Increased pollen viability resulting from transport to the upper boundary layer

Previous studies have examined the rate of viability loss in pollen grains based on surface conditions but some pollen grains are lifted throughout the atmospheric boundary layer to heights where temperature and moisture differ markedly from near the surface. This transport may affect pollen viability in maize pollen which has been linked to its moisture content. The objective of this study was to examine how predictions of pollen viability may differ when considering the effects of boundary layer transport rather than only considering the conditions at the pollen source. We used Large-Eddy Simulation to simulate pollen dispersion and predict pollen viability upon deposition. We compared the predicted viability that was diagnosed using the atmospheric conditions at the pollen source when a pollen grain was released to viability diagnosed using the atmospheric conditions following the pollen grain's trajectory as it moved through the atmospheric boundary layer. Using surface values provided a reasonable prediction of viability for pollen grains that traveled less than a kilometer from the source field, but underpredicted pollen viability by as much as 20% for pollen that traveled several kilometers. The difference is attributed to the tendency for longer range transport to require lofting of pollen grains into the upper part of the atmospheric boundary layer, where cooler temperature and higher relative humidity are conducive to increased viability. Our results suggest that pollen grains traveling many kilometers are more likely to pollinate a receptive silk than would be expected based on the atmospheric conditions at the pollen source.