Variation in leaf carbon isotope discrimination in Encelia farinosa: implications for growth, competition, and drought survival.

Population-level variation in the leaf carbon isotope discrimination (Δ) values was examined in Encelia farinosa, a common Sonoran Desert shrub. There was approximately a 2‰ range in Δ values among different plants. These differences in Δ values among neighboring plants were maintained through time, both under conditions when neighbors were present and after neighbors had been removed. Individuals with high Δ values were found to have an accelerated growth rate when these plants were released from competition for water. Individuals with low Δ values were better able to persist through long-term drought. These data suggest possible tradeoffs between conditions favoring high- and low-Δ-value plants within a natural population. Given the temporal variability in precipitation between years and spatial variability in microhabitat quality in the Sonoran Desert, variation in Δ values among E. farinosa plants will be maintained within a population.