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Spatial heterogeneity in the relationship between precipitation and carbon isotopic discrimination in C3 plants: Inferences from a global compilation
- Basu, Sayak, Ghosh, Sambit, Sanyal, Prasanta
- Global and planetary change 2019 v.176 pp. 123-131
- C3 plants, C4 plants, Miocene epoch, air, altitude, arid zones, basins, carbon, data collection, latitude, leaves, linear models, paleoecology, spatial variation, stable isotopes, temperature
- Understanding the causes of large variations in carbon isotopic composition of C3 plants (δ13CC3) is a key challenge for paleoenvironmental reconstruction. Several investigations have attempted to study the global patterns in the δ13CC3 values and their correlation with the precipitation variability. Sparse representation of dataset from low-latitude and equatorial regions in the existing global compilation hinders to understand the precipitation-δ13CC3 gradient at different latitudinal-bands. In the present study, available global compilation has been extended with the newly measured dataset, and the new compilation (ca. 1.5 times larger than previous dataset) comprises results from 720 sites across the world. All the δ13CC3 values have been converted to carbon isotopic discrimination between air and leaf (Δair-leaf). Mann-Whitney analysis indicates distinct region-specific distribution of the Δair-leaf values. The average Δair-leaf value in mid-latitude region of the Northern Hemisphere is ca. 2‰ lower than equatorial sites. Multiple linear models have been used to investigate relative influence of climatic (precipitation and temperature) and geographical factors (altitude and latitude) on the Δair-leaf values. This analysis shows that precipitation controls the Δair-leaf values in every latitudinal-bin though the effect of precipitation is negligible beyond 1500 mm. Furthermore, the Δair-leaf-precipitation gradient has a large spatial variability and the most prominent changes in the Δair-leaf values have been observed at arid regions in mid-latitudes of the Southern Hemisphere (maximum 1.3‰ 100 mm−1). Region-specific distribution of δ13C values of plant and Δair-leaf-precipitation gradient prompt to recalculate the relative abundance of C3–C4 plants in the Siwalik sections of the Himalayan foreland basin. Our results show that earlier investigations in the Siwaliks for the Middle-Late Miocene have underestimated the abundance of C4 plants by ca. 20%. The recalculation shows that C4 plants existed in these regions earlier (ca. 17 Ma) than the previously proposed timings.