The Stable Carbon Isotope Composition of Pinus yunnanensis Pollen and Leaf in Northwestern Yunnan, China

The basis for the delta C-13 values of plant tissues used to infer past ecological environments is their relationships with modern ecological conditions. A total of 71 pairs of pollen and leaf samples were collected from Pinus yunnanensis, an endemic species of the Yunnan plateau, in northwestern Yunnan, China. Their carbon isotopic composition was examined to investigate the two tissues' difference of stable carbon isotopes, possible factors affecting their delta C-13 values, and their distinctiveness within Pinus and Pinaceae. Our study showed that pollen delta C-13 values range from -32.92 to -26.34 parts per thousand with an average of -30.88 parts per thousand, whereas leaf delta C-13 values vary between -33.79 and -28.96 parts per thousand with an average value of -31.2 parts per thousand, suggesting an isotope fractionation between the two tissues. A statistically significant negative correlation between the pollen delta C-13 values and altitudes of the sampling sites as well as no significant correlation between the leaf delta C-13 values and altitudes suggested that pollen may be more sensitive to some climatic parameters than leaf. A comparison of the pollen and leaf delta C-13 values from Pinus yunnanensis with the available data from other Pinus species and other genus species of Pinaceae indicated that the pollen and leaf delta C-13 values of Pinus yunnanensis are the lowest, partially due to the effects of water availability.