Elevation-induced climate change as a dominant factor causing the late Miocene C₄ plant expansion in the Himalayan foreland.

摘要

During the late Miocene, a dramatic global expansion of C₄ plant distribution occurred with broad spatial and temporal variations. Although the event is well documented, whether subsequent expansions were caused by a decreased atmospheric CO₂ concentration or climate change is a contentious issue. In this study, we used an improved inverse vegetation modeling approach that accounts for the physiological responses of C₃ and C₄ plants to quantitatively reconstruct the paleoclimate in the Siwalik of Nepal based on pollen and carbon isotope data. We also studied the sensitivity of the C₃ and C₄ plants to changes in the climate and the atmospheric CO₂ concentration. We suggest that the expansion of the C₄ plant distribution during the late Miocene may have been primarily triggered by regional aridification and temperature increases. The expansion was unlikely caused by reduced CO₂ levels alone. Our findings suggest that this abrupt ecological shift mainly resulted from climate changes related to the decreased elevation of the Himalayan foreland.