Abstract
ABSTRACTThe morphology and size variability of pollen grains of Cedrus atlantica were investigated using a novel approach employing laser diffraction granulometry. We provide new insights into size variability and present high-quality light microscopy (LM) and scanning electron microscopy (SEM) imagery of Cedrus atlantica pollen. Grains have an average size of 59.1 ± 4.0 µm, measured on millions of grains from 91 samples. Analysis showed there is high variability of grain size within individual samples, although variability between samples is not significant. We found no significant relationships between grain size and climate (including temperature, precipitation and aridity), and suggest that grain size of fossil Cedrus pollen would not be a good proxy for climate reconstruction. Grain size may be influenced by a number of complex factors such as genome size or adaptations to support wind pollination, while variability within individual samples may result from the irregular development of pollen. The laser diffraction method produced repeatable, robust measurements on millions of pollen grains which are highly correlated with measurements taken using LM (r = 0.91, p = 0.002). Where grain size information is crucial for pollen identification, for developing isolation techniques for geochemical analysis, for investigating climatic and environmental influence, or for investigating links between genomes and grain size, particle size analysis by laser diffraction provides a reproducible and robust method for quickly determining pollen grain size on many samples.
Highlights
Detailed information on pollen morphology and grain size is critical for palynologists to accurately identify vegetation from fossil pollen assemblages for pollen analysis
We have shown that laser diffraction granulometry provides a reliable and consistent method of determining pollen grain size, and produces results in line with existing light microscopy (LM) methods of grain size measurement
In additional testing of the method, we found similar results with Pinus pollen between the grain size reported by laser diffraction granulometry and LM measurements; further testing of the method is needed on other pollen types with different morphologies, and pollen types with smaller grains
Summary
Detailed information on pollen morphology and grain size is critical for palynologists to accurately identify vegetation from fossil pollen assemblages for pollen analysis. Geochemical studies utilising pollen, such as stable isotope analysis for palaeoclimate reconstructions (Amundson et al 1997; Loader & Hemming 2004; Nelson et al 2006, 2007; King et al 2012; Nelson 2012; Bell et al 2017) and biomarker analysis for UV-B reconstructions (Rozema et al 2001, 2002; Fraser et al 2011; Willis et al 2011; Lomax et al 2012; Jardine et al 2017), require detailed knowledge of grain size for developing techniques to isolate specific grains from fossil assemblages. A positive relationship was found between temperature and pollen size in 232 plant species from 11 taxonomic groups, suggesting possible climatic influence on size during the flowering period (Ejsmond et al 2015) and offering potential for pollen grain size to aid in reconstructions of past environments
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