Carbon isotope discrimination in C3 land plants is independent of natural variations in pCO2

Abstract

doi: 10.7185/geochemlet.1604The d 13 C of terrestrial C3 plant tissues and soil organic matter is important for understanding the carbon cycle, inferring past climatic and ecological conditions, and predicting responses of vegetation to future climate change. Plant d 13 C depends on the d 13 C of atmospheric CO 2 and mean annual precipitation (MAP), but an unresolved decades-long debate centres on whether terrestrial C3 plant d 13 C responds to p CO2 . In this study, the p CO2 -dependence of C3 land plant d 13 C was tested using isotopic records from low-and high-p CO2 times spanning historical through Eocene data. Historical data do not resolve a clear p CO2 -effect (-1.2 ± 1.0 to 0.6 ± 1.0 ‰/100 ppmv). Organic carbon records across the Pleistocene-Holocene transition are too affected by changes in MAP, carbon sources, and potential differential degradation to quantify p CO2 -effects directly, but limits of ≤1.0 ‰/100 ppmv or ~0 ‰/100 ppmv are permissible. Fossil collagen and tooth enamel data constrain p CO2 -effects most tightly to -0.03 ± 0.13 and -0.03 ± 0.24 ‰/100 ppmv between 200 and 700 ppmv. Combining all constraints yields a preferred value of 0.0 ± 0.3 ‰/100 ppmv (2 s.e.). Recent models of p CO2 -dependence imply unrealistic MAP for Cenozoic records.

Multiple negative carbon-isotope excursions during the Carnian Pluvial Episode (Late Triassic)

“…relative abundance of different sporomorph taxa, which likely had different 13 C signatures (Van de Schootbrugge et al, 2008). In higher plants, carbon-isotope fractionation increases with increasing mean annual precipitation and increasing pCO 2 (Diefendorf et al, 2010;Schubert and Jahren, 2012;Kohn, 2016). The magnitude of the NCIEfor example, could have been amplified due to increasing higher-plant carbon-isotope fractionation,…”

Abrupt plant physiological changes in southern New Zealand at the termination of the Mi-1 event reflect shifts in hydroclimate and pCO2

“…Kürschner et al, 1997;Lammertsma et al, 2011;Schubert and Jahren, 2012). However, because g c[op] and Δ are sensitive to C i (Šantrůček et al, 2014), the attribution of changes in leaf properties to just C a is controversial (Poole et al, 1996;Seibt et al, 2008;Kohn, 2016). For example, decreased moisture availability and increased C a could lead to the same physiological leaf response (Beerling and Woodward, 1995;Drake and Gonzàlez-Meler, 1997): each of these environmental changes is expected to result in decreased ζ, which would diminish C i (and result in decreased Δ), and lead to diminution of g c[max] in successive leaf generation (Šantrůček et al, 2014).…”

“…However, while a C a impact on δ 13 C has been observed in short-term experimental conditions (e.g. Schubert and Jahren, 2012), in field studies, and over timescales of decades to millennia and longer, various studies have concluded that the impact of C a on δ 13 C values is negligible (Diefendorf et al, 2015;Kohn, 2016). In agreement with these latter studies, our investigation of historical (1900-2012) leaves indicates that the ~33% increase in pCO 2 during the 20th century (295-390 ppm) had a negligible effect on L. calicaris δ 13 C values (Appendix C, Fig.…”

Holocene hydroclimatic variability in the Zanskar Valley, Northwestern Himalaya, India

“…Significance of δ 13 C and Rb/Sr data δ 13 C org records from terrestrial plant tissues and soil organic matter (SOM) derived from C 3 -dominated vegetation has been used to reconstruct past climatic and ecological conditions (e.g., Cerling 1984;Quade et al 1989Quade et al , 1995Kohn 2010Kohn , 2016. The mean annual precipitation, latitude, and altitude are the most significant controlling factors of δ 13 Cvalues of terrestrial C 3 plants (Diefendorf et al, 2010;Basu et al, 2015Basu et al, , 2019Kohn 2016;Rao et al, 2017).…”

“…Significance of δ 13 C and Rb/Sr data δ 13 C org records from terrestrial plant tissues and soil organic matter (SOM) derived from C 3 -dominated vegetation has been used to reconstruct past climatic and ecological conditions (e.g., Cerling 1984;Quade et al 1989Quade et al , 1995Kohn 2010Kohn , 2016. The mean annual precipitation, latitude, and altitude are the most significant controlling factors of δ 13 Cvalues of terrestrial C 3 plants (Diefendorf et al, 2010;Basu et al, 2015Basu et al, , 2019Kohn 2016;Rao et al, 2017). Hence, the δ 13 C value of SOM under C 3 -dominated vegetation has a negative correlation with precipitation (Kohn, 2010;Rao et al, 2013Rao et al, , 2017Basu et al, 2015Basu et al, , 2019 and has been successfully used to reconstruct climate variability in the eastern Himalaya (Ali et al, 2018).…”