Climatic controls on C4 grassland distributions during the Neogene: A model-data comparison

摘要: Grasslands dominated by taxa using the C4 photosynthetic pathway evolved on several continents during Neogene and Quaternary, long after photosynthesis first among grasses. The histories of these ecosystems are relatively well documented in geological record from stable carbon isotopes (fossil vertebrate herbivores, paleosols) plant microfossil (pollen, phytoliths). distinct biogeography ecophysiology modern C3 grasses have led to hypotheses explaining origins grasslands terms term changes Earth system, such as increased aridity decreasing atmospheric pCO2. However, proxies for key parameters (e.g., temperature, precipitation, pCO2) still development, not yet widely applied, and/or remain contentious, so testing globally remains difficult. To understand better possible links between system origin grasslands, we undertook a global scale comparison observational records grass abundances Miocene Pliocene localities compiled literature three increasingly complex models dominance abundance. compilation comprises >2,600 δ13C values both fossil vertebrates paleosol carbonates. We forced vegetation with simulated monthly climates HadCM3 family coupled ocean-atmosphere GCMs over range pCO2 each epoch model or abundance grid cells months per year exceeding temperature at which net assimilation is greater than (crossover model); number crossover having sufficient precipitation growth (≥25 cm/yr; Collatz Sheffield Dynamic Global Vegetation Model (SDGVM), multiple functional types (C3 grasses, evergreen deciduous trees). Model-data agreement generally statistically weak, suggesting that regional local ecological interactions, continent specific evolutionary histories, climatic conditions represented may been equally strong stronger driving evolution system.