Relationship between climatic conditions and the relative abundance of modern C3 and C4 plants in three regions around the North Pacific.

Using -24‰ and -14‰ as the endpoints of stable carbon isotopic composition of total organic carbon (δ¹³ C_TOC) of surface soil under pure C₃ and C₄ vegetation, and surface soil δ₁₃ C_TOC data from eastern China, Australia and the Great Plains of North America, we estimate the relative abundance of C₃/C₄ plants (i.e., the ratio of C₃ or C₄ biomass to local primary production) in modern vegetation for each region. The relative abundance of modern C₃/C₄ vegetation from each region is compared to the corresponding climatic parameters (mean annual temperature and precipitation) to explore the relationship between relative C4 abundance and climate. The results indicate that temperature controls the growth of C₄ plants. However, even where temperature is high enough for the growth of C₄ plants, they will only dominate the landscape when precipitation declines as temperatures increase. Our results are consistent with those of other investigations of the geographic distribution of modern C4 plant species. Therefore, our results provide an important reference for interpretation of past C₃/C₄ relative abundance records in these three regions. [ABSTRACT FROM AUTHOR]