High Tibetan Plateau: a Nature Reserve of C3 Flora

Abstract:

Uplift of the Tibetan Plateau and associated climate changes leading to enhanced seasonality in precipitation and drying, are argued to have induced a global ecological shift from C₃-frorest to C₄-grassland between 8 and 5 million years ago. However, both tectonic and climatic changes predate the timing of the C₃-C₄ transition, with paleoaltimetry studies pointing to a high Tibetan Plateau no later than 10 Ma and the existence of an intense monsoon since ca. 11 Ma.

To better understand the role of the Tibetan Plateau, we present results of a paleoecology study based on the carbon isotope compositions of leaf-wax n-alkanes (δ¹³C_alk) from Qaidam basin, an intermontane basin on the youngest and the northernmost portion of Tibetan Plateau. Samples were collected from a 5-km thick, fluvial-lacustrine sequence dated 15 Ma to 1.8 Ma. Organic geochemical indices and detrital thermochronological studies preclude post-depositional thermal alteration of the studied materials.

Our results, which show persistently low δ¹³C_alk values, are consistent with the dominance of C₃ flora on the Tibetan Plateau, in contrast to the prominent C₄ rise surrounding the Tibetan Plateau and around the globe. We argue that a high Tibetan Plateau, established prior to the global ecological C₃-C₄ shift, served as a shelter of C₃ flora since the Miocene. High-elevation and cold environments provided a competitive advantage for C₃ by damping/counteracting the physiological advantage of C₄ which outperforms C₃ plants under warm, high-irradiance, water-stress and low pCO2 conditions.