HERITABILITY OF CARBON ISOTOPE DISCRIMINATION IN GUTIERREZIA MICROCEPHALA (ASTERACEAE)

The carbon isotope composition (¹³C/¹²C) of C₃ plant tissues provides a long-term, integrated measure of photosynthetic metabolism. Quantitative genetic methods were used to study the inheritance of carbon isotope composition and several morphological characters in Gutierrezia microcephala, a short-lived desert perennial. Open-pollinated seed was collected from a population located near Lee's Ferry, Arizona, in an area that was disturbed approximately 20 years ago. Seeds were germinated and seedlings grown in a common greenhouse environment. Carbon isotope discrimination (Δ) and all morphological characters varied significantly among maternal families. Heritability of Δ was estimated as 81% in the greenhouse and as 92% using the regression of family mean Δ on parent Δ from field samples. Using both field and greenhouse data, we estimated a lower bound for heritability in nature of 54%. Offspring size and biomass both showed significant, positive correlations with Δ. The corresponding genetic correlations were similar in magnitude and direction, but did not differ significantly from zero. These results imply the existence of heritable differences in physiology associated with carbon assimilation and water loss within populations, and the potential for microevolutionary change through natural selection.