rainfall and delta15N found in Kalahari C3 plants (Swap et al. 2004) is used to interpret the delta15N values in this W. mirabilis population. Initial results indicate that the fog deposition may significantly affect the nutrition of these unusual plants from the Namib Desert.