UV-B absorbing pigments in spores: biochemical responses to shade in a high-latitude birch forest and implications for sporopollenin-based proxies of past environmental change

Current attempts to develop a proxy for Earth’s surface ultraviolet-B (UV-B) flux focus on the organic chemistry of pollen and spores because their constituent biopolymer, sporopollenin, contains UV-B absorbing pigments whose relative abundance may respond to the ambient UV-B flux. Fourier transform infrared (FTIR) microspectroscopy provides a useful tool for rapidly determining the pigment content of spores. In this paper, we use FTIR to detect a chemical response of spore wall UV-B absorbing pigments that correspond with levels of shade beneath the canopy of a high-latitude Swedish birch forest. A 27% reduction in UV-B flux beneath the canopy leads to a significant (p<0.05) 7.3% reduction in concentration of UV-B absorbing compounds in sporopollenin. The field data from this natural flux gradient in UV-B further support our earlier work on sporopollenin-based proxies derived from sedimentary records and herbaria collections

FTIR spectra from grass pollen: a quest for species-level resolution of Poaceae and Cerealia-type pollen grains

Palynological analysis based on spore and pollen morphology is well established in the field of palaeo-environmental reconstruction but is currently not fully exploited for understanding the history and development of cereal cultivation due to difficulties in visually differentiating between grass species (Poaceae). Here we employ a chemotaxonomic approach, by examining the chemical differences among Poaceae taxa, based on Fourier-transform infrared (FTIR) microspectroscopy data to overcome problems associated with morphological similarities across the Poaceae family. FTIR spectra of untreated and acetolysed pollen from 19 Poaceae taxa were used in our study. We used both populations and individual pollen grains to explore how we can minimise the effect of Mie scattering (spectral distortions caused by scattering of the incident IR beam) on spectra from individuals. Random forest classification algorithms were applied to explore our ability to differentiate taxa at the species level. We found that pollen grains treated with acetolysis yield better classification results (86% for individuals and 97% for populations) compared to untreated samples (65.7% for individuals and 83% for populations), since they are less affected by Mie scattering. The high classification success at species level on acetolysed individual pollen grains suggests that our chemotaxonomic method holds substantial promise in numerous areas of grass and in particular cereal pollen research, including elucidating the history of agriculture

Pollen-vegetation richness and diversity relationships in the tropics

Tracking changes in biodiversity through time requires an understanding of the relationship between modern diversity and how this diversity is preserved in the fossil record. Fossil pollen is one way in which past vegetation diversity can be reconstructed. However, there is limited understanding of modern pollen-vegetation diversity relationships from biodiverse tropical ecosystems. Here, pollen (palynological) richness and diversity (Hill N1) are compared with vegetation richness and diversity from forest and savannah ecosystems in the New World and Old World tropics (Neotropics and Palaeotropics). Modern pollen data were obtained from artificial pollen traps deployed in 1-ha vegetation study plots from which vegetation inventories had been completed in Bolivia and Ghana. Pollen counts were obtained from 15 to 22 traps per plot, and aggregated pollen sums for each plot were &gt; 2,500. The palynological richness/diversity values from the Neotropics were moist evergreen forest = 86/6.8, semi-deciduous dry forest = 111/21.9, wooded savannah = 138/31.5, and from the Palaeotropics wet evergreen forest = 144/28.3, semi-deciduous moist forest = 104/4.4, forest-savannah transition = 121/14.1; the corresponding vegetation richness/diversity was 100/36.7, 80/38.7 and 71/39.4 (Neotropics), and 101/54.8, 87/45.5 and 71/34.5 (Palaeotropics). No consistent relationship was found between palynological richness/diversity, and plot vegetation richness/diversity, due to the differential influence of other factors such as landscape diversity, pollination strategy, and pollen source area. Palynological richness exceeded vegetation richness, while pollen diversity was lower than vegetation diversity. The relatively high global diversity of tropical vegetation was found to be reflected in the pollen rain