Ecological Correlates of Carbon Isotope Composition of Leaves: A Comparative Analysis Testing for the Effects of Temperature, CO 2 and O 2 Partial Pressures and Taxonomic Relatedness on δ 13 C

Abstract

1 In order to eliminate the possible effects of relatedness on associations between carbon isotope composition (6 '3C) and the altitudinal and latitudinal distributions of plant species, we have reanalysed previously published data sets using information on taxonomic relationships. 2 Although there was a significant positive effect of altitude on, we did not find the effect of latitude reported in previous studies in either of the two comparisons testing the effect of this factor. When altitude was not controlled for statistically, plant lifeform had a significant effect on 613C, with more negative 613C values in plants of greater height (forbs < shrubs < trees), and for woody plants relative to forbs. 3 However, when 6 I3C was compared among life-forms within an altitude category, life-form had no effect on carbon isotope composition for any of the three altitude categories. 4 We conclude that differences in atmospheric composition (CO2 and 02 partial pressures), as represented by altitude, are sufficient to explain observed differences in carbon isotope composition. 5 We recommend that the evolutionary comparative techniques applied here should be adopted when multispecific data sets are analysed for the purpose of inferring functional relationships in plant ecology.