AN OVERVIEW OF CARBON STABLE ISOTOPE ANALYSIS OF POLLEN

Different in photosynthetic ways,plants have their C₃ and C₄ distinct in ranges of δ¹³C values, which may be used to indicate modern or ancient environmental and ecological conditions. The measured δ¹³C values from modern pollen grains show that they are consistent with the values from other tissues of the plants, and therefore may also indicate the photosynthetic pathways and the climatic conditions of the plants. Compared to the plant tissues, chemical compositions of pollen grains are less variable and are formed in a relatively short period, which means they may have higher temporal resolution in reflecting climatic conditions and features of rain-water and CO₂ during the blooming period. The preliminary research shows that the pollen δ¹³C value is nearly linear with the mean temperature of the flowering time. However, more exploring work is needed to confirm this conclusion. More precise reconstruction based on pollen δ¹³C value also relies on improved experimental technology because some conditional methods may not be applied. Some research has shown that the acetylation methods of pollen preparation may introduce contamination of carbon isotope. A substitution method is the non-carbon containing acid extraction technique to isolate sporopollenin. A spooling-wire microcombustion device interfaced with an isotope-ratio mass spectrometer (SWiM-IRMS) may allow the analysis of δ¹³C from a single pollen grain, although the error range is still large.