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 (DELTA) values was examined in Encelia farinosa, a common Sonoran Desert shrub. There was approximately a 2 part-per-thousand range in DELTA values among different plants. These differences in DELTA values among neighboring plants were maintained through time, both un conditions when neighbors were present and after neighbors had been removed. Individuals with high DELTA values were found to have an accelerated growth rate when these plants were released from competition for water. Individuals with low DELTA values were better able to persist through long-term drought. These data suggest possible tradeoffs between conditions favoring high- and low-DELTA 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 DELTA values among E. farinosa plants will be maintained within a population.