Relevance Between The Shape Of Fossil Populus Davidiana Dode And Paleoenvironment

Leaf morphology has been used widely for the research of classification and identification of extant and fossil plant. But the data in the leaf morphology is used rarely. In this paper, we choose the leaves of the extant Populus davidiana Dode from Herbarium, Institute of Botany, Chinese Academy of Sciences(CAS) as sample and analyze them with a variety of mathematical analysis software and graphics software. The mathematical model method is used also. All the photos of the leaves are from Herbarium Institute of Botany, CAS database website. In the study, we define and extract the leaf morphology parameter of the extant Populus davidiana and named k for it. Mathematical models are established to analyze the relationship between the values of k and the altitude, mean annual temperature(MAT) and mean annual precipitation(MAP). Three groups of extant Populus davidiana leaves which collected from Tianzhu, Gansu Province are used to test and verified the variation of k. The results show that the values of k are stable at the same altitude. When the altitude is less than2000m, the values of k are larger, but as the altitudes above2000m, the values of k are all at a low level. The values of k calculated from the fossil Populus davidiana, which collected from Oligocene Hanjiajing Formation in Duitinggou, Gaolan County, Lanzhou City, show that the palaeo-elevation of the study area was about2950m. And the value is much higher than that of the current altitude. In addition, there is a similarity between the regularity of change along with altitude of MAT and MAP and k-value of Populus davidiana leaf shape. We set up a certain relationship according to comparing the regularity of MAT and MAP of change along with altitude to the regularity of change with altitude with the k-value of extant Populus davidiana. We deduce that the paleo-MAT of the growth period of the fossil Populus davidiana in the Hanjiajing Formation was6.7℃while paleo-MAP was625.5mm. Therefore, by comprising the morphology between the fossil and the extant Populus davidiana. the paleoenvironment can be reconstructed.