A comparison of pollen counts: Light versus scanning electron microscopy

Palynologists use compound light microscopy (LM) for pollen identification and interpretation and scanning electron microscopy (SEM) for morphological comparisons and taxonomy. As we are unaware of any published reports comparing LM and SEM pollen counts and identifications of the same sample, we decided to examine a surface soil sample using both microscopes. Standard palynological extraction techniques were used. Two, 300 grain counts were made using LM, and two, 300 counts with SEM. Pollen grains viewed with SEM were also divided into three categories, ‘‘identifiable,’’ ‘‘obscured,’’ and ‘‘virtually impossible to identify’’. Eighty-six (86) percent of the pollen grains counted with SEM were classified as ‘‘identifiable’’ or ‘‘obscured.’’ Pollen concentration values ranged from 385,714 (LM Count #2) to 900,000 (SEM Count #1) per gram of soil. Regardless of the microscope used, Ligustrum spp., Myrtaceae-type, and Tilia spp. had the greatest number of pollen grains. A total of 73 taxa were found. A scan of the unexamined portion of the stubs resulted in 20 additional taxa. There were no significant differences between the counts made with the two microscopes (ANOVA, pw0.05, F50.18, df576). However, there were significantly more taxa found with SEM than with LM (t-test, T50.05). Sample preparation and the time needed to count, analyze, photograph and print the micrographs are the same regardless of the microscope used. The sample, information needed, and funding will determine which technique to use.