Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate

Abstract

A broad compilation of modern carbon isotope compositions in all C3 plant types shows a monotonic increase in δ 13 C with decreasing mean annual precipitation (MAP) that differs from previous models. Corrections for temperature, altitude, or latitude are smaller than previously estimated. As corrected for altitude, latitude, and the δ 13 C of atmospheric CO 2 , these data permit refined interpretation of MAP, paleodiet, and paleoecology of ecosystems dominated by C3 plants, either prior to 7-8 million years ago (Ma), or more recently at mid-to high latitudes. Twenty-nine published paleontological studies suggest preservational or scientific bias toward dry ecosystems, although wet ecosystems are also represented. Unambiguous isotopic evidence for C4 plants is lacking prior to 7-8 Ma, and hominid ecosystems at 4.4 Ma show no isotopic evidence for dense forests. Consideration of global plant biomass indicates that average δ 13 C of C3 plants is commonly overestimated by approximately 2‰.aridity | carbon cycle | closed canopy | paleoprecipitation P lants exhibiting C3 photosynthesis have dominated the history of terrestrial vegetation, as CAM plants occupy only a small percentage of typical ecosystems (e.g., 1), and C4 plants became abundant in grasslands only within the last 7-8 million years (2). C3 plants exhibit a large range of carbon isotope compositions (−20 to −37‰, V-PDB; Fig. 1), generally reflecting a physiological response to aridity (anomalously high δ 13 C) and a combination of low light levels plus leaf litter recycling (anomalously low δ 13 C; 3). Past studies have conflicted on the dependence of δ 13 C on mean annual precipitation (MAP). Most studies support a negative correlation (e.g., 4), but some have reported no correlation (5) or even a positive correlation (6).This study explores carbon isotope systematics of C3 plants through a comprehensive compilation of literature data, minimizing local differences that have given rise to disparate interpretations. This work directly benefits paleodietary and paleoecological studies by providing estimates of MAP in ancient environments as well as clearer boundaries for identifying the understory of closed-canopy forests and the contribution of non-C3 plants to diet, which is used to gain insights into C4 origins (2). The new compilation also helps refine models of the modern carbon cycle by providing a better estimate of global C3 δ 13 C values (7). The present analysis differs from a recent investigation of correlations between tree þ shrub δ 13 C and MAP or plant functional type (8) in that it is several times larger on a site-by-site basis, spans the full range of plant growth forms (including trees, bushes, grasses, and herbs), averages data from each site to minimize sampling bias (4), and regresses an arguably more appropriate function to the data. Selection criteria of climate and isotopic data also differ slightly. This broader approach of considering all C3 plants and averaging compositions is important when evaluating herbivore paleodiets, whic...

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

“…Additional support for the idea that during the ice age muskoxen and caribou fed in the plant communities most similar to the ones dominating the landscape today comes from the inverse correlation between d 15 N and mean annual precipitation (Heaton, 1999;Hedges et al, 2005) and the positive correlation between mean annual temperature and d 13 C that exists in some regions (Van Klinken et al, 1994;Heaton, 1999;Iacumin et al, 2006). As to why more enriched bone d 13 C values are associated with moister vegetation types, as opposed to more depleted ones as would be predicted by global patterns of d 13 C and precipitation (Diefendorf et al, 2010;Kohn, 2010), we can only point out that isotope fractionation occurs through multiple interacting processes and that the patterns exhibited in local vegetation trump global trends when interpreting bone isotopes. The lower pH and nutrient levels found in moist acidic tundra compared to well-drained, graminoid-dominated vegetation (Heaton, 1999) might have contributed to the higher d 13 C values found in the bones of caribou and muskoxen exploiting the moister, warmer parts of the ice-age vegetation mosaic.…”

Carbon and oxygen stable isotope compositions of late Pleistocene mammal teeth from dolines of Ajoie (Northwestern Switzerland)

“…These δ 13 C values indicate that the megaherbivores fed exclusively on a C 3 -plant diet. Since δ 13 C values of C 3 plants can be significantly influenced by environmental factors (Heaton, 1999;Diefendorf et al, 2010;Kohn, 2010), the environmental and climatic conditions were probably not very different during both time intervals. A relatively humid and open landscape partially covered by bushes, shrubs and trees developed under temperate climatic conditions (Becker et al, 2009(Becker et al, , 2013.…”

“…Mammuthus primigenius particularly shows the lowest mean δ 13 C value of all taxa, despite its similar digestive physiology and diet as those of woolly rhinoceroses and horses (hindgut fermenters). According to different studies on mammoth's stomach contents, tree barks and twigs probably constituted a small but significant part of their winter diet (e.g., Vereschagin and Baryshnikov, 1982;Van Geel et al, 2008, 2010. Such lignin rich plant parts have lower δ 13 C values and may explain the low mean enamel value of the mammoths, even though they predominantly ate grasses and herbs.…”

Investigating the carbon isotope composition and leaf wax n-alkane concentration of C3 and C4 plants in Stiffkey saltmarsh, Norfolk, UK

“…The 13 C/ 12 C ratio of plant tissue can be used to distinguish between C 3 and C 4 species (Park and Epstein, 1960;O'Leary 1988;Farquhar et al, 1989) and has been extensively used in the reconstruction of past climates (e.g., Meyers, 1997Meyers, , 2003Kohn, 2010;Tipple et al, 2010;Royles et al, 2012). Leaf wax n-alkyl 13 C/ 12 C can be interpreted in a manner similar to that for bulk plant tissue, and therefore has also been used to identify shifts in the relative percentage of C 3 and C 4 vegetation in the sedimentary record (e.g., Huang et al, 2000Huang et al, , 2001Freeman and Colorusso, 2001;Schefuß et al, 2003;Tipple and Pagani, 2007).…”