Environmental influences on the stable carbon isotopic composition of Devonian and Early Carboniferous land plants

Abstract Systematic analysis of the stable carbon isotopic composition of fossil land plants (δ 13 C p ) has the potential to offer new insights regarding paleoclimate variation and plant-environment interactions in early terrestrial ecosystems. δ 13 C p was measured for 190 fossil plant specimens belonging to 10 genera of Early to Late Devonian age ( Archaeopteris , Drepanophycus , Haskinsia , Leclercqia , Pertica , Psilophyton , Rhacophyton , Sawdonia , Tetraxylopteris , and Wattieza ) and 2 genera of Early Carboniferous age ( Genselia and Rhodeopteridium ) collected from sites located mainly in the Appalachian Basin (22–30°S paleolatitude). For the full carbon-isotopic dataset (n = 309), δ 13 C p ranges from −20.3‰ to −30.5‰ with a mean of −25.5‰, similar to values for modern C 3 land plants. In addition to a secular trend, δ 13 C p exhibits both intra- and intergeneric variation. Intrageneric variation is expressed as a small (mean 0.45‰) 13 C-enrichment of leaves and spines relative to stems that may reflect differential compound-specific compositions. Intergeneric variation is expressed as a much larger (to ~5‰) spread in the mean δ 13 C p values of coeval plant genera that was probably controlled by taxon-specific habitat preferences and local environmental humidity. Among Early Devonian taxa, Sawdonia yielded the most 13 C-depleted values (−27.1 ± 1.7‰), reflecting lower water-use efficiency that was probably related to growth in wetter habitats, and Leclercqia , Haskinsia , and Psilophyton yielded the most 13 C-enriched values (−23.0 ± 1.6‰, −22.3 ± 1.3‰, and −24.8 ± 1.6‰, respectively), reflecting higher water-use efficiency probably related to growth in drier habitats.